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The Neoproterozoic Jiangnan orogenic belt records the accretion and collision between the Yangtze and Cathaysia blocks in South China. The orogen is divisible into three units: a northeastern domain (also referred to as the Huaiyu or Shuangxiwu domain), a central domain (Jiuling domain) and an undifferentiated southwestern domain. Detrital zircons from the oldest sequences (Shuangqiaoshan, Lengjiaxi, Fanjingshan and Sibao groups) in the central and southwest domains yield similar age spectra with major age populations at c. 875–820 Ma, along with minor Palaeo- to Mesoproterozoic and Archaean ages. The dominance of detrital ages close to the deposition ages of the units, along with juvenile zircon Hf isotopic compositions and arc-like whole-rock compositional data, indicate the sedimentary units accumulated adjacent to a convergent plate margin magmatic arc. The presence of Mesoproterozoic and older zircons, both as detritus in the units and as xenocrysts within igneous rocks displaying a subduction-related signature, along with the compositional data, place the magmatic arc along a continental margin. In the northeastern domain, the oldest coeval sequence (Shuangxiwu and Qigong groups) and arc igneous suites are dated at c. 970–850 Ma, and lack older detritus and xenocrysts, indicating they represent an accreted oceanic arc system. [ABSTRACT FROM AUTHOR]

Highlights • Neoproterozoic sedimentation during 863–820 and 797–780 Ma. • Regional angular unconformity constrains the Jiangnan orogeny to have lasted until ca. 820–800 Ma. • A multi-phase crustal evolution model is proposed for the Jiangnan Orogen. Abstract The Neoproterozoic amalgamation and timing of collision between the Yangtze and Cathaysia sub-blocks along the Jiangnan Orogen in South China remain disputed. With a view to constrain the crustal evolution in this major orogen, here we present new results from petrology, geochemistry, zircon U-Pb chronology and Lu-Hf isotopes, on a suite of meta-sedimentary rocks from the Shuangqiaoshan Group and tuffaceous rock from the Liantuo Formation in the Jiuling terrane of central Jiangnan Orogen. Magmatic zircon grains in meta-sedimentary and sedimentary samples from the bottom to top part of the lower and upper Shuangqiaoshan groups constraints the deposition during 863–820 Ma and 797–780 Ma, respectively. The unconformities were formed during 820–797 Ma, reflecting the final amalgamation of Yangtze with Cathaysia sub-blocks along the central Jiangnan Orogen. Our data also identify four major events at 1000–800, 1500–1900, 1900–2200, 2300–2600 Ma. The Neoproterozoic detrital zircons in the lower Shuangqiaoshan Group possess variable εHf(t) values of −44.0 to +13.4. Combined with the geochemical features, these data suggest that the lower Shuangqiaoshan Group was deposited in a back-arc basin with a mixed provenance of granitic and felsic volcanic components, whereas the upper Shuangqiaoshan Group was formed in a rift basin with more granitic or felsic components in the source region. Integrating the results presented in this study with those from previous works, a five-stage crustal evolution model is proposed for the Neoproterozoic Jiangnan Orogen involving (1) intra-oceanic subduction beneath the Huaiyu oceanic island arc (1000–880 Ma), (2) collision between Huaiyu arc and Yangtze Sub-block (880–860 Ma), (3) back-arc extension beneath the Yangtze Sub-block (860–830 Ma), (4) collision between Cathaysia and Yangtze sub-blocks (830–800) and (5) intracontinental rifting throughout South China Block (800–750 Ma). [ABSTRACT FROM AUTHOR]

