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Hardly any previous studies have focused on the granitic dykes which intrude into the Paleoproterozoic Liaohe Group in the Liaodong Peninsula, northeast of the North China Craton. In situ zircon U-Pb dating, Lu-Hf isotopic and geochemical analyses on three representative monzogranite dykes were taken in this study. These dykes have relatively high content of SiO2 (72.20%–74.78%) and K2O (2.83%–6.37%), and have characteristics of high-K calc-alkaline to shoshonite series. Two dyke samples have I-type granite features and have high Sr/Y ratios and positive Eu anomalies, showing an adakitic feature. Another dyke has a high ratio of Ga/Al, but has a low Zr saturation temperature, which differs from the typical A-type granite. Zircon grains from these three dykes have typical magmatic zoning in CL images and yield consistent U-Pb ages of ~1859–1852 Ma, which are interpreted as the crystallization ages of these dykes. Hf isotopic analyses yield mainly negative εHf(t) values and TDM2 ages of 2782–2430 Ma, similar to those of the 2.2–2.1 Ga granitoids and meta-sedimentary rocks (the Liaohe Group), indicating these monzogranitic dykes may have been sourced from melting of Paleoproterozoic granitoids and meta-sedimentary rocks. The monzogranitic dykes were generated under a post-collisional geological setting after the Jiao-Liao-Ji orogeny process. [ABSTRACT FROM AUTHOR]

Special Issue on Tectonic, Magmatic and Metallogenetic Evolution of the Central China Orogenic Belt. [ABSTRACT FROM AUTHOR]

The Gubaoquan area is located in the southern part of the Palaeozoic Beishan Orogenic Collage of the Central Asian Orogenic Belt in northwest China. Structural analysis of the Gubaoquan area has documented multiple phases of deformation, which challenge previous tectonic models and suggest that the eclogites formed through in-situ metamorphism. The study area is a highly deformed belt of metamorphic tectonites, intruded by syn-tectonic granitoids. The belt largely consists of D3 fabrics that developed after peak metamorphism, with only local preservation of D1 eclogite-facies fabrics in the cores of mafic boudins. Fabrics associated with D1–D4 document a clockwise metamorphic trajectory, characterised by eclogite–facies metamorphism (D1) followed by a large decrease in pressure and small decrease in temperature (D2), high-temperature low-pressure conditions (D3) and greenschist-facies metamorphism (D4). D2–D4 is associated with widespread N–S shortening and local extension. We propose that the metamorphic tectonite belt hosting the Gubaoquan eclogite represents Meso- to Neo-Proterozoic crust that underwent Ordovician–Silurian, north-directed subduction to various depths. The eclogite and its host were detached from the down-going slab, probably due to slab break-off and leading to extensive syn-tectonic magmatism. Exhumation probably occurred in an extruding-wedge-type setting. Convergence continued until the emplacement of the Silurian–Devonian granitoids. [ABSTRACT FROM AUTHOR]

The Jiangnan Orogenic Belt in South China formed as a result of the amalgamation between the Yangtze Block and the Cathaysian Block and records the geological information of collision. However, the timing of the amalgamation of two blocks remains controversial. Here, structural deformation and zircon U-Pb geochronological results from Precambrian metamorphosed sedimentary-volcanic rock units at the eastern domain of the Jiangnan orogenic belt in southern Anhui Province are presented. The pre-Nanhua rocks in the study area were widely involved in the metamorphism and deformation to with NW or SE-dipping foliation, tight folds and local development of strike-slip ductile shear zones, which is induced by collision of Yangtze Block and the Cathaysia Block. In this study, a mylonitic granodiorite sample intruding in the Xikou Group, a mylonitic dacite sample from Jingtan Formation and two deformed quartz veins samples in the Shexian region were dated by LA-ICP-MS zircon U-Pb dating method. Zircons from the mylonitic granodiorite and dacite yield the weighted mean ages of 811.2 ± 7.5 Ma (MSWD = 0.51, n = 30) and 779 ± 7.4 Ma (MSWD = 0.42, n = 29), respectively, interpreted as the crystallization ages of the original rocks, whereas the zircons from deformed quartz veins yield the weighted mean ages of 779 ± 14 Ma (MSWD = 2.6, n = 22) and 769 ± 16 Ma (MSWD = 2.4, n = 16), respectively, representing the crystallization age of the quartz veins. Combined with previous data, our results show that the metamorphosis and deformation of Pre-Nanhua rocks took place during the period of 820–770 Ma. Therefore, we consider that the Yangtze Block and the Cathaysian Block the eastern Jiangnan Orogenic Belt don't amalgamate until 770 Ma. [ABSTRACT FROM AUTHOR]

