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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]

This paper presents new zircon U–Pb, Hf isotope, and whole-rock major and trace element data for early Paleozoic igneous rocks of the Lesser Xing'an Range, NE China, in order to constrain the early Paleozoic tectonic evolution of the eastern Central Asian Orogenic Belt (CAOB). Zircon U–Pb dating indicates that early Paleozoic magmatic events within the northern Songnen–Zhangguangcai Range Massif (SZM) can be subdivided into four stages: Middle Cambrian (~ 505 Ma), Late Cambrian (~ 490 Ma), Early–Middle Ordovician (~ 470 Ma), and Late Ordovician (460–450 Ma). The Middle Cambrian monzogranites are K-rich, weakly to strongly peraluminous, and characterized by pronounced heavy rare earth element (HREE) depletions, high Sr/Y ratios, low Y concentrations, low primary zircon ε Hf (t) values (− 6.79 to − 1.09), and ancient two-stage model (T DM2 ) ages (1901–1534 Ma). These results indicate derivation from partial melting of thickened ancient crustal materials that formed during the amalgamation of the northern SZM and the northern Jiamusi Massif (JM). The Late Cambrian monzonite, quartz monzonite, and monzogranite units are chemically similar to A-type granites, and contain zircons with ε Hf (t) values of − 2.59 to + 1.78 and T DM2 ages of 1625–1348 Ma. We infer that these rocks formed from primary magmas generated by partial melting of Mesoproterozoic accreted lower crustal materials in a post-collisional extensional environment. The Early–Middle Ordovician quartz monzodiorite, quartz monzonite, monzogranite, and rhyolite units are calc-alkaline, relatively enriched in light REEs (LREEs) and large ion lithophile elements (LILEs; e.g., Rb, Th, and U), depleted in HREEs and high field strength elements (HFSEs; e.g., Nb, Ta, and Ti), and contain zircons with ε Hf (t) values of − 7.33 to + 4.98, indicative of formation in an active continental margin setting. The Late Ordovician alkali-feldspar granite and rhyolite units have A-type granite affinities that suggest they formed in an extensional environment. A comparison of early Paleozoic magmatic events and Hf isotopic model ages between the northern SZM and the JM indicates that these two massifs have similar histories of Mesoproterozoic and early Paleozoic crustal accretion and reworking, although the SZM contains much older crustal materials than the JM. [ABSTRACT FROM AUTHOR]

Once situated between the Central Tianshan and Junggar terranes during Paleozoic time, the Junggar Ocean was a major southern branch of the Paleo-Asian Ocean. Thus, when and how it was closed are essential in understanding the final assembly of the Central Asian Orogenic Belt. However, the exact closure time of the Junggar Ocean remains unresolved due to the lack of reliable timing of collision-related regional metamorphism. This paper reports whole-rock geochemical and zircon U–Pb and Lu–Hf isotopic data for granitic gneisses from the northern margin of the Central Tianshan block, which can provide crucial constraints on the final closure of the Junggar Ocean. Mineral assemblages and geochemical suggest that the protoliths of the Central Tianshan gneisses are weakly peraluminous high-K calc-alkaline I-type granites, possessing typical subduction-related features such as strong enrichment in LREE and LILE and depletion in HFSE. Negative Eu anomalies (δEu = 0.46–0.81) and highly variable zircon Hf isotope compositions indicate various amounts of residual plagioclase in the source and crustal contamination during magma formation. LA-ICPMS U–Pb dating on magmatic-type zircons (72%), characterized by euhedral to subhedral shapes, concentric oscillatory zoning, high Th/U ratios (0.30–2.05) and large ranges of ε Hf (t) values (− 3.4 to + 8.7; up to 6 epsilon units in each sample), yields consistent weighted mean 206 Pb/ 238 U ages of ca. 325–320 Ma, interpreted as the crystallization ages of the granitic protoliths. Geochemical signatures and dominantly positive zircon ε Hf (t) values reveal that the protoliths were emplaced in a continental arc setting, pinpointing the development of a late Early to early Late Carboniferous continental arc system on the northern margin of the Central Tianshan block, probably related to the southward subduction of the Junggar oceanic plate. Meanwhile, younger ages at ca. 303–301 Ma were obtained on recrystallized zircon-rims and unzoned/homogeneous zircons (25%) with narrow ranges of ε Hf (t) values (− 1.8 to + 7.2; < 3 epsilon units in each sample), considered as the timing of a later tectonothermal event, which was associated with strong deformation that formed the gneissosity of the granitic gneisses. Combined with previous studies, we suggest that this event most likely resulted from the arc–continent collision/accretion between the island arcs (e.g. Bogda, Dananhu) in the Junggar Ocean and the Central Tianshan block during the final closure of the Junggar Ocean, which led to the final assembly of the Eastern Tianshan during the latest Carboniferous time. [ABSTRACT FROM AUTHOR]

