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The origin of magmatic microgranular enclaves has been investigated in the Mesoproterozoic granitoid Krasnopol intrusion (1.5 Ga), part of the AMCG (anorthosite–mangerite–charnockite–granite) Mazury Complex in the East European Craton (NE Poland). The granitoids are ferroan and metaluminous, and display the typical characteristics of A-type granites, with high contents of Zr, Nb, Ga and rare earth elements (REEs). The enclaves are metaluminous and have a broad compositional range with two groups distinguished: silica-poor (45–50 wt% SiO2) and silica-rich (54 to 59 wt% SiO2), the latter overlapping in composition with the granitoid samples. The silica-poor enclaves are enriched in REEs compared to the silica-rich type, while the silica-rich enclaves exhibit trace-element patterns similar to those of the granitoids. Initial whole rock εNd values range between -3.8 and -4.0 for the granitoids and give a slightly wider range from -2.6 to -3.8 for the enclaves. The 87Sr/86Sr initial values vary from 0.7084 to 0.7138 for the granitoids and between 0.7052 and 0.7075 for the enclaves and indicate that the granitoids and enclaves are not isotopically identical. These may suggest that the two magmatic systems represented by the granitoid host rock and the enclaves, were probably derived from different sources, but with sufficient interaction, which led to a progressive change in the composition of the enclaves towards intermediate composition. We suggest that the mafic melts of the enclaves were generated at the base of the thickened crust through partial melting of the lower crustal source, with a significant contribution from mantle material. The increase in temperature resulted in anatexis of the lower crust and the formation of the granitoid parental magma. [ABSTRACT FROM AUTHOR]

In this study, laser ablation–multicollector–inductively coupled plasma–mass spectrometry (LA–MC–ICP–MS) of apatites and LA–ICP–MS of zircons are used to collect U–Pb geochronological data, Rb–Sr isotope chronology is used to analyze alkaline feldspar and plagioclase, and archival apatite geochemistry data for the exposed Naitoushan basalt and Heishigou dike in the Changbaishan Tianchi volcano (CTV) are accessed to examine the petrogenesis and determine the origin of basaltic magmatism in the CTV. The Naitoushan basalt and Heishigou dike formed at 22.2–18.7 and 0.230–0.218 Ma, respectively. In situ oxides, volatiles, trace element geochemistry and Sr–Nd isotopes of apatite are reported for two samples. Most apatites are in the early crystallization phase and form inclusions in plagioclase that are euhedral or subhedral. They have higher MgO and K2O/Na2O concentrations; lower F and Cl concentrations; Ba, Sr, Nb, Ta, Zr, Hf, K, and Ti depletion; and Th, U, Ce, Pb, P, and Nd enrichment. All apatite samples are enriched in light rare earth elements (REEs) relative to heavy REEs and have relatively homogeneous Th/U, Zr/Hf, La/Sm, and Nd/Tb ratios and Sr–Nd isotopic compositions; thus, their host magmas potentially have the same magmatic origin as oceanic island basalt. The apatite La, Yb, and U contents, Eu/Eu* and La/Yb values, and high REE contents show a weak crystallization sequence in the mafic magma. This study demonstrates that the pre-shield and post-shield mafic magmas in the CTV were likely derived from an enriched mantle source with an I-type signature related to the rollback of the Pacific plate. [ABSTRACT FROM AUTHOR]

Early Paleozoic A-type granites in South China are rare, and their petrogenesis is still highly debated. This study focuses on the controversial Epo pluton in the Wuyi-Yunkai Orogen and conducts petrological and petrogeochemical research to discuss its origin. The Epo granites were emplaced at approximately 414 Ma and exhibit petrological and geochemical features of A-type granites. They contain only one ferromagnesian mineral, ferrum biotite. The granites mostly have high alkalis contents (Na2O + K2O = 6.48–8.85 wt.%), high field strength element (HFSE) contents (Zr + Nb + Ce + Y = 353–461 ppm), and high Ga/Al (104×Ga/Al = 2.50–3.72) and FeOT/(FeOT + MgO) (0.74–0.85) ratios. Besides, they formed under high-temperature (>850°C) and low-pressure (≤5 kbar) conditions. Their high A/CNK (average 1.20) and Eu/Eu* (average 0.46) values as well as Sr (average 128 ppm) and Ba (average 628 ppm) contents but relatively low Zr contents (approximately 200 ppm) further suggest a strongly peraluminous A-type affinity, a distinctive subtype of A-type granites. The Epo granites display enriched Sr-Nd-Hf isotope compositions with a whole-rock87Sr/86Sri average ratio of 0.712, whole-rock εNd(t) values ranging from − 8.9 to − 7.6, and zircon εHf(t) values clustering at − 8. Their two-stage Nd and Hf isotope model ages are 1.7 Ga to 2.0 Ga, suggesting ancient crustal sources. Furthermore, Nb/U (average 7.46), Ce/Pb (average 4.06) and other trace element ratios indicate negligible contributions from juvenile mantle materials. Our data on the Epo pluton, coupled with other contemporary A-type granites in South China, suggest that the high-temperature melting of metasedimentary basements generated strongly peraluminous A-type granites, while the involvement of metaigneous rocks or mantle-derived magmas resulted in metaluminous to weakly peraluminous A-type granites. Source diversity leads to different aluminium saturations. The heat required to produce high-temperature A-type magmas was supplied by upwelling mantle-derived magma in a postcollisional extensional setting. [ABSTRACT FROM AUTHOR]

The Clarence Stream intrusion-related gold deposit is hosted within metasedimentary and metavolcanic sequences of the Ordovician Cookson and Silurian Mascarene groups that were intruded by several phases of the Late Silurian to Early Devonian Saint George Plutonic Suite. Based on geochemical and geochronological data, the intrusive rocks in the deposit are categorized into three distinct suites, including gabbroic, granitoid, and Whittier Ridge Granite (WRG). The gabbroic suite is the same as the East Branch Brook metagabbro intrusion, which exhibits a subalkaline mafic composition fractionated from a depleted mantle in a suprasubduction zone setting. The granitoid suite shows the same geochemical characteristics and age as the metaluminous to slightly peraluminous Magaguadavic Granite and its fractionated phases. The WRG suite reflects characteristics of calc-alkaline, metaluminous to peraluminous I-type granites in the area, such as Sorrel Ridge and Mount Douglas granitic plutons. In situ U-Pb zircon geochronology yielded an age of 419.5 ± 3.8 Ma for a monzodiorite from the gabbroic suite. Porphyritic granite and alkali granite from granitoid suite yielded U-Pb zircon age of 402.4 ± 1.8 Ma and 394.3 ± 3.8 Ma, respectively. Geochronologic data from the WRG suite reflect two different crystallization ages of 383.8 Ma (382.4 ± 3.1 to 385.1 ± 4) and 372.4 Ma (367.4 ± 1.3 to 377.1 ± 1.9). Several pieces of evidence demonstrate that the gold mineralizing events occurred after the emplacement of the East Branch Brook metagabbroic dykes and are linked to the various intrusive phases of the nearby syntectonic Early Devonian Magaguadavic Granite. The absence of gold and sulphide mineralization in felsic dykes related to the WRG confirms that this plutonic body formed adjacent to the gold zones after the main gold mineralizing event. [ABSTRACT FROM AUTHOR]

The geochemical compositions of apatite are commonly used to provide reliable constraints on the intrinsic magmatic variables of the parental magma. There is a widespread distribution of Mesozoic granitic rocks in the eastern Jiangnan Orogen (EJNO), which include I-type and A-type granitoids. This study aims to investigate the geochemical composition of apatite in 11 representative I-type and A-type granitic intrusions from the EJNO to understand their petrogenesis, intrinsic magmatic variables, and polymetallic mineralization potential. The results show that apatites in these granitoids were characterized by oscillatory zonation and homogeneous texture, and exhibited high F, and low Cl contents, as well as high REE, Y, and Th contents, indicating magmatic origin. These apatites were divided into two groups depending on their geochemical characteristics and original rock types. In Group I apatites (in the I-type granitoids), the absence of an abrupt change in major and trace element concentrations from the core to the rim of the apatite crystals, combined with their low levels of MgO, Sr, and HREY (HREE+Y), serves as evidence to classify the I-type granitoids as low Sr-Y adakitic granitoids with a low Mg#, which can be attributed to the partial melting of the thickened lower crust. In Group A apatites (in the A-type granites), the normal increase in incompatible elements from the core to the rim, as well as the presence of a flat REE pattern with pronounced Eu anomalies, can be attributed to crystal fractionation of plagioclase, allanite, and zircon. Furthermore, Group I apatites have higher SO3, Cl, and molar OH/F and Cl/F ratios compared to Group A apatites. Quantitative calculation by apatite-melt partitioning and modelling suggests that the I-type granitic magmas were more volatile-rich and more oxidized than A-type granitic magmas. Taken together, based on the relationship between the intrinsic magmatic variables and the behaviour of ore-forming elements, our study demonstrates that early I-type granitoids of the EJNO have a strong W-Mo-Cu polymetallic mineralization potential, while late A-type granites may possess rare metal mineralization potential. [ABSTRACT FROM AUTHOR]

Triassic granitoids are widespread in the East Kunlun Orogen (EKO), with Middle Triassic granitoids being dominant and Late Triassic granitoids being subordinate. This paper presents new whole-rock geochemical and Sr – Nd isotope, and zircon U – Pb age and Lu – Hf isotope data for eight granitoids in the Lalingzaohuo area, western EKO, northern Tibetan Plateau. These granitoids yield Middle and Late Triassic ages of 245–239 and 223–220 Ma, respectively. The granitoids from the Lalingzaohuo area have features typical of I-type granites and belong to the high-K calc-alkaline series. They exhibit variable rare earth and trace element patterns, and Sr – Nd – Hf isotopic compositions, indicative of different petrogenetic processes. The Middle Triassic samples have higher ISr values of 0.71440–0.71572 and lower εNd(t) values of −6.18 to −4.26 than the Late Triassic samples (ISr = 0.71139–0.71348; εNd(t) = –3.23 to −1.51), which are consistent with I-type granitoids derived from the lower crust. Geochemical and isotopic data indicate that the two stages of I-type granitoids had a significant mantle contribution. The Middle Triassic granitoids in the EKO, particularly the western EKO, have adakitic characteristics and formed by partial melting of lower continental crust. The T2–T3 granites formed by oceanic slab breakoff related to subduction and mantle convection, and the Late Triassic granites formed by lithospheric thinning and asthenospheric upwelling after slab breakoff. [ABSTRACT FROM AUTHOR]