The Neoproterozoic sedimentary strata in the central Jiangnan Orogen of South China are separated into the Lengjiaxi and Banxi groups by a mid-Neoproterozoic angular unconformity. This unconformity, previously interpreted as the evidence of continental collision between the Yangtze and Cathaysia blocks, is crucial for understanding the Neoproterozoic tectonic regime in the South China Craton. Here we report U-Pb ages and in situ Lu-Hf isotopes of detrital zircon grains from the sedimentary rocks near this unconformity. Zircon grains in meta-sandstone samples collected from the top part of Lengjiaxi Group yield maximum depositional ages of ∼827 Ma, ∼828 Ma and 836 Ma, and combined with other available age data, we suggest that the upper limit of the sedimentation for Lengjiaxi Group is at ca. 825 Ma. Zircon U-Pb analysis for two sandstone samples collected from the bottom of Banxi Group and Nanhuan strata yields two youngest ages of 797 Ma and 719 Ma, marking the initial depositional ages for these strata. All the samples contain abundant Neoproterozoic euhedral zircon grains, suggesting their near-source provenance. The Hf isotopic model ages of detrital zircons with positive εHf(t) values reveal two periods of juvenile crustal growth at 1.5–0.9 Ga and 2.8–1.6 Ga in the Yangtze Block. Several grains display core-rim structure with ages of rim part ranging from 864 to 851 Ma. We correlate these metamorphic ages with the amalgamation of Yangtze and Cathaysia blocks in the central segments. Our data in combination with those from other studies suggest that a back-arc basin existed in the central Jiangnan belt during ca. 860 Ma to ca. 825 Ma. We propose a four-phase crustal evolution model for the central Jiangnan belt. [ABSTRACT FROM AUTHOR]

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

The Jiangnan Orogen and Cathaysia Block constitute integral components in the geological framework of the South China Craton. However, the tectonic attributes of these two regions remain controversial. In this study we present LA–ICP–MS zircon U–Pb ages, Lu–Hf isotopes, and major and trace elements data from a suite of clastic rocks. Two hundred and forty seven zircon U–Pb ages obtained from the Neoproterozoic meta-sandstones in western Jiangnan Orogen define three major age populations: 2564–2395 Ma, 2068–1849 Ma and 963–730 Ma, corresponding to the early Paleoproterozoic crustal growth, amalgamation of the supercontinent Columbia and tectonics associated with Rodinia. Two hundred and forty three zircon U–Pb age data from Cambrian and Ordovician sandstones in the western Cathaysia yield five age populations: 2626–2392 Ma, 2050–1518 Ma, 1173–904 Ma, 857–708 Ma and 630–502 Ma, which can be correlated to the Neoarchean–early Paleoproterozoic continental growth, the tectono-thermal events associated with the Columbia supercontinent, the assembly and breakup of Rodinia, as well as the Pan-African event. The 630–502 Ma population correlates with the assembly of Gondwana supercontinent during late Neoproterozoic to early Paleozoic, although direct geological evidence for this event has not yet been reported from this region. These results suggest that the western Jiangnan belt and western Cathaysia Block have distinct crustal evolution histories albeit with close affinities. The REE geochemisty and Lu–Hf isotope data also indicate that the provenances of the Neoproterozoic and early Paleozoic detritus in western Jiangnan belt and western Cathaysia are mostly composed of reworked crustal materials. The metamorphic rims of zircon grains with core–rim structures yield ages of 912–891 Ma and 853–835 Ma, suggesting two phases of metamorphic events during Neoproterozoic in the source areas. These two events are likely associated with the tectonics related to the collision of Yangtze and Cathaysia blocks in the western and eastern segments, respectively. [ABSTRACT FROM AUTHOR]

The Central Asian Orogenic Belt is an accretionary orogen with many distinct terranes including the Chinese Central Tianshan, whose Precambrian tectonic affinity is not yet clearly known. We present Precambrian age spectra of inherited/xenocrystic zircons from magmatic rocks in the Chinese Central Tianshan, collected from published papers. The age patterns are dominated by zircons with ages ranging from 3261 to 541 Ma. These spectra provide robust clues regarding the Precambrian affinity of the Chinese Central Tianshan. The age spectra record two major tectonothermal events, represented by salient age peaks of c. 950 and 900 Ma within the ‘Grenville Orogeny’ period, and age peaks at c. 750 and 630 Ma, synchronous with magmatic events corresponding to Rodinia break-up. These results are consistent with the hypothesis that the Chinese Central Tianshan was part of the Tarim craton during Precambrian time as well as documenting its incorporation into, and separation from the Rodinia landmass. [ABSTRACT FROM AUTHOR]

