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Eocene-Oligocene adakitic and non-adakitic shoshonitic felsic intrusions from the southwest margin of the Yangtze Craton provide a crucial geological record for studying crust-mantle interactions at the craton boundary. Despite their significance, the petrogenesis and source properties of these intrusions remain debated. This study suggests that the adakitic and non-adakitic features of these intrusions result from the re-melting of Neoproterozoic juvenile lower crust, as evidenced by zircon U-Pb dating, geochemical analyses, and petrogenetic investigations. The Ninglang-Yongsheng shoshonitic felsic intrusions, characterized by high Mg#, MgO, Ni, and Cr contents, exhibit isotopic characteristics akin to mantle-derived magma and juvenile mafic lower crust. Their U-Pb ages span 32–36 Ma, and they show similar patterns in major and trace elements, rare earth elements (REEs), and isotopes, with enrichment in large ion lithophile elements (LILEs) and depletion in high field strength elements (HFSEs) like Nb, Ta, and Ti. These intrusions also demonstrate significant fractionation between light and heavy REEs, with a modest negative Eu anomaly. Their (87Sr/86Sr) i and ε Nd (t) values range from 0.7060 to 0.7069 and − 4.4 to −1.5, respectively, while Pb isotopic compositions vary slightly. This paper, along with prior research, has developed a genetic model for the Ninglang-Yongsheng shoshonitic felsic intrusions. The adakitic quartz monzonite porphyries likely originated from high-degree partial melting of the juvenile lower crust, whereas the non-adakitic shoshonitic syenite porphyries resulted from lower-degree melting. The composition of the juvenile lower crust may be garnet amphibolite-pyroxenite. This suggests distinct compositional variations within the Ninglang-Yongsheng juvenile lower crust. Moreover, the region's shoshonitic felsic intrusions have assimilated mantle-derived magma. In conclusion, the juvenile lower crust on the Yangtze Craton's southwest margin displays zonal characteristics, with the Liuhe-Beiya area's lower crust showing higher potassium content and more enriched isotopic signatures compared to the Ninglang-Yongsheng region. • Sanjiang adakitic felsic suites formed by re-melting of the juvenile lower crust. • Sanjiang adakitic and non-adakitic felsic suites may have the same origin. • The lower crust along the western margin of the Yangtze craton is heterogeneous. • The thickened lithospheric mantle delamination near the ASRR occurred earlier. [ABSTRACT FROM AUTHOR]

Serpentinite-derived fluids play a crucial role in mass exchange between the Earth's crust and mantle. However, there is currently a limited understanding of how serpentinite-derived fluids influence the Si isotope composition of mantle and subducted crustal materials. Whiteschists in the Dora-Maira Massif of the Western Alps and leucophyllites in Austria of the Eastern Alps were formed through serpentinite-derived fluid metasomatism of metagranite protoliths. Thus, they can provide valuable insights into the geochemical diversity of such rocks resulting from fluid–rock interactions. A special focus is on Si isotope compositions, which were analyzed in whiteschists, leucophyllites, and their corresponding country rocks. The aim of this paper is to investigate the impact of serpentinite-derived metasomatic fluids on the Si isotope compositions of subducted continental crust. With the exception of one whiteschist sample, which contains high amounts of pyrope, and one pyrope megablast, all other whiteschists and leucophyllites exhibit Si isotope compositions similar to those of their country rocks. This observation suggests that the Si isotopes of whiteschists and leucophyllites were inherited from their respective country rocks; fluid metasomatism did not significantly modify the Si isotope compositions of whiteschists and leucophyllites. Because pyrope has much lower δ30Si values than quartz and phengite as further major mineral constituents of the studied whiteschists, the samples with high pyrope contents reveal lighter Si isotopes than those containing lower amounts of pyrope. Interestingly, the metagranites and the majority of whiteschists and leucophyllites exhibit Si isotope compositions below the igneous array, implying that their protoliths are S-type granites. These granites commonly contain sedimentary components derived from their sources. Our results document that Si behaves immobile during serpentinite-derived fluid metasomatism of the subducted continental crust. Combined with previous results, we were able to show that slab derived fluids, including serpentinite-derived fluids, produce only a minimal influence on the Si isotope composition of the overlying mantle wedge and its derived magmas. Thus, the Si isotope compositions of rocks, even if highly affected by metasomatizing fluids, can be used as significant fingerprints that refer to their unaltered precursors. • Whiteschist and leucophyllite are formed by serpentinite-derived fluid metasomatism. • The δ30Si values of most whiteschists and leucophyllites are same to country rocks. • Serpentinite-derived fluids did not affect Si isotopes of metagranites and mantle. • Pyrope has much lower δ30Si values than quartz and phengite. • The samples with high pyrope contents have lighter Si isotopes. [ABSTRACT FROM AUTHOR]

Supracrustal rocks offer a window into tectonic processes of the early Earth, since they are common in the Archean lithosphere. However, these rocks are usually affected by several episodes of metamorphism that can compromise their U Pb systematics, leading to equivocal interpretations of depositional ages and sources. In northeast Brazil, supracrustal rocks are frequent within the Archean basement of the São José do Campestre Massif. These metapelitic migmatites show a high-temperature mineral assemblage, with garnet + sillimanite ± spinel and retrograde cordierite, with abundant anatectic melt migration at conditions of upper amphibolite to granulite facies. Zircon U Pb dating coupled to trace elements analysis through LA-ICP-MS, as well as zircon internal zoning patterns suggest a maximum depositional age of 3305 ± 16 Ma followed by high-temperature metamorphism in the Mesoarchean, Paleoproterozoic and Neoproterozoic. Mesoarchean high temperature metamorphism occurred between 3084 ± 4 and 3006 ± 6 Ma and generated a wide range of textures that could be grouped in, at least, three stages of zircon growth. The first, during prograde heating, led to dissolution of detrital cores through the process of Ostwald Ripening and reprecipitation in oscillatory zoned rims. The second, probably at peak conditions, occurred above the stability of monazite, as evidenced by high Th/U ratios within zircon grains, rounded shape and sector-zoned cores. The third, during retrograde cooling, is mostly driven by garnet breakdown, and resulted in the crystallization of convoluted rims. Ti-in-zircon temperatures indicate minimum temperatures of 712 ± 21 °C for prograde/retrograde stages and 881 ± 50 °C for peak conditions. The Paleoarchean sedimentation and Mesoarchean metamorphism are coeval with similar events in Kaapvaal and Dharwar Cratons (South Africa and South India, respectively), but show no correlation to any Archean domains in South America to date. Solid-state recrystallization during the Paleoproterozoic (ca. 2.0 Ga) and the Neoproterozoic (ca. 0.6 Ga) correlates with orogenic events in both the Borborema Province and São Francisco Craton, suggesting a common evolution since the Rhyacian. [Display omitted] • Revised maximum depositional age indicate Paleoarchean sedimentation and Mesoarchean high-temperature metamorphism. • Zircon growth and recrystallization during prograde, peak and retrograde stages. • Paleoproterozoic and Neoproterozoic solid-state recrystallization. • Implications for provenance investigations in rocks affected by multiple metamorphic events. • Correlations with Mesoarchean metamorphic events in Dharwar and Kaapvaal Cratons. [ABSTRACT FROM AUTHOR]

The occurrence of the polymetallic Nb layer in the upper Permian Xuanwei Formation in southwest China has been documented extensively. The origin of Nb, as well as other metals like Zr and rare earth elements (REEs), has received much research attention; however, the source of these elements remains enigmatic. In recent studies, an uncommon Nb-rich titanite (CaTiSiO 5) has been discovered in the Emeishan basalts beneath the Xuanwei Formation in the eastern Yunnan–western Guizhou region. However, its origins and genetic relationship to the polymetallic Nb layer remain unclear. In this study, we used in situ microanalytical and U Pb dating techniques to investigate the titanite in these Emeishan basalts. Our objectives were to determine the origins of the titanite and its relationship to the polymetallic Nb layer in the lowermost Xuanwei Formation. The basalts consist of approximately 70%–90% phenocrysts and 10%–30% matrix. The phenocrysts are mainly coarse-grained (>30 μm) plagioclase, clinopyroxene, and Fe-Ti oxides (ilmenite and magnetite), whereas the matrix comprises mainly fine-grained (<30 μm) titanite and glass. The titanite is hypautomorphic or xenomorphic and occurs as small, disseminated grains within the matrix. The titanite U-Pb dating of basalt sample reveals a Tera–Wasserburg lower intercept age of ca. 259.6 ± 4.3 Ma, which corresponds to the age of the eruption timing of Emeishan large igneous province (ELIP; 260.9–257.4 Ma). This implies that the formation of titanite within the matrix can be attributed to rapid cooling of residual melt subsequent to fractional crystallization of a substantial quantity of phenocrysts. The LA-ICP-MS analysis reveals that the trace element composition of titanites in the Emeishan basalts exhibits similarities to weathering-type titanite, as evidenced by elevated La N /Yb N ratios and low concentrations of Y, ΣREE, Th, and U, as well as reduced Lu/Hf and Th/U ratios. Thus we propose that these titanites crystallised during the late-stage magmatic evolution, resulting from magmatic fractional crystallization and subsequent weathering alteration. The materials required for titanite crystallization in the basalt matrix primarily sourced from the residual melt, while weathering dissolution of plagioclase and clinopyroxene in the phenocrysts may have provided additional Ca and Eu for titanite formation. As weathering progressed, the Nb-rich titanite underwent a transformation into Nb-rich anatase and gradually became enriched in the regolith. This material was subsequently transported to nearby basins and deposited in terrestrial environments, resulting in formation of the polymetallic Nb layer in the lowermost Xuanwei Formation. Our findings provide insights into the origins and evolution of titanite in the Emeishan basalts, as well as formation of the polymetallic Nb layer in the lowermost Xuanwei Formation in the eastern Yunnan–western Guizhou region, southwest China. [Display omitted] • Nb-rich titanite is widely present in the Emeishan basalts in the southwest China. • The titanite originated from fractional crystallization and weathering alteration. • The Nb-rich anatase in the Xuanwei Formation was derived from ELIP basalts. [ABSTRACT FROM AUTHOR]

Many granitoids and their eruptive equivalents are substantially derived from the uppermost proportion of continental crust, and so their petrogenesis and source are significant in understanding the evolution and characteristics of continental crust. The Eocene felsic rocks in the Qiangtang block (central Tibet) commonly have enriched Nd isotope compositions and have been considered to be related to the recycling of ancient continental crustal material. In this paper we report new data on early Eocene felsic rocks with positive ε Nd (t) values in the northeastern Qiangtang block, which can be used to help understand Cenozoic evolution and characteristics of continental crust in the Qiangtang block. These rocks consist of rhyolites and occur in the Shanglaxiu and Xialaxiu areas in the north−eastern Qiangtang block. Zircon U−Pb dating yields ages of 47.8 ± 0.6 and 44.2 ± 0.7 Ma for the Shanglaxiu and Xialaxiu rhyolites, respectively, and so they represent the earliest record of Eocene magmatism in the Qiangtang block. The Shanglaxiu−Xialaxiu rhyolites have relatively low calculated zircon saturation temperatures (719–819 °C), along with high SiO 2 (74.8–83.3 wt%) and K 2 O (5.1–7.8 wt%) contents, and low MgO (0.2–0.3 wt%), Cr and Ni contents. They are enriched in light rare earth elements (LREEs), Rb, K, Th, Zr, and Hf, and are depleted in Nb, Ta, Ti, Sr, and P, with moderately negative Eu anomalies. The Shanglaxiu rhyolites have positive whole−rock ε Nd (t) (0.3–0.4) and zircon ε Hf (t) (1.8–10.4), and variable zircon δ18O (6.3–7.3‰). The Xialaxiu rhyolites have slightly different whole−rock ε Nd (t) (−1.5 to −1.6), but similar zircon ε Hf (t) (2.2–7.7) and δ18O (6.7–7.2‰). We propose that the Shanglaxiu−Xialaxiu rhyolites were most probably generated by partial melting of the pre−existing juvenile crust with the addition of minor sedimentary material. This partial melting was possibly triggered by the south−dipping continental subduction of the Songpan−Ganzi block. The pre−existing juvenile crust was probably formed during the subduction of Paleo−Tethyan oceanic slab in Paleozoic−Early Mesozoic. • The Shanglaxiu-Xialaxiu rhyolites were formed at 44–48 Ma. • These rhyolites were generated by partial melting of juvenile crust and sediments. • These rhyolites were formed during continental subduction. • The juvenile crust might be formed during Paleozoic-Early Mesozoic. [ABSTRACT FROM AUTHOR]