Himalayan leucogranite is an excellent target for understanding the orogenic process of the India–Asia collision, but its origin and tectonic significance are still under debate. An integrated study of geochronology, geochemistry, and in situ Sr-Nd-Hf isotopes was conducted for a tourmaline-bearing leucogranite in the eastern Tethyan Himalaya using LA-ICP-MS, X-ray fluorescence spectroscopy, and ICP-MS and LA-MC-ICP-MS, respectively. LA-ICP-MS U-Pb dating of zircon and monazite showed that it was emplaced at ~19 Ma. The leucogranite had high SiO2 and Al2O3 contents ranging from 73.16 to 73.99 wt.% and 15.05 to 15.24 wt.%, respectively. It was characterized by a high aluminum saturation index (1.14–1.19) and Rb/Sr ratio (3.58–6.35), which is characteristic of S-type granite. The leucogranite was enriched in light rare-earth elements (LREEs; e.g., La and Ce) and large ion lithophile elements (LILEs; e.g., Rb, K, and Pb) and depleted in heavy rare-earth elements (e.g., Tm, Yb, and Lu) and high field strength elements (HFSEs; e.g., Nb, Zr, and Ti). It was characterized by high I Sr (t) (0.7268–0.7281) and low ε Nd (t) (−14.6 to −13.2) and ε Hf (t) (−12.6 to −9.47), which was consistent with the isotopic characteristics of the Higher Himalayan Sequence. Petrogenetically, the origin of the leucogranite is best explained by the decompression-induced muscovite dehydration melting of an ancient metapelitic source within the Higher Himalayan Sequence during regional extension due to the movement of the South Tibetan Detachment System (STDS). The significantly high lithium and beryllium contents of the leucogranite and associated pegmatite suggest that Himalayan leucogranites possess huge potential for lithium and beryllium exploration. [ABSTRACT FROM AUTHOR]

A flare‐up of granitoids occurred at 465–445 Ma in the South Altyn Tagh, synchronously with the exhumation of subducted continental crust. Nevertheless, it remains enigmatic whether a petrogenetic connection exists between them. Here, we report a 454–451 Ma monzogranite pluton, which is characterized by abundant inherited zircons, located in the northern margin of the South Altyn Tagh high‐pressure (HP)—ultrahigh‐pressure (UHP) metamorphic terrane. U–Pb ages and Hf–O isotopic compositions of inherited and synmagmatic zircons are investigated to trace the source rocks and petrogenesis of this pluton. The inherited zircons (zircons that predate the magmatism) exhibit a wide range of ages from 2618 to 484 Ma, displaying three major peaks at 1800–1100 Ma, 1000–800 Ma and 500 Ma. By comparing these inheritance age patterns with zircon spectra of main (meta‐)sedimentary sequences and the widespread Early Neoproterozoic granites (presently as granitic gneisses) in South Altyn Tagh, along with zircon εHf(t) and whole‐rock Nd isotopic composition, we argue that the main source rocks of the studied monzogranite are Early Neoproterozoic granitic gneisses and Late Mesoproterozoic paragneisses from the South Altyn Tagh HP–UHP metamorphic terrane. The ca. 500 Ma inherited zircons have a metamorphic origin, which is simultaneous with the peak metamorphic ages of HP–UHP metamorphic rocks in the Altyn Tagh Complex. These observations indicate that the source rocks of the monzogranite pluton are the subducted continental crust, which underwent metamorphism at ca. 500 Ma and followed by partial melting at 454–451 Ma. In addition, synmagmatic zircons exhibit variable δ18O and εHf(t) values ranging from 5.4 to 11.7‰ and from −19 to +10.3, respectively, indicating a minor contribution of mantle‐derived melts in the formation of the monzogranite. Given the studied pluton and contemporaneous extensive granitoids (465–445 Ma), characterized by similar geochemistry and source rocks, are synchronous with the final exhumation of subducted South Altyn Tagh continental crust, we propose that the reworking of exhumed continental crust at middle to lower crustal depths is their main petrogenesis. [ABSTRACT FROM AUTHOR]

Geochronological (U-Pb zircon, ID-TIMS), isotope-geochemical (Nd, Sr, Pb), and geochemical studies of rocks of the Amanan and Amudzhikan intrusive complexes and volcanic rocks of the Ukurey Formation in the eastern part of the West Stanovoy superterrane of the Central Asian Orogenic Belt were performed. The assignment of granitoids of these complexes to high-potassium C-type adakites is substantiated. It is established that the studied rocks are cogenetic and can be ascribed to a single Amudzhikan volcano-plutonic association formed in the age range of 133 ± 1–128 ± 1 Ma. The igneous complexes of this association belong to the Stanovoy volcano-plutonic belt, which extends in the sublatitudinal direction from the Pacific Ocean inward the North Asian continent for more than 1000 km, subparallel to the Mongol-Okhotsk suture zone, and assembles the tectonic structures of the Dzhugdzhur-Stanovoy and West-Stanovoy superterranes. The formation of the Stanovoy Belt is related to the closure of the Mongolo-Okhotsk Ocean and the collision between North Asian and Sino-Korean continents at ~140 Ma. The subsequent collapse of the collisional orogen, which was accompanied by large-scale lithospheric extension and delamination of the lower part of the continental lithosphere, led to upwelling of asthenospheric mantle. This caused melting of the lithospheric mantle and continental crust and, as a consequence, the formation of both mafic (shoshonitic) melts and anatectic crustal melts of the adakite type. The mixing of these melts led to the formation of the parental magmas of the Amudzhikan magmatic association. The crustal component in the source was of heterogeneous nature and finally formed as a result of the Early Cretaceous collision event. It is characterized by the upper-crustal isotopic signatures: increased Rb/Sr and U/Pb ratios and a decreased Sm/Nd ratio in the source. The mantle component is represented by enriched lithospheric mantle of the Central Asian Orogenic Belt, the formation of which is associated with subduction processes and closure of the Mongol-Okhotsk paleoocean. Metasomatic transformation of the mantle with the introduction of melts and fluids with isotopic parameters of an EMII-type source or upper crust occurred at this stage. [ABSTRACT FROM AUTHOR]

We present U – Pb zircon geochronology and whole-rock Sr-Nd-Pb isotopic compositions of monzonitic plutons from NE Turkey to elucidate their genesis and provide significant insights into the generation of post-collisional I-type shoshonitic magmas. Zircon U – Pb dating of the monzonitic plutons yielded an emplacement of the Middle Eocene (44–39 Ma). Geochemically, the monzonitic plutons are I-type, metaluminous, and shoshonitic in composition, and have high contents of total alkalis and LILE, high ratios of LREE/HREE and LREE/HFSE, and show negative Nb-Ta-Ti and Eu (EuN/Eu* = 0.69–0.84) anomalies. The monzonitic plutons have homogeneous and moderately low initial 87Sr/86Sr (0.70464–0.70495), positive εNd(t) values (0.33 to 1.28), and narrow variation of the initial Pb isotope contents with 206Pb/204Pb (18.74–18.82), 207Pb/204Pb (15.64–15.65), and 207Pb/204Pb (38.81–38.90). The combined use of whole-rock trace elements and isotopic compositions with regional geology suggests that parental magmas of the monzonitic plutons were generated from mainly melt-metasomatized sub-continental lithospheric mantle source and lesser crustal components in an extensional orogenic setting, and then monzonitic magmas have evolved by dominantly fractional crystallization in crustal levels. [ABSTRACT FROM AUTHOR]

During the initial stages of Pangea amalgamation in the Carboniferous period, the Rheic Ocean basin experienced subduction prompted by the convergence between Gondwana and Laurasia, culminating in the basin's closure that preceded the paleocontinent collision. This tectonic episode promoted the Carboniferous (Mississippian and Pennsylvanian) tholeiitic to calc-alkaline magmatism, represented in the Colombian Andes through the tonalite and diorite-gabbro facies of the El Carmen Pluton. We investigate the two main facies (felsic and mafic facies) of the plutonic body, which crop out in the Central Cordillera of the Colombian Andes. U-Pb zircon crystallization ages are 326 ± 1 Ma for the mafic facies and 313 ± 1 Ma for the felsic facies. Positive ɛHf(i) isotopes ranging from +5.4 to +10.9 suggest mantle-derived magma with low crustal assimilation. The progressive increase in Eu anomaly (Eu × 0.64 to 1.15) and high LREE/HREE ratios underscore a continental magmatic arc formation in congruence with a subduction context. Thermobarometric analyses of mineral geochemistry across both facies reveal the magmatic emplacement at temperatures spanning 753–910°C, pressures between 3 and 4.65 kbar, and depths approximating 9–14 km. The simultaneous presence of two magmatic facies bearing tholeiitic and calc-alkaline characteristics, separated by ~13 Ma crystallization gap, infers a magmatic recharge episode. The results highlight a slightly thickened crust due to the arc maturity, or a transition from shallow-dipping to steep-angle subduction, consistent with tectonic slab-rollback mechanisms. The modest crustal thickening, indicative of low arc maturation between 326 and 313 Ma, is concomitant with the closure of the western part of the Rheic Ocean basin. [ABSTRACT FROM AUTHOR]

The Ririwai anorogenic alkaline complex harbours extensive rare metal (Nb-Zr-Sn-Zn) mineralization. However, uncertainty still surrounds their origin and magmatic-hydrothermal processes responsible for their rare metal mineralization. The complex is composed of peralkaline arfvedsonite ± albite-bearing granites, mildly peralkaline fayalite-bearing granite porphyries, and weakly peraluminous biotite-bearing granites, all of which show diagnostic A1-type characteristics. Zircon U-Pb dating reveals emplacement ages between 181.4 ± 0.81 and 188.6 ± 7 Ma for the three rock units. Sm-Nd and Pb isotopes (εNd (t) = –0.6 to −5.4, 206Pb/204Pb = 17.68–17.93) constrained the Ririwai A-type granites to represent highly fractionated products of enriched mantle-derived magmas. Mass-balance modelling suggests that magma evolution was fuelled by extensive fractional crystallization of 50 ~ 60 vol.% K-feldspar, 30 ~ 35 vol% fayalite, 5 ~ 10 vol.% amphibole, and ~ 5 vol.% apatite under reduced and water-undersaturated (ΔFMQ = –1.55; logfo2 = –18.63; H2O = <2.0 wt.%) conditions and assimilation of ~ 50 vol.% crust. Whole rock and amphibole compositions revealed an increasing degree of fractionation from the fayalite-bearing granite porphyries through biotite-bearing granites to the arfvedsonite ± albite-bearing granites. This extended fractionation at the late stage of magma differentiation, facilitated by fluorine dissolution and concentration of excess HFSE and REE as alkali-fluorocomplexes in the fluorine-rich silicate melt, allowed the accumulation of economic rare metal pyrochlore and columbite mineralizations in the highly fractionated arfvedsonite± albite- and biotite-bearing granites, respectively. Nonetheless, the metasomatic reaction rim textures around the magmatic pyrochlore, coupled with the M-type lanthanide tetrad effect (TE1,3 >1.10) indicate the subsequent effect of hydrothermal processes. Tectonically, reactivated shear fractures and transcurrent faults following lithospheric stresses in a transtensional regime allowed magma uprising and emplacement of A-type granites in the Ririwai complex. [ABSTRACT FROM AUTHOR]