The tectonic evolution of the Chinese Tianshan Belt which is located in the southern margin of the Central Asian Orogenic Belt remains controversial. In order to reveal the evolutionary history of this belt, we investigate metasedimentary rocks from the Tianshanmiao of Harlik domain and Xingxingxia area of central Tianshan domain in this study. The Permian siltstones from Xingxingxia contain six zircon populations with ages peak at 280, 815 and 910, 1590, 1855 and 2340 Ma, suggesting a diverse provenance. The 2544–2294 Ma ages correlate with the generation of continental nuclei in Tarim. The tectonothermal events during 1855, 1590, 910 and 815 Ma may correspond to the assembly and breakup of the Columbia and Rodinia supercontinents, respectively. Similar Precambrian age spectra and “event signature” curves suggest that the central Tianshan was most likely a part of the Tarim block in the Proterozoic. The detrital zircon U–Pb ages of Ordovician meta-greywackes from the Tianshanmiao sequence reveal six zircon populations with peaks at 460, 933, 1382, 1850, 2000 and 2462 Ma, among which the zircons with dominant age peaks (460 Ma and 930 Ma, more than 70%) are euhedral, low sphericity and exhibit clear oscillatory zoning, suggesting local derivation from the proximal Ordovician and Neoproterozoic granitoids. The range of εHf(t) values (−5.4 to +21) of zircon grains from Ordovician rocks suggests that these were derived from depleted mantle or through partial melting of juvenile crust, similar to the case for the Early Paleozoic magmatism in Chinese Altai. Our detrital zircon data suggest that the provenance of the Harlik was neither the Tarim nor the Junggar, and instead, we propose a connection with the Chinese Altai-Tuva–Mongol Arc along the southern margin of the Siberia craton at ∼500 Ma. The Harlik domain drifted southward and then collided with the central Tianshan in the Carboniferous-Permian as a result of the closure of Paleo-Tianshan Ocean. [ABSTRACT FROM AUTHOR]

Granitoids are the predominant geological constituents of South China and important for the understanding of the formation and evolution of continental crust. We describe field structural features of four small-scale granitic plutons and their country rocks in southern Jiangxi Province and present new zircon U-Pb and mica 40Ar/39Ar ages that are used to discuss the tectonic-magmatic evolution and thermal overprint events, that is, the tectonic rejuvenation of continental crust of the Cathaysia Block. The muscovite-bearing granite of Mashuang pluton shows sub-north-south mylonitic foliation and stretching/mineral lineation that shallowly plunges to the northeast, generally consistent with fabrics in the host rocks that are composed of widely migmatized metasediments. Zircons and muscovites yielded U-Pb and 40Ar/39Ar ages at 457±4 and 199±1 Ma, which are considered to represent the ages of emplacement and postmylonitic thermal overprint, respectively. The undeformed granites of Tianjiu and Junmenling plutons display massive structure, porphyritic texture bearing huge phenocrysts of feldspar, and a sharp contact with the host rocks that consist of greenschist- to amphibolite-facies metamorphic rocks and/or early Paleozoic granite. New dating results suggest that these granites formed during 235 ± 2 to 231 ± 2 Ma and cooled down at 224 ± 3 Ma. The biotite K-feldspar granite of Jitan pluton has an apparent compositional foliation in northeast-southwest direction defined by grain shape-preferred orientation of euhedral feldspar, biotite, and hornblende; such foliation is indicative of a syntectonic crystallization dominated by a southeast-northwest compressional stress field. The age of emplacement of this biotite K-feldspar granite is constrained at 158 ± 3 Ma, and the granite was reheated at 98 ± 1 Ma. On the basis of our observations and chronological data combined with previously published results, it is suggested that the continental crust of the Cathaysia Block was subjected to multistage rejuvenation during the Phanerozoic, including (1) reworking of crustal rocks induced by partial melting mainly in early Paleozoic and also in the Triassic to the Cretaceous by mixing of crustal melts with increasing involvement of juvenile materials and (2) tectonic and thermal overprints during early Paleozoic and Triassic intracontinental deformation events and Jurassic to Cretaceous magmatism. [ABSTRACT FROM AUTHOR]