As a major Precambrian microcontinent in the southernmost Central Asian Orogenic Belt (CAOB), the Central Tianshan block (CTS) in the Chinese Tianshan is essential for understanding the final assembly of the southern CAOB. It experienced multistage Paleozoic magmatism and metamorphism, but the detailed processes are still controversial and far from being completely understood. This paper reports coupled U–Pb and Lu–Hf isotopic data of detrital zircons from late Paleozoic (meta-)sedimentary strata in the South Tianshan belt, which can provide new insight into deciphering the Paleozoic evolution of the eastern segment of the CTS block. Characterized by typical oscillatory zoning and high Th/U ratios (> 0.2), detrital zircons in the Permian sedimentary samples yield dominant age populations at ca. 505–490 Ma, 475–440 Ma, 430–400 Ma and 340–250 Ma, pinpointing the development of four episodes of magmatism in the eastern CTS block. Particularly, Ordovician–Silurian (475–440 Ma) zircons, possessing low negative ε Hf (t) values, predominate in sedimentary strata in and surrounding the CTS block, indicating that the 475–440 Ma magmatic rocks probably constitute the main body of the CTS block. The origin of this (early Paleozoic) episode of magmatism was most likely related to the southward subduction of the Junggar Ocean beneath the CTS block. Carboniferous–Triassic (340–250 Ma) zircons have dominantly positive ε Hf (t) values, probably derived from the post-collisional juvenile rocks in the CTS block. Combined with previous studies, our data suggest that the single source terrane for the sampled strata was the CTS block, which had been a topographic high providing substantial detritus to the surrounding areas at least since the Early Permian. In the metasedimentary sample, detrital zircons mostly show partially/fully recrystallized internal textures and low Th/U ratios (< 0.2), probably sourced from the amphibolite- to granulite-facies metamorphosed rocks in the eastern CTS block. The youngest zircons suggest that the sampled metasedimentary strata were Carboniferous (341–305 Ma) in age, rather than Neoproterozoic (or Early Sinian in Chinese literatures) as previously interpreted. Based on U–Pb–Hf isotopes and Ti-in-zircon thermometer of metamorphic zircons in this study, as well as previous investigations, we suggest that the eastern CTS block has experienced (a) a 400–370 Ma collisional event, related to the closure of the eastern segment of the South Tianshan Ocean, and (b) a 360–340 Ma extensional event, as a result of post-collisional mantle upwelling. Therefore, the final assembly of the Eastern Tianshan took place during Late Carboniferous time. [ABSTRACT FROM AUTHOR]

Voluminous Early Paleozoic intrusive rocks occur in the Qilian orogenic belt, northeastern margin of the Tibetan Plateau. Their petrogenesis can provide insights into the tectonic evolution of Qilian and its adjacent areas. This paper carries out an integrated study of U–Pb zircon dating, geochemical and Sr–Nd–Hf isotopic compositions for the Bamishan and Heishishan plutons in the eastern Qilian orogen. Both the Bamishan and Heishishan plutons consist of mafic, intermediate and felsic intrusive rocks. U–Pb zircon dating yielded the magma crystallization ages of 459–449 Ma for the Bamishan pluton and 447–438 Ma for the Heishishan pluton. Their geochemical and Sr–Nd–Hf isotopic data show that the parental magmas of the Bamishan monzogranites and quartz diorites were generated by slab (MORB and overlying sediments) melting. The Bamishan hornblende gabbros have extremely high Cr (1159–1163 ppm), Ni (220–353 ppm) and Mg# (73–74), indicating a cumulate origin. The Heishishan granodiorite–granite has adakitic geochemical signatures and they were produced by partial melting of the mafic lower crust. The Heishishan hornblende gabbro and quartz diorites were derived from the enriched lithospheric mantle metasomatized by subduction-related fluid/melt. In light of the available data, we propose that there was an Early Paleozoic ocean basin between the Central-South Qilian and Qaidam–West Qiling belts. The northward closure of this basin and subsequent continental collision and post-collisional processes resulted in the generation of the Early Paleozoic magmatism in the eastern Central Qilian. The Late Ordovician to Early Silurian (~ 460–440 Ma) intrusive rocks in the eastern Central Qilian formed in a post-collisional setting. A slab break-off model may account for the magma generation. [ABSTRACT FROM AUTHOR]