Fault geometry, kinematics, geophysics, the tectonic stress field and tectonic evolution of the Zhouwang fault in the southern Jiangnan tectonic transition zone of the Lower Yangtze region, eastern China are examined. Field observations show the fault is composed of a series of nearly E–W trending, N–S dipping faults, and four stages of tectonism (sinistral strike‐slip, thrust nappe, normal fault, and dextral strike‐slip) developed in turn. Geophysical data show that the fault trends almost linearly E–W along a flat, steep gravity gradient at shallow depth, with distinct gravity anomalies to the north and south and different in the north and south. Also, the deep part is characterized by northward dip and a gradual slowing down. Tectonic stress field analysis indicates that the fault experienced four tectonic movements: NNE–SSW compression, NNW–SSE compression, NEE–SWW extension, and E–W compression. Combined with regional tectonic background and previous research results, this indicates that: (1) the Zhouwang fault experienced sinistral strike‐slip movement during the Indosinian Period (260–200 Ma); (2) thrust nappes developed during the early Yanshanian Period (163–145 Ma); (3) a normal fault occurred in the late Yanshanian Period (125–65 Ma); and (4) dextral strike‐slip movement occurred in the Himalayan Period (ca. 50–37 Ma). The results reveal the tectonic evolution of the fault during Mesozoic deformation in the area, and also reveal the geological evolution and tectonic transformation of the Lower Yangtze region, which is key to our understanding of intracontinental deformation in eastern China. [ABSTRACT FROM AUTHOR]

The North Qinling Orogen underwent subduction and collision processes during the Palaeozoic, but the tectonic framework remains unclear. To investigate the tectonic evolution of the North Qinling Orogen, we selected the Devonian granites from the northeastern margin of the North Qinling Terrane. Integrated petrographic, geochemical, and geochronological studies, as well as Sr–Nd–Hf isotopic analyses, were carried out on the newly identified Devonian granites from the Hengjian area in the northeastern North Qinling Terrane, Qinling Orogenic Belt. Zircon laser ablation inductively coupled plasma mass spectrometry U–Pb dating reveals that these granites were crystallized at 396–387 Ma. The granite samples are metaluminous to weakly peraluminous (A/CNK = Al2O3/(CaO+Na2O+K2O) = 0.86 to 1.12), with high SiO2 (60.6–76.5 wt%) and high total alkaline (Na2O + K2O = 8.45–11.0 wt%) contents. The granites are enriched in Th, rare‐earth element, Zr, and Hf and depleted in Sr, Nb, Ta, P, Eu, and Ti. They are characterized by high Zr + Nb + Ce + Y contents (511–990 ppm) and 10,000*Ga/Al ratios (2.71–3.32), as well as high zircon‐saturation temperatures (TZr = 819–885°C, average = 845°C), which indicate that they are typical A‐type granites. The granites have low Y/Nb (0.39–0.67) and Yb/Ta (0.56–0.83) ratios, resembling those of the A1‐type granite, which indicates that they are formed in anorogenic settings. They also have low (87Sr/86Sr)i ratios (0.7055–0.7071) and negative εNd(t) values (−10.1 to −8.40) and variable zircon εHf(t) values (−8.46 to +14.7), with the two‐stage model ages of 2.0–1.8 Ga and 1.9–0.4 Ga, respectively. These geological features suggest that the granites of the Hengjian area were most likely generated by partial melting of mafic lower crust induced by asthenospheric ascent. The A‐type granites were generated in a continental rift environment during 396–387 Ma, corresponding to the closure of the Shangdan Ocean and the opening of the Palaeo‐Tethyan Ocean during the Early Devonian. [ABSTRACT FROM AUTHOR]