Abstract: A suite of Paleozoic granitoids in Central Tianshan was studied for both geochemistry and geochronology in an effort to constrain their origin and tectonic setting. We combined LA-ICP-MS dating of zircon, standard geochemical analyses and Hf-isotopic studies of zircon to develop our tectonic model. Based on our analysis, the granitoids formed in three distinctive stages: ~450–400Ma, ~370–350Ma and ca. 340Ma. The first stage (450–400Ma) granitoids exhibit metaluminous, magnesian, high-K to shoshonitic characteristics of I-type granitoids (arc-setting), that are enriched in LREE relative to HREE with high (La/Yb)CN values, show negative Eu anomaly and are depleted in Nb, Ta and Ti. This phase of granitoid emplacement was most likely related to the southward subduction of the Paleo-Tianshan Ocean beneath the Tarim block and the subsequent Central Tianshan arc. In contrast, the second stage granitoids (370–350Ma) are distinctly different and are classified as calc-alkaline or shoshonitic plutons with a weak positive Eu anomaly. Within the second stage granitoids, it appears that the earlier (~365Ma) granitoids fit within the A-type field whereas the younger (~352Ma) granitoids plot within the post-collisional potassic field. These granitoids formed during collisions between Central Tianshan and the Tuha terrane that occurred along the northern margin of Central Tianshan. Lastly, the ca. 340Ma granitoids are typical of volcanic arc granitoids again that probably formed during the northward subduction of the South Tianshan Ocean beneath the Central Tianshan landmass or the subsequent southward subduction of the residual Paleo-Tianshan Ocean. The Hf isotopic data of zircons from all the studied granitoids were pooled and yielded three prominent Hf TDM C model age populations: ca. 2400Ma, ca. 1400Ma and ca. 1100Ma. The Hf-data shows a significant input of juvenile crust in addition to crustal recycling. We interpret these three phases of juvenile crustal addition to phases of global growth of continental crust (~2400Ma), the addition of juvenile crust during the breakup of the Columbia supercontinent (~1400Ma) and the assembly of Rodinia (~1100Ma). [Copyright &y& Elsevier]

Abstract: The Jiangnan Orogen, the eastern part of which comprises the oceanic Huaiyu terrane to the northeast and the continental Jiuling terrane to the southwest, marks the collision zone of the Yangtze and the Cathaysia Blocks in South China. Here, zircon U–Pb geochronological and Lu–Hf isotopic results from typical basement and cover meta-sedimentary/sedimentary rock units in the eastern Jiangnan Orogen are presented. The basement sequences in southwestern Huaiyu terrane are mainly composed of marine volcaniclastic turbidite, ophiolite suite and tuffaceous phyllite, whereas those in the northeastern Huaiyu consist of littoral face pebbly feldspathic sandstones and greywacke interbedded with intermediate-basic volcanic rocks. Combined with previous studies, the present data show that the basement sequences exhibit arc affinities. Zircons from the basement phyllite in the southwestern margin of the Huaiyu terrane, representing a Neoproterozoic back-arc basin, yield a single age population of 800–900Ma. The basement greywacke from northeastern Huaiyu terrane, representing fore-arc basin, is also characterized by zircons that preserve a single tectono-thermal event during 800–940Ma. However, the late Neoproterozoic cover sequence preserves zircons from multiple sources with age populations of 750–890Ma, 1670–2070Ma and 2385–2550Ma. Moreover, Hf isotopic data further reveal that most detrital zircons from the basement sequences yield positive εHf(t) values and late Mesoproterozoic model ages, while those of the cover sequence mostly show negative εHf(t) values. The Hf isotopic data therefore suggest that the basement sequences are soured from a Neoproterozoic arc produced by reworking of subducted late Mesoproterozoic materials. The geochronological and Hf isotopic data presented in this study suggest ca. 800Ma for the assembly of the Huaiyu and Jiuling terranes, implying that the amalgamation of the Yangtze and Cathaysia Blocks in the eastern part occurred at ca. 800Ma. [Copyright &y& Elsevier]