The Late Paleozoic tectonic setting and location of the southernmost boundary of the Central Asian Orogenic Belt (CAOB) with respect to the Alxa Block or Alxa-North China Craton (ANCC) are debated. This paper presents new geochronological, petrological, geochemical and zircon Hf isotopic data of the Late Paleozoic intrusions from the Shalazhashan in northern Alxa and discusses the tectonic setting and boundary between the CAOB and ANCC. Using zircon U–Pb dating, intrusions can be broadly grouped as Late Carboniferous granodiorites (~ 301 Ma), Middle Permian gabbros (~ 264 Ma) and granites (~ 266 Ma) and Late Permian granodiorites, monzogranites and quartz monzodiorites (254–250 Ma). The Late Carboniferous granodiorites are slightly peraluminous and calcic. The remarkably high zircon Hf isotopes (ε Hf (t) = + 6–+ 10) and characteristics of high silica adakites suggest that these granodiorites were mainly derived from “hot” basaltic slab-melts of the subducted oceanic crust. The Middle Permian gabbros exhibited typical cumulate textures and were derived from the partial melting of depleted mantle. The Middle Permian granites are slightly peraluminous with high-K calc-alkaline and low ε Hf (t) values from − 0.9 to + 2.9. These granites were most likely derived from juvenile materials mixed with old crustal materials. The Late Permian granodiorites, monzogranites and quartz monzodiorites are characterized as metaluminous to slightly peraluminous, with variable Peacock alkali–lime index values from calc-alkalic to alkali-calcic. These rocks were mainly derived from juvenile crustal materials, as evidenced by their high ε Hf (t) values (+ 3.3 to + 8.9). The juvenile sources of the above intrusions in the Shalazhashan are similar to those of the granitoids from the CAOB but distinct from the granitoids within the Alxa Block. These findings suggest that the Shalazhashan Zone belongs to the CAOB rather than the Alxa Block and that its boundary with the Alxa block can be regarded as the southernmost boundary of the CAOB. The recognition of Late Carboniferous typical adakite magmatism in the region provides evidence for the subduction of the oceanic crust of the CAOB. The Middle–Late Permian magmatisms (266–250 Ma) display a bimodal association with high-K calc-alkaline features and are interpreted as forming in a post-collision setting. These studies, by interaction of regional geology, provide new constraints on the tectonic evolution of the southern CAOB during the Late Paleozoic and the location of the southernmost margin of the CAOB. [ABSTRACT FROM AUTHOR]

Details on processes of the early-middle Paleozoic Wuyi–Yunkai orogeny in South China remain poorly defined. Most Silurian–Devonian granites in South China are S-type or I-type granites, which are suggested to be petrogenetically related to the Wuyi–Yunkai orogeny. This paper firstly reported a systematic study on two Devonian A-type granites in the central Jiangxi Province. LA-ICP-MS zircon U–Pb dating results imply that the Huitong and Epo granites were emplaced at about 415 Ma. Both of the two granites have the petrographic and geochemical characteristics of A-type granites. Interstitial biotites occur along the boundary of euhedral plagioclase and quartz and they formed later than plagioclase and quartz. It implies that the primary magma could have been anhydrous. Biotites from the two granites are Fe-rich and have high Fe 2 + /(Fe 2 + + Mg 2 + ) ratios (0.60–0.74). The magmatic temperatures estimated from zircon saturation thermometer are 802–920 °C for the two granites, higher than common I-type and S-type granites. The two granites show high contents of total alkalis (Na 2 O + K 2 O = 6.96–9.39 wt.%), high field strength elements (e.g. Zr = 181–437 ppm, Y = 22.1–39.7 ppm, Nb = 18.6–30.3 ppm and Zr + Nb + Ce + Y = 324–555 ppm), rare earth elements (total REE = 155–312 ppm) as well as high Ga/Al ratios (10,000 × Ga/Al = 2.50–3.44). These geochemical characteristics are similar to those of A-type granites. The Huitong and Epo granites have relatively low ε Nd (t) values of − 10.4 to − 7.7, and low zircon ε Hf (t) values (peak value of − 8.0). Whole-rock two stage Nd isotopic model ages and zircon Hf isotopic model ages mostly vary from 1.78 Ga to 2.00 Ga. According to these data, we suggest that the two granites might have derived from partial melting of pre-Cambrian sedimentary rocks which had been granulitized during an earlier thermal event. The two granites contain abundant contemporaneous mafic microgranular enclaves (MMEs). The MMEs display igneous textures and contain acicular apatites, suggesting quenching of mafic magmas that have co-mingled with the host granites. The MMEs might have derived from the enriched lithospheric mantle source. This study on the Devonian Huitong and Epo A-type granites, together with previous studies on Paleozoic granites in South China, indicated that the Wuyi–Yunkai orogeny in South China had changed from syn-collisional crustal thickening to post-collisional extension at least from 415 Ma. [ABSTRACT FROM AUTHOR]