Basalts from the Late Carboniferous to Early Permian are extensively developed in the central Lhasa subterrane, southern Tibet. Studying the petrogenesis of these rocks may have implications for the late Paleozoic arc magmatism along the central Lhasa subterrane uncovering more of the evolution of the Sumdo Paleo‐Tethys Ocean and its dynamic mechanism. Basalt samples from the Luobadui Formation in the Leqingla area, NW of Linzhou City in the central Lhasa subterrane, southern Tibet exhibit arc‐like geochemical signatures in a subduction‐zone tectonic setting characterized by high Al2O3 and low TiO2 contents, fractionated REE patterns with low Nb/La ratios and high LREE concentrations, and negative HFSE anomalies. Based on their higher Th/Ce, Nb/Zr, and lower Ba/Th, Pb/Nd ratios, slightly negative to positive εNd(t) values, and the relatively high Sr‐Pb isotopic compositions, these samples were probably derived from partial melting of a depleted mantle source of garnet + spinel lherzolite, metasomatized by subducted sediments around 297 Ma. Modeling of the trace elements indicates that these basalts experienced fractional crystallization of olivine, clinopyroxene and minor plagioclase during magma ascent and eruption. It is proposed that these Late Carboniferous–Early Permian basalts are associated with the northward subduction of the Sumdo Paleo‐Tethys Ocean seafloor along the southern margin of the central Lhasa subterrane. [ABSTRACT FROM AUTHOR]

Insights into the source and partial melting conditions of tonalite–trondhjemite–granodiorite (TTG) intrusive suites provide essential constraints on the tectonic regimes prevailing before 2.5 Ga. As case studies on individual suites increase, the TTG group becomes more heterogeneous, offering detailed insights into the evolution of the Archean crust. This study focuses on the La Dauversière pluton, a TTG suite in the Chibougamau area, Abitibi greenstone belt, Canada, to unravel complex differentiation processes in a pluton with a relatively limited volume. According to whole-rock and zircon chemistry, the La Dauversière pluton is a TTG suite that contains less Na and light rare earth elements (LREE) than other TTG suites of the Abitibi greenstone belt. Whole-rock chemistry and melt inclusions in zircon also point to an atypical fractional crystallization process that favors K enrichment, contrasting with the Na enrichment trends observed in most TTG suites globally. Magma hybridization, with late magma pulses interacting with early phases partially crystallized at depth, likely explains the chemistry of the La Dauversière pluton. The source of these magmas differs from the basaltic source that gave rise to most TTG suites of the Abitibi greenstone belt, possibly because older basement occurs in the Chibougamau area and is lacking in the rest of the greenstone belt. The La Dauversière pluton underscores the importance of interpreting the petrogenesis of individual TTG suites before inferring global source processes and geodynamic settings. [ABSTRACT FROM AUTHOR]

Two magmatic REE-rich occurrences, located near Jamestown, Colorado, and hosted in the Precambrian Longs Peak granite batholith, exhibit unusual textures that suggest formation by fluoride-silicate melt immiscibility. Both contain small (<2 mm diameter) globular F-, P-, and REE-rich segregations of fluorite and monazite-(Ce). In addition, the northern of the two localities preserves evidence of a second melt immiscibility event in the form of larger (up to several cm diameter) aplite-hosted globular segregations of fluorite and the REE minerals allanite-(Ce), monazite-(Ce), fluorbritholite-(Ce), törnebohmite-(Ce), and cerite-(Ce). The southern of the two localities lacks these cm-scale globular textures, but instead contains much larger aggregates of these same REE minerals, with up to >57 wt. % ΣREE2O3, yet no fluorite, as well as large aggregates of allanite-(Ce) and quartz, and an amphibole-bearing REE-rich rock containing allanite-(Ce), other REE minerals, quartz and minor apatite. A new Nd-Sm laser ablation age of 1.422(24) Ga on monazite-(Ce) and allanite-(Ce) from the southern locality implies the same age of formation of 1.420(25) Ga as for the northern locality, with equally similar initial εNd1.42Ga values of these REE minerals. A newly discovered third locality, containing primarily allanite-(Ce), minor monazite-(Ce), and thorite, without fluorite, extends the number, spatial distribution and total volume of these mineralogically unusual magmatic REE occurrences. We suggest that the REE were concentrated in these three localities by multiple stages of fluoride-silicate melt immiscibility. For the southern locality, slower cooling of a possibly larger magma volume, or in a deeper environment, allowed greater aggregation of the immiscibly separated REE-rich phases, as well as loss of the volatile element F, resulting in a greater availability of Ca accommodated by the crystallization of amphibole and minor apatite. [ABSTRACT FROM AUTHOR]

The Paleocene ore deposits related to the India–Asia continental collision are widely distributed in the Gangdese metallogenic belt. Among these, Sinongduo is the first discovered epithermal Ag-Pb-Zn deposit in the Lhasa terrane. However, there is still controversy over the ore-forming magma in this deposit. This study mainly reports new zircon U-Pb isotopic ages, whole-rock geochemistry, and Sr-Nd isotopic data for the granite porphyry from the Sinongduo deposit, aiming to discuss the petrogenesis and tectonic setting of the granite porphyry and its genetic link between the Ag-Pb-Zn mineralization. The results show that zircon U-Pb analyses yield ages of 62.9 ± 0.5 Ma and 59.0 ± 0.7 Ma for the granite porphyry, indicating that it formed during the Paleocene period. The timing of the granite porphyry intrusion is contemporaneous with the mineralization, suggesting that it is most likely the ore-forming magma in the Sinongduo deposit. The granite porphyry has high SiO2 and K2O, moderate Al2O3, and low Na2O, CaO, and FeOT contents, and it displays significant enrichments in LREEs and LILEs and depletions in HREEs and HFSEs, with negative Eu anomaly. The granite porphyry is a peraluminous series and can be classified as S-type granite. Moreover, the granite porphyry shows relatively high ratios of (87Sr/86Sr)i and low values of εNd(t). The geochemical and isotopic compositions of the granite porphyry from the Sinongduo area are similar to those of the upper continental crust, which suggests that the granite porphyry was most likely derived from the melting of the upper continental crust in the Lhasa terrane during the India–Asia collisional tectonic setting. [ABSTRACT FROM AUTHOR]

The Kunduleng granite hosts one of several significant uranium anomalies within the southern Great Xing'an Range, NE China. Whole-rock geochemistry and mineral chemistry data, along with the zircon U-Pb-Hf isotope have been used to constrain the petrogenesis of this granitic intrusion and the origin of the uranium anomaly. Microscopically, quartz, alkali-feldspar, and plagioclase are the essential mineral constituents of the granite, with minor biotite, while monazite, apatite, xenotime, and zircon are accessory minerals. Geochemically, the silica- and alkali-rich granites show a highly fractionated character with "seagull-shaped" REE patterns and significant negative anomalies of Ba and Sr, along with low Zr/Hf and Nb/Ta ratios. The granite has positive zircon εHf(t) values ranging from +12.7 to +14.5 and crustal model ages (TDM2) of 259–376 Ma, indicating a Paleozoic juvenile crustal source. Uraninite and brannerite are the main radioactive minerals responsible for the uranium anomaly within the Kunduleng granite. Uraninite presents well-developed cubic crystals and occurs as tiny inclusions in quartz and K-feldspar with magmatic characteristics (e.g., elevated ThO2, Y2O3, and REE2O3 contents and low CaO, FeO, and SiO2 concentrations). The calculated U-Th-Pb chemical ages (135.4 Ma) are contemporaneous with the U-Pb zircon age (135.4–135.6 Ma) of the granite, indicating a magmatic genesis for uraninite. The granites are highly differentiated, and extreme magmatic fractionation might be the main mechanism for the initial uranium enrichment. Brannerite is relatively less abundant and typically forms crusts on ilmenite and rutile or it cements them, representing the local redistribution and accumulation of uranium. [ABSTRACT FROM AUTHOR]

This paper presents a detailed study including LA-ICP-MS zircon U-Pb dating, geochemical, zircon Hf isotope, and whole rock Sr-Nd isotope analysis of magmatic rocks from the Yitong County, Jilin Province, NE China. These data are used to better constrain the Middle Silurian–Middle Devonian tectonic evolution in the eastern segment of the northern margin of the North China Craton (NCC). Zircon U-Pb dating results show that the Ximangzhang tonalite formed in the Late Silurian (425 ± 6 Ma); the basalt, andesite, and metamorphic olivine-bearing basalt in the Fangniugou volcanic rocks formed in the Middle Silurian (428 ± 6.6 Ma) and Middle Devonian (388.4 ± 3.9 Ma, and 384.1 ± 4.9 Ma). The Late Silurian tonalites are characterized by high SiO2 and Na2O and low K2O, MgO, FeOT, and TiO2, with an A/CNK ratio of 0.91–1.00, characteristic of calc-alkaline I-type granite. They are enriched in Rb, Ba, Th, U, and K, and depleted in Nb, Sr, P, and Ti, with positive εNd(t) (+0.35) and εHf(t) (+0.44 to +6.31) values, suggesting that they mainly originated from the partial melting of Meso–Neoproterozoic accretionary lower crustal material (basalt). The Middle Silurian basalts are characterized by low SiO2, P2O5, TiO2, and Na2O and high Al2O3, FeOT, and K2O, enriched in Rb, Ba, Th, U, and K and depleted in Nb, Ta, Sr, P, and Ti, indicative of shoshonitic basalt. The Late Silurian tonalites have positive εNd(t) (+4.91 to +6.18) values and primarily originated from depleted mantle magmas metasomatized by subduction fluids, supplemented by a small amount of subducted sediments and crustal materials. The Middle Devonian volcanic rocks exhibit low SiO2, TiO2, and Na2O and high K2O, and MgO, enriched in Rb, K, and LREEs and depleted in Nb, Ta, Sr, and HREEs, characteristic of shoshonitic volcanic rocks. Their εNd(t) (+2.11 to +3.77) and εHf(t) (+5.90 to +11.73) values are positive. These characteristics indicate that the Middle Devonian volcanic rocks primarily originated from depleted mantle magmas metasomatized by subduction fluids, with the addition of crustal materials or subducted sediments during their formation. Based on regional geological data, it is believed that the study area underwent the following evolutionary stages during the Silurian–Devonian period: (1) active continental margin stage of southward subduction of the Paleo–Asian Ocean (PAO) (443–419 Ma); (2) arc-continent collision stage (419–405 Ma); (3) post-collision extension stage (404–375 Ma); (4) active continental margin stage, with the PAO plate subducting southward once again (375–360 Ma). [ABSTRACT FROM AUTHOR]