Late Neoarchean to early Paleoproterozoic potassic granites and mafic dykes are widely distributed across the Eastern Block (EB) of the North China Craton (NCC), which provide important information about the geodynamic origin and tectonic evolution of Archean terranes. Here, we are first to report the zircon U–Pb–Hf isotopic and whole-rock compositions of potassic granites and mafic dykes from the Liaoxi Rise of the Liaodong Bay Depression (LBD) in the offshore Bohai Sea Basin (OBSB) of the northeastern NCC. The potassic granites have crystallization ages of 2499–2460 Ma and are characterized by variable SiO 2 content (63.2 to 72.3 wt%) and high K 2 O (3.27–6.88 wt%). In addition, they show geochemical features akin to post-collisional related granites and possess positive zircon ε Hf (t) values of 0.9 to 4.95, suggesting that they mainly originated from the partial melting of high-K mafic rocks and formed under the post-collisional setting. The mafic dykes have a crystallization age of 2485 Ma. They show high Nb (8.64–9.39 ppm) and high Nb/U ratio (10.3–14.8), as well as radiogenic initial zircon Hf isotopes (﹢1.26–﹢4.39). These values indicate affinities with Nb-enriched basalts and that they originated from mantle-derived magma under a subduction-related back-arc extensional setting. Combined with previous research results, we believed that magmatic rocks of the LBD area may have formed under remote effects of oceanic slabs being subducted from the northwest to southeast of the eastern Hebei–western Liaoning Province back-arc basin system during the late Neoarchean to early Paleoproterozoic. Meanwhile, the K-rich granitoid rocks and coeval mafic dyke sequences imply the increased maturity of the continental crust and late Neoarchean to early Paleoproterozoic basement initiation of cratonization in the NCC. • Potassic granites and mafic dykes from offshore Bohai Sea formed at ca. 2.5 Ga. • Their geochemical and geochronological investigation reveal a back-arc extensional setting. • They recorded the Late Neoarchean basement initiation of cratonization in the North China Craton. [ABSTRACT FROM AUTHOR]

It is widely believed that the melting of mantle wedge in a subduction zone is triggered by the influx of fluids. However, experimental petrology studies have yielded conflicting results regarding temperatures for the wet solidus of mantle metasomatite, either below or above that of mantle wedge. In the latter case, the influx of fluids cannot trigger mantle melting, particularly in a cold subduction zone. Late Paleozoic magmatic rocks in the Western Yunnan Tethyan belt have been interpreted as being products of the first-stage subduction-related magmatism in the cold subduction zone and are thought to carry crucial information about mantle–wedge melting. Here, we report zircon ages and whole-rock geochemical data for these magmatic rocks to identify both the origin of the magmatism and the mechanism of mantle melting. Rock samples collected from the Nanlianshan complex and the Daxinshan Formation yielded zircon ages ranging from 303 Ma to 297 Ma. The samples can be classified into two groups based on geochemical features. Group I magmatic rocks have higher Ba/Th and lower Th/Nb ratios and depletion in Nd Hf isotopes [ε Nd (t) 2.9–5.0; ε Hf (t) 5.7–14.6], whereas Group II rocks show relatively lower Ba/Th and higher Th/Nb ratios and relative enrichment in Nd Hf isotopes [ε Nd (t) 0.7–4.0; ε Hf (t) 4.1–10.7]. The two groups of rocks may have originated from different mantle domains that were metasomatized by slab-derived aqueous fluids and by sediment-derived melts, respectively. We hypothesize that slab rollback during closure of the Paleo-Tethyan Ocean prompted mixing of different mantle domains; subsequently, the multiple mantle was heated by the laterally flowing asthenosphere, and partial melting occurred. • Two groups of Carboniferous magmatic rocks can be recognized in Nanlianshan, Tethyan Yunnan. • Slab-derived fluid and sediment-derived melt successively modified the mantle wedge. • Rollback of slab triggered melting of different mantle domains without extra fluid influx. [ABSTRACT FROM AUTHOR]

Rodingitization is the metasomatic transformation of mafic lithologies into rodingite, a Ca-rich and Si-poor rock associated with serpentinized ultramafic bodies. Serpentinization and rodingitization occur simultaneously but it remains challenging to obtain absolute ages on these events in order to identify the geodynamic setting of their formation. In this study, we investigate rodingites from an occurrence in the Western Carpathians with the aim to define the timing of rodingite formation during the tectono-metamorphic evolution of the Carpathian Orogen. The rodingites consist mainly of vesuvianite, diopside, garnet and chlorite. They are noticeably characterized by the presence of Fe Ti rich aggregates composed of ilmenite, rutile, titanite and calcite. Textural relationships and chemical compositions of the investigated Fe Ti minerals document their hydrothermal-metamorphic origin. These minerals are characterized by considerable rare earth element (REE) concentrations with prevailing positive Eu anomaly, which presumably derives from the plagioclase-rich protolith of the investigated rodingites. Moreover, the similarity of REE patterns between the analysed phases suggests that the REE concentrations in Fe Ti minerals are controlled by the immobility and availability of these elements in the system. A particular lamellae texture composed of rutile and calcite originated from titanite destabilization. The titanite destabilization was triggered by cooling, silica leaching and influx of CO 2 -rich fluids. In situ U Pb dating of rutile, which have formed by retrograde breakdown of titanite during rodingitization, yields a crystallization age of 102.6 ± 19.9 Ma. This age is in good agreement with Cretaceous ages of the regional alpine metamorphic evolution reported in the literature and suggests that the rodingitization and serpentinization processes took place during the exhumation and cooling of the accretionary wedge resulting from the closure of the Meliata Ocean. • Fe-Ti rich aggregates occur in rodingites from the Western Carpathians. • The aggregates consist of ilmenite, rutile, titanite and calcite. • Rutile formed by retrograde breakdown of titanite. • Crystallization age of rutile is 102.6 ± 19.9 Ma, consistent with Alpine metamorphism. • Rodingitization took place during exhumation and cooling of an accretionary wedge. [ABSTRACT FROM AUTHOR]

The Bangong–Nujiang suture zone (BNSZ) is the remnants of the Meso-Tethyan main oceanic basin in the Tibetan plateau. It is noted that several microcontinents, e.g., Amdo and Jiayuqiao, occur within the Meso-Tethyan ocean basin. These microcontinents were strongly reworked associated with the subduction and closure of this ancient ocean, thus they play a key role in understanding the evolution of this ocean. In this contribution, we report newly documented Early Jurassic gabbros (ca. 182–175 Ma) from the Amdo microcontinent in the middle segment of the BNSZ. The gabbros can be subdivided into two groups, i.e., OIB (ocean island basalt) and MORB (mid-ocean ridge basalt) groups. The OIB-group gabbros are characterized by highly enriched Nd Hf isotopic characteristics (zircon ε Hf (t) = −11.7 to −8.9; whole-rock ε Nd (t) = −11.0 to −10.1). They are geochemically similar to OIB and are interpreted to be products of the partial melting of a relatively deep mantle source (> 85 km) and subsequent continental crustal inputting. The MORB-group gabbros belong to the tholeiitic series and have similar compositions to those of MORB. They were most likely derived from a depleted mantle source (zircon ε Hf (t) = +3.7 to +16.5; whole-rock ε Nd (t) = +4.9 to +8.1) in a relatively shallow depth (< 85 km). Integrating previous studies with the data presented in this contribution, we suggest that the generation of coeval OIB- and MORB-like gabbros are related to lithospheric delamination after the Qiangtang-Amdo collision and the closure of the Bangong-Nujiang ocean basin. This result will give new constraint on the evolution of the Meso-Tethyan Ocean. • Early Jurassic gabbroic dikes were newly documented in the Amdo microcontinent, central Tibet. • Gabbroic rocks display different geochemical compositions with OIB and MORB features. • Zircon U-Pb dating on gabbroic rocks yielded nearly uniformed ages of 182–175 Ma. • Gabbroic rocks were formed by the lithospheric delamination after the Qiangtang-Amdo collision. [ABSTRACT FROM AUTHOR]

Crystal-rich (>30 vol%) volcanic rocks, which are generally thought to be formed by the eruption of crystal-rich mush after its reactivation, have provided an important lens through which to view the connection of volcanic and plutonic rocks in the calderas worldwide. The crystal-rich rhyolitic porphyritic lava is widely exposed in Cretaceous calderas in the southeast China. However, the petrogenesis of crystal-rich porphyritic lava still remains controversial. Xiangshan caldera is a uranium mineralization related volcanic-plutonic complex, which is composed of first subcycle rhyodacite and second subcycle tuff, crystal-rich rhyolitic porphyritic lava, granite porphyry and quartz monzonitite porphyry. All the volcanic and plutonic rocks have consistent zircon U-Pb ages (135 to 133 Ma). Sr-Nd-Hf-O isotopic characteristics show that they all mainly originated from crust derived intermediate-silicic magma. Zircon ε Hf (t) values for inherited zircons from rhyolitic porphyritic lava and rhyodacite range from −6.9 to +9.5. Correspondingly, zircon Hf two-stage model ages of inherited zircons are 2.12 to 1.10 Ga, suggesting their derivation from the Neoproterozoic juvenile crust and the Archean to Paleoproterozoic ancient crust. The rhyolitic porphyritic lavas show higher SiO 2 contents and Rb/Sr ratios, and more obvious negative anomalies of Eu/Eu*, Ba, Sr, P and Ti; The granite porphyry show lower SiO 2 contents and Rb/Sr ratios, with weak negative anomalies of Eu/Eu*, Ba, Sr, P and Ti. Combined with similar Sr-Nd-Hf-O isotopic composition, they may be derived from the same magma reservoir. Lower ε Nd (t), ε Hf (t), δ 18O values and older model ages of tuff indicate more contribution of older crustal material. The cathodoluminescence (CL) brightness is strongly correlated with Ti concentration in quartz. The CL of selected quartz grains from crystal-rich rhyolitic porphyritic lava and granite porphyry show brightness zoned mantles (Ti = 19 to 77 ppm) and bright rims (high-Ti; >70 ppm). Some grains have dark cores (low-Ti; <9 ppm). However, the Ti contents of the quartz in the tuff of the second subcycle are homogeneous. Resemble the crystal-rich rhyolitic porphyritic lavas, the rims of quartz phenocrysts in the granite porphyry have consistent CL-brightness with the quartz in groundmass and have small embayments caused by growth impediments in them, which is due to the pressure release. It indicates that the granite porphyry also migrated upward rather than in situ cumulate. The repeated rise of CL brightness and Ti contents in the mantle of quartz phenocrysts recorded the rise of temperature and/or the injection of more primitive magma, indicating several times of magma recharge in the magma reservoir. The timescale of Ti diffusion in the compositional zoned mantle of quartz documented an ephemeral reactivation and remobilization of the crystal-rich mush within several to 16 thousand years with at least 7 times of magma recharge which lasted for 17 years to >11 thousand years each time. [Display omitted] • Decoupling of zircon Hf-O isotopes may indicate the recharge of crustal magma. • The magma derived from reactivated mush may show some features of accumulation. • The remobilization of mush with multiple recharges is probably an ephemeral event. • The reactivation often includes multiple magma recharges in the magma reservoir. [ABSTRACT FROM AUTHOR]

Zoned magmatic enclaves (MEs) within granitic intrusions provide valuable insights into the pre-intrusive processes involved in the formation of granitic magmas. This study focuses on the Taejongdae granite in Busan, Korea, which features uniquely zoned MEs, and aims to constrain the processes involved in their formation. Through a whole-rock geochemistry analysis, SHRIMP U-Pb zircon dating, and Lu-Hf isotope data, we investigated the geochemical characteristics and origin of the two magmas responsible for the zoned MEs (that is, dioritic and host granite magmas). Our findings have shown that the host granite aligns with the Bulguksa granites in the Gyeongsang Basin, which represent the I-Type magma resulting from the fractionation of magma generated through partial melting of the continental crust. In contrast, the dioritic magma exhibits a low K 2 O composition, high Sr content, and a positive-to-no Eu anomaly, indicating its formation via amphibole-dominated fractional crystallization under different pressure–temperature conditions. Both magmas share the same Cretaceous age and Hf ratios. The zoned MEs in the study area provide compelling evidence of magma mixing processes that occur between the outer dioritic zone and mafic core of the enclaves. However, the relationship between the outer dioritic zone and the host granite suggests limited interaction between the enclaves and host granite. This implies that mixing within the zoned enclaves occurred prior to enclosure in the host granite. By highlighting the significance of zoned magmatic enclaves, this case study advances our understanding of the pre-intrusive processes involved in the formation of granitic magmas, including magmatic mixing, mingling, and fractionation. These results offer important insights into the origin and geochemical characteristics of the two magmas and their interactions, thus contributing to a broader understanding of crustal evolution in subduction-related settings. • This study focused on uniquely zoned magmatic enclaves in the Taejongdae granite. • SHRIMP U-Pb dating and Lu-Hf isotopes were used for the study of zoned enclaves. • The low-K and Bulgusa magmas of Taejeongdae share origins, but not fractionation. • Zoned MEs reflect the magmatic processes that took place before pluton intrusion. • Zoned enclaves can form if a magma entrained another (chemically different) magma. [ABSTRACT FROM AUTHOR]

Identifying the spatio-temporal variations of arc-relation magmatism is critical for determining the polarity, geometry, localization, and onset of subduction zones on Earth. When and how the Paleo-Asian oceanic plate subducted beneath the northern margin of the North China Block (NCB) have been widely debated. Here we conducted systematic petrological, geochronological, and geochemical investigations on the Paleozoic magmatic rocks in the northern NCB. The Early Paleozoic magmatic rocks (ca. 490–420 Ma) are only distributed in the Bainaimiao arc and show typical continental arc geochemical characteristics, indicating a south dipping subduction zone. The Devonian alkaline rocks (ca. 400–370 Ma) constitute a ∼ 900 km-long magmatic belt in the northern margin of the NCB. Combined with a striking ca. 370–355 Ma magmatic quiescence and the absence of high-pressure rocks during that period, a flat-slab subduction model is proposed to better account for the tectonic evolution of the northern NCB. Subsequently, the Carboniferous to Permian calc-alkaline arc magmatism (ca. 355–250 Ma) began to emerge and showed northward younging and migration, suggesting slab retreat with roll-back of the subducting Paleo-Asian slab and again opening of mantle wedge along the northern NCB. Our findings therefore suggest that the Paleozoic magmatism in the northern NCB records an entire spatio-temporal evolution of the Paleo-Asian oceanic plate from early subduction angle deepening to flat-slab subduction, then slab rollback and finally normal subduction. This is tentatively interpreted as a combined effect from the Paleo-Asian oceanic plate subduction angle change and a migrating keel in the mantle wedge region. • Three Paleozoic magmatic pulses are recognized in northern North China Block (NCB). • Paleozoic magmatism records subduction from deeping to shallowing, and to rollback. • Subducting oceanic plate angle change dominates the features of northern NCB. [ABSTRACT FROM AUTHOR]