The Solonker suture zone records the termination of convergence in the southern Central Asian Orogenic Belt (CAOB). The timing of termination of the Solonker suture and the tectonic style of the southern CAOB have long been controversial. The Baolidao arc-accretion complex and the Ondor Sum subduction-accretion complex are located immediately to the north and south of the Solonker suture zone respectively. However, the tectonic settings and formation ages of these two complexes are debated. In this paper, we present a systematic study of LA-ICPMS U-Pb zircon ages of multiple units and lithologies from both the complexes to constrain the timing of final collision between the South Mongolian microcontinent and the North China craton. The geochronological results indicate that the northward subduction of the Paleoasian Oceanic lithosphere beneath the South Mongolian microcontinent at ~ 452 Ma induced extensive melting of overriding continental crust. Continuous subduction led to accretionary wedge-continent collision at the southern margin of the South Mongolian microcontinent, represented by the 416 ± 3 Ma granitic activity in the southern margin of the Baolidao arc-accretion complex. After Early Paleozoic collision, widespread magmatism occurred at 316-302 Ma in response to transient extension along the southern margin of the South Mongolian microcontinent. There was a deep marine basin during Permian times to the south of the microcontinent. The closure of this oceanic basin led to Late Paleozoic-Early Triassic north-dipping subduction and final suturing of the CAOB during Late Permian to Middle Triassic times. Proximal forearc sediments composed of arc volcanic and plutonic materials with crystallization ages varying from 299 ± 3 Ma to 267 ± 3 Ma, and some intrusions at 274 ± 2 Ma caused by the melting of continental crust were produced along the northern margin of the Solonker suture zone. Accretion and collision occurred at ~ 263 Ma. The southward subduction of the Paleoasian Oceanic lithosphere beneath the North China craton at ~ 451 Ma induced high-grade metamorphism and partial melting in the south-dipping subduction zone. An arc/forearc-related ocean at the northern margin of the North China craton existed during the southward subduction (324-300 Ma) and was filled during transient regional extension (299-290 Ma) in Linxi area to form the protolith of the Shuangjing Schist, accompanied with widespread Late Carboniferous to Early Permian arc volcanic and plutonic activity in the CAOB. Initial subduction of the arc/forearc-related oceanic basin occurred during 290-280 Ma, and was followed by the convergence of the North China craton and the South Mongolian microcontinent until ~ 230 Ma. The eastern section of the CAOB formed by bivergent Early Paleozoic to Middle Triassic accretion until ~ 263-230 Ma that ended in the closure of the Paleoasian Ocean. [ABSTRACT FROM AUTHOR]

Voluminous and discrete early Paleozoic bimodal magmatic suites are thought to be the result of post-collisional extension following the amalgamation of East Kunlun and Altyn Tagh. In this paper, four representative magmatic units were studied for their geochemical fingerprint in conjunction with geochronological studies. The 467-445 Ma Mangya mafic suite shows E-MORB type rare earth element (REE) patterns that are the result of asthenospheric interaction with a metasomatized subcontinental lithosphere. High-K calc-alkaline granodiorites, intruded at ca. 450 Ma, are characterized by high Mg#, the least fractionated REE pattern without an Eu anomaly, as well as high Sr and low Rb/Sr ratio. We interpret these geochemical signals to result from lower crustal melting of garnet amphibolite at pressures between 16 and 22 kbar. A 430-420 Ma A-type granite is interpreted to result from the melting of metaigneous rocks at middle to lower crustal depths. Lastly, a late magmatic pulse occurs between 400 and 380 Ma and is represented by the Alk granite. The Alk granite is interpreted to be a product of metapelite melts and is associated with a smaller volume of mafic melts. U-Pb zircon geochronology of Paleozoic igneous rocks of the Qimantagh-South Altyn reveals that most of the magmatic episodes are either coeval with, or post, extensional deformation. This phase of extension is supported by the exhumation of HP/UHP metamorphic rocks and crustal anatexis. Collectively, the evolutionary stages documented in this study correspond to a succession of post-collisional, postorogenic and, ultimately, within plate magmatic episodes. The overall features support orogenic collapse via removal of a thickened lithospheric root beneath the East Kunlun-Altyn Tagh collisional orogen during early Paleozoic. [ABSTRACT FROM AUTHOR]

Abstract: The Cantabrian Zone of NW Iberia preserves a voluminous, almost continuous, sedimentary sequence that ranges in age from Ediacaran to Early Permian. Its tectonic setting is controversial and recent hypotheses include (i) passive margin deposition along the northern margin of Gondwana, (ii) an active continental margin, or (iii) the margin of a drifting ribbon continent and (iv) a combination of the three aforementioned possibilities. In this paper we present geochemical data from 21 samples taken in detrital rocks in the Cantabrian Zone from Ediacaran to Early Permian age. The results, together with previously published detrital zircon ages from these strata, allow a comprehensive analysis of changing tectonic scenarios and provenance through time. Collectively, these data indicate that this portion of Iberia was an active margin during the Ediacaran that evolved to become part of the passive margin of Gondwana at least from Ordovician to Late Devonian times. Changes in geochemistry, zircon age distribution and Sm/Nd isotopes during the Carboniferous are attributed to the far-field effects of the onset of the collision between Gondwana and Laurussia, and related processes such as recycling of older sedimentary sequences, as well as the involvement of the rocks formed during the Variscan orogeny and oroclinal buckling. Latest Carboniferous and Permian show a more juvenile Sm/Nd and higher values of illite cristallinity that may support the hypothesis of lithospheric foundering after oroclinal buckling. [Copyright &y& Elsevier]