The bimodal association of basalts and rhyolites in the Hongshankou area of the East Tianshan area (NW China) provides an important suite to investigate magma petrogenesis and tectonics evolution in a convergent margin setting. In this study we present petrological, geochemical and zircon U–Pb geochronological data from the basalts and rhyolites. Zircons from the basalts yield crystallization ages of 347.1±3.9Ma whereas those from the rhyolites are dated as 344.4±1.9 and 345.0±2.5Ma. The major and trace element signatures of basalts suggest high alumina basalt (HAB) as the source magma which was generated from metasomatised asthenosphere mantle. Both the mafic and felsic rocks are enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE), and are depleted in high field strength elements (HFSE). Broadly homogenous Rb–Sr and Sm–Nd isotopic compositions of mafic and felsic rocks are also characteristic. The basalts display a distinct enrichment in incompatible elements and positive εNd(345Ma) (from +5.87 to +8.25). We envisage a subduction-related origin to account for the LILE enrichment with arc-like melts (enriched in Th and LREE and depleted in Nb, with εNd(345Ma)>+6) produced through the partial melting of a depleted-mantle source, and the involvement of minor crustal component. The rhyolites also display high εNd(345Ma) (from +6.35 to +8.53). Consequently, we suggest a mixing process between a source similar to mid-ocean ridge basalt (depleted end-member mantle) and arc-like magmas for the petrogenesis of the mafic rocks, whereas the rhyolites are best interpreted to have formed by fractional crystallization from the parental magma of the basalts. Several lines of evidence from elemental and isotopic geochemistry suggest a close genetic relationship between the mafic and felsic rocks in the Hongshankou bimodal suites. We propose that the essentially bimodal character of this complex reflects the features of back-arc extensional magmatism, induced by the subduction of the Junggar plate during the Late Paleozoic. [ABSTRACT FROM AUTHOR]

We report petrologic, geochemical, and zircon U−Pb and Hf isotope data from an early Palaeozoic mafic-intermediate suite of rocks in Baluntai, heartland of the Central Tianshan. Analysed major elements of the intermediate rocks show a close affinity to metaluminous I-type granitoids, resembling arc plutons. The mafic rocks display depletions of Nb, Ta, and Ti typical of volcanic arc basalts (VAB). All of the samples fall within the subduction-related field in tectonic discrimination diagrams. Zircons from a granodiorite and a hornblende diorite yield indistinguishable crystallization ages of 475.1 ± 1.7 million years and 473.7 ± 1.6 Ma, indicating an early Palaeozoic magmatic event. Zircons in the mafic rocks yield younger crystallization ages of 427 ± 1 Ma and 426.5 ± 1.4 Ma. Combined with previous published results, our data suggest that the southward subduction of the Palaeo-Tianshan oceanic crust beneath the northern margin of the Tarim block probably began no later than Early Ordovician time and did not end prior to the middle Silurian. Zircons from the granodiorite and hornblende diorite show ϵHf(t) values of −11.19 to −5.98 and −12.85 to −6.01, respectively, suggesting the reworking of ancient crust. Correspondingly, these zircons yield twoTDM2age ranges: 2140–1812 Ma and 2241–1812 Ma, probably representing a significant episode of juvenile addition during the assembly of Columbia. In contrast, zircons from the mafic rocks yield ϵHf(t) values of 3.12–8.91 and 3.19–8.76, corresponding to theTDM1ages ranging from 911 to 685 Ma and from 905 to 688 Ma, respectively, suggesting crustal growth in the Central Tianshan microcontinent associated with the initial break-up of Rodinia. [ABSTRACT FROM AUTHOR]