The Abaga volcanic rocks are intraplate basalts that formed in the late Cenozoic period and are located in eastern central Inner Mongolia. Previous studies have discussed the genesis of the studied basalts. However, limited information about subducted recycled materials (the water content, sediments, and melts of the subducted plate), which control the generation of basalts, in the studied basalts has been reported. In this study, the major element abundances and crystallization temperatures and pressures of clinopyroxenes have been reported to estimate the water content of the studied magma, which has been applied to the Wulanhada volcanic field. The calculated result displays that the water content in the Abaga melts are between 0.5% and 1.7% (standard error estimate: 0.45%; average value: 1.3%). These estimated values are in range of the Aershan–Chaihe basalts (0.19–2.7%), while it is higher than those of the mid-ocean ridge basalts (MORBs: 0.16–0.47%). The high-water content of the studied basalts may have a close relationship with the mantle transition zone, which has also been reported to contain high concentrations of H 2 O. Subduction related sediments and slab may contribute to high-water content of magma. In addition, the clinopyroxene-melt thermobarometer shows that clinopyroxenes generally crystallized at 1113–1246 °C at the crustal level (3.8–12.4 kbar), while olivines formed at 1243–1392 °C (assuming pressure is 13 kbar, H 2 O = 1.3%). We also studied whole-rock major and trace elements and Sr–Nd–Hf–O isotope compositions of the Abaga basalts. High (Ta/U) N and (Nb/Th) N values that are higher than 1, Nd Hf isotopic values that plot between sediments and oceanic crust, and low δ18O values (4.51–5.59‰) of the alkali basalts illustrate that a subducted oceanic slab may have been added to the studied mantle source. In addition, we decipher that sediments may also exist in the source with Ba/Th, Nb/La, Ce/Pb and Ba/La ratios and Nd Hf isotopic values locating between sediments and altered oceanic crust. We use sediments, depleted MORB mantle (DMM), and recycled oceanic crust to simulate mixing features among these endmembers, which demonstrates that 80% of depleted MORB mantle, 15% of altered oceanic crust, and 5% of global subducting sediment (GLOSS), with 4–5% partial melting of peridotite or pyroxenite is a proper result with which to interpret the genesis of the studied alkali basalts. • Clinopyroxene crystallized at 1113–1246 °C (3.8–12.4 kbar), while olivines formed at 1243 to 1392 °C. • δ18O values (4.51–5.59 ‰) of the basalts illustrate that subducted oceanic slab has been added to the mantle source. • The water content in the Abaga melts is about 0.5–1.7%, which may attribute to mantle transition zone. [ABSTRACT FROM AUTHOR]

The East Qinling Orogen as an important segment of central China that records a complex tectonic evolution history. The Huangbeiling pluton is a rare S-type granite in this orogen and has vital significance in understanding the tectonic evolution of the Qinling Orogen during the Late Mesozoic. The biotite monzogranite of this pluton is the major ore-hosting rocks of the Yumugou Mo-W deposit. In this study, we newly reported a muscovite monzogranite and conducted detailed petrological, geochemical (whole-rock, biotite, muscovite major and trace elements), and zircon U-Pb dating investigations on both the biotite and muscovite monzogranites from the Huangbeiling pluton, with a view to reveal their physico-chemical conditions of formation, petrogenesis and tectonic evolution. Zircon U-Pb dating yielded a weighted mean 206Pb/238U age of 126.8 ± 0.6 Ma for muscovite monzogranite, integrated with published zircon U-Pb age (156–132 Ma) of biotite monzogranite, indicating that the Huangbeiling pluton was produced by two episodes of magmatism during the Late Mesozoic. The pluton shows formation temperatures in the range of 670–772°C, and is classified as cold granites that formed in a subduction-related setting. The emplacement depth of Huangbeiling pluton is constrained at ca. 0.3–4.6 km, with an average depth of 2.0 km. The biotite monzogranite has higher oxygen and fluorine fugacities than the muscovite monzogranite, suggesting high potential for Mo mineralization. Geochemically, the muscovite monzogranite is identified as a S-type granite sourced from crust-derived clay-rich mudstone, and underwent muscovite dehydration melting and subsequent fractional crystallization of K-feldspar and plagioclase during magma ascend. In combination with the syn - to post-collision geochemical affinities of the Huangbeiling pluton and the Late Mesozoic tectonic evolution of the Qinling Orogen, we propose two episodes of magmatism in the Huangbeiling pluton during the tectonic transition (150–125 Ma) from compression to extension in the Qinling Orogen. The first episode (156–132 Ma) of magmatism is correlated with the delamination of lithospheric mantle and intra-continental subduction of the North China Craton under compressional tectonics, whereas the second episode (∼126 Ma) of magmatism occurred through muscovite dehydration melting during pressure decrease. [Display omitted] • Two episodes of Late Mesozoic magmatism developed in the Huangbeiling pluton. • The Early Cretaceous S-type granite is identified in the East Qinling Orogen. • Huangbeiling granites belong to cold granite related to subduction tectonics. [ABSTRACT FROM AUTHOR]

The Strandja Zone (SE Bulgaria/ NW Turkey) comprises tectonic units affected by Late Jurassic to Early Cretaceous upper greenschist- to amphibolite-facies metamorphism. A contemporaneous tectonothermal event occurred in the Rhodope Metamorphic Complex, which has led to many authors correlating both zones. Three tectonic units can be distinguished in the Bulgarian part of the Strandja Zone: the Sakar, Strandja and Veleka units. This study focuses on albitized rocks of the Sakar Unit that are suspected to be related to this tectonothermal event. Albitized samples were collected from the Late Carboniferous Sakar Batholith, while for comparison country-rock orthogneiss unaffected by albitization was also analyzed. Geochemical and petrological studies indicate that albitization was coupled with the removal of quartz and the growth of rutile-rich aggregates replacing titanite. U Pb rutile dating of an orthogneiss (ca. 154 Ma) confirms Late Jurassic amphibolite-facies conditions, whereas rutile from albitized metagranitoids yields Early Cretaceous ages (ca. 125–116 Ma). Zr-in-rutile thermometry reveals similar crystallization temperatures (∼530-620 °C) for the albitized Sakar granitoids and country rock orthogneiss. U Pb zircon and titanite dating implies a Late Carboniferous crystallization age for various granitoids forming the Sakar Batholith. Our results indicate that at least some parts of the Sakar Unit were affected by thermal events and associated albitization in the Early Cretaceous. However, this did not lead to the formation of a new penetrative fabric, unlike in the Rhodopes, where contemporaneous regional metamorphism is associated with penetrative deformation. • U Pb rutile dating reveals two thermal events in the Strandja Zone. • Early Alpine metamorphism affected the Strandja Zone in the Late Jurassic. • The NW Strandja Zone was also affected by a thermal event in the Early Cretaceous synchronous with albitization. • Zr-in-rutile thermometry showed that these events reached similar temperatures (∼530-620 °C). • Albitization caused the breakdown of titanite to rutile-rich aggregates. [ABSTRACT FROM AUTHOR]

Fluid and mineral inclusions in metamorphic rocks allow the understanding of fluid-involved processes in subduction-zones providing essential contributions to the nature of geochemical processes and element cycling in present day subduction zones. In this work, we studied ultramafic granulite from the high-pressure (HP) and high-temperature (HT) metamorphic series of the Cabo Ortegal Complex, Spain, combining quartz-in-garnet and zircon-in-garnet Raman spectroscopy-based elastic geothermobarometry with Ti-in-quartz trace element thermometry. The studied quartz and zircon inclusions occur within garnet, together with rutile and multiphase fluid inclusions (MFI). Textural evidence, like occurrence in the same 3D cluster and common intergrowth of mineral inclusions, shows that both crystal inclusions and MFI were likely entrapped simultaneously. Hence, the application of elastic thermobarometry to quartz and zircon inclusions in these rocks provides excellent opportunity to define P-T environment of entrapment. Results from Raman spectroscopy on multiple quartz and zircon inclusions showed that the remnant elastic inclusion pressure (P inc) at room conditions for both (on average 0.51 ± 0.04 GPa and 0.72 ± 0.05 GPa for the quartz and zircon inclusions, respectively) fall within the range of 2σ uncertainty confirming the crystallization within the same growth-stage of garnet. Intersection of the entrapment isomekes is at a P-T of 1.8 ± 0.2 GPa and 880 ± 70 ° C. Electron microprobe measurements on quartz inclusions from the same garnet zone show uniform Ti concentrations (45–59 ppm). Isopleths calculated from Ti-in-quartz thermometer intersect the average quartz-in-garnet isomeke within the P-T range indicated by the intersection of quartz and zircon entrapment isomekes, which is P = 1.8 ± 0.2 GPa and T = 860 ± 70 °C. Besides, we made a comparison of different reference materials applied for zircon-in-garnet elastic thermobarometry verified by independent Ti-in-quartz trace element thermometry. Our findings indicate that elastic thermobarometry on mineral inclusions provide a reliable constraint on the entrapment P-T conditions of coexisting fluid inclusions. • Mineral and fluid inclusion entrapment at 1.8 ± 0.2 GPa, 870 ± 70 °C in granulite. • Combined use of zircon-in-garnet elastic and Ti-in-quartz trace element thermometry. • Quartz and zircon in garnet provide P-T entrapment data on fluid inclusions. • Elastic thermobarometry can be successfully combined with fluid inclusion studies. [ABSTRACT FROM AUTHOR]

Abstract Whole-rock major and trace elements, zircon U Pb geochronology and Hf isotopic data have been implemented for the felsic rocks from the Sishijia pluton in southeastern Inner Mongolia, North China, in order to determine their petrogenesis and futher constrain the termination of Paleoasian Oceanic subduction in southeastern Central Asian Orogenic Belt. Petrographic observation indicates that Sishijia granitoids mainly consist of syenogranites and porphyritic granites, with the major mineral compositions of alkaline feldspar, quartz, plagioclase and biotite, without any alkaline melanocratic or peraluminous minerals. Miarolitic structures are widely developed in these granitoids, indicating for the characteristics of shallow emplacement depth and rapid condensation. Zircon LA-ICP-MS U Pb dating yields weighted mean ages of 256.2 ± 1.4 and 250.9 ± 1.2 Ma for syenogranites, and 251.6 ± 1.4 Ma for porphyritic granites, representing a Late Permian magmatism record. These granitoids exhibit weakly peraluminous nature (A/CNK = 1.03–1.08) with high SiO 2 (76.50–81.92 wt%) and K 2 O (3.64–5.56 wt%) concentrations and differentiation index values (D.I. = 93.8–97.2). Chondrite-normalized REE patterns of these samples display enrichment of LREE with high ratios of (La/Yb) N (12.29–30.34) and significant negative Eu anomalies (δEu = 0.15–0.53). In mantle-normalized multielement variation diagrams, they are all characterized by typical depletions of Ba, Nb, Ta, Sr, P, and Ti and enrichments of Rb, Th, U, and K. Petrological and geochemical features of the pluton indicate a highly fractionated I-type affinity. Zircon Hf isotope analyses show variably negative ε Hf (t) values ranging from −13.7 to −4.0 and corresponding two-stage model ages varying of 2148–1540 Ma, indicating that they were derived from an Paleo- to Mesoproterozoic crustal source with minor juvenile materials. In combination with previous geological evidences, it is reasonable to propose that the Sishijia granitoids emplaced in a post-collisional extension regime during the transformation from pre-collision to post-orogenic, which symbolize a Late Permian final closure of Paleo-Asian Ocean in southeastern segment of the Central Asian Orogenic Belt. Highlights • Late Permian (256–250 Ma) granites from southeastern Inner Mongolia • They are of high-K calc-alkaline series with highly fractionated I-type affinity. • These granites were emplaced in a post-collisional extension geodynamics setting. • The final closure of the Paleo-Asian Ocean occurred in the Late Permian. [ABSTRACT FROM AUTHOR]

Abstract The origin, evolution and long-term preservation of andesitic continents within the context of destructive plate boundaries are still enigmatic for geoscientists. Here we use U Pb zircon geochronology and whole-rock geochemical data of arc and forearc lithologies from the Mexican convergent margin to show that subducted trench sediments and eroded forearc debris are being tectonically transported and magmatically reworked into a typical intermediate continental volcanic arc edifice: Malinche volcano. We find that the remarkable variety of inherited zircons carried by the Malinche magmas — with ages ranging from the Early Miocene (~16 Ma) to the Paleoproterozoic (~1.8 Ga) — have not been acquired during ascent through the upper plate crust but incorporated into a subduction mélange constituted by a heterogeneous mixture of tectonically eroded forearc debris, sediments, hydrous mantle and altered ocean floor basalts. We suggest that partial melting of subduction mélanges can form intermediate volcanoes like Malinche without the intervention of parental basalts. These findings imply a fast and efficient connectivity between subduction inputs and magmatic outputs and indicate that a significant proportion of the subducted continental crust is being reincorporated back into continents by primitive intermediate arc magmatism. Highlights • A variety of inherited zircons are found in a continental arc volcano. • Inherited zircons come from recently 'relaminated' subducted debris. • Intermediate arc magmas form by melting of subduction mélanges. • Subducted continental crust is efficiently reincorporated back into continents. [ABSTRACT FROM AUTHOR]