Abstract: In the eastern South China Block (SCB), the presence of middle Paleozoic volcanics and mafic rocks is poor in spite of the extensive occurrence of granites in response to the synchronous (Kwangsian) intracontinental orogen event. The nature of the lithosphere and its associated orogenic process are poorly known for such a major orogen. In this paper, a set of new U–Pb zircon geochronological, elemental and Sr–Nd isotopic data are presented for several gabbroic plutons, which were recently identified in the Cathaysia Block. The representative samples of the Longhugang, Xinchuan and Xinsi plutons yielded the weighted mean 206Pb/238U ages of 423±8Ma, 434±6Ma and 420±3Ma, respectively, and their gneissoid country-rocks are dated at 442–466Ma. This evidences the presence of Silurian mafic rocks in the Cathaysia Block. These gabbroic rocks can be geochemically classified into three groups. Group 1 from the western Longhugang pluton exhibits flat REE patterns represented by (La/Yb)cn=1.1–1.7, (Gd/Yb)cn=0.99–1.15, and δEu=1.29–1.51 with negative Nb–Ta and P and markedly positive Sr anomalies. It shows enrichment in LILEs and 87Sr/86Sr(t) ratios of 0.70412–0.70727 and εNd(t) values of −2.6 to −0.6. Group 2 from the Xinchuan, Zhouya and Yunlu plutons is characterized by high MgO (11.4–15.8wt.%), mg-number (66–74) and Cr and Ni contents. It is marked by significantly negative Nb–Ta, Zr–Hf and P–Ti anomalies with high 87Sr/86Sr(t) (0.70920–0.71072) and low εNd(t) values (−3.9 to −7.9). Group 3 from the Xinsi and eastern Longhugang plutons has εNd(t) values from −2.8 to −5.7 and shows high Nb content of 7.05–9.89ppm with pronounced enrichment in LILE and weak depletion in HFSE, resembling Nb-enriched arc basalt in HFSE composition. A synthesis of these geochemical data points to the following petrogenesis: Groups 1 and 2 derived from a spinel-bearing, plagioclase-rich source and a garnet-bearing, orthopyroxene-rich source, respectively, proportionally modified by slab- and sediment-derived melts plus fluid fluxing from the earliest Neoproterozoic subduction. The HFSE composition for Group 3 inherited from a metasomatized mantle wedge column with the input of large-proportional slab melts and the absence of residual rutile during partial melting. In conjunction with other available observations, it is proposed that there preserved a paleosubduction-modified wedge column beneath the Cathaysia Block, which might be undisturbed until the Kwangsian intracontinental orogen. During the Silurian post-orogenic collapse of the event, the elevated lithosphere thermal boundary facilitated the partial melting of the column to generate these Silurian gabbroic rocks. [Copyright &y& Elsevier]

Abstract: In this paper, we study the geochronology, mineral chemistry, and whole-rock elemental, stable (O, C, D) and Sr-Nd isotopic data for alkaline ultrabasic–basic massifs of the Vitim alkaline province (Sayzhenski complex) in the Central Asian Orogenic Belt, near the boundary with the Siberian craton, to evaluate their petrogenesis and geodynamic significance. U-Pb zircon dating results in Early Paleozoic (520–486Ma) and Late Paleozoic (306–294Ma) stages of alkaline rock formation. The mineralogy and geochemistry exhibit a wide range of SiO2 (38–73wt.%), enrichment in Sr, Ba, LREE and Ta and, most significantly, in Na and Al. The rocks crystallized from a parental CO2- and H2O-rich silica-undersaturated melt. Isotopically, the rocks are highly variable, with (87Sr/86Sr)i – 0.705595–0.707729 and (143Nd/144Nd)i – 0.512237–0.512643. The geochemical and isotope data suggest that the rocks were derived from a source composed of three distinct components: PREMA, EM II and marine carbonate. Additionally, stable (O, C, D) isotope data display the shifting influence of assimilated organic sediments in the source of melts and a partial secondary isotope exchange between the late-magmatic fluids and minerals. [Copyright &y& Elsevier]

Abstract: The Xuefengshan Belt, characterized by large-scale fold and thrust structures and widespread granites, is a key area to decipher the tectonic evolution of the South China block. In this belt, two magmatic episodes are recorded by Early Paleozoic and Early Mesozoic granites. In this paper, we carried out precise SIMS zircon U and in situ Lues measurements on these granitic plutons. Our study indicates that the Early Paleozoic and the Early Mesozoic granites are late-orogenic products of the Early Paleozoic orogen and the Middle Triassic Xuefengshan orogen, respectively. In the Xuefengshan Belt, the Early Paleozoic event is poorly registered, since this area corresponds to the outer zone of the early Paleozoic orogen. The Silurian–Early Devonian granites are late-orogenic plutons emplaced after the main tectonic and metamorphic stage in the Wuyi–Baiyun–Yunkai belt, coeval with a widespread, subsequent extensional event in eastern and southern South China. On the other hand, Triassic granites are formed in an intracontinental environment with weakly to strongly peraluminous signatures. Zircon Uresented here, associated with a summary of newly acquired data in the same region, suggest that the emplacement of anatectic granites occurred around 225–215Ma, not in a rather wide range of ca. 245–200Ma. In situ zircon εHf(t) values indicate a crust-derived source without a mantle-derived input for the two generations of granites. Combining our data with recent studies, we infer that the central area of the South China block has experienced two tectonothermal events: the Early Paleozoic magmatism developed as a result of the collapse of the Early Paleozoic orogen, while these Early Mesozoic granites can be the late-orogenic products of the intracontinental Xuefengshan orogen, most likely manifesting the far field effect by the subduction of the Paleo-Pacific ocean plate at the southeastern margin of the South China block. [Copyright &y& Elsevier]