We carried out an integrated study of zircon U–Pb geochronology, Hf isotopes and geochemistry on the paragneisses and amphibolites from the Chencai area, South China. The detrital zircon ages of four paragneisses range from 2974 to 501 Ma with the main peak at ca. 820 Ma. The detrital materials with Neoproterozoic age may derive from the Jiangnan Orogen and those of Palaeo–Mesoproterozoic age may come from the Wuyi terrane. The youngest age indicates that the protoliths of the paragneisses were formed after ca. 501 Ma. The εHf(t) values (−20.6 to +20.9) of the detrital zircons suggest that the detrital materials of the protoliths are composed of old crustal and juvenile materials. The geochemical characteristics suggest that the protoliths of the paragneisses are greywackes, which formed in an active continental margin or continental island arc environment. The metamorphic ages of the three amphibolites are 428 ± 4, 430 ± 4, and 438 ± 3 Ma. The protoliths of the amphibolites are tholeiites, which can be divided into two groups. Group 1 is characterized by low ∑REE contents and (La/Yb)N ratios showing left‐inclined REE patterns and Nb, Ta depletion which resembles N‐MORB. Group 2 has higher ∑REE contents and (La/Yb)N ratios, with Eu negative anomalies showing affinity to E‐MORB. The data show that the Chencai Group is composed of oceanic crust remnants and continental crust materials, indicating it should be a subduction accretionary complex rather than a metasedimentary sequence and thus it cannot be regarded as the Precambrian basement of the Cathaysia Block. [ABSTRACT FROM AUTHOR]

The nature of the Precambrian basement in the Cathaysia Block of South China is controversial, which inhibits our understanding of the pre‐Devonian tectonic evolution of the region. In this study, a suite of amphibolites and marbles in northern Fujian area located in the north of the Cathaysia Block were subjected to LA–ICP–MS U–Pb zircon geochronological and geochemical analyses. Results show that the protolith of the amphibolite formed after ca. 459 Ma, and its metamorphism happened at ca. 429 Ma. The protolith of the marble was deposited after ca. 518 Ma, and its metamorphic age is ca. 437 Ma. The amphibolites are divided into two groups based on geochemical data. Group 1 has an OIB‐like feature that might have formed in an environment characterized by oceanic islands and seamounts. Magmas associated with Group 1 were derived from an enriched mantle source with OIB characteristics. The protolith of Group 2 shows IAB feature that formed in an island arc environment. Marbles are interpreted to represent metamorphosed marine carbonate rocks. Integration of geochronological and geochemical study indicates that the marble and amphibolite should be an early Palaeozoic oceanic island–seamount association. It suggests the Cathaysia Block underwent oceanic subduction during collisional orogenesis in the early Palaeozoic. This subduction is thought to have initiated prior to ca. 437 Ma. The U–Pb zircon ages of younger intrusive granites indicate that final amalgamation occurred before ca. 392 Ma. During this process, east and west Wuyi were amalgamated to form the unified Cathaysia Block. Thus, it suggests that there was no unified pre‐Devonian basement in the Cathaysia Block. The pre‐Devonian tectonic setting of the Cathaysia Block was an accretionary orogeny. [ABSTRACT FROM AUTHOR]

An integrated study of zircon U-Pb geochronology and geochemistry, together with Nd-Hf isotopes, have been carried out on the rhyodacite and rhyolitic tuff of the Jingtan Formation in the eastern part of the Jiangnan orogen. SIMS zircon U-Pb dating of two samples yielded weighted mean 206 Pb/ 238 U ages of 784 ± 6 Ma and 788 ± 6 Ma, respectively. Geochemically, they are peraluminous (A/CNK mostly around 1.2) and are characterized by enrichments in Rb, Th, REEs and HFSEs (e.g. Zr and Y) but depletions in Ba, Sr, P, Eu and Ti. The volcanic rocks show a clear A-type granite geochemical signature with high total alkalis (K 2 O + Na 2 O = 5.3–7.64 wt%), FeO t /MgO ratios and low CaO, MgO and TiO 2 contents. They have negative whole-rock ε Nd (t) (−4.2 to −1) and positive zircon ε Hf (t) (+1.26 to +11.6) values, illustrating decoupled Nd-Hf isotopes which may be genetically related to their petrogenesis process. The positive ε Hf (t) values and juvenile T Hf DM1 (0.89–1.3 Ga) of zircons indicate that the volcanic rocks may have been derived from the partial melting of the Neoproterozoic to late Mesoproterozoic crustal materials. Combined with the occurrence of significant volumes of contemporary bimodal volcanic rocks in eastern section of the Jiangnan orogen, it is inferred that the Jingtan felsic volcanic rocks formed during post-collisional extension shortly after the final amalgamation of Yangtze and Cathaysia blocks. [ABSTRACT FROM AUTHOR]