Abstract U Pb and Lu Hf isotope ratios measured in zircon crystals from magmatic and metamorphic rocks provide crucial information to understand the origin and tectonothermal evolution of allochthonous terranes, and can contribute to paleogeographic reconstructions and to the understanding of orogenic processes. We investigate the age of magmatic and tectonothermal events, and the provenance of a high-pressure unit from the Ossa-Morena Complex (SW Iberian Massif). Zircons for LA-ICP-MS analyses were separated form garnet-bearing amphibolites (retroeclogites) and quartzo-feldspathic gneisses from the Central Unit (Coimbra-Córdoba shear zone). Recent geological correlations propose that the high-pressure units cropping out in the Ossa Morena Complex of the SW Iberian Massif are equivalent to the Basal Allochthonous Units of NW Iberian Massif, and one of the objectives of the study is to check the validity of the proposed correlation. The new obtained ages presented in this study indicate that the high-pressure metamorphism of the Central Unit developed in the Variscan cycle. The metamorphic zircons reveal two distinct events: a younger one well constrained by an age of 339 ± 4 Ma and an older one of 377 ± 19 Ma. The former coincide with the age of the high-grade and post-high-P metamorphism described in other areas of the Ossa-Morena Complex, whereas the second one is interpreted as the age of the high-P metamorphism. The igneous ages of metabasites and metagranitoids (c. 585–615 Ma and c. 480–577 Ma, respectively) reveal a diachronism between magmatic events in Allochthonous Units from the SW and the NW Iberian Massif, suggesting that both domains were located in different parts of the North-Gondwanan margin. The magmatic ages of the metagranitoids resemble the evolution described for the lower paleozoic rifting in the Ossa-Morena Complex. The relatively juvenile character of the basic and acid Cadomian magmatism in the Central Unit, revealed by the new Lu Hf data, indicate limited mixing of mantle melts with crustal components, which is compatible with a generation in a continental magmatic arc. These similarities in the metamorphic and magmatic evolution support the correlation of the Basal Allochthonous Units from the SW and NW domains of the Iberian Massif. Highlights • The age of the High- P metamorphism in the Ossa-Morena Domain is Variscan. • The juvenile Cadomian magmatism points to generation in a continental magmatic arc. • The magmatic ages suggest diachronism along the North-Gondwanan margin. [ABSTRACT FROM AUTHOR]

The Saveh magmatic complex is a composite intrusion of diorite to tonalite. It is part of the Urumieh-Dokhtar magmatic arc in central Iran. Zircon U Pb dating indicates that emplacement and cooling occurred 37–40 Ma ago in late Eocene (Bartonian) time. Saveh igneous rocks define a continuous mafic-felsic continuum in terms of SiO 2 (55.4–70.8 wt%), Al 2 O 3 (14.2–19.8 wt%) and CaO (6.4–17.1 wt%) contents. The initial values of 87 Sr/ 86 Sr and ɛ Nd (t) are 0.7048 to 0.7062 and + 2.6 to +3.4 (Mean = +2.9). Nd model ages (T DM  = 555 to 616 Ma) are consistent with derivation from Iranian continental crust and subcontinental lithospheric mantle of Cadomian age (500–600 Ma). Saveh igneous rocks are enriched in K, Cs and Pb and depleted in P, Nb and Ta, indicating that the magma source was moderately affected by slab-derived fluids, as expected for the Eocene tectonic environment. The continuum of rock types from diorite to graphic eutectic tonalite indicates that magmatic evolution was controlled by the F (FeO + MgO + MnO)-Anorthite (An)-Orthoclase (Or) cotectic with minor contamination by supra-crustal components. Similar initial ratios of 87 Sr/ 86 Sr and 143 Nd/ 144 Nd for all of the rocks and the slightly younger age of tonalitic rocks (2–3 Ma younger) further indicate that the crystallization of quartz and plagioclase with graphic texture occurred in the final stage of magmatic differentiation. Saveh magmas reflected partial melting of Iranian subcontinental lithospheric mantle due to extension above the Neo-Tethys subduction zone. [ABSTRACT FROM AUTHOR]

The ultra-high pressure metamorphic rocks of the West Gondwana Orogen are the earliest evidence of deep subduction on Earth. The West Gondwana Orogen resulted from the closure of the Pharusian-Goianides Ocean in the Late Neoproterozoic, leading to the formation of the Santa Quitéria Continental Magmatic Arc (SQCMA) in NE Brazil and the Forquilha Eclogitic Zone, located on the western margin of the SQCMA, suggesting subduction from W to E. This research investigated and reports the occurrence of a coesite-bearing eclogite on the eastern margin of SQCMA, bringing new insights into the regional tectonic evolution of the West Gondwana Orogen. Although extensively retrogressed during exhumation, the coesite-bearing eclogite still records UHP conditions. The multiple stages of the pressure-temperature path were reconstructed by combining textural relationships, integrating symplectite domains in compositional maps, phase equilibrium modeling and Zr-in-rutile thermometry. The pressure peak is estimated at 35.8 ± 5.2 kbar, reached at a temperature from 700 ± 15 °C to 804 ± 15 °C. Retrogression formed symplectite and corona textures at ca. 18 kbar and 760–860 °C. Our results indicate a clockwise P-T path that is characterized by a nearly isothermal decompression associated with a slight temperature increase after the baric peak, followed by decompression and cooling. Geochronological data indicate that the UHP rocks were metamorphosed in the Brasiliano/Panafrican orogenic event during the Western Gondwana amalgamation in the Neoproterozoic. Remnants of intra-oceanic arcs were described at the SQCMA eastern margin. We propose two main tectonic models for the evolution of these rocks: i) double subduction with convergent polarities to E -SE and W-NW, which can be correlated to the scenario proposed to the Hoggar belt in NW Africa and is also supported by geophysical data, and ii) exhumation of the eclogite as a diapir in the mantle wedge. • New UHP occurrence of coesite-bearing retroeclogite in the Western Gondwana margin. • Two UHP eclogites occurrences separated by a continental magmatic arc in the NE Brazil. • UHP conditions are revealed by coesite relics and phase equilibrium modeling. • U-Pb rutile dating reveals different exhumation ages for the two UHP retroeclogite. • Two possible tectonic models: a double subduction and a diapirism-related exhumation. [ABSTRACT FROM AUTHOR]

Multi-mineral petrochronology can effectively track changes in the thermochemical environment experienced by rocks during metamorphism. We demonstrate this concept using garnet–chlorite schists from the Walter-Outalpa Shear Zone of the southern Curnamona Province, South Australia, which reveal a cryptic and protracted (c. 39 Myr) record of high thermal gradient metamorphism. Petrochronological data including in situ monazite U–Pb and garnet Lu–Hf and Sm–Nd dating suggest elevated geotherms were persistent between at least c. 519–480 Ma, throughout the duration of garnet growth. Additional in situ xenotime U–Pb dating implies that partial garnet breakdown occurred between c. 480–440 Ma, likely induced by fluid-rock interaction or exhumation. Although metamorphism temporally overlaps with the timing of the regional Delamerian Orogeny (c. 520–480 Ma), the thermal mechanism to sustain elevated temperatures has remained enigmatic. One-dimensional thermal models are used to appraise the role of radiogenic heat production in driving the observed high thermal gradient metamorphism. The models reveal that with only modest crustal thickening during orogenesis, the endogenous radiogenic heat production hosted within the basement rocks could plausibly provide the thermal impetus for metamorphism. • Protracted metamorphism in the southern Curnamona Province between c. 519–480 Ma. • Fluid-rock interaction or exhumation occurred between c. 480–440 Ma. • Radiogenic heat produced by basement lithologies likely drove metamorphism. [ABSTRACT FROM AUTHOR]

Diverse assemblages of metal alloys occur within ultramafic rocks from a wide range of tectonic settings and geological environments. Alloys are typically small and can be difficult to find and identify, but they can host Re and Os, which are significant for geochronology, as well as other elements of economic interest, and can act as catalysts that help to form organic compounds. The alloys typically form from elements that show chalcophile and siderophile characteristics, indicating that alloys generally form under reducing, S-poor conditions. These conditions can be generated by a range of mechanisms that differ amongst alloy-forming environments, but include desulfidation during melting, exsolution from magmatic S-bearing phases during melt crystallisation, auto-hydrothermal, and sub-solidus processes involving a reduction in f S 2 , and electron transfer processes related to serpentinisation. Alloy formation during serpentinisation is typically associated with the formation of a companion phase that hosts Fe3+, such as Fe3+-bearing serpentine, magnetite, ferrit-chromite, or andradite, recording disproportionation of Fe2+ released by olivine alteration to form Fe0 and Fe3+. An additional source of electrons for alloy formation is provided by the reduction of H+ in water to H 2 , and the reduction of water activity couples with a reduction in f S 2 , driving desulfidation reactions and facilitating alloy formation. Other electron donors, such as methane, may also contribute to alloy formation. Alloy-forming serpentinites are strongly internally-buffered, but can follow a range of trajectories through compositional space. Serpentinite-hosted alloys offer opportunities to better understand a range of geological processes with applications within earth and material sciences. However, these advances require new thermodynamic data and activity composition models for all but the most common alloys, and better characterisation of alloy compositions. • Alloys are common within serpentinised ultramafic rocks from most geodynamic settings. • High spatial resolution analysis and mapping strategies aid discovery and characterisation of alloys. • A diverse range of PGE alloys records PGE mobilisation during serpentinisation on some length scale • Awaruite is typically associated with Fe3+-bearing minerals. • Reducing conditions during serpentinisation may result from the formation of Fe3+-bearing minerals in SiO 2 -poor systems. [ABSTRACT FROM AUTHOR]

Demantoid is a rare Cr-bearing variety of andradite garnet historically mined in the Middle Urals of Russia, where its mode and time of formation remain controversial. A first direct in situ U-Pb LA-ICP-MS dating of demantoid was carried out on samples with extremely low U content obtained from the Karkodinskoe and Poldnevskoe deposits, both of which are located in the Karkodin meta-ultramafic massif of the Middle Urals. In both locations, demantoid mineralization occurred within cracks in ca. 400 Ma serpentinite host rocks composed of chrysotile and antigorite, calcite and aragonite, and magnesite. Magnetite, chromite, and pyrite occur as accessory minerals. The results yielded ages of 343 ± 4 Ma and 292 ± 1 Ma for the Karkodinskoe and Poldnevskoe deposits, respectively. These ages correspond to the times of continental collision and subsequent exhumation in the Middle Urals during the Uralian orogeny. Geochronology combined with trace element data of Uralian demantoid suggests that mineralization was induced by hydrothermal processes at T < 300 °C. But trace-element signatures point to different origins for the two hydrothermal fluids. Rare-earth element (REE) patterns in garnet from Karkodinskoe deposit appear to be inherited from syenitic rocks, whereas REEs in demantoid from Poldnevskoe show affinities with skarn environments. During the collision stage, magmatic fluids that were probably associated with syenitic rocks of the Kozlinogorsky complex were re-activated leading to the re-working of the meta-ultramafic protolith of the Karkodin massif. Metamorphic processes during the exhumation stage subsequently resulted in the mobilization of hydrothermal fluids likely linked to skarns. Their migration into fractures within meta-ultramafic rocks developed the demantoid mineralization in Poldnevskoe occurrence. • U-Pb LA-ICP-MS dating of andradite (var. demantoid) with extremely low U and high common Pb. • U-Pb ages cluster at ca. 343 ± 4 Ma and 292 ± 1 Ma for two neighbouring occurrences with similar mineralization. • Two ages correspond to the continental collision and exhumation stages occurred during the Uralian orogeny. • The REE patterns of demantoid garnets of two occurrences showed similarities to those found in skarn and syenitic rocks. [ABSTRACT FROM AUTHOR]

Bora-Baricha-Tullu Moye is a Late Quaternary volcanic system in the Main Ethiopian Rift, characterised by products of both explosive and effusive volcanic eruptions. The petrological and geochemical characteristics of the volcanic products are investigated using a combination of petrography, major and trace element whole rock analyses and in-situ major element analyses of phenocryst phases, matrix glass and melt inclusions. The bulk rock compositions vary from basalt to peralkaline rhyolite (comendite and pantellerite), and the chemical variability can largely be explained by fractional crystallisation processes with minor crustal assimilation and magma mixing. The dominant mineral phases such as clinopyroxenes and feldspars show a tendency for Fe and Na enrichment respectively from the basalts towards the pantellerites. The comendite and pantellerite deposits show systematic variations towards more evolved glass and mineral composition with the stratigraphy. The combination of thermometry (i.e., clinopyroxene-liquid, feldspar-liquid, olivine-liquid and clinopyroxene-only) and barometry (i.e., clinopyroxene-liquid and clinopyroxene-only) modelling suggests that the basaltic magmas are stored at high temperature (1070–1190 °C) at mid-to-deep-crustal levels (∼7–29 km). The peralkaline rhyolite melts are stored at lower temperature (i.e., 805–900 °C for comendite; 700–765 °C for pantellerite) at shallow crustal levels (∼4 km). The conditions of pre-eruptive storage as recorded in the comendite and pantellerite rocks in combination with stratigraphic constraints, suggests a progressive temporal evolution of the magma reservoirs to cooler storage temperatures. • BBTM is characterised by explosive and effusive volcanic products. • Rock compositions vary from basaltic to peralkaline rhyolite those result from fractional crystallisation process with minor crustal assimilation. • Basalt and peralkaline melts stored at different pre-eruptive magmatic conditions. [ABSTRACT FROM AUTHOR]