Abstract: To achieve a better understanding of the Kwangsian orogenic event of the eastern South China Block, this paper documents a set of new zircon U–Pb geochronological and Hf isotopic data and whole-rock elemental and Sr–Nd isotopic analytical results for the representative massive granite intrusions across the Jiangshan-Shaoxing fault. The studied samples are classified into two groups, representing the rocks from the Cathaysia Block to the east of the Jiangshan-Shaoxing Fault (Group 1) and those from the eastern Yangtze Block between the Anhua-Luocheng and Jiangshan-Shaoxing faults (Group 2). The Group 1 samples gave the zircon U–Pb ages of 405–454Ma and εHf(t) values of −3.6 to −15.2 with Hf model ages of 1.6–2.4Ga. Group 2 yielded the zircon U–Pb ages of 400–432Ma and εHf(t) values of −0.2 to −12.7 with Hf model ages of 1.3–2.2Ga. Geochemically, the Group 1 samples (A/CNK=1.02–1.43) have relatively lower Al2O3, MgO, CaO, P2O5 and εNd(t) but higher K2O+Na2O than those of Group 2 (A/CNK=0.93–1.44). Both groups show similar chondrite-normalized patterns of rare-earth elements with Eu/Eu* values of 0.15–0.92 and strongly negative Ba, Sr, Nb, P and Ti anomalies in primitive mantle-normalized spider diagrams. Their εNd(t) values range from −11.1 to −8.0 for Group 1, and −8.9 to −5.0 for Group 2, generally similar to those of Precambrian paragneiss and contemporaneous gneissoid granites in the eastern South China Block. Our geochronological results indicate that the Kwangsian massive granites in the eastern South China Block were crystallized between 400Ma and 454Ma, synchronous to the Kwangsian gneissoid granites along the Wugong and Wuyi-Baiyun-Yunkai domains in the eastern South China Block. The synthesis of these whole-rock geochemical and in-situ zircon Hf isotopic data suggests that both the Group 1 and 2 granites across the Jiangshan-Shaoxing Fault were predominantly derived from a crustal source with some proportional metapelitic and metaigneous components from the Precambrian basement. The input of juvenile mantle-derived magma is insignificant. Taking into account other available evidences, it is proposed that the Jiangshan-Shaoxing Fault might be a pre-existing boundary between the Yangtze and Cathaysia Blocks, which was reactivated during the middle Paleozoic (Kwangsian) orogenic event. The massive granitic magmatism was probably resulted from the doubly crustal thickening and subsequent isostatic readjustment in an intracontinental tectonic regime. [Copyright &y& Elsevier]