Abstract: The unified South China Block, comprising the Yangtze Block to the northwest and the Cathaysia Block to the southeast, has been central to recent studies on the Precambrian crustal evolution and position of South China in Proterozoic supercontinents. Here we present results from detailed U–Pb geochronology, Lu–Hf isotopes and rare earth geochemistry on zircons from three Ordovician and Devonian sandstone samples of southeastern Yangtze, together with those from a granodiorite sample and three Triassic sandstone samples in northeast and southeast Cathaysia. The southeastern Yangtze Block is characterized by extensive tectono-thermal events during 850–730Ma and 470–410Ma, which corresponded to the breakup of Rodinia and the Caledonian orogenic event, respectively. Major zircon populations with ages of 2800–2500Ma, 1990–1580Ma and 1260–920Ma are recorded from southeastern Yangtze, which are correlated, respectively, with the Neoarchean crustal growth, and histories of the Paleo-Mesoproterozoic Columbia and Neoproterozoic Rodinia supercontinents. In contrast, zircon U–Pb ages from southeast Cathaysia reveal prominent magmatic events during 2630–2300Ma, 2030–1770Ma and 280–190Ma, correlated with Neoarchean continental growth and the tectonothermal regimes associated with the history of the Columbia supercontinent as well as the Indosinian movement. The sector-zoned zircons from the granodiorite in northeast Cathaysia yielded weighted mean ages of 846.7±9.8Ma and 826.4±7.6Ma and positive ɛHf values, constraining the initial breakup of South China at ca. 848 Ma and extensive rift-related magmatism at ca. 826Ma. The Hf data suggest important episodes of juvenile magmatic addition at 3.1–2.8Ga and 2.4–1.5Ga for Yangtze, and at 3.3–2.3Ga for Cathaysia, indicating the existence of older crustal components in South China. The Hf data suggest that most zircons in both the blocks were derived from crustal magmas. Our results suggest distinct crustal evolution histories for the Yangtze and Cathaysia Blocks albeit with close affinities. [Copyright &y& Elsevier]

Abstract: This paper reports some new results from U–Pb geochronological, Hf isotopic and REE geochemical studies of detrital zircons in the Ordovician sandstones from South Jiangxi within Cathaysia. 426 groups of U–Pb age determinations define five major age populations: 2560–2380Ma (a peak of 2460Ma), 1930–1520Ma (a peak of 1700Ma), 1300–900Ma (a major peak at 970Ma and two subordinate peaks at 1250Ma and 1130Ma), 850–730Ma (a prominent peak of 780Ma) and 670–530Ma (a major peak at 540Ma and a subordinate peak at 650Ma). We also report zircon U–Pb concordia age of 3.96Ga, which is the oldest age so far obtained from Cathaysia. The age peak at 2460Ma correlates with similar ages reported for Neoarchean global continental growth. The 1930–1520Ma population broadly overlaps with the time of amalgamation and disruption of the Columbia supercontinent. The major age peak at 970Ma and two secondary peaks at 1250Ma and 1130Ma reflect multiple tectonothermal events associated with the assembly of Rodinia. Similar ages are widely reported from the South China Craton (SCC). Our study reveals that the 850–730Ma population is consistent with the breakup period of Rodinia, suggesting that the SCC within Rodinia began to break up since 850Ma. Geologically, the evidence for this breakup event is widespread and presented by Neoproterozoic granites, bimodal igneous rocks, basic dyke swarms and formation of continental rift type basins. Our study also reveals a 670–530Ma population that correlates well with the assembly of Gondwana during end Neoproterozoic. However, direct geological evidence for this event has not yet been found within the studied area. Furthermore, the Hf isotopic model age data suggest two major stages of crustal evolution within Cathaysia. The first is the event dated at 1.6–2.8Ga and the second one at 3.5–3.9Ga. The zircons show a large range of εHf(t) values from +8.64 to −30.54, suggesting that they have different origins with a similar age of crystallization. The fact that most detrital zircons show negative εHf(t) values suggests the ancient provenances of Cathaysia were dominated by reworked crustal materials. [Copyright &y& Elsevier]