The Zhuguangshan complex, composed of Caledonian, Indosinian, and Yanshanian granites, and Cretaceous mafic dykes, is one of the most important granite-hosted uranium producers in South China. Here we present LA-ICP-MS zircon U-Pb and hornblende 40 Ar/ 39 Ar geochronology and whole-rock and biotite geochemistry for the granites in this complex to evaluate the magmatism and its constraints on uranium mineralization. Samples collected from the Fuxi, Youdong, Longhuashan, Chikeng, Qiling, and Sanjiangkou intrusions yield zircon weighted 206 Pb/ 238 U ages of 426.7 ± 5.4 Ma, 226.4 ± 3.5 Ma, 225.0 ± 2.7 Ma, 152.2 ± 3.0 Ma, 153.9 ± 2.1 Ma, and 155.2 ± 2.1 Ma, respectively. A new Ar-Ar dating of the hornblende of the diabase from the Changjiang uranium ore field yields a plateau age of 145.1 ± 1.5 Ma. These results coupled with published geochronological data indicate that six major magmatic events occurred in the study area at 420−435 Ma, 225−240 Ma, 150−165 Ma, ~140 Ma, ~105 Ma, and ~90 Ma. Both U-bearing and barren granites occur in this complex, and they display differences in whole-rock and biotite geochemistry. The barren granites show higher Al 2 O 3 , CaO, TFMM, Rb, Zr, Ba, SI, Mg#, (La/Yb) N , and Eu/Eu*, but lower SiO 2 , ALK, Rb, DI, Rb/Sr, and TiO 2 /MgO than those of the U-bearing granites. Biotites in the U-bearing granites are close to the Fe-rich siderophyllite-annite end member with Fe/(Fe + Mg) ratios higher than 0.66, whereas those in the barren granites are relatively close to the Mg-rich eastonite-phlogopite end member with Fe/(Fe + Mg) ratios <0.66. The U-bearing granites were mainly derived from the partial melting of pelitic sedimentary source, whereas the psammitic source generated the barren granites. In addition, the barren granites show higher TFMM, Ba, and Eu/Eu* but lower SiO 2 , Rb/Sr and Al 2 O 3 /TiO 2 ratios with higher zircon saturation temperatures relative to the U-bearing granites. These results indicate that the geochemical compositions of the U-bearing and barren granites are dictated not only by the compositions of source rocks but also the physicochemical conditions of partial melting. Our study suggests that these two factors are also the major factors that control uranium ore potential of the granites in the Zhuguangshan complex. The geochemical variations of U-bearing and barren granites can serve as a potential detector for granite-hosted uranium deposits. [ABSTRACT FROM AUTHOR]

In situ zircon U–Pb ages, whole-rock major and trace elements, and Sr–Nd isotopic compositions of the Sucun, Yunfeng, and Jingning intrusions from southwest Zhejiang, NE South China Block, are presented to trace their petrogenesis and shed light on its lithosphere evolution. LA–ICP–MS U–Pb zircon dating shows that the Sucun quartz monzonite and Jingning monzogranite were emplaced at ~135 Ma, and the Yunfeng quartz monzonite and Jingning granite were emplaced at 104 and 112 Ma, respectively. All these intrusions are metaluminous to weakly peraluminous and lie within high-K calc-alkaline to shoshonite series field (SiO 2  = 66–76 wt%, A/CNK = 0.95–1.09, K 2 O/Na 2 O = 0.78–1.77). The Yunfeng quartz monzonite clearly have lower K 2 O and total REE contents, and higher CaO, Na 2 O, Al 2 O 3 , P 2 O 5 , MgO, and TiO 2 contents, and relatively less enriched Sr–Nd isotopic compositions than those of the Sucun quartz monzonite, indicating that the Yunfeng quartz monzonite were derived from partial melting of a more juvenile lower crust sources compared with the magma source of the Sucun quartz monzonite. The Jingning monzogranite exhibit similar major elements covariations and Nd isotopic compositions, but higher Ba, Sr, and Eu contents and lower Rb, Th, and U contents than those of the Jingning granite. The geochemical features imply that the Jingning monzogranite and granite were fluid-present and fluid-absent anatexis products of the same Paleoproterozoic crustal source, respectively. Whole-rock Sr–Nd isotopic data imply that the estimated amounts of juvenile mantle-derived melts input into the mature crust show southeastward decreasing trend away from the Jiangshan–Shaoxing fault. We propose that roll-back and retreat of the Paleo-Pacific subducting plate might cause extensive asthenosphere mantle upwelling in East China, and the mantle-derived melts tend to rise through the regional main fault zones and preferentially modify the lithosphere nearby these faults. [ABSTRACT FROM AUTHOR]

This study presents new zircon U–Pb–Hf and whole-rock geochemical data for intrusive rocks in the Xing'an Massif of NE China, with the aim of furthering our understanding of the evolution and spatial influence of the Mongol–Okhotsk tectonic regime. Zircon U–Pb dating indicates that five stages of Mesozoic magmatism are recorded in the Xing'an Massif, namely during the Middle Triassic (~237 Ma), the Late Triassic (~225 Ma), the Early Jurassic (~178 Ma), the Middle Jurassic (~168 Ma), and the late Early Cretaceous (~130 Ma). The Middle Triassic–Early Jurassic intrusive rocks in the Xing'an Massif are dominantly granodiorites, monzogranites, and syenogranites that formed from magma generated by partial melting of newly accreted continental crust. Geochemistry of the Middle Triassic–Early Jurassic granitoid suites of the Xing'an Massif indicates their formation at an active continental margin setting, related to the southwards subduction of the Mongol–Okhotsk oceanic plate. The Middle Jurassic monzogranites in the Xing'an Massif are geochemically similar to adakites and have ε Hf (t) values (+3.8 to +5.8) and Hf two-stage model ages (T DM2 ; 979–850 Ma) that are indicative of derivation from magma generated by partial melting of thickened juvenile lower crust. The Middle Jurassic monzogranites formed in a compressional setting related to the closure of the Mongol–Okhotsk Ocean. The late Early Cretaceous intrusive rocks in the Xing'an Massif are dominated by A-type granitoids that are associated with bimodal volcanic rocks, suggesting their formation in an extensional environment related to either (i) delamination of a previously thickened region of the crust, associated with the Mongol–Okhotsk tectonic regime; (ii) the subduction of the Paleo-Pacific Plate; or (iii) the combined influence of these two tectonic regimes. [ABSTRACT FROM AUTHOR]

We present geochemical and Sr–Nd–Pb–Hf isotope data as well as the results of single grain U–Pb zircon dating for ten granitoid and alkaline intrusions of the Alai segment of Kyrgyz South Tien Shan (STS). The intrusions comprise four geochemically contrasting series or suites, including (1) I-type and (2) shoshonitic granitoids, (3) peraluminous granitoids including S-type leucogranites and (4) alkaline rocks and carbonatites, closely associated in space. New geochronological data indicate that these diverse magmatic series of the Alai segment formed in a post-collisional setting. Five single grain U-Pb zircon ages in the range 287–281 Ma, in combination with published ages, define the main post-collisional magmatic pulse at 290–280 Ma, which is similar to ages of post-collisional intrusions elsewhere in the STS. An age of 287 ± 4 Ma, obtained for peraluminous graniodiorite of the Liayliak massif, emplaced in amphibolite-facies metamorphic rocks of the Zeravshan-Alai block, is indistinguishable from ca. 290 Ma age of peraluminous granitoids emplaced coevally with Barrovian-type metamorphism in the Garm block, located ca. 40 km south-west of the research area. The Sr-Nd-Pb-Hf isotopic compositions of the studied intrusions are consistent with the reworking of crustal material with 1.6–1.1 Ga average crustal residence times, indicating the formation of the Alai segment on a continental basement with Mesoproterozoic or older crust. The pattern of post-collisional magmatism in the Alai segment, characterized by emplacement of I-type and shoshoninitic granitoids in combination with coeval Barrovian-type metamorphism, is markedly different from the pattern of post-collisional magmatism in the adjacent Kokshaal segment of the STS with predominant A-type granitoids that formed on a former passive margin of the Tarim Craton. We suggest that during the middle-late Carboniferous the Alai segment probably comprised a microcontinent with Precambrian basement located between the Turkestan Ocean to the north and an inferred oceanic basin to the south, where the evidence of supra-subduction magmatism was largely destroyed by subsequent tectonic processes. In this scenario, after collision, the position of the Alai microcontinent between two major sutures enabled delamination of its lithospheric mantle, which resulted in production of diverse post-collisional magmatic series by interaction of ascending asthenospheric material with lithospheric mantle and various crustal protoliths. [ABSTRACT FROM AUTHOR]

The question of whether continental subduction processes in collisional orogenic belts can trigger wide-spread mantle metesomatism and crustal material recycling remains unresolved. Miocene (25–8 Ma) ultrapotassic rocks in southern Tibet are the only mantle-derived magmatic rocks emplaced after the collision between India and Asia and they have been linked to the onset of east-west extensional stresses as the surface uplift of the Tibetan Plateau reached near-maximum elevation. However, their petrogenesis remains highly controversial, particularly the issue of whether their extremely enriched Sr-Nd isotopic characteristics were related to metasomatism derived from subducted Indian continental materials during the Cenozoic. Here we report on a Paleocene silicate-unsaturated, pseudoleucite phonolitic dike, in the Rongniduo area of central Lhasa terrane. In-situ SIMS (secondary ion mass spectrometry) apatite U-Pb age indicates the dike was generated at 64.1 ± 4.2 Ma, which slightly predates the age of initial India and Asia collision (about 55–50 Ma). This is the oldest age yet reported for ultrapotassic rocks in southern Tibet. Samples from this dike have distinctly more depleted Sr-Nd (whole rock: ( 87 Sr/ 86 Sr) i = 0.7064 to 0.7062, εNd(t) = − 1.5 to 0.4; in situ apitite: ( 87 Sr/ 86 Sr) i = 0.7059 to 0.7060, εNd(t) = − 2.0 to 0.4) isotopic compositions, than those of Miocene (25–8 Ma) ultrapotassic rocks in the central Lhasa terrane (( 87 Sr/ 86 Sr) i = 0.7106 to 0.7399, εNd(t) = − 10.6 to − 18.5). Our new data provides important constraints on pre-collisional mantle characteristics beneath the Lhasa terrane. We suggest that these ~ 64 Ma pseudoleucite phonolitic rocks were derived from the enriched lithospheric mantle metasomatized by subducted Tethyan oceanic materials in response to Neo-Tethyan slab roll-back. As a consequence, the younger Miocene ultrapotassic rocks, which display different geochemical compositions from the pre-collisional ultrapotassic rocks, were most probably derived from a mantle source metasomatized by subducted Indian continental materials after ~ 64 Ma. Our results indicate that the addition of subducted continental components plays an important role in changing mantle constituents beneath collisional orogenic belts. [ABSTRACT FROM AUTHOR]

The tectonic evolutionary history of the Lhasa and Qiangtang collision zones remains hotly debated because of the lack of pivotal magmatic records in the southern Qiangtang subterrane, central Tibet. We present zircon U–Pb dating, whole-rock major and trace-element geochemical analyses, and Sr–Nd isotopic data for the newly discovered Biluoco volcanic rocks from the southern Qiangtang subterrane, central Tibet. Zircon U–Pb dating reveals that the Biluoco volcanic rocks were crystallized at ca. 95 Ma. The samples are characterized by low SiO 2 (50.26–54.53 wt%), high Cr (109.7–125.92 ppm) and Ni (57.4–71.58 ppm), and a high Mg# value (39–56), which plot in the magnesian andesites field on the rock classification diagram. They display highly fractionated rare earth element patterns with light rare earth element enrichment ([La/Yb] N  = 21.04–25.24), high Sr/Y (63.97–78.79) and no negative Eu anomalies (Eu/Eu* = 0.98–1.04). The Biluoco volcanic rocks are depleted in Nb, Ta and Ti and enriched in Ba, Th, U and Pb. Moreover, the eight samples of Biluoco volcanic rocks display constant ( 87 Sr/ 86 Sr) i ratios (0.70514–0.70527), a positive ε Nd (t) value (2.16–2.68) and younger Nd model ages (0.56–0.62 Ga). These geochemical signatures indicate that the Biluoco volcanic rocks were most likely derived from partial melting of the mantle wedge peridotite metasomatized by melts of subducted slab and sediment in the subducted slab, invoked by asthenospheric upwelling resulting from the slab break-off of the northward subduction of the Bangong–Nujiang oceanic lithosphere. Identification of ca. 95 Ma Biluoco magnesian andesites suggests they were a delayed response of slab break-off of the northward subduction of the Bangong–Nujiang oceanic lithosphere at ca. 100 Ma. [ABSTRACT FROM AUTHOR]