The South China Block, a region renowned for its extensive granite distribution and rich metal deposits, serves as a natural laboratory for the study of granite-related mineralization. This research focuses on the Tongtianmiao granite pluton, which is located at the intersection of the Qin-Hang and Nanling metallogenic belts and has been confirmed as a significant lithium mineral resource. Despite its discovery and ongoing development, the lithium-rich Tongtianmiao pluton has been understudied, particularly concerning its petrogenesis, which has only recently come to the forefront of scientific inquiry. By integrating an array of petrogeochemical data with geochronological studies derived from zircon and monazite dating, this study provides insights into the magmatic processes related to lithium enrichment in the Tongtianmiao granites. The Tongtianmiao granites are classified as A-type granites characterized by high SiO2 contents (69.18–78.20 wt.%, average = 74.08 wt.%), K2O + Na2O contents (4.59–8.34 wt.%, average = 6.86 wt.%), A/CNK > 1.2, and low concentrations of Ca, Mg, and Fe. These granites are enriched in alkali metals such as Li, Rb, and Cs but are significantly depleted in Ba, Sr, and Eu. They show no significant fractionation of light or heavy rare-earth elements but present characteristic tetrad effects. A finding of this study is the identification of multiple ages from in situ zircon U–Pb dating, which implies a prolonged history of magmatic activity. However, given the high uranium content in zircons, which could render U–Pb ages unreliable, emphasis is placed on the monazite U–Pb ages. These ages cluster at approximately 172.1 ± 1.1 Ma and 167.9 ± 1.6 Ma, indicating a Middle Jurassic period of granite formation. This timing correlates with the retreat of the Pacific subduction plate and the associated NE-trending extensional fault activity, which likely provided favorable conditions for lithium enrichment. The study concluded that the Tongtianmiao granites were formed through partial melting of crustal materials and subsequent underplating by mantle-derived materials, and were contaminated by strata materials. This process resulted in the formation of highly differentiated granite through magmatic differentiation and external forces. These findings have significant implications for understanding the petrogenesis of lithium-rich granites and are expected to inform future exploration endeavors in the Tongtianmiao pluton. [ABSTRACT FROM AUTHOR]

Voluminous Neoproterozoic intermediate to felsic rocks intruded the Neoarchean Douling Complex in the South Qinling Belt of Central China, which may provide new constraints on the controversial issue about the nature of the continental margin of the Yangtze Block during the Neoproterozoic. This study presents zircon U–Pb geochronology, whole‐rock geochemistry and Sr–Nd isotope of the Douling dioritic–granodioritic–granitic intrusion, aiming to clarify its petrogenesis and tectonic significance. The dioritic–granodioritic–granitic rocks yield similar zircon U–Pb ages ranging from 735 to 705 Ma. The enrichment of light rare earth elements (LREEs) and large‐ion lithophile elements (LILEs), and depletion of high‐ field‐strength elements (HFSEs) (e.g., Nb, Ta) are typical features of arc magmatic rocks. The whole‐rock Sr–Nd isotopic compositions show initial 87Sr/86Sr ratios ranging from 0.7034 to 0.7059, and εNd(t) values from −7.3 to −1.4. Elemental and isotopic data suggest that the Neoproterozoic dioritic–granodioritic–granitic rocks were co‐genetic and were generated by partial melting of lower crust materials combined with mantle‐derived melts. The granites were the derivative product of dioritic rocks by fractional crystallization of amphibolite, plagioclase, mica and zircon. Combined with literature data, we infer a subduction‐related setting for the northern margin of the Yangtze Block during the Middle Neoproterozoic, and a tectonic model of accretion along an Andean‐type active continental margin after the collision of the Douling micro‐block with the northern Yangtze Block is further proposed. [ABSTRACT FROM AUTHOR]

Permian alkaline granitoids are widely distributed throughout the Tien Shan Orogen and adjacent region of the southern Central Asian Orogenic Belt. However, their petrogenesis and related tectonic setting remain equivocal. A detailed mineralogical, U-Pb zircon dating, in situ elemental and Sr-Nd-Hf isotopic studies of the uranium-rich Akkulen syenite intrusion in the Northern Tien Shan of Kyrgyzstan were undertaken to better understand its magmatic processes and geodynamic evolution. Four independent oxygen barometers have shown that the oxygen fugacity of the Akkulen syenitic magma evolved from initial low fO2 (NNO +1) during magma ascent and cooling; Apatite geochemical characteristics also indicate that the magma is relatively high F (2.9–5.1 wt.%), with low Cl (0.053–0.13 wt.%) and anhydrous (<4 wt %) contents. According to whole-rock geochemical data, the syenite samples have abnormally high U (38.5–57.1 ppm) and Th (96.2–137 ppm) concentrations, we suggest that high F content and moderate oxygen fugacity are beneficial for uranium enrichment. Zircon grains from a syenite sample yielded a weighted 206Pb/238U age of 283.5 ± 2.6 Ma. The intrusion has an A-type granite affinity with high alkali (Na2O + K2O) contents and Fe/(Fe+Mg) ratios, high LREE/HREE (~5), and low Sr, Ba, and Eu contents. They have negative εNd(t) (−5.2 to −3.6) values with Mesoproterozoic two-stage model ages (T DM2 = 1.35–1.47 Ga), and variable εHf(t) values (−4.6 to +2.4) with Mesoproterozoic two-stage model ages (T DM2 = 1. 2–1.59 Ga), which suggest these rock derivations from the relatively old crustal with minor contribution from juvenile crustal melts. In comparison with regional available dataset, we propose that the alkaline Permian granitoids in Kyrgyz Northern Tien Shan may have been originated from large-scale partial melting of Mesoproterozoic metamorphic basement with minor juvenile crustal material in a post-extensional setting. In contrast, the Early Permian granitoid magmatism in the Tarim Craton may have been caused by the partial melting of Neoproterozoic basement rocks associated with Permian mantle plume activities. [ABSTRACT FROM AUTHOR]

The generation and modification of silicic magma systems are essential processes in resolving the differentiation of continental crust. This understanding motivated the geo-chronological and geochemical study of the early Permian Hongliujing granite complex, consisting of quartz monzonite, granite, and leucogranite in the Central Tianshan microcontinent of the southern Central Asian Orogenic Belt. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon U-Pb dating of the Hong-liujing complex rock units revealed almost identical ages (279 ± 2 Ma to 270 ± 2 Ma). The high-silica leucogranite and granite are characterized by positive Rb and negative Eu anomalies and Ba, Sr, P, and Ti depletions. The zircon trace elements are characterized by relatively low Ti and Th/U and high Yb/Gd. In contrast, the quartz monzonite and its mafic microgranular enclaves display minor negative Ba, Sr, P, Ti, and Eu anomalies, while the zircon trace elements are characterized by relatively high Ti and Th/U and low Yb/Gd. The complex has similar zircon Hf and whole-rock Nd isotopic compositions, with Hf and Nd model ages younger than 1.4 Ga, suggesting that their magmas were derived from an isotopically depleted mantle, with some contributions from crustal melts. The leucogranites further showed relatively large variations of eHf(Z) and lower eNd(Z) values, implying that their magma was affected by higher amounts of crustal contamination. We suggest that crystal-melt segregation was the major mechanism responsible for the evolution of the magmatic system, and that the early Permian magmatism represents a crust-forming episode triggered by slab rollback of the subducting South Tianshan oceanic plate beneath the eastern Central Tianshan microcontinent. Thus, our study reveals that microcontinents with Precambrian crustal basement were major sites of juvenile continental growth during the accretionary evolution of the Central Asian Orogenic Belt. [ABSTRACT FROM AUTHOR]

The purpose of this study is to find out study of Element Abundance in Volcanic Rocks in the Beruang Kanan Region, Gunung Mas Regency, Central Kalimantan. Soil elements, based on their abundance in the earth's crust and petrogenetic analysis aim to divide soil elements into several groups, namely major elements, trace elements and rare earth elements (REE). The research location is located in the Beruang Kanan area, Tumbang Miri District, Gunung Mas Regency, Central Kalimantan Province. The major elements and trace elements of the host rock were obtained from Xray fluorescence (XRF) analysis and Plasma-Coupled Mass Spectrometry (ICP-MS) methods. Volcanic rocks from the Kanan Bear prospect The volcanic magmatic affinity in the study area is calc-alkaline this chemical characteristic is clearly reflected by the type of volcanic rock which is determined based on its chemical classification, which is generally igneous rock of the calc-alkaline magma series type so it is interpreted to originate from a convergent tectonic environment continental edge. [ABSTRACT FROM AUTHOR]