Abstract: This paper provides some new evidences on stratigraphic sequence, zircon SHRIMP dating from ophiolite, granitoids, and fold-and-thrust tectonic styles in the South China Block (SCB). Stratigraphic studies suggest that the eastern and central parts of the SCB show a SW-dipping palaeoslope framework during the Late Palaeozoic–Early Mesozoic. These areas were not in a deep-sea environment, but in a shallow-sea or littoral one. Coeval volcanic rocks are missing. Deep-water deposits and submarine volcanism only took place in the western part of the SCB. The three ophiolitic mélanges of the eastern SCB formed in the Neoproterozoic, but not in the Permian or the Triassic. The sedimentary rocks associated with the Neoproterozoic oceanic relics contain abundant Proterozoic acritarchs, but no radiolarians. The Early Mesozoic granitoids (235–205Ma) belong to the post-collision peraluminous S-type granites; they are widely exposed in the central-western SCB, and rare in the eastern SCB. The fold-and-thrust belt developed in the eastern SCB shows a top-to-the-south displacement, whereas the Xuefengshan Belt of central SCB indicates a north- or northwest-directed shearing. The geodynamic settings of the different parts of the SCB during the Triassic are discussed. [Copyright &y& Elsevier]

The Central Asian Orogenic Belt (CAOB) is one of the largest accretionary orogens in the world. It was formed mainly by amalgamation of island arcs, accretionary wedges and microcontinents. Revealing the origins of the Precambrian continental blocks is essential for the understanding of the tectonic framework and geodynamic evolution of the CAOB. In this paper we present detrital zircon U–Pb ages of Precambrian meta-sedimentary rocks and late Paleozoic undeformed sandstone from the northern Yili Block, Chinese North Tianshan, in order to better understand the regional tectonic evolution. Two mica-schist samples from the Wenquan Metamorphic Complex (WMC) show similar zircon age distribution patterns with peaks at ∼0.43 Ga, ∼0.54 Ga, ∼0.65–0.68 Ga, ∼0.74–0.79 Ga, ∼0.89–0.92 Ga, ∼1.3–1.55 Ga and ∼1.69–1.70 Ga, respectively. Minor age peaks of ∼1.1 and ∼2.2 Ga are also separately recognized in individual samples. A phyllite from the Mesoproterozoic Changcheng System yielded detrital zircon ages mainly ranging from 855 to ∼1500 Ma with a single peak at ∼906 Ma. According to the analysis of age data and corresponding CL images of the dated zircon grains, protoliths of the mica-schists and phyllite should have deposited later than 645 Ma and 850 Ma, respectively, and were subjected to medium- to low-grade metamorphism during mid-late Silurian time. The good agreement between the age patterns of the meta-sediments and those of the nearby granitic and high-grade metamorphic rocks of the WMC indicates that the detrital zircon grains were mainly derived from the local metamorphic/crystalline basement. Occurrence of much older zircons (∼1.0–2.2 Ga) in the mica-schists and absence of such zircon populations in the phyllite suggest that (1) the protoliths of the mica-schists and phyllite had distinct sources and were deposited at different time, and (2) Mesoproterozoic to Paleoproterozoic rocks probably existed in the northern Yili Block. Three undeformed sandstone samples yielded consistent single age peak at ∼368–376 Ma and contain only a few Proterozoic detrital zircon grains. The peak age is in agreement with ages of neighboring late Paleozoic arc magmatic rocks in the Chinese North Tianshan. Thus, the sandstone was probably deposited during latest Devonian to earliest Carboniferous time in a forearc or interarc basin, around which Proterozoic basement was not exposed or completely isolated. A comparison between the zircon age patterns of the northern Yili Block and the surrounding cratons and microcontinents leads us to conclude that (1) the northern Yili Block had a Proterozoic basement similar to that of the Chinese Central Tianshan and Kyrgyz North Tianshan, and (2) these microcontinental blocks share the same origin as the Tarim Craton, but are distinguished from the Siberian Craton. [ABSTRACT FROM AUTHOR]