The Urumieh-Dokhtar magmatic belt of Central Iran runs parallel to the Zagros orogenic belt and has been resulted from Neotethys ocean subduction underneath Eurasia. The Bahr Aseman volcanic-plutonic complex (BAC), covering an area ~ 2000 km 2 in the Kerman magmatic belt (KMB) in the southern section of the Urumieh-Dokhtar belt, has long been considered as the earliest manifestation of extensive Cenozoic arc magmatism in KMB. The nature and timing of the magmatism, however, is poorly constrained. An area ~ 1000 km 2 , in BAC and adjacent Razak volcaniclastic complex and Jebal Barez-type granitoids, was mapped and sampled for geochemistry and geochronology. Andesite and basaltic andesite are the main volcanic components in the study area; plutonic bodies vary from tonalite to quartz diorite, granodiorite and biotite-granite. The rocks in BAC display dominantly normal calc-alkaline character. On spider diagrams, the rocks are characterized by enrichments in LILE relative to HFSE and enrichments in LREE relative to HREE. These features suggest a subduction related setting for the BAC. La N /Yb N ratios for the intrusive and volcanic rocks range from 1.41 to 5.16 and 1.01 to 6.42, respectively. These values are lower than those for other known granitoids in KMB, namely the abyssal, dominantly Oligocene Jebal Barez-type (La N /Yb N = 1.66–9.98), and the shallow, dominantly late Miocene Kuh Panj-type (La N /Yb N = 12.97–36.04) granitoids. This suggests a less evolved magma source for the BAC igneous rocks. In Y vs. Nb and Th/Yb vs. La/Yb discrimination diagrams, an island-arc setting is defined for the BAC rocks. The rocks further plot in primitive island-arc domain in Nb vs. Rb/Zr and Y/Nb vs. TiO 2 diagrams. The BAC volcanic and plutonic rocks yielded zircon U–Pb ages of 78.1 to 82.7 Ma and 77.5 to 80.8 Ma, respectively. Zircon U–Pb dating of volcanic rocks and granitoids from the adjacent Razak complex and the Jebal Barez-type granitoids indicated 48.2 Ma and 26.1 Ma ages, respectively, consistent with earlier works on similar rocks elsewhere in KMB. The new data allow a revision of the chronostratigraphy/tectonic history of KMB. In Late Cretaceous, a back arc rift developed extending from Nain to Baft (NB back arc) to the northeast of the Sanandaj-Sirjan magmatic arc. Along with shrinking of the Neotethys Ocean, the dip angle of the subducting slab decreased during the Late Cretaceous, and arc magmatism moved from the Sanandaj-Sirjan zone landward. Meanwhile, Bahr Aseman volcanic-plutonic complex formed as an island-arc in NB back arc rift. Later with arc shift, due to shallowing of subducted slab, magmatism moved toward continent leading to extensive volcanism in Kerman magmatic arc during Eocene and Oligocene, represented by volcanic-sedimentary Razak and Hezar Complexes, respectively. [ABSTRACT FROM AUTHOR]

The Early Cretaceous Yangshan granite is an A-type granitic intrusion that was emplaced along the eastern Jiangnan Orogen in southern Anhui Province, South China. The Yangshan intrusion mainly consists of syenite porphyry (127.0 ± 0.6 Ma) and alkali-feldspar granite porphyry (126.0 ± 1.0 Ma). As a part of Qingyang–Jiuhuashan complex intrusion, the Yangshan A-type granites have lower MgO, CaO, Co, Sr, and higher Rb, Nb, Th and HREE contents, with enrichment in large-ion lithophile elements (LILE) and light rare earth elements (LREE), and slightly negative Eu anomalies. However, the syenite porphyry and the alkali-feldspar granite porphyry differ in terms of zircon ε Hf ( t ) values: small variations in the syenite porphyry from − 5.5 to − 3.7, corresponding to Hf model ages ( t DM C ) between 1.42 Ga and 1.53 Ga, and large variations in the alkali-feldspar granite porphyry from − 6.4 to + 4.4, yielding t DM C of 0.90–1.59 Ga. While both rocks also have similar ε Nd ( t ) values ranging from − 7.02 to − 5.47, corresponding Nd model ages ( T DM C ) are 1.37–1.49 Ga, falling within the Hf model ages. We take these features to indicate that the Qingyang I-type granites, which are isotopically similar, and Yangshan A-type granites were originated from partial melting of Mesoproterozoic–Neoproterozoic crust, with minor juvenile crust input for the alkali-feldspar granite porphyry, followed by fractional crystallization. In combination with previous studies, we propose that the Cretaceous A-type granitic rocks formed between 135 Ma and 122 Ma, implying an important Mesozoic extensional event in eastern Jiangnan Orogen, which facilitated underplating of mantle-derived magma and crustal heating. This may have occurred in a back-arc extension in response to the drift of subduction direction of the Paleo-Pacific plate, which started as early as ~ 135 Ma ago. [ABSTRACT FROM AUTHOR]

Constraints on the composition of the depleted mantle Sm–Nd and Lu–Hf crust formation ages have a long history of scientific debate. When calculating mantle extraction ages, and constructing crustal growth models, a linear evolution of incompatible trace elements in a depleted mantle since > 4 Ga is routinely used. Mantle depletion however varies regionally and over time and subduction of sediments and oceanic crust renders a mantle-wedge variously enriched relative to a modelled depleted mantle. Here we show that primitive mantle-derived subduction related gabbroic intrusions from southern Fennoscandia have Hf isotope compositions that are enriched relative to a MORB-like linear depleted mantle evolution curve. Extrapolation of primitive Paleoproterozoic gabbro suites enables the construction of a regional mantle evolution curve, providing improved constraints on model ages, crustal residence times and the fraction of juvenile versus reworked continental crust. Convergent margins are assumed to be one of the main sites of continental crust growth, and using an overly depleted mantle source yield model ages that are too old, and hence cumulative crustal growth models show too much crust generation early in the Earth's history. The approach of using the Hf isotope composition of zircon from primitive subduction related gabbroic intrusions as a proxy for mantle Hf isotope composition, piloted in this study, can be applied to other convergent margins. [ABSTRACT FROM AUTHOR]

A combined study of zircon U-Pb ages and Lu-Hf isotopes, whole-rock major-trace elements and Sr-Nd isotopes as well as mineral chemistry and O isotopes was carried out for Triassic granitoids from the South Qinling orogen in central China. Model calculations were also performed to examine the trace element fractionation during partial melting of crustal rocks. The results provide insights into the nature of magma sources for these granitoids. LA-ICPMS zircon U-Pb dating yields concordant ages of 208 ± 2 to 216 ± 3 Ma for these granitoids from the Shahewan (SHW), Caoping (CP) and Zhashui (ZS) plutons, and no relict zircon cores are identified by the CL imaging and U-Pb dating. The SHW and CP granitoids contain hornblende and are metaluminous with A/CNK ratios of 0.84 to 0.93. They exhibit relatively low SiO 2 contents (62.88–69.04 wt.%) but high contents of FeO T , MgO and TiO 2 , and slightly to negligibly negative Eu anomalies (δEu = 0.79–0.89). Zircons from them show mantle-like δ 18 O values of 4.71 to 5.72‰. In contrast, the ZS granites contain no hornblende and are metaluminous to weakly peraluminous with A/CNK ratios of 0.99 to 1.03. They show relatively high SiO 2 contents (69.32–75.94 wt.%) but low FeO T , MgO and TiO 2 contents, and moderate negative Eu anomalies (δEu = 0.63–0.81). They have slightly low zircon δ 18 O values of 4.60 to 4.83‰. All of these granitoids show arc-like trace element distribution patterns with enrichment in LREE and LILE ( e.g. , Rb, K and Pb) but depletion in HFSE ( e.g. , Nb, Ta and Ti). Geochemical comparison and modeling indicate that these granitoids are different from adakitic rocks originating from the thickened lower continental crust. Compared with the composition of felsic melts produced by petrological experiments of various lithologies, it appears that these granitoids are derived from dehydration melting of metabasaltic sources at normal lower crustal depths, and experienced varying degrees of fractional crystallization. The SHW and CP granitoids were crystallized under the conditions of variably low pressures of 0.7–2.3 kbar, temperatures of 628–766 °C and higher f O 2 than the ZS granites. On the other hand, these granitoids show moderate whole-rock initial 87 Sr/ 86 Sr ratios of 0.7045 to 0.7055 and slightly negative ε Nd (t) values of − 4.0 to − 1.5 as well as slightly negative to positive zircon ε Hf (t) values of − 1.3 to 3.2. They have two-stage Nd model ages of 1.05–1.38 Ga and Hf model ages of 1.04–1.39 Ga. These whole-rock ε Nd (t) and zircon ε Hf (t) values are comparable with those for Neoproterozoic Yaolinghe metabasalts and mafic-ultramafic intrusions in South Qinling but inconsistent with those for Neoproterozoic Bikou metavolcanics and mafic-ultramafic intrusions in the northern margin of the Yangtze craton. Together with their non-adakitic features, it is suggested that they were derived from partial melting of the mafic lower crust in South Qinling rather than the subducted Yangtze continental crust beneath South Qinling. The continental collision between the North China Block and South China Block in the Late Triassic would have brought about reworking of the mafic lower crust for the granitoid magmatism in the Qinling orogen. [ABSTRACT FROM AUTHOR]

The Carlos Chagas batholith (CCB) is a very large (~ 14,000 km 2 ) S-type granitic body formed during the syn-collisional stage of the Araçuaí orogen (southeastern Brazil). Zircons extracted from the CCB record a wide range of U–Pb ages (from 825 to 490 Ma), indicating a complex history of inheritance, magmatic crystallization and partial melting during the evolution of the orogeny. Magmatic zircons (ca. 578–588 Ma) are marked by similar Hf isotope compositions and REE patterns to those of inherited cores (ca. 825–600 Ma), indicating that these aspects of the chemical signature of the magmatic zircons have likely been inherited from the source. The U–Pb ages and initial 176 Hf/ 177 Hf ratios from anatectic and metamorphic zircon domains are consistent with a two-stage metamorphic evolution marked by contrasting mechanisms of zircon growth and recrystallization during the orogeny. Ti-in-zircon thermometry is consistent with the findings of previous metamorphic work and indicates that the two metamorphic events in the batholith reached granulite facies conditions (> 800 °C) producing two generations of garnet via fluid-absent partial melting reactions. The oldest metamorphic episode (ca. 570–550 Ma) is recorded by development of thin anatectic overgrowths on older cores and by growth of new anatectic zircon crystals. Both domains have higher initial 176 Hf/ 177 Hf values compared to relict cores and display REE patterns typical of zircon that grew contemporaneously with peritectic garnet through biotite-absent fluid partial melting reactions. Hf isotopic and chemical evidences indicate that a second anatectic episode (ca. 535–500 Ma) is only recorded in parts from the CCB. In these rocks, the growth of new anatectic zircon and/or overgrowths is marked by high initial 176 Hf/ 177 Hf values and also by formation of second generation of garnet, as indicated by petrographic observations and REE patterns. In addition, some rocks contain zircon crystals formed by solid-state recrystallization of pre-existing zircon, which exhibit similar Hf isotope composition to those of inherited/magmatic core domains. The first anatectic event is interpreted as result of crustal thickening after the intrusion of the batholith. This introduced the batholith to a depth in excess of 30 km and produced widespread anatexis throughout the batholith. The second event was associated with asthenospheric upwelling during extensional thinning and gravitational collapse of the orogen, this produced anatexis in parts from the CCB that had been re-fertilized for anatexis by retrogression along shear zones following the first granulite facies event. [ABSTRACT FROM AUTHOR]

Carboniferous igneous activity in the Sierra de Velasco (NW Argentina) led to the emplacement of several magmas bodies at shallow levels (< 2 kbar). One of these, the San Blas intrusive complex formed over millions of years (≤ 2–3 m.y.) through three periods of magma additions that are characterized by variations in magma sources and emplacement style. The main units, mostly felsic granitoids, have U-Pb zircon crystallization ages within the error range. From older to younger (based on cross-cutting relationships) intrusive units are: (1) the Asha unit (340 ± 7 Ma): a tabular to funnel-shaped intrusion emplaced during a regional strain field dominated by ~ WSW-ENE shortening with contacts discordant to regional host-rock structures; (2) the San Blas unit (344 ± 2 Ma): an approximate cylindrical-shaped intrusion formed by multiple batches of magmas, with a roughly concentric fabric pattern and displacement of the host rock by ductile flow of about 35% of shortening; and (3) the Hualco unit (346 ± 6 Ma): a small body with a possible mushroom geometry and contacts concordant to regional host-rock structures. The magma pulses making up these units define two groups of A-type granitoids. The first group includes the peraluminous granitic rocks of the Asha unit generated mostly by crustal sources (εNd t = − 5.8 and εHf t in zircon = − 2.9 to − 4.5). The second group comprises the metaluminous to peraluminous granitic rocks of the youngest units (San Blas and Hualco), which were formed by a heterogeneous mixture between mantle and crustal sources (εNd t = + 0.6 to − 4.8 and εHf t in zircon = + 3 to − 6). Our results provide a comprehensive view of the evolution of an intrusive complex formed from multiple non-consanguineous magma intrusions that utilized the same magmatic plumbing system during downward transfer of host materials. As the plutonic system matures, the ascent of magmas is governed by the visco-elastic flow of host rock that for younger batches include older hot magma mush. The latter results in ductile downward flow of older, during rise of younger magma. Such complexes may reflect the plutonic portion of volcanic centers where chemically distinct magmas are erupted. [ABSTRACT FROM AUTHOR]