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The Godar-e-Siah Eocene monzodiorite stock is located in the southwest of the Jandaq area (NE of Isfahan) and northwest of the Central-East Iranian Microcontinent (CEIM). The main minerals in these monzodiorites are plagioclase, K-feldspar, clinopyroxene, phlogopite, and garnet, which are set in a fine-grained groundmass of feldspars. The main textures are granular, porphyritic, and poikilitic. In some cases, these rocks contain euhedral to subhedral garnet crystals with inclusions of the igneous clinopyroxene and groundmass minerals including feldspar and graphite. These garnets exhibit Ti-andradite and Ca-melanite composition from the solid solution series of andradite-grossular. The chemical zoning patterns of the studied garnets confirm that these garnets have a non-magmatic origin and metamorphic nature. In the investigated monzodiorites, the presence of euhedral garnet crystals with inclusions of igneous clinopyroxenes metasomatic scapolite, and metasomatic phlogopite shows that these garnets are of metasomatic origin, which formed due to the alteration of igneous clinopyroxenes. All geochemical and petrographic evidences from the studied garnets indicate that they have formed as a result of the intrusion of Eocene monzodiotites into the carboniferous limestones (or dolomites), leading to the creation of endoskarn or reactions skarn that can be distinguished at the millimetric scale in microscopic studies. Introduction Garnet is a general mineral forms in metamorphic rocks derived from the sedimentary and igneous protoliths and at all metamorphic grades above the greenschist facies (Baxter et al., 2017). However, the presence of garnet in certain types of igneous rocks, such as peraluminous granite and ultramafic rocks in the upper mantle, introduces complexities in unraveling the petrogenesis of garnets in igneous and metamorphic rocks (Rong et al., 2018). Titanium-rich garnets are enriched in andradite, occur in various types of rocks, including a variety of igneous rocks, encompassing trachytes and phonolites (Dingwell and Brearley 1985), syenites and carbonatites, nephelinites and tephrites (Gwalani et al., 2000), as well as ultramafic lamprophyres, rodingites (Schmitt et al., 2019); high temperature metamorphic rocks and skarns. The composition of titaniferous garnets besides their paragenetic relationships is one of the significant petrology factors (Chakhmouradian and McCammon, 2005). The study area is situated in the northwestern part of the CEIM (northwestern part of the Yazd block), and southwest of the Jandaq City. The rock units of the Jandaq area are mainly include Paleozoic metamorphic rocks, Upper Paleozoic sedimentary rocks, Cretaceous and Paleocene sediments, Eocene intrusive rocks, Eocene subvolcanic (dikes) and volcanic rocks (Jamshidzaei et al., 2021), the Pis-Kuh upper Eocene sedimentary rocks (flysch), and Early Oligocene lamprophyric rocks, and alkali basalts (Torabi, 2010; Berra et al., 2017; Sargazi et al., 2019; Jamshidzaei et al., 2021). In this paper, the chemical characteristics of the monzodiorite stock and origin of garnet mineral are discussed. Material and methods To determine the chemical compositions of minerals, JEOL JXA-8800 WDS at the Department of Earth Science, Kanazawa University, Kanazawa, Japan was used. Chemical analyses of minerals was performed under an accelerating voltage of 20 kV, a probe current of 20 nA, and a focused beam diameter of 3μm. The ZAF program was used for data correction. Natural minerals and synthetic materials with well-characterized compositions serve as standards for calibration and validation purposes. The Fe2+# and Mg# parameters of minerals are represented by the atomic ratios of Fe2+/(Fe2++Mg) and Mg/(Mg+Fe2+), respectively. To recalculate the FeO and Fe2O3 concentrations from Fe2O3*, recommended ratios of Middlemost (1989) is used. The mineral abbreviations used in this context are derived from Whitney and Evans (2010). Results and discussion The monzodiorites of the Godar-e-Siah area mostly show fine to coarse-grained granular, porphyritic and poikilitic textures. These rocks are mesocrate in color, displaying massive and mineralogically homogeneous nature in their outcrops. K-feldspars are the primary minerals and garnet mineral is imposed on these rocks. The main minerals of this monzodiorite stock are plagioclase, K-feldspar, clinopyroxene, phlogopite, and garnet, set in a fine-grained matrix of feldspars. These rocks have mainly granular, porphyritic, and poikilitic textures. In some cases, these rocks contain euhedral to subhedral garnet crystals with inclusions of igneous clinopyroxene and groundmass minerals including feldspar and graphite. These garnets have a composition of Ti-garnet and Ca-melanite from the solid solution series of andradite-grossular. Based on the EPMA data, the clinopyroxenes show diopside to hedenbergite compositions, indicating that two types of clinopyroxene are in these rocks. The first group of this mineral contain MgO (6.9-10.20 wt.%), FeO*(11-16.88 wt.%), Al2O3 (2-5.84), and Na2O (1.1-1.9 wt.%), is reactive pyroxenes. The second category contains MgO (9.98-12.89 wt.%), FeO* (9.13-13.87 wt.%), Al2O3 (1.82-3.11 wt.%), and Na2O (0.7-1.42% Wt.%), is igneous pyroxenes. Chemistry of the pyroxenes reveals that reactive pyroxenes have higher concentrations of FeO* and Al2O3 than igneous pyroxenes. Chemistry of the feldspars indicates that the K-feldspars is orthoclase in composition. Also, chemical analyses of mica show that these minerals contain high concentrations of MgO (21.54-22.60 wt.%) and low values of Al2O3 (12.89-13.30 wt.%). The mica from the studied rocks of the Jandaq area plots in the phlogopite field. The garnet grains in these rocks contain 61.94-66.39 mol.% almandine (Fe2Al2Si3O12), 18.60-23.40 mol.% grossular (Ca3Al2Si3O12), 10.06-15.11 mol.% pyrope (Mg2Al2Si3O12), and 1.09-4.32 mol.% spessartine (Mn2Al2Si3O12). These garnets have a composition of Ti-garnet and Ca-melanite from the solid solution series of andradite-grossular. The chemical zoning patterns of the studied garnets confirm that these garnets have a non-magmatic origin and metamorphic nature. The presence of discontinuous chemical zoning and the pattern of variations in the end-member compositions of these garnets indicate that they were formed under disequilibrium conditions accompanied by changes in the environmental oxidation conditions. In the studied monzodiorites, the presence of euhedral garnet crystals with inclusions of igneous clinopyroxenes, metasomatic scapolite, and metasomatic phlogopite shows that these garnets are of metasomatic origin which formed due to the alteration of igneous clinopyroxenes. The geochemical characteristics and petrographic evidences from the studied garnets; including the presence of euhedral crystals with distinct boundaries to contact minerals, the occurrence of inclusions of background minerals and igneous clinopyroxenes in the garnets, as well as the presence of discontinuous chemical zoning, confirms that they have formed as a result of the intrusion of Eocene monzodiotites into the carboniferous limestones (or dolomites), leading to the creation of endoskarn or reactions skarn.

The Hardawu granites in the eastern segment of the ultrahigh-pressure metamorphic belt, the northern Qaidam Basin, were studied by whole-rock major and trace elements and in-situ zircon U-Pb geochronology and Hf isotopes to discuss the petrogenesis and tectonic evolution. Geochronological results show that the granites have a crystallization age of 401 ± 3 Ma, suggesting that they were formed in the Early Devonian. The granites have SiO2 contents of 75.32 wt.%–76.05 wt.%, total alkali contents of 8.23 wt.%–8.36 wt.%, and K2O/Na2O ratios of 1.62–1.91. They were rich in K2O, poor in TiO2, MnO, MgO, and P2O5, and have A/CNK values of 1.05–1.07, Rittmann index δ values of 2.05–2.14, and differentiation index (DI) values of 92.85–94.18. They are high potassium calc-alkaline, weak-peraluminum, and highly differentiated I-type granites. The granites also show enrichment of large ion lithophile elements (LILE) such as Rb, Ba, and Th, and depletion of high field strength elements (HFSE) such as Nb, Ta, and Ti. The total REE concentrations range from 169 ppm to 232 ppm, with enrichments of light rare earth elements and negative Eu anomalies (δEu = 0.39–0.55). The zircon εHf(t) values range from −0.65 to −2.29, and the two-stage model ages (tDM2) changed within a small range of 1.44 to 1.54 Ga, indicating that the magma of the Hardawu granites was originated from the partial melting of Mesoproterozoic lower crustal materials. Combined with previous studies, we suggest that the Hardawu granites were formed in the extensional tectonic setting after the collision between the Qaidam Block and the central and southern Qilian Block in the Early Devonian. [ABSTRACT FROM AUTHOR]

Aillikite dikes of carbonate–biotite composition, intersecting Paleoproterozoic banded iron formations, were discovered in the Kursk block of Sarmatia for the first time. Their age is 2.10–2.07 Ga. The aillikite dikes underwent epidote–amphibolite facies metamorphism (550°С, 2–3 kbar), and they are deformed and foliated. Primary magmatic olivine and pyroxene were not preserved. In terms of geochemistry, ultramafic lamprophyres of the Kursk block are similar to petrotypical aillikites. They are depleted in SiO2 and Al2O3 and enriched in MgO, TiO2, K2O, Cr, Ni, and Nb with highly fractionated LREE and HREE. The highly radiogenic neodymium isotopic composition is indicative of a juvenile enriched (metasomatized) mantle source of aillikites. Positive Nb and Ti anomalies suggest metasomatic alterations of the depleted lithosphere mantle by OIB melts under opening of the Tim back-arc basin. The aillikite dikes and carbonatites of the Dubravinsky complex could have been formed at different melting degrees of a single deep, lithospheric source, enriched in lithophile elements shortly before the melting episode, possibly in a suprasubduction setting about 2.1 Ga. [ABSTRACT FROM AUTHOR]

During the Late Precambrian, the North Eastern Desert of Egypt underwent significant crustal evolution in a tectonic environment characterized by strong extension. The Neoproterozoic alkali feldspar granite found in the Homret El Gergab area is a part of the Arabian Nubian Shield and hosts significant rare metal mineralization, including thorite, uranothorite, columbite, zircon, monazite, and xenotime, as well as pyrite, rutile, and ilmenite. The geochemical characteristics of the investigated granite reveal highly fractionated peraluminous, calc–alkaline affinity, A-type granite, and post-collision geochemical signatures, which are emplaced under an extensional regime of within-plate environments. It has elevated concentrations of Rb, Zr, Ba, Y, Nb, Th, and U. The zircon saturation temperature ranges from 753 °C to 766 °C. The formation of alkali feldspar rare metal granite was affected by extreme fractionation and fluid interactions at shallow crustal levels. The continental crust underwent extension, causing the mantle and crust to rise, stretch, and become thinner. This process allows basaltic magma from the mantle to be injected into the continental crust. Heat and volatiles were transferred from these basaltic bodies to the lower continental crust. This process enriched and partially melted the materials in the lower crust. The intrusion of basaltic magma from the mantle into the lower crust led to the formation of A-type granite. [ABSTRACT FROM AUTHOR]

The Gangdese metallogenic belt in Tibet is an important polymetallic metallogenic belt formed during the subduction of the Neo-Tethys Ocean and subsequent India–Asia collision. Adakitic rocks are widely distributed in this belt and are considered to be closely related to porphyry–skarn Cu-Mo polymetallic mineralization. However, the petrogenesis and geodynamic setting of the Late Cretaceous adakites in the Gangdese belt remain controversial. In this study, we focus on the quartz diorite in the Nuri Cu-W-Mo deposit along the southern margin of the eastern Gangdese belt. LA-ICP-MS zircon U-Pb dating yields a Late Cretaceous age of 93.6 ± 0.4 Ma for the quartz diorite. Whole-rock geochemistry shows that the quartz diorite possesses typical adakitic signatures, with high SiO2, Al2O3, and Sr contents, but low Y and Yb contents. The relatively low K2O content and high MgO, Cr, and Ni contents, as well as the positive zircon εHf(t) values (+6.58 to +14.52), suggest that the adakites were derived from the partial melting of the subducted Neo-Tethys oceanic slab, with subsequent interaction with the overlying mantle wedge. The Late Cretaceous magmatic flare-up and coeval high-temperature granulite-facies metamorphism in the Gangdese belt were likely triggered by Neo-Tethys mid-ocean ridge subduction. The widespread occurrence of Late Cretaceous adakitic intrusions and associated Cu mineralization in the Nuri ore district indicate a strong tectono-magmatic-metallogenic event related to the Neo-Tethys subduction during this period. This study provides new insights into the petrogenesis and geodynamic setting of the Late Cretaceous adakites in the Gangdese belt, and has important implications for Cu polymetallic deposit exploration in this region. [ABSTRACT FROM AUTHOR]