Abstract: The Precambrian Aksu blueschist terrane (ABT) located in the northwestern Tarim Craton was formerly regarded as a Mesoproterozoic or an early Neoproterozoic complex. Yet, its tectonic significance remains poorly understood due to the lack of reliable age. We have conducted a detrital zircon U–Pb geochronological study of both the metasedimentary rocks from the ABT and the unmetamorphosed sandstones from the overlying Sinian succession to better constrain the age of the ABT. In addition, geochemical analyses were performed on the metasedimentary rocks to establish the broad tectonic setting of the source region of sediments. Our first U–Pb dating results suggest a maximum deposition age of ca. 730Ma for the protolith of the metasedimentary rocks in the ABT and a maximum deposition age of 602Ma for the unmetamorphased Sinian sandstones immediately overlying the ABT. Therefore, the blueschist-facies metamorphism in the ABT must have taken place after ca. 730Ma, but prior to 602Ma. This metamorphism may manifest the Pan-African orogeny (ca. 700–500Ma), which is related to the assemblage of Gondwana, in the northern Tarim. Furthermore, the age range of 1.3–0.9Ga was not recorded in the detrital zircons from both the metasedimentary rocks and the Sinian sandstones, suggesting that the northern Tarim Craton may not be significantly affected by the Grenville-age orogeny. A major age population at Paleopreoterozoic (ca. 2.0–1.8Ga) was found in all samples, implying a Paleoproterozoic orogeny in the northern Tarim, which is coincident with the timing of the orogeny associated with the assembly of the Columbia supercontinent. Taking together the geochemical and chronological data, we propose that the northern margin of the Tarim Craton was probably a late Neoproterozoic active continental margin and a major source for the sedimentary rocks of the ABT, which provided a mixture of both old recycled sedimentary material from the basement rocks and juvenile material from the igneous rocks. [Copyright &y& Elsevier]

Abstract: U–Pb geochronology and Lu–Hf isotopic studies on detrital zircons from late Neoproterozoic sediments of the Cathaysia block, South China, show abundant Grenville-age (∼1.0Ga) and Neoarchaean populations, and minor Eoarchaean (∼3.8Ga), Paleo- to Mesoarchaean (3.3–3.0Ga), Mesoproterozoic (1.7–1.4Ga) and Pan-African (0.70–0.54Ga) populations. This is the first report of ∼3.8Ga material in the crust of the Cathaysia block. The presence of euhedral ∼1.0Ga zircons indicates that a Grenville orogenic belt was within or very close to the southern Cathaysia block. However, the provenance containing the ∼3.8Ga, 3.3–3.0Ga, ∼2.5Ga, ∼1.0Ga and 0.70–0.54Ga zircon populations cannot be found in the South China Block; the combination of zircon age distributions and the rounded, strongly abraded shapes of the Archean zircons suggesting long transport is consistent with derivation from other continental terranes previously linked with the southern part of the South China Block. Comparison with the tectono-magmatic history and compositions of rocks in western Laurentia – eastern Australia and eastern India – East Antarctica – western Australia, we suggest that these late Neoproterozoic sediments may have originated mainly from Eastern India-East Antarctica. This indicates that the South China Block was linked with the Eastern India - East Antarctica continents in the late Neoproterozoic rather than being located between the western Laurentia and eastern Australia continental blocks. U–Pb and Hf-isotope studies on detrital zircons provide an important independent constraint on the palaeogeography of the South China Block in the context of the breakup of Rodinia and the subsequent assembly of Gondwana in late Neoproterozoic time, and insights into the relationship between the Cathaysia and Yangtze blocks. [Copyright &y& Elsevier]