New zircon U–Pb ages, mineral chemical data, whole-rock geochemistry and Sr–Nd isotopes from the potassium-rich intrusions in the Yunnan area, SW China, were determined to provide constraints on the uplift of the Eastern Tibetan Plateau. The intrusive rocks consist of shoshonitic syenites (high-Mg syenites, low-Mg syenites and syenite porphyries) and potassic granitoids (granite porphyries). Zircon LA-ICP-MS U–Pb dating indicates coeval emplacement ages of ~ 35 Ma. The shoshonitic syenites have alkaline affinities and the enrichment in LILEs and LREEs (e.g. La, Sr, U, Pb), with depletion of HFSEs (e.g. Nb, Ti, Ta) and weak Eu anomalies. They display uniform Sr–Nd–Lu–Hf isotopic compositions with similar initial 87 Sr/ 86 Sr ratios (0.7073–0.7079), enriched ε Nd (t) values (− 6.8 to − 4.3) and mostly negative zircon ε Hf (t) values ranging from − 4.6 to + 0.1. The high-Mg syenites have high MgO, Fe 2 O 3 T , TiO 2 , CaO, Cr, Ni concentrations and relatively high Mg # (60–68), indicating an origin from enriched lithospheric mantle. The low-Mg syenites and syenite porphyries are geochemically distinct with the high-Mg syenites, but the insignificant variations in major elements, linear trends of La against (La/Yb) N and similar Sr–Nd isotopic compositions to the high-Mg syenites suggest that they were produced by different degrees of partial melting of the same enriched mantle source. The potassic granitic intrusions are sub-alkaline with a strongly peraluminous character. They display an S-type granite affinity, with high Al 2 O 3 /TiO 2 and low CaO/Na 2 O and K 2 O/Al 2 O 3 ratios, suggesting a pelitic source. They are LREE-enriched and have relatively flat HREE patterns with weakly negative Eu anomalies and positive Rb, U, and Pb anomalies and negative Nb, Ta, and Ti anomalies. They have relatively high initial 87 Sr/ 86 Sr ratios (0.7143) and enriched Nd isotopic compositions [ε Nd (t) = − 4.1]. Their zircon ε Hf (t) values (− 4.0 to + 0.09) and old two-stage Hf model ages (T DM c = 1.16–1.36 Ga) suggest that they were generated by partial melting of an ancient K-rich crust. The petrogenesis of the potassic intrusive rocks with their uniform Nd model ages (T DM = 968–1168 Ma) indicates that the lithospheric mantle beneath Yunnan was enriched by metasomatism related to ancient oceanic subduction. Considering the widespread and coeval nature of potassium-rich rocks in Eastern Tibet, we consider that delamination of metasomatized lithospheric mantle beneath Yunnan in the Eocene was a result of the India–Asia collision, which triggered partial melting of both the lithospheric mantle and the K-rich crust, and contributes to uplift of the Eastern Tibetan Plateau. [ABSTRACT FROM AUTHOR]

The evolution of the tectonic regime that was responsible for the Indosinian granitoids in the South China Block (SCB) is still controversial. Investigations on A-type granites can provide important information regarding this tectonic evolution. A detailed study that utilizes whole-rock elemental, Sr–Nd isotopic, in situ zircon U–Pb and Lu–Hf isotopic geochemistry is conducted on the Miantuwo biotite granite in northern Guangdong Province and the Pingtian biotite monzogranite in southern Jiangxi Province, South China. The new data indicate that both the Miantuwo and Pingtian granites were emplaced at 233 ± 2 Ma and show metaluminous to slightly peraluminous A-type granite affinity. The two granites are characterized by high amounts of rare earth elements (total REEs = 247 ppm–557 ppm and 251 ppm–342 ppm) and high field strength elements (Zr + Nb + Ce + Y = 325 ppm–605 ppm and 343 ppm–496 ppm) and high Ga/Al ratios (10,000 × Ga/Al = 2.50–2.98 and 2.62–2.70). Calculations from a zircon saturation thermometer and apatite saturation thermometer indicate that the magmatic temperatures were 800 °C–980 °C for both granites. Both the Miantuwo and Pingtian granites show relatively high initial 87 Sr/ 86 Sr ratios (0.7151–0.7185 and 0.7170–0.7189), low ε Nd (t) values (− 9.8 to − 8.6 and − 9.7 to − 9.1) and low to moderate zircon ε Hf (t) values (− 10.4 to − 6.6 and − 9.5 to − 4.6). Based on these data, we suggest that these two A-type granites were derived from the partial melting of existing mafic to intermediate rocks in the lower crust in response to the underplating and/or intraplating of mantle-derived magma. Our study on the Miantuwo and Pingtian granites, alongside previous studies on other Triassic A-type granites in South China, indicates an extensional tectonic environment during the Late Triassic in the interior of the Cathaysia Block. Alongside existing geological observations and the tectonic evolution in the SCB, we suggest that the interior of the SCB was dominated by a compressional tectonic environment during the Late Permian–Middle Triassic in response to the collisions between the SCB and ambient blocks, and then a tectonic transition from this compressional environment to a post-collisional extension environment began at approximately 233 Ma. [ABSTRACT FROM AUTHOR]

The Mangling granitoid pluton, located along the southern margin of the North China Craton, consists mainly of monzogranite with minor amounts of diorite. The monzogranite contains abundant mafic microgranular enclaves (MMEs) and is intruded by numerous mafic dikes, providing an opportunity to study magma mixing and its role in the formation of the granitioid pluton. In this paper, we present in situ analysis of U–Pb isotopes and trace element compositions of titanite from the MMEs and the host monzogranite using Laser Ablation–Inductively Coupled Plasma-Mass Spectrometry to document the role of magma mixing in the formation of the Mangling granitoid pluton. Titanite grains from the MMEs (type 1) are euhedral with patchy zoning, whereas the varieties from the closely associated host monzogranite are euhedral and consist of two types (type 2 and type 3). Type 2 titanite is more abundant and has oscillatory zoning without Fe–Ti oxide inclusions, whereas type 3 grains commonly have Fe–Ti oxide inclusions in the core that is rimmed by inclusion-free overgrowths with weak oscillatory zoning. Titanite from monzogranite without MMEs (type 4) is euhedal and has weak oscillatory zoning, with rare ilmenite inclusions in the core. Titanite from a mafic dike intruding the monzogranite (type 5) is anhedral and has sector zoning. Titanite grains from MMEs and the monzogranite (type 1, 2 and 3) have U–Pb ages that are indistinguishable (149 ± 1 Ma, 148 ± 1 Ma and 148 ± 2 Ma, respectively). These ages agree well with zircon U–Pb ages of 150 ± 1 Ma, 150 ± 1 Ma and 149 ± 1 Ma for the MMEs, host monzogranite, and mafic dike, respectively. The age consistency thus confirms coeval formation of the MMEs, the host monzogranite, and the mafic dikes, demonstrating a mafic magmatic, rather than extraneous or restitic origin for the MMEs. Titanite grains from the MMEs (type 1) and mafic dike (type 5) have much lower Al 2 O 3 , REE, Nb/Zr, Y/Zr, and Lu/Hf, but higher (Ce + Nd)/Y and La/Ce ratios compared to those from the monzogranite (type 2 and type 4). These compositional differences suggest that titanite grains from the MMEs and the host monzogranite crystallized from different magmas. Type 3 titanite contains abundant Fe–Ti oxide inclusions and is characterized by dissolution and reprecipitation textures; the composition of its core and rims are comparable to those of type 1 and type 4 titanites, respectively. The compositional variation between the core and rims of the type 3 titanite grains implies that they were re-equilibrated with high temperature mafic magma and then continued to crystallize within the granitic magmas with low f O 2 . The textural, geochronological, and geochemical data of titanite grains can be best explained in term of mixing of mafic and felsic magmas. We conclude that both the fine-grained MMEs and the host monzogranite are hybrid products of mafic and felsic end-member magmas. When combined with other geological and geochronological data in the North China Craton, our results suggest that the widespread late Jurassic to early Cretaceous granitoid intrusions were generated in an extensional setting related to craton destruction. [ABSTRACT FROM AUTHOR]

Rutile is a robust heavy mineral that can survive multiple sedimentary cycles. It is common in high-grade metamorphic rocks and hydrothermally-altered rocks. Hence, it can be a recorder of either the deep crust or of ores and fluids. In this review paper we cover a range of different topics concerning the use and application of detrital rutile as a means of retrieving these records and highlight some important recent advances. We discuss the occurrence of rutile formed at different pressures and temperatures and how we can use it to fingerprint metamorphic processes, with a focus on the use of combined Zr-thermometry and mineral inclusion geothermobarometry. We then present a review and discussion on the approaches made using detrital rutile trace element and isotopic geochemistry in provenance studies. We present some of the strengths and limitations of combining trace element and U–Pb isotopic dating to detrital rutile, including a discussion on U–Pb detrital rutile dating and different trace element diffusivities with an evaluation of potential decoupling between these. We then discuss some of the applications of detrital rutile in unravelling large scale geodynamic or tectonic processes. We also summarise the main features of rutile associated to ores and how these may be used using detrital rutile as an ore mineral vector. We finish with some considerations regarding the stability of detrital rutile in the upper crust, either by means of metamorphic or fluid-related processes, and how this may affect studies relying on detrital rutile. [Display omitted] • Detrital rutile behaves as a P-T capsule that can survive multiple sedimentary cycles. • Strengths and limitations of combining U-Pb and trace element to detrital rutile • Detrital rutile can be used as an effective ore exploration vector for Au and W. • Dissolution and reprecipitation processes can modify detrital rutile signatures. [ABSTRACT FROM AUTHOR]

Accurately constraining the age and source of primary U mineralization is commonly difficult as diverse U minerals are affected by α-recoils and subjected to overprints of multi-stage fluids. Titanite has a good potential in revealing rock-forming and metallogenic information, and widely occurs in magmatic, metamorphic, and hydrothermal U deposits. However, the textural and chemical characteristics of titanite from these U deposits are poorly documented and little is known about the relationship between titanite and U mineralization. At the western margin of the Yangtze Block, a series of U occurrences and uraninite-predominant ores are hosted in the leucocratic dykes, ranging from fine-grained (albitised) monzogranite to pegmatitic quartz vein. The genesis of U mineralization remains unclear largely because of the uncertainties as to the timing of mineralization and the origin of metals. Here, we present comprehensive U Pb and Sm Nd isotopic data, and major and trace element compositions for metamorphic (Ttn-I) and magmatic/hydrothermal (Ttn-II) titanites from the leucocratic dykes and/or amphibolitic wall rocks. Ttn-I is in direct contact with metamorphic hornblende and plagioclase or occurs as xenoliths hosted in the leucocratic dykes, and is thus inferred to result from amphibolite facies metamorphism. Chemically, Ttn-I is characterized by low Fe/Al ratios, LREE-depleted patterns and weakly negative to positive Eu anomalies. By contrast, magmatic/hydrothermal Ttn-II crystals intergrown with uraninite in the leucocratic dykes generally display flatter REE patterns, more negative Eu anomalies, higher Fe/Al ratios, and U, Nb, REE and Y contents, which could be applied as an indicator for U exploration. LA-ICP-MS U Pb dating on Ttn-I yielded ages of ∼860 Ma for amphibolite facies metamorphism. Instead, U Pb dating on syn -ore Ttn-II yielded ages of ∼786–779 Ma for U mineralization, which is coeval with the emplacement of leucocratic dykes. Uraninite and intergrown Ttn-II have uniform, negative εNd(t) values (−5.7 to −15.5), indicating the initial melts were predominantly sourced from the old crustal materials (T DM2 = ∼1.9–2.7 Ga). Considering the occurrences as dykes, feldspar-quartz-dominant lithologies, and wide textural and compositional variations of leucocratic dykes, we infer that low-degree partial melting of U-rich protolith is the main factor controlling U concentration in the melt. Variable REE patterns and ThO 2 contents in different uraninite types seem to imply there have been multi-stage U mineralization. • Dyke-hosted U mineralization at the western margin of the Yangtze Block formed at ∼786–779 Ma. • The uraniferous leucogranitic magma was derived from old crust with a T DM2 of ∼1.9–2.7 Ga. • Low-degree partial melting process may be the main factor controlling U concentration. • Titanite with high REE, Y, Nb, and U contents could be applied as an indicator for U exploration. [ABSTRACT FROM AUTHOR]

The Jiamusi–Khanka Block, located in the easternmost segment of the Central Asian Orogenic Belt (CAOB), is one of the least understood blocks in northeastern China. The age of its basement, the timing of the high-grade metamorphism, and the tectonic affinity of this block have all been subjects of controversy. Here we describe newly discovered Neoproterozoic orthogneisses from the Mishan region in the central Jiamusi–Khanka Block. SIMS and LA–ICP–MS U–Pb dating of the magmatic cores of zircons from three of these high-grade orthogneisses yielded weighted mean ages that range from 898 ± 4 to 891 ± 13 Ma, indicating that early Neoproterozoic magmatism did occur in the Jiamusi–Khanka Block. Twenty-two analyses of metamorphic zircons (rims as well as some grains) gave two groups of concordant ages, one at ca. 563 Ma, interpreted as the timing of the high-grade metamorphism, and the other around 518–496 Ma, interpreted as representing a subsequent retrograde metamorphism. The orthogneisses represent metamorphosed peraluminous syn-collisional syenogranites with SiO 2 = 71.29–78.08 wt%, A/CNK = 1.06–1.99, and Na 2 O/K 2 O = 0.03–1.49, and they belong chemically to the high-potassium calc-alkaline series. They have low Sr (32–134 ppm) contents and Sr/Y ratios (1.6–16.9), and display strongly fractionated to nearly flat REE patterns with negative Eu anomalies (δEu = 0.22–0.95) and depletions in Nb–Ta. These geochemical characteristics suggest that the syenogranitic rocks were derived under low pressures from a crustal source with a high proportion of sedimentary rocks, perhaps in a subduction-related setting that was undergoing transition from compression to extension. In the context of the reconstruction of Gondwana, the ca. 898–891 Ma magmatic activity and the ca. 563 Ma high-grade metamorphism in the Mishan region provide constraints on the possible linkages between the Jiamusi–Khanka Block and East Gondwana during the Neoproterozoic to early Paleozoic. [ABSTRACT FROM AUTHOR]