Oceanic intraplate volcanoes with linear age progressions are usually accepted to be derived from melting of an upwelling mantle plume. Several seamount groups in NW Pacific, however, show complex age-distance relationships that are difficult to explain using the classic "mantle plume hypothesis", and thus their origins are controversial. In this study, we present 40Ar-39Ar age, geochemical, and Sr-Nd-Pb-Hf isotopic data of lavas from Hemler, Vlinder, and Il'ichev seamounts in NW Pacific, to elucidate their petrogenesis and geodynamic process. The lavas from Hemler, Vlinder, and Il'ichev seamounts are classified as alkali basalt, basanite/nephelinite, and trachyte. Lavas with MgO>8 wt.% exhibit high contents of CaO, FeOT, and TiO2, similar to the composition of melts formed from reaction between carbonated eclogite-derived melts and fertile peridotite. These lavas have elevated Zr/Hf ratios (40.6–45.2) and negative Zr and Hf anomalies, indicating the presence of a carbonate component in the mantle source. They are enriched in incompatible trace elements and have enriched mantle 1 (EM1)-like Sr-Nd-Pb-Hf isotopic compositions. The isotopic compositions of Vlinder, Il'ichev basanite, and Hemler lavas in this study are similar to the Rarotonga hotspot. Although occurring at the same seamount, the Il'ichev alkali basalts display more depleted Sr-Nd-Hf isotopic compositions compared to Il'ichev basanite. According to plate tectonic reconstruction results, the ages of Hemler (100.1 Ma), Vlinder pre- (100.2 Ma) and post-shield (87.5 Ma), and Il'ichev (56.4 Ma) lavas clearly deviate from the Macdonald, Arago, Rarotonga, and Samoa hotspot tracks, indicating that they cannot directly originate from mantle plumes. We propose that in the mid-Cretaceous, when the Pacific plate passed over Rarotonga hotspot, melting of Rarotonga plume formed the Vlinder (main-shield stage), Pako, and Ioah seamounts. The Rarotonga (and possibly Samoa) plume materials would have been dispersed into the surrounding asthenosphere by mantle convection. These diffuse plume materials would undergo decompression melting beneath lithosphere fractures that are widely distributed in the Magellan area, generating non-hotspot related Hemler and pre- and post-shield Vlinder lavas. The Il'ichev alkali basalts and basanite probably result from lithospheric fracture-induced melting of heterogeneous enriched components randomly distributed in the asthenosphere. [ABSTRACT FROM AUTHOR]

Bhilangana granitoid is a batholithic size body exposed in Bhilangana Valley and later thrusted over rocks of Lesser Himalaya. It comprises mylonitized porphyritic granite gneiss, psammitic gneiss, and its variants, containing primary biotite and muscovite, and S-type in nature. Bhilangana granitoid is intruded by basic intrusive. The variation in chemical signatures and associated petrogenetic issues of Bhilangana granitoid are dealt with detailed petrographic, geochemical and mineral chemical study. In the vicinity of basic intrusive, the porphyritic granite gneiss shows enrichment of MgO, whereas its evolved part, psammitic gneiss shows more boron enrichment with the presence of tourmaline nodules surrounded by quartzo-feldspathic rim. The major mineral assemblage in Bhilangana granitoid is quartz–K-feldspar–plagioclase–biotite–muscovite with tourmaline, epidote, zircon, ilmenite, apatite and monazite. The granite is peraluminous with ASI values always >1. Biotite shows variation from Fe-rich siderophyllitic to Mg-rich eastonitic composition, indicating involvement of both Al-rich crustal and Mg-rich mafic sources, inferring source heterogeneity or mixing of felsic-mafic magma. Granitoid melt was buffered below QFM to NNO and partly above HM, indicating a strong reducing to the oxidizing condition of melt. The melt was saturated with the presence of 3.3–6.8 wt.% H2O content. The crystallization temperature of Bhilangana granitoid (TZr) ranges between 697° and 807°C with a solidification pressure of about 2.92–4.31 kbar, implying crystallization at a depth of 8.76–13 km. The presence of greisens assemblage of quartz–mica–tourmaline–epidote, along with the presence of fluorite, is a representative greisens assemblage for Sn–W mineralization. Thus, the Bhilangana granitoid represents the fertile nature and potentiality of Sn–W minerals. Research highlights: Bhilangana granitoid is S-type, peraluminous granitoid, formed by anatexis of crustal material The biotite chemistry reveals the variation in the redox condition and modification in the oxidation state, preserved in the different variant of granite representing the magma mixing or source heterogeneity in protolith. The Bhilangana granitoid has attended the crystallization temperature (TZr) of 697–807 °C under pressure of about 2.92–4.31 kb implying the depth of crystallization of 8.76–13 km. The presence of greisenization favours the potential of Sn–W minerals. The geochemical results shows abnormal enrichment of W and Sn in the Bhilangana granitoid. The Bhilangana granitoid appears to have fertile nature for Sn–W mineral potential. [ABSTRACT FROM AUTHOR]

The Tirodi Gneissic Complex (TGC) represents the basement sequence of the Central Indian Tectonic Zone (CITZ), underlying the Proterozoic supracrustal sequences of the Sausar and Betul Groups of rocks. Lithologically, the TGC constitutes a combination of pink and grey granitic gneiss assemblages, characterised by biotite-rich, hornblende-biotite-rich, and muscovite-biotite-rich granite gneiss. Compositionally, the TGC granitoids represent tonalite-trondhjemite-granodiorite to granite, and have calc-alkaline lineage with metaluminous to peraluminous characteristics. Geochemically, they dominantly belong to A2-type granitoids. Chondrite normalised REE ratios of La/Sm, La/Yb, La/Gd, and Gd/Yb indicate diverse LREE/HREE enrichment. Multi-element patterns for the TGC granitoids are characterised by light rare earth elements (LREE) and large ion lithophile elements (LILE) enrichment and depletion of high field strength elements (HFSE: Nb, P, and Ti) and strong positive Pb and Th anomalies. The observed negative anomalies for HFSE are attributed to diverse crustal/lithospheric sources, with some influence from K-feldspar, plagioclase and Ti-oxide fractionation. Sm–Nd data presents initial 143Nd/144Nd (t = 1.7 Ga) ratios (0.509898 to 0.510508), and εNd (t = 1.7 Ga) is (+ 0.58 to -10.59), with TDM model ages ranging from 2.11 to 2.95 Ga. Such a wide range of εNd (t = 1.7 Ga), indicates heterogeneous crustal/lithosphere sources, which have probably experienced longer crustal residence times. Zircon U–Pb ages for individual TGC samples are 1506 ± 11 Ma (TG-01), 1534 ± 26 Ma (MU-5), 1675 ± 9 Ma (BT-4), 1724 ± 11 Ma (BT-3), 1730 ± 13 Ma (BT-4), and 1960 ± 2 Ga (Ms-2), respectively. These ages have probably recorded the key periods of the Columbia supercontinent's assembly, growth, and breakup. Geochemical and geochronological results suggest that the TGC granitoids have a crustal/lithospheric origin and are formed by partial melting of felsic sources in dominantly VAG (volcanic arc granite) and, to some extents, WPG (within-plate granite) settings. [ABSTRACT FROM AUTHOR]

The majority of Neoproterozoic rocks exposed in southern Libya, are comprised of intrusive coarse-grained porphyritic, two-mica, and high K-calc alkaline granite. The Jabal Fezzan Granite (JFG) is located in southwestern Libya. In this study, trace elements and whole-rock geochemistry have been used to understand the origin and the process of petrogenesis of the studied granites. The JFG is high-Si, Rb, Y, Nb, and (ASI values greater than 1.1). Mineralogically, it is characterized by the presence of minor muscovite and biotite and a lack of hornblende, exhibiting features of S-type granites, and having a character that belongs to an alkali-calcic series. According to geochemical value, light REE-enriched, characterized by moderate enrichments in LREE (La/Sm), HREE, and weak negative Eu-anomalies. The geochemical modeling of the (JFG) reveals that the JFG derived from the melting of the crust and underwent high fractional crystallization (~50%) of plagioclase and K-feldspar at (H-P) conditions (750–980°C/1–4 GPa). The Jabal Fezzan (JFG) formed during Pan-African orogenic events during the destabilization of the interior Saharan metacraton due to compression stress and transpressive movements along pre-existing weakness and reactivation of shear zones inherited from Paleoproterozoic evolution. The Neoproterozoic basement forms the northernmost margin of the intracratonic Muruzq Basin, as evidenced by (greenschist facies) and intruded granitic rocks derived at the syn-collision stage (630–540 Ma). [ABSTRACT FROM AUTHOR]

This paper presents the results of petrographical, mineralogical, geochemical, and isotope-geochemical studies of granophyres and host ferrogabbros, quartz ferromonzogabbros, quartz monzodiorites, and quartz monzonites in the Mesoproterozoic Valaam sill in the Ladoga Graben on the Karelian Craton. The sill is poorly layered: the ferrogabbros compose the lower part of the sill, the middle part consists of quartz gabbro-monzonites and quartz monzonites, while graphic leucogranites (granophyres) form a dense network of veins mainly in the upper part of the sill. Geochemical features of ferrogabbro, iron-rich composition of olivine and pyroxene, and low Ca composition of plagioclase indicate the evolution along the Fenner trend. The granophyres have petro- and geochemical characteristics of anorogenic alkaline granites, with negative Eu/Eu* = 0.15–0.49 and REE distribution patterns similar to those of granophyres of layered intrusions. All rocks of the sill have close Sr isotopic composition (87Sr/86Sr)T = 0.7043–0.7066, and εNd values ranging from −9.6 to −11.2. Model calculations show that fractional crystallization can lead the initial ferrogabbro melt into the immiscibility field. Ilmenite–magnetite–silicate microstructures have been identified in the ferrogabbro and ferromontzogabbro from the sill; similar microstructures in layered intrusions are considered as evidence for the immiscibility of Fe-rich and Si-rich liquids (Holness et al., 2011; Dong et al., 2013). The segregation of the high-silica melt may have occurred in an intermediate crustal chamber at around 350 MPa and 960oC; magma was supplied as crystalline mush at the sill emplacement level at around 70 MPa and acidic melt migrated through it. This melt underwent fractional crystallization and interacted with host minerals. At the level of sill emplacement, it crystallized under supercooling into granophyre aggregates. The example of the Valaam sill shows that when the Fenner fractionation reaches the final composition–-ferrogabbro, its further evolution with a conjugate decrease in SiO2 and Fe contents can be related to the incomplete separation and mixing of Fe-rich melts and immiscibly split felsic melt. Such a mechanism can be implemented for the formation of the mafic part of AMCG-type massifs. [ABSTRACT FROM AUTHOR]