North East (NE) China forms the easternmost part of the Central Asian Orogenic Belt. However, its Paleozoic geological evolution process remains controversial, especially the complex subduction-accretion-orogeny processes of the Paleo-Asian Ocean plate, as well as the linking magmatism-metallogenic with tectonic evolution during that time. This paper reports the results of geochemical, geochronological, and isotopic analyses of igneous rocks at the Handagai skarn Fe–Cu deposit to elucidate the late Paleozoic tectonic framework and evolution of NE China and the setting of ore formation. New zircon LA–ICP–MS U–Pb data for monzogranite, quartz diorite, and quartz monzodiorite record Carboniferous ages of 350 ± 2 Ma, 321 ± 3 Ma, and 319 ± 2 Ma, respectively. The monzogranites have high SiO 2 (69.57–71.97 wt%) and total-alkali (6.68–7.56 wt%) contents and relatively low MgO contents (0.60–1.03 wt%) and Mg numbers (33–41). They have arc-type trace-element signatures, with enrichment in large-ion lithophile elements and light rare earth elements, together with depletion in Nb, Ta, P, and Ti. Their whole-rock Sr–Nd–Pb and zircon in-situ Lu Hf isotopic compositions ((87Sr/86Sr) i = 0.7008–0.7062; ε Nd (t) = −1.9 to +1.9; (206Pb/204Pb) t = 17.900–19.006; ε Hf (t) = 5.04–15.28) and young two–stage Nd–Hf model ages (T DM2 = 1105–749 Ma and 899–574 Ma, respectively) indicate that their precursor magma was derived from partial melting of Mesoproterozoic to Neoproterozoic juvenile lower crust that had been metasomatized by fluids/melts from an enriched mantle wedge. The quartz diorites and quartz monzodiorites are characterized by intermediate SiO 2 (58.21–61.47 wt%), high MgO (3.62–5.42 wt%), and low CaO (3.15–4.96 wt%) contents, and high Cr (151–222 ppm) and Ni (97–131 ppm) contents, as well as elevated Sr and Ba. They have strong Nb and Ta depletion and highly fractionated rare earth elements, indicating a geochemical affinity to typical high-Mg andesites. These rocks exhibit mid-ocean ridge basalt (MORB)-like whole-rock Nd–Sr–Pb–Hf isotopic characteristics, with high ε Nd (t) and ε Hf (t) values of +1.60 to +3.20 and + 10.21 to +13.61, respectively, and relatively low (87Sr/86Sr) i and (206Pb/204Pb) i ratios of 0.7028–0.7045 and 16.768–17.856, respectively. They also have low Sr/Y (30–59), Ba/Th (75–213), and Ba/La (26.05–38.24), but elevated Th/Yb (4.51–7.36), Th/Nb (0.78–1.17), and Rb/Y (2.79–6.29) ratios. We conclude that they were generated by partial melting of depleted lithospheric mantle previously metasomatized by subduction-related fluids and sediment melts. These results, integrated with regional geological, geochronological, and geochemical data, constrain the tectonic evolution of NE China during the late Paleozoic. This involved normal subduction at 400–335 Ma, ridge subduction at 333–319 Ma, and slab break–off at 315–272 Ma. The high-Mg andesitic/dioritic magmas had high oxygen fugacities and high water and volatile (e.g., Cl, S) contents, and sufficient ore resources (e.g., Cu, Au, Fe) from the mantle wedge to be favorable for Cu (–Au–Fe) mineralization. [Display omitted] • The first ca 320 Ma ore-related high-Mg diorites were identified in NE China. • The late Paleozoic tectonic evolution of NE China experienced three episodes. • High-Mg andesitic/dioritic magma is favorable for Cu-Au-Fe mineralization. [ABSTRACT FROM AUTHOR]

The occurrence of adakitic rocks can provide insight into the evolution of continental crust and deep geodynamic processes in subduction zones. In this paper, we investigated zircon U-Pb ages and Hf isotope, whole-rock major and trace elements, and whole-rock Sr-Nd-Pb isotopes of the Lianghu quartz diorites and Shigong monzogranites in the Dunhuang Block, to understand their petrogenesis and tectonic setting as well as the tectonic evolution of the Dunhuang Block in the early Paleozoic. LA-ICP-MS zircon U-Pb dating results suggest that the Lianghu quartz diorites and Shigong monzogranites were emplaced at ca. 455 ± 3 Ma and 431 ± 3 Ma, respectively. The Ordovician quartz diorites exhibit relatively high Sr (734–904 ppm) contents, negative-to-negligible Eu anomalies (Eu/Eu* = 0.87–0.99), high Sr/Y (52.5–124) ratios, but low Yb (0.68–1.32 ppm) and Y (7.27–14.0 ppm) contents. Moreover, they exhibit relatively high Mg# (52.0–54.7) values, Cr (23.1–88.0 ppm) and Ni (15.0–53.3 ppm) contents, similar to those of adakitic rocks originating from subducted oceanic crust. The quartz diorites display low initial 87Sr/86Sr (0.703464–0.704783), negative ε Nd (t) of −3.2 to −1.3, and positive ε Hf (t) of +3.8 to +8.0, with two-stage model ages for the Nd and Hf systems of 1.12 to 1.09 Ga and 1.17 to 0.91 Ga, respectively, indicative of a heterogeneous magma sources. They have relatively high radiogenic 206Pb/204Pb(t) (18.219–19.066), 207Pb/204Pb(t) (15.616–15.669), and 208Pb/204Pb(t) (39.042–39.198), signifying that some subduction-related materials (e.g., ocean island basalts) may be involved as sources. These characteristics indicate that the Lianghu quartz diorites were derived from the partial melting of subducted oceanic slabs (sediments + fluids), and that they underwent subsequent interaction with peridotite in the mantle wedge, with limited assimilation of crustal materials during magma ascent. The Silurian monzogranites contain high Sr content (655–674 ppm) but very low contents of Y (2.49–4.19 ppm) and Yb (0.24–0.37 ppm), yielding high Sr/Y ratios (161–263); those values, together with low MgO (0.30–0.41 wt.%), Mg# (40.6–41.4), Cr (2.39–3.28 ppm), and Ni (2.19–2.95 ppm) contents, resemble those of thickened lower crust-derived adakitic rocks. They show ε Hf (t) and ε Nd (t) values of −2.5 to +3.0 and −3.6, with the respective two-stage model ages of 1.55 to 1.20 Ga and 1.32 Ga. Their low Pb values, 206Pb/204Pb(t) = 18.184, 207Pb/204Pb(t) = 15.595, and 208Pb/204Pb(t) = 37.717, also suggest addition of minor mantle-like melts. These geochemical features indicate that the parent magmas of the monzogranites originated either from the melting of heterogeneous crustal sources, or through mixing of thickened juvenile crust, Mesoproterozoic crust materials, and minor mantel-derived materials in the stability field of garnet-bearing amphibolite. Given the coeval regional magmatism and tectonic setting, we propose that the continental crust thickening of the Dunhuang Block began roughly in the late Ordovician (~35 km) and culminated in the early Silurian (~50–55 km), as evidenced by the La/Yb ratios of quartz diorites (12.2–25.2) and monzogranites (57.6–60.9). The corresponding transition of the tectonic regime from subduction to collisional setting occurred at ~440 Ma. The Dunhuang Block could undergo thickening processes associated with underplating of mantle-derived magmas during subduction of the southern Paleo-Asian Ocean, and subsequently collided with the Shibanshan terrane (a Paleozoic continental arc) along the southern Beishan orogen at ca. 440–430 Ma. Our results show that the Dunhuang Block represents a continental arc in the early Paleozoic, and was involved in the Paleozoic orogenesis of the Central Asian Orogenic Belt. • Two adakitic plutons were identified in the northern Dunhuang Block. • Crustal thickness is up to ~50–55 km in the early Silurian (~430 Ma). • Thickening was likely triggered by magmatic underplating and continental collision. • Dunhuang block should be a continental arc in the early Paleozoic. [ABSTRACT FROM AUTHOR]