Limited geochronological and geochemical data from Early Cretaceous igneous rocks of the Gangdese Belt have resulted in a dispute regarding the subduction history of Neo-Tethyan Ocean. To approach this issue, we performed detailed in-situ zircon U–Pb and Hf isotopic, whole-rock elemental and Sr–Nd isotopic analyses on Late Mesozoic volcanic rocks exposed in the Liqiongda area, southern Lhasa terrane. These volcanic rocks are calc-alkaline series, dominated by basalts, basaltic andesites, and subordinate rhyolites, with a bimodal suite. The LA–ICPMS zircon U–Pb dating results of the basaltic andesites and rhyolites indicate that these volcanic rocks erupted during the Early Cretaceous (137–130 Ma). The basaltic rocks are high-alumina (average > 17 wt.%), enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), and depleted in high field strength elements (HFSEs), showing subduction-related characteristics. They display highly positive zircon ε Hf (t) values (+ 10.0 to + 16.3) and whole-rock ε Nd (t) values (+ 5.38 to + 7.47). The silicic suite is characterized by low Al 2 O 3 (< 15.4 wt.%), Mg # (< 40), and TiO 2 (< 0.3 wt.%) abundances; enriched and variable concentrations of LILEs and REEs; and strongly negative Eu anomalies (Eu/Eu* = 0.08–0.19), as well as depleted Hf isotopic compositions (ε Hf (t) = + 4.9 to + 16.4) and Nd isotopic compositions (ε Nd (t) = + 5.26 to + 6.71). Consequently, we envision a process of basaltic magmas similar to that of MORB extracted from a source metasomatized by slab-derived components for the petrogenesis of mafic rocks, whereas the subsequent mafic magma underplating triggered partial melting of the juvenile crust to generate acidic magma. Our results confirm the presence of Early Cretaceous volcanism in the southern Lhasa terrane. Combined with the distribution of the contemporary magmatism, deformation style, and sedimentary characteristics in the Lhasa terrane, we favor the suggestion that the Neo-Tethyan oceanic lithosphere was flat-lying beneath the Lhasa terrane during the Early Cretaceous. [ABSTRACT FROM AUTHOR]

Abundant early Paleozoic granitoid plutons are widely distributed in the North Altun orogenic belt. These rocks provide clues to the tectonic evolution of the North Altun orogenic belt and adjacent areas. In this paper, we report an integrated study of petrological features, U–Pb zircon dating, in situ zircon Hf isotope and whole-rock geochemical compositions for the Abei, 4337 Highland and Kaladawan Plutons from north to south in the North Altun orogenic belt. The dating yielded magma crystallization ages of 514 Ma for the Abei Pluton, 494 Ma for the 4337 Highland Pluton and 480–460 Ma for the Kaladawan Pluton, suggesting that they are all products of oceanic slab subduction because of the age constraint. The Abei monzogranites derived from the recycle of Paleoproterozoic continental crust under low-pressure and high-temperature conditions are products of subduction initiation. The 4337 Highland granodiorites have some adakitic geochemical signatures and are sourced from partial melting of thickened mafic lower continental crust. The Kaladawan quartz diorites are produced by partial melting of mantle wedge according to the positive ε Hf (t) values, and the Kaladawan monzogranite-syenogranite are derived from partial melting of Neoproterozoic continental crust mixing the juvenile underplated mafic material from the depleted mantle. These results, together with existing data, provide significant information about the evolution history of oceanic crust subduction during the 520–460 Ma. The initiation of subduction occurred during 520–500 Ma with formation of Abei Pluton; subsequent transition from steep-angle to flat-slab subduction at ca.500 Ma due to the arrival of buoyant oceanic plateaus, which induces the formation of 4337 Highland Pluton. With ongoing subduction, the steep-angle subduction system is reestablished to cause the formation of 480–460 Ma Kaladawan Pluton. Meanwhile, it is this model that account for the temporal–spatial distribution of these early Paleozoic magmatic rocks in the North Altun orogenic belt. [ABSTRACT FROM AUTHOR]

Debate on whether the Early Paleozoic tectono-magmatic event in South China is related to a subduction–collision or an intracontinental orogen has been lasted for decades within the geoscience community. This study deals with LA-ICP-MS zircon U–Pb ages, whole-rock chemistry, rare earth elements, trace elements and Hf isotopes from granitoid samples collected in the Yunkai domain in order to better constrain the Early Paleozoic tectonic evolution of the South China Block. The weighted mean 206 Pb/ 238 U ages for eight samples range from 426 Ma to 443 Ma, representing the crystallization ages of the magma. Fourteen samples were analyzed for geochemistry, all of which are characterized by a peraluminous signature with A/CNK values greater than 1.0. The REE geochemistry reveals enrichment in light rare earth element. LREE/HREE values range from 2.81 to 30.36 and (La/Yb) N vary from 1.23 to 55.14 (mean of 14 analyses is 14.69). All the samples exhibit distinct negative Ba, Sr and Nb anomalies and enrichment in Rb, Th, U and Pb. Hf isotopic analyses indicate negative εHf (t) values mainly ranging from − 3 to − 12, corresponding to two model age distributing from 1637 Ma to 2208 Ma. The geochemical analyses indicate that the Silurian granitic magmas in the Yunkai domain were derived from partial melting of crustal materials with little or no input of mantle source. These new data support the intracontinental subduction model already proposed to account for the Early Paleozoic tectonic, metamorphic and magmatic event of South China. [ABSTRACT FROM AUTHOR]

The Sumdo complex is a Permian–Triassic eclogitic metamorphic belt in south-east Tibet, which marks the location of a suture zone that separates the northern and southern Lhasa terranes. An integrated geochronological and petrological study of a mafic eclogite from the complex has constrained its tectonometamorphic history and provides a case study of zircon growth in eclogite as a product of prograde dissolution–precipitation. In situ U–Pb geochronology indicates that the eclogite contains a single population of zircon with a crystallisation age of 273.6 ± 2.8 Ma. The morphology and chemistry of the zircon grains are consistent with growth by dissolution–precipitation of protolith magmatic zircon. The presence of zircon grains as inclusions in the cores of peak phases indicates that zircon dissolution–precipitation occurred during prograde metamorphism, and calculated pressure and temperature conditions over which mineral inclusions in zircon are stable suggest that the zircon most likely precipitated at ~15.5–16.5 kbar and 500–560 °C. Subsequent peak metamorphism is calculated to have reached pressure–temperature conditions of 27 ± 1 kbar and 670 ± 50 °C. Previous studies, which have documented a range of peak metamorphic conditions from high- to ultrahigh-pressure at c. 266–230 Ma, indicate that the Sumdo complex is a composite belt that experienced protracted eclogite exhumation. The results of this study are consistent with this interpretation, and extend the age range of high-pressure metamorphism in the complex to over 40 Myr. Analysis of published pressure–temperature–time data indicates two systematic behaviours within this spread. First, peak metamorphic temperatures declined over time. Second, eclogite exhumation occurred in two discrete intervals: soon after formation, and during the demise of the subduction zone. The latter behaviour serves as a reminder that eclogite exhumation is the exception rather than the rule. [ABSTRACT FROM AUTHOR]

The Lüliang Complex is located at the western margin of the middle segment of the Trans-North China Orogen, along which the Western and Eastern Blocks collided to form the North China Craton. The complex mainly consists of metamorphosed granitic plutons and supracrustal rocks, of which the latter are subdivided into the Jiehekou, Lüliang, Yejishan, Lanhe and Heichashan Groups. The Lanhe Group is composed of meta-conglomerates, quartzites, and phyllites with minor meta-basalts, whereas the Heichashan Group consists of molasse-like meta-conglomerates and coarse-grained quartzites. Geochemistry of the Yejishan meta-sedimentary rocks indicates weak source weathering and dominantly chemical immature features, whereas the Lanhe and Heichashan samples display opposite features. U–Pb ages of detrital zircons from the Lanhe Groups yield four age peaks at ~ 2180 Ma, ~ 2370 Ma, ~ 2520 Ma and ~ 2700 Ma. The former three peaks coincide with ages of the Chijianling–Guandishan TTG gneisses (2199–2151 Ma) and meta-volcanic rocks from the Lüliang and Yejishan Groups (2213–2156 Ma), age of the Gaijiazhuang porphyritic gneisses (2375–2364 Ma) and age of the Yunzhongshan TTG gneisses (2499 Ma) respectively, whereas detrital zircons forming the oldest age peak were most likely derived from the early Neoarchean crust of the Eastern Block. For the Heichashan Group, the dominant 2.2–2.0 Ga detrital zircons were probably recycled from the underlying Jiehekou Group and the minority is directly derived from the early Paleoproterozoic granitoids in the Lüliang Complex. The youngest detrital zircon age peaks of ~ 2.17 Ga and ~ 1.82 Ga place maximum depositional ages on the Lanhe and Heichashan Groups respectively, whereas the local 1.81–1.79 Ga massive granites place constraint on their minimum depositional ages. Taking into account the lithostratigraphic features, provenance and formation ages, we suggest that the Lanhe Group formed in a shrinked remnant back-arc basin and the Heichashan Group was deposited in a foreland basin. Conversion of the tectonic basin from the middle Paleoproterozoic back-arc basin to the late Paleoproterozoic foreland basin is well consistent with the model that the single collision to form the basement of the North China Craton happened at ~ 1.85 Ga. [ABSTRACT FROM AUTHOR]

Early Mesozoic granitoids and volcanic rocks are widespread throughout the structures of all of the continental massifs in the eastern part of the Central Asian Orogenic Belt, although its tectonic setting is not yet clear. Generally, they are associated with subduction and plume processes or rifting. Such uncertainty is mostly explained by the unequal investigation of Early Mesozoic magmatism. This paper presents the results of geochemical, Sm-Nd isotope, and U–Pb geochronologic (ID-TIMS) studies of “key-type” Early Mesozoic magmatic rock complexes of the Bureya Terrane. This is one of the largest continental massifs in the eastern Central Asian Orogenic Belt and knowledge of its geological structure is of fundamental importance in understanding the history of its formation. It has been established that the leucogranites of the Altakhtinsky Complex and the trachyrhyolites of the Talovsky Complex are practically coeval ( ~ 209–208 Ma). The subalkaline leucogranites of the Kharinsky Complex have a slightly younger age of ~ 199 Ma. These data correspond to the general stage of Early Mesozoic magmatic and metamorphic events (236–180 Ma) in most continental massifs in the eastern Central Asian Orogenic Belt. We believe that large-scale Early Mesozoic events were related to the amalgamation of the continental massifs of the eastern Central Asian Orogenic Belt into a single continental structure (the Amur superterrane or microcontinent Amuria) and collision with the North Asian Craton. It should be noted that the collision processes were followed by crustal thickening, thus creating the conditions for metamorphism and formation of magmatic rock complexes of various geochemical types. [ABSTRACT FROM AUTHOR]

The Xiaerchulu Au deposit, located in the Southern Orogenic Belt (SOB) of Western Inner Mongolia (WIM), is hosted in an Early Permian (271–261 Ma) volcanic-plutonic sequence. Mineralization took place in silicified biotite granites or along the contact zone between the Neoproterozoic Baiyinbaolage Group and the biotite granite. In order to constrain the timing of the Xiaerchulu mineralization and discuss the petrogenesis of the hosting granites, molybdenite Re–Os, and zircon U–Pb and, Lu–Hf, and REE, geochemical, and Sr–Nd isotopic studies were completed in this study. We measured Re–Os isotopes of six molybdenite samples from the main ore body, which yielded a weighted average model age of 261.7 ± 1.5 Ma with a MSWD of 0.55, indicating that the time of mineralization was at ca. 262 Ma. High precision U-Pb dating for the studied granites yields Permian 206 Pb/ 238 U ages ranging from 271 to 269 Ma. These age data confirm that both the intrusion and related mineralization were initiated in Early Permian period. These granites are strongly peraluminous with A/CNK = 1.11–1.12, high SiO 2 –K 2 O contents, as well as containing biotite and muscovite, indicating a petrogenesis of typical S-type granites, the above consideration is also consistent with the result of discrimination diagrams. The Re contents of molybdenite, εNd(t), and zircon εHf(t), as well as the 176 Hf/ 177 Hf values of the granites, fall into the ranges from 1.153 to 2.740 μg/g, − 11.1 to − 9.3, − 8.8 to − 0.9, and 0.282358 to 0.282688, respectively. All of this evidence suggests that the metals were derived from a predominantly crustal source, the granites originated from crust in an extensional setting, and the rejuvenation of the continent may have play an important role during the ore-forming processes of the Early Permian epoch. [ABSTRACT FROM AUTHOR]