The Late Cretaceous magmatic history of the Eastern Pontides Orogenic Belt (NE Turkey) was generally characterized by common I-type and lesser A-type plutons in varying size and composition. Of these, A-type plutons from the Şebinkarahisar (Giresun) area yield SHRIMP zircon U-Pb age of 77.36 ± 0.96 Ma. The rocks of these plutons display a wide range of SiO2 contents (53.63 to 70.96 wt.%) and Mg-numbers (6.2–32.19) with A-type affinities characterized by enrichment in K2O and Na2O, Ga, Zr, and strong negative Eu anomalies. They also show arc-type petrochemical features including enrichment of large-ion lithophile elements (e.g. Cs, K, Rb) and light rare earth elements (LaN/LuN = 6.27–15.61), but depletion in high strength field elements (e.g. Nb, Ta, Ti, and P). The (87Sr/86Sr)i ratios and ɛNd(i) values of the studied rocks are in the range of 0.705129 to 0.0705347 and −3.64 to −3.12, respectively, while bulk rock ɛHf(i) values are between 1.86 and 4.36. They are characterized by positive zircon ɛHf(i) (1.74 to 10.88) plotting between the chondrite and depleted mantle evolutionary line values. Our data combined with the previous studies suggest that the magmas, that formed the Late Cretaceous plutons, were generated in an extensional tectonic environment due to slap roll-back and trench ward migration of the subduction zone to the south. The generation of hybrid magmas forming the studied plutons is in response to the melts derived from a metasomatized lithospheric mantle source, a relatively deeper mantle source, and the juvenile crust along with the heat transfer and decompression. Multi-sourced magmas rise through the continental crust and reach the final composition by predominantly fractional crystallization processes. [ABSTRACT FROM AUTHOR]

The only occurrence of Lower Triassic silicic volcanic rocks within the South China Block is in the Qinzhou Bay area of Guangxi Province. LA‐ICP‐MS zircon U‐Pb dating reveals that volcanic rocks of the Beisi and Banba formations formed between 248.8 ± 1.6 and 246.5 ± 1.3 Ma, coeval with peraluminous granites of the Qinzhou Bay Granitic Complex. The studied rhyolites and dacites are characterized by high SiO2, K2O, and Al2O3, and low MgO, CaO, and P2O5 contents and are classified as high‐K calc‐alkaline S‐type rocks, with A/CNK = 0.98–1.19. The volcanic rocks are depleted in high field strength elements, e.g., Nb, Ta, Ti, and P, and enriched in large ion lithophile elements, e.g., Rb, K, Sr, and Ba. Although the analyzed volcanic rocks have extremely enriched zircon Hf isotopic compositions (εHf(t) = –29.1 to –6.9), source discrimination indicators and high calculated Ti‐in‐zircon temperatures (798–835°C) reveal that magma derived from enriched lithospheric mantle not only provided a heat source for anatectic melting of the metasedimentary protoliths but was also an endmember component of the S‐type silicic magma. The studied early Triassic volcanics are inferred to have formed immediately before closure of the Paleo‐Tethys Ocean in this region, as the associated subduction would have generated an extensional setting in which the mantle‐derived upwelling and volcanic activity occurred. [ABSTRACT FROM AUTHOR]

The early Triassic (~250 Ma) hornblende gabbro from the Tengxian area of Yunkai Massif, South China, contains a mineral assemblage of clinopyroxene, hornblende, biotite, plagioclase, K-feldspar and quartz and accessory apatite, and zircon and ilmenite. Based on mineral association and crystallization sequence, two generations of the mineral assemblage have been identified: clinopyroxene + plagioclase + apatite (zircon) in Generation I and ilmenite + hornblende + biotite + K-feldspar + quartz in Generation II. The high crystallization temperature (T = 999–1069 °C) of clinopyroxene and its coexistence with labradorite (An = 52–58) indicate that Generation I crystallized in a basaltic magma, while the hornblende's relatively low crystallization temperature (T = 780–820 °C) and coexistence with K-feldspar and quartz suggest that Generation II formed in an evolved alkaline melt. The mineralogical records are likely attributed to pulsed intrusion of the late-stage evolved magma into a crystal mush, like in Generation I. The bulk-rock geochemical data include a sub-alkaline affinity, arc-type trace element features, and highly enriched Sr-Nd-Pb-Hf isotopic compositions, consistent with the isotopic records from the accessory minerals, e.g., the very high δ18O values in both zircon and apatite and significantly negative εHf(t) in zircon. The combined mineral and bulk-rock geochemical data suggest that the primary magma for the Tengxian hornblende gabbro was derived from a mantle wedge that had been metasomatized by voluminous subducted terrigenous sediment-derived melts in response to subduction of the Paleo-Tethys Ocean. [ABSTRACT FROM AUTHOR]

Texturally and chemically sector-zoned garnet crystals in two contiguous metapelitic rocks from the Danba dome, eastern Tibetan Plateau (SW China) were investigated. A petrographic boundary in one of the rocks (sample 21DB103) separates a thin section into two zones. Whereas one zone containing sector-zoned garnet and fined-grained matrix is enriched in graphite and quartz, the other zone encompasses garnets with relatively regular habit in a coarse-grained matrix poor in graphite and quartz. The two zones are distinct with regards to the chemical compositions of biotite and plagioclase, as well as the major and trace element zoning patterns of garnet. Electron back-scattered diffraction analysis shows that all the investigated garnet crystals in this sample are single crystals. Relatively higher P-T conditions are estimated for the initial growth of sector-zoned garnet (~ 5.0 kbar / ~540 ℃) compared to the regular garnet (~ 3.8 kbar / ~510 ℃) in this rock, possibly indicating that growth of the sector-zoned garnet postdates growth of the regular garnet. Texturally and chemically radial sectors with garnet-quartz intergrowths and irregular sectors of garnet are preserved in the other graphite-rich rock (sample 21DB104). Isopleth thermobarometry applied to the core of the largest garnet crystal exhibiting sector zoning in this sample reveals P-T conditions of initial garnet crystallization (~ 4.4 kbar / ~512 ℃) that deviate far (~ 0.8 kbar/~45 ℃) from equilibrium, potentially indicating significant overstepping required for garnet nucleation. Plagioclase inclusions in garnet display varying trace element abundances, indicating their replacements of different preexisting phases. These results suggest that abundant graphite may play a pivotal role in changing fluid conditions and reducing the solubility of SiO2 to grow sector-zoned garnet, as well as impeding matrix coarsening. Development of sector-zoned core and dodecahedral faces of garnet may be related to rapid growth with changes in crystal morphology. Irregular sectors may have developed through fluid infiltration and local chemical adjustments. [ABSTRACT FROM AUTHOR]

Earth's first continental crust is formed by Archaean and mainly consisted of tonalite–trondhjemite–granodiorite with a small amount of diorites (DTTGs), which has an essential role in probing early crust–mantle dynamic regime and in understanding the formation mechanism of continental crust. Here, we present zircon U‒Pb dating and Lu‒Hf isotopes, whole-rock geochemistry, and petrography on DTTGs rocks in the Dunhuang Block. Three episodes of DTTGs were emplaced circa 2.67 Ga, 2.60 Ga, and 2.50 Ga. The circa 2.67 Ga TTGs exhibit high SiO2 contents (68.14–71.70 wt%), low MgO contents (0.65–1.31 wt%), and high ratios of (La/Yb)N (146 on average), with their enriched Nd-Hf isotopes [ƐHf (t) = -5.48–3.19 and ƐNd (t) = -5.77–0.53], indicating origination from partial melting of amphibolites at thickened lower crust. In contrast, the circa 2.60 Ga transitional TTGs exhibit relatively high MgO contents (2.80–3.39 wt%), flat REE (Rare earth element) patterns with moderate ratios of (La/Yb)N (20.49 on average), and dispersed Nd-Hf isotopes [ƐHf (t) = -5.48–3.19 and ƐNd (t)= −3.99–3.08]. Accordingly, circa 2.60 Ga transitional TTGs melts were produced by partial melting of the shallower crust induced by mantle-derived magma upwelling. The circa 2.50 Ga diorites exhibit low SiO2 (55.72–59.11 wt%) but high MgO (3.51–4.52 wt%) contents with positive Nd-Hf isotopes [ƐHf (t) = -0.16–4.17 and ƐNd (t) = 2.00–4.45], suggesting that they originated from partial melting of mantle wedges metasomatized by fluid from subduction slabs. Combined with the detailed petrogenetic studies and crustal thickness variation, we conclude that the complex crust–mantle interaction may be an essential reason for the Neoarchaean diversity of DTTGs from the Dunhuang Block, which experienced prolonged arc accretion before Neoarchaean, followed by delamination between 2.67 and 2.60 Ga and subsequently transitioned to subduction. [ABSTRACT FROM AUTHOR]

The late Paleozoic tectonic setting of the Zongwulong Belt (ZWLB), a significant unit located in the northern Qaidam margin, Qinghai province, remains uncertain. Diabase dykes in the western part of the Zongwulong Belt offer insights into this issue. Field investigations reveal that the dips of the dykes are almost vertical, and they have sharp boundaries with the host rocks. These dykes consist of plagioclase, clinopyroxene, and opaque minerals exhibiting a characteristic porphyritic texture and massive structure. Zircon U-Pb dating of the dykes yields a weighted 206Pb/238U age of 289 ± 1 Ma. The dykes exhibit relatively high concentrations of TFeO, K2O + Na2O, and TiO2, while the SiO2 and MgO concentrations are relatively low. They display relative light-over-heavy REE enrichment, and lack negative Nb-Ta and Eu anomalies. The dykes underwent negligible crustal contamination, and experienced extensive fractional crystallization of olivine, clinopyroxene, and Fe-Ti oxides. Originating from the spinel–garnet transition zone at depths of approximately 75 km, the dykes result from garnet facies low-degree melting (5%–10%) in a continental rift setting. Combining these findings with regional geological data, we propose that the ZWLB likely experienced a continental rift in the west and exhibited a narrow oceanic environment in the east in the late Paleozoic period, potentially representing the most distant north branch of the East Paleo-Tethys Ocean. [ABSTRACT FROM AUTHOR]