The northern Alxa orogenic belt, a junction between the western and eastern Central Asian Orogenic Belt (CAOB), is not well understood, especially in its Carboniferous to Permian tectonic history. In this paper, an integrated study incorporating the geochronology, geochemistry, and isotopes of magmatic rocks and provenance analysis of clastic rocks is conducted to address the above issue. The zircon U Pb age data, both in this study and in previous studies, indicates that the Permian magmatic activities in the Alxa Block were intensive and peaked at ca. 276 Ma. The magmatic zircons yield negative ε Hf (t) values with a wide range, indicating their dominant derivation from the crustal reworking of the Alxa Block with the addition of juvenile materials. The Permian high-K to shoshonitic, I-type granitoids combined with the A-type granitoids/rhyolites were most likely formed in extensional settings. The late Carboniferous sandstones collected along the Badain Jaran fault yield a high proportion of early Paleozoic zircons peaked at ca. 429 Ma with both positive to negative Hf (t) values and a low proportion of Precambrian zircons with positive to negative Hf (t) values. Thus, their provenance were likely the Precambrian to Paleozoic rocks in the Alxa Block and in the terranes in the CAOB. The zircon age spectra with no indicators of Carboniferous zircons approximating their depositional age supports an extensional setting. The Permian A-type granites and volcanic rocks in the Alxa area have some geochemical affinity with the Permian alkaline granitoids in the eastern Tianshan–Beishan and central-north Inner Mongolia regions. These findings support the extension of the Gobi–Tianshan belt in the Alxa area. • The Permian magmatic rocks were predominantly reworked from the Alxa Block. • The clastic rocks were sourced from the Alxa Block and the terranes in the CAOB. • An extensional setting was proposed for the Alxa area. [ABSTRACT FROM AUTHOR]

The long-standing controversies in tectonic boundary, the nature of basement rocks, and the Phanerozoic continental crustal growth in the eastern Central Asian Orogenic Belt (CAOB) in NE China have been the key barriers in the understanding of the regional tectonic evolution. In this paper, we integrated published and new zircon U–Pb and Hf isotopic data of the Phanerozoic granitoids from the Jiamusi Block and the Lesser Xing'an-Zhangguangcai Range (LXZR) for a zircon Hf isotopic mapping of the region. The mapping results outlined three Hf isotopic provinces on the basis of T DM C ages: Province I (T DM C = 2.0–1.6 Ga, ε Hf (t) = −7.0 to −5.2) and Province II (T DM C = 1.6–1.1 Ga, ε Hf (t) = −4.6 to +3.9) represent the ancient basements in the Jiamusi Block; Province III (T DM C = 1.1–0.4 Ga with ε Hf (t) = +2.1 to +13.1) represents the juvenile crustal components in the LXZR. Province I (total area ~ 6000 km2) is sporadically exposed within Province II (~121,000 km2); the latter is bounded to Province III (~144,000 km2) along a sharp SE-NW boundary ~130 km west of the Mudanjiang Fault. This suggests that at least the part of the Songnen Block to the east of this boundary was in the same tectonic unit with the Jiamusi Block in the Paleozoic. Province III spatially accounts for about 53% of the study area, indicating a significant Mesozoic growth of continental crustal in the easternmost CAOB. • Hf isotopic mapping determines three provinces in the Jiamusi Block and LXZR • The juvenile crust accounts for 53% of the study area, indicating a huge crustal growth • The Jiamusi Block has a heterogeneous Precambrian basement • The eastern Songnen was in the same tectonic unit with the Jiamusi in the Paleozoic [ABSTRACT FROM AUTHOR]