The Jingdezhen ductile shear zone is evolved from the Neoproterozoic Zhangyuan ophiolite mélange belt in the eastern Jiangnan Orogen, South China. Comprehensive study of geometry, kinematics, quartz c-axis fabric, temperature-pressure conditions and geochronology were conducted in this study. The Jingdezhen shear zone extends ∼180 km along the NE orientation with two groups of subvertical foliation and subhorizontal lineation. One group of foliation strikes NEN orientation whereas another one NEE orientation. Field investigation, microscopic observation and quartz c-axis fabric show that sinistral shearing along NEN-striking foliation occurred earlier than dextral shearing along NEE-striking foliation. Syn-tectonic staurolite porphyroblasts and deformation manner of feldspar imply that sinistral shearing occurred at 530-420 ºC and 6-2 kbar. Deformation manner and c-axis fabric of quartz and pre-tectonic staurolite porphyroblasts indicate that dextral shearing took place at 420-300 ºC. LA-ICP-MS zircon U-Pb and mica 40Ar/39Ar dating indicate that the sinistral shearing occurred during Neoproterozoic orogeny (830-800 Ma) whereas the dextral shearing at 447±12 Ma. The sinistral shearing resulted from the Neoproterozoic final assembly between the Yangtze and Cathaysia blocks. The dextral shearing was caused by Early Paleozoic orogen parallel extension and clockwise rotation. [ABSTRACT FROM AUTHOR]

Abstract: Large‐scale magmatism affected the Tongbai‐Dabie orogenic belt during post‐collisional lateral tectonic extension in the Cretaceous, which was suggested to account for the widespread deformation and migmatization in the Tongbai‐Dabie complexes. However, it cannot explain the most deformations in the shear zones. The northwest‐southeast shear zones are developed around or wrapped the Tongbai‐Dabie complexes. They play an important role for the interpretation of the tectonic evolution of the Tongbai‐Dabie orogenic belt. By a systematically observation and description of the geometry and kinematics of these shear zones, we found that the shear zones to the north dip NE and have a uniform sinistral shear sense, the shear zone to the south dips SW and has a uniform dextral shear sense, and the shear zones at the core are sub‐horizontal and have a uniform top‐to‐NW sense of shear. Combining with the comparison of previous and our geochronological studies, we interpret these associations as indicating that these shear zones were originally a single, more flat‐lying and sub‐horizontal shear zone with a uniform top‐to‐NW shear sense before the folding‐doming of the Tongbai‐Dabie complexes and suggest that the Tongbai‐Dabie orogenic belt experienced a uniform top‐to‐NW orogen‐parallel extension in the ductile lithosphere before the widespread magmatism in the Cretaceous. [ABSTRACT FROM AUTHOR]

The Tongbai orogenic belt has an overall antiformal geometry and the hinge of the antiform is sub-horizontal and trends NW–SE. The Tongbai complex (TBC) in the core of the antiform is bounded by the S-dipping Yindian–Malong shear zone in the south, the sub-horizontal Taibaiding shear zone at the top and the N-dipping Hongyihe–Tongbai shear zone in the north. The three shear zones have dextral, top-to-NW and sinistral movement, respectively. They are parts of a single shear zone, termed the Tongbai shear zone, that has a uniform top-to-NW sense of shear. Three samples of deformed granitoid (mylonite or protomylonite) from the shear zone have U–Pb zircon ages of 145 ± 6 Ma, 142 ± 2 Ma and 131 ± 6 Ma, respectively. An L-tectonite in the TBC yielded a metamorphic age of 137 ± 8 Ma and a migmatite an age of 137 ± 1 Ma. The Tongbai shear zone is intruded by undeformed Early Cretaceous granite and dykes and deformation in the shear zone is constrained to ca. 140–135 Ma, synchronous with metamorphism and migmatization in the TBC. Early Cretaceous magma emplacement and the associated uplift modified the TBC into a gentle antiform and the uplift may have continued to ca. 102–85 Ma. Similar geometry and kinematics have been documented in the Dabie orogenic belt to the east, which suggests that the Central Orogenic Belt in China probably experienced a uniform orogen-parallel extension and top-to-NW shearing in the ductile lithosphere in the Early Cretaceous. [ABSTRACT FROM PUBLISHER]