Despite of the relatively rare occurrence of alkaline igneous rocks on Earth, they are the most diverse group of igneous rocks due to variations in their mineral assemblages and geochemical compositions. Alkaline igneous rocks are generally characterized by Si undersaturation, and K-Na (and in some cases C) enrichment. Although there is no unified alkaline igneous rock classification scheme, diagrams such as total alkalis-SiO2 or K2O-SiO2 can be used to classify alkaline igneous rocks. The origins of silica-saturated alkaline rocks (SiO2>52 wt.%) are relatively complex because multiple episodes of magmatism are often involved, therefore most studies have focused on the origins of silica-undersaturated alkaline magmas. Numerous experimental petrological studies have been conducted in the past few decades. Initially, it was considered that enrichment of trace elements was only achieved by low-degree partial melting of mantle peridotite, but the experimental melts could not reproduce the geochemical composition of natural alkaline igneous rocks. Subsequent studies have focused on carbonate-bearing eclogites that represent the average component of subducted oceanic crust. Although experimental studies indicate that silica-undersaturated and alkali-oversaturated melts can be generated from eclogites, some studies have considered that natural silica-undersaturated alkaline igneous rocks are the result of multi-stage source enrichment by incompatible elements. Low-degree partial melts of the mantle can be emplaced in the lithospheric mantle, forming veins consisting of phlogopite, amphibole, and pyroxene. Melting experiments including these components show that the produced melts better reproduce the naturally occurring silica-undersaturated alkaline magmas. Silica-deficient alkaline igneous rocks occur in various tectonic settings. Those in intraplate and divergent settings (i.e., mainly continental rifts) normally involve contributions from recycled components such as subducted slabs at the mantle transition zone (MTZ) or metasomatized lithospheric mantle. At convergent plate boundaries, silica-undersaturated alkaline magmas can be derived by the melting of mélange or the focused breakdown of phlogopite at back-arc depths. We compiled global data for alkaline igneous rocks and discovered that silica-undersaturated alkaline igneous rocks in continental collisional zones are K-rich and differ from those from other tectonic settings. We suggest that subducted continental sediment is an important K-rich end-member, which contributes a large amount of K to the alkaline magmas in the collision zone. Moreover, the solidus of K-rich minerals in the subducted plate implies that K can only participate in magmatism in the subduction zone. Before the plate reaches a depth of ∼300 km, the mica-group minerals, K-feldspar, evaporitic minerals, and other K-rich minerals are gradually consumed and rarely participate in deeper processes. In contrast, relatively Na-rich minerals such as pyroxene can be transported into the deeper mantle with eclogitic oceanic crust, and the resultant melt can enter the lithosphere owing to convective mantle flow. This forms metasomatic minerals, such as amphibole, in the lithospheric mantle, which melt to generate Na-rich and low-Si alkaline magmas. [ABSTRACT FROM AUTHOR]

The Ramagiri greenstone terrane (RGT) of Central Dharwar craton, India, is recognized as remnants of Archean oceanic crust squeezed between ancient proto‐continental terranes. The granites and gneisses formed as a result of partial melting, resisted subduction and collided, sinking the intervening ocean basin. The geochemical characteristics of the bimodal metavolcanics of RGT were carefully assessed using suitable proxy. An insight into them suggests that the mafic rocks bear characteristics of island arc tholeiites belonging to suprasubduction zone setting, as corroborated by their low TiO2/Yb (avg 443) and high Th/Nb (avg 0.8). Their high V/Ti (avg 0.3) ratio points towards a mantle source that has been influenced by subduction, whereas low Ti/Yb echoes high degrees of shallow melting with little residual garnet. The felsic rocks on the other hand are metaluminous–peraluminous, mostly calc‐alkaline and geochemically akin to I‐ and S‐type syncollisional and volcanic arc granite emplaced during intercontinent collision. Their immobile element plot with low Nb + Y (avg 25) concentration also points towards a volcanic arc environment. [ABSTRACT FROM AUTHOR]

Modern analogues of Archaean charnockite are important because they facilitate investigations into processes of early crustal formation and tectonic transition. Herein, we present the results of the petrography, geochemistry, and isotope geochronology of Late Neoarchean charnockites in the Daqingshan terrane at the northern margin of the North China Craton. The sources, petrogenesis, and tectonic implications of the samples obtained are determined based on their geochemical characteristics. Charnockites mainly exhibit magnesian and calc–alkaline characteristics; furthermore, they contain high amounts of light rare-earth elements, with slightly positive Eu anomalies. Analysis of zircon U–Pb dating using a sensitive high-resolution ion microprobe reveals that Hademengou–Xiwulanbulang (HDMG–XWLBL) charnockites were emplaced during the (i) Late Neoarchean (ca. 2500 Ma), with zircon εHf(t) values ranging from 1.57 to 7.81; (ii) single-stage model ages (TDM1) from 2529 to 2637 Ma; and (iii) two-stage model ages (TDM2) from 2710 to 2820 Ma. A comparative study has performed on the petrography, geochemistry, and geochronology of charnockite and granulite shown that the parent magma of the charnockites is the product of the partial melting of granulite. Combining our results with geological data pertaining to the Archaean structural evolution of the Daqingshan terrane, we speculate that the Late Neoarchean HDMG–XWLBL charnockite was formed during a subduction-related thermo-tectonic event in the northern margin of the North China Craton. [ABSTRACT FROM AUTHOR]

The composition of the sub-arc mantle and the mode and nature of geodynamic processes during the India-Asia collision that controlled the melt evolution beneath the Gangdese belt (southern Tibet) are still unclear. Here, we present new U-Pb ages and Hf isotopes of zircon, and whole-rock geochemical and Sr-Nd-Pb isotopic data of the Paleocene-Eocene Najinla gabbros from the East Gangdese magmatic belt, aiming to track the transitioning magmatism formed from oceanic subduction to continental collision in the region. Zircon U-Pb analyses of these mafic rocks yield emplacement ages of 54 ± 1 Ma and 63 ± 1 Ma. The gabbros are characterized by variable SiO2 (45.87-55.44 wt%), MgO (1.03-8.18 wt%), FeOT (3.74-12.33 wt%), and Al2O3 (13.45-25.45 wt%) contents. Most samples exhibit high Al2O3 (17.15-25.45 wt%) and relatively low MgO (1.03-6.11 wt%), similar to typical high-alumina basalts and high-alumina basaltic andesites. The Najinla gabbros show characteristic subduction-related signatures with enriched large-ion lithophile elements and depleted high field strength elements. They have depleted Sr-Nd isotopic compositions with low and relatively homogeneous initial 87Sr/86Sr isotopic ratios of 0.7045-0.7049 and positive εNd(t) ratios of +2.2 to +3.2. The Najinla gabbroic rocks also have positive zircon εHf(t) values, ranging from +5.6 to +10.9. These results collectively suggest that magmas of the gabbros formed by partial melting of the asthenosphere with negligible crustal contamination during their emplacement. We propose that the mantle source of the Najinla gabbros was strongly influenced and metasomatized by subducted Neotethyan oceanic crust-derived fluids in the mantle wedge. Rollback of the subducted Neotethyan slab in the early Eocene led to partial melting of the subduction-modified mantle and the formation of these gabbros. [ABSTRACT FROM AUTHOR]

Sedimentation on river floodplains is a complex process that involves overbank flooding, crevasse splaying, and river avulsion. The resulting floodplain stratigraphy often exhibits floodplain aggradation cycles with alternating fine-grained overbank flooding deposits that underwent significant petrogenesis, and coarser-grained, avulsionbelt deposits largely devoid of pedogenic impact. These cycles are linked to lateral migration and avulsion of channels driven by internal dynamics, external factors, or a combination of both. To better understand the spatial and vertical variability of such floodplain aggradation cycles, we map these in three dimensions using a photogrammetric model of the lower Eocene Willwood Formation in the northern Bighorn Basin, Wyoming, USA. This allows identifying 44 floodplain aggradation cycles in ~300 m of strata with an average thickness of 6.8 m and a standard deviation of 2.0 m. All the cycles are traceable over the entire model, pointing to their spatial consistency over the 10 km² study area. At the same time, rapid lateral thickness changes of the floodplain aggradation cycles occur with changes up to 4 m over a lateral distance of 400 m. Variogram analyses of both field and numerical-model results reveal stronger consistency of floodplain aggradation cycle thicknesses along the paleoflow direction compared to perpendicular to paleoflow. Strong compensational stacking occurs at the vertical scale of 2-3 floodplain aggradation cycles (14-20 m), while full compensational stacking occurs at larger scales of more than six floodplain aggradation cycles (>41 m). The lateral and vertical thickness variability of the floodplain aggradation cycles, as well as their compensational stacking behavior, are interpreted to be dominantly driven by autogenic processes such as crevasse splaying and avulsing that preferentially fill topographic lows. External climate forcing may have interacted with these autogenic processes, producing the laterally persistent and vertically repetitive floodplain aggradation cycles. The spatial variability of floodplain aggradation cycles demonstrated in this study highlights again the need for three-dimensional data collection in alluvial floodplain settings rather than depending on one-dimensional records. [ABSTRACT FROM AUTHOR]

The central part of Java, Indonesia, is located on the southern margin of Sundaland, and records the tectonic-magmatic history of the easternmost Neo-Tethys. Elucidating the petrogenesis and its tectonic setting of the Cretaceous Luk Ulo granites in Central Java is key to reconstructing the late subductionaccretion history of the easternmost Neo-Tethys. This study reports for the first time the zircon U-Pb geochronology, Hf-O isotope, whole-rock major and trace elements, and Sr-Nd isotope geochemistry of two granitoid episodes from Central Java. Zircon U-Pb dating results show that the Luk Ulo granites formed in two Cretaceous episodes at ca. 115 Ma and ca. 70 Ma. These two Cretaceous granitoid episodes contain both calcalkaline with enriched large-ion lithophile elements and light rare earth elements and depleted high field strength elements, exhibiting arc geochemical signatures. The older (ca. 115 Ma) granites show slightly higher (87Sr/86Sr)i values of 0.70772 to 0.70784 and weakly negative εNd(t) values of -2.37 to -1.67, indicating the contribution of ancient crust. However, the scattered zircon εHf(t) values of +0.23 to +11.39 suggest a probable mixture of ancient crustal components and juvenile crustal additions in the magma source. The high zircon δ18O values (+8.86‰ to +14.24‰) show the possible incorporation of supracrustal components (sediments and fluids) in the magma formation. In contrast, the younger (ca. 70 Ma) granites show low (87Sr/86Sr)i values of 0.70427-0.70442, strong positive εNd(t) values of +3.89 to +4.03, and zircon εHf(t) values of +14.04 to +17.38 and slightly higher zircon δ18O values of +5.01‰ to +6.49‰ than the depleted mantle, indicating that the magma was predominantly derived from the juvenile crust with negligible supracrustal involvement. In general, zircon εHf(t) values and whole-rock εNd(t) values of the Late Cretaceous (after ca. 90 Ma) granitic rocks in the southwest margin of Sundaland were higher than those of the Early Cretaceous granitoids, suggesting a change in the source region from ancient to the juvenile in response to the rollback of the Neo-Tethys ocean. Our findings from the two Cretaceous granitoid episodes in Central Java provide new insights into the tectonomagmatic evolution along the southwestern margin of Sundaland and the two different episodes of crustal growth in the easternmost Tethys during the Cretaceous. [ABSTRACT FROM AUTHOR]