The basis for understanding continental tectonics to a large degree relies on terrane recognition. However, discrepant identifications and interpretations of the same terrane as well as its boundary are still commonly seen in South China. For years, the central debate has been revolving around the Yangtze-Cathaysia boundary and West-East Cathaysia boundary. Here we characterized the geochemical patterns (or differences) of the proposed terranes and located their boundaries by using a big geochemical dataset of South China, which consists of compositions of 75 elements in 5231 sediment samples. To extract valuable information from this big geochemical dataset, we applied multiple data mining techniques, including principal component analysis, sequential binary partition, Sobel operator, and support vector machine. Our results show that the geochemical patterns vary distinctly at regional scale across both the subblocks (i.e., Yangtze and Cathaysia) and terranes (i.e., Jiuling, Huaiyu, and Youjiang). Accordingly, we conclude that 1) the Northeast Jiangxi fault marks not only the Jiuling-Huaiyu boundary but also the north-eastern Yangtze-Cathaysia boundary; 2) the Yangtze-Cathaysia boundary extends westward along the Jiangshan-Pingxiang-Chaling fault; and 3) a fault zone comprising the Northwest Fujian fault and Zhenghe-Dapu fault possibly demarcates the West and East Cathaysia. The boundaries defined by the contrasting geochemical patterns in this study are also supported by geophysical, Nd isotopic, and geological evidence. Our observations will allow better explanation of where the proposed terranes originated and how South China was assembled. Our work demonstrates that data mining techniques are effective in deriving and integrating information for solving geoscience problems. • We characterized geochemical patterns of multiple terranes of South China. • Big geochemical dataset containing 75 element compositions in 5231 sediments were used. • We located terrane boundaries in South China by applying multiple data mining methods. • Geophysical, isotopic, and geological studies support the boundaries defined herein. [ABSTRACT FROM AUTHOR]

Abstract: A SHRIMP U–Pb zircon age along with geochemical and Nd–Hf isotopic results are reported for the Tieshajie volcanic rocks in the southeastern Yangtze Block, South China. The Tieshajie volcanic rocks are bimodal in composition and are dominantly transitional alkaline basalts and alkaline rhyolites, with an eruption age of 1159±8Ma. The basaltic samples have high TiO2 (2.14–3.12%) and relatively low Mg# (36–49) with variable ɛ Nd(t) values (−2.2 to +1.2), and display OIB-like incompatible elemental patterns, similar to many alkali basalts in continental rifts. These geochemical characteristics indicate that the primary magma of these basalts was probably derived from a moderately depleted asthenospheric mantle source and underwent fractional crystallization plus minor crustal contamination. The rhyolitic rocks are highly enriched in Th, Ta, Nb, REE, Zr, Hf and Y and depleted in Sr, P, Eu and Ti, showing affinity to A1-type granites. Combined with their slightly positive ɛ Nd(t) values (+1.3 to +1.6) and negative ɛ Hf(t) values (−2.45 to −12.7), the Tieshajie rhyolites were most likely generated by partial melting of mafic lower crust induced by basaltic underplating following asthenospheric ascent. The Tieshajie alkaline bimodal volcanic sequence is proposed to have developed within a continental rift setting on a passive continental margin. Combined with documented rift events in Yangtze Block during the late Mesoproterozoic, they may indicate onset of the amalgamation of Yangtze Block with other blocks within the Rodinia supercontinent. Integrating our data with the oldest arc-related igneous events in eastern Zhejiang, the transition of the regional tectonic regime from intracontinental rifting to interplate convergence occurred between ca. 1159Ma and 970Ma in the southeastern Yangtze Block. [Copyright &y& Elsevier]

Abstract: Amphibolites occur in a number of localities in the Cathaysia Block, some of them have been migmatised and their protoliths represent basaltic magmas erupted in various tectonic settings. Four migmatised amphibolites were collected from Jiangxi and Fujian Provinces. Cathodo-luminescence images of zircons extracted from the representative amphibolites show unzoned or sector-zoned structure. LA-ICP-MS analysis indicates that most zircons have high Th/U ratios and yield U–Pb zircon ages of 446±5, 435±2, 434±4 and 423±2Ma, respectively. Lu–Hf isotopic analysis on these zircons gives Hf model ages ranging from 900 to 1200Ma. Based on lithological observations and previously published geochronological data, we interpret that these U–Pb ages record an important tectonothermal event that led to the migmatization. This early Paleozoic (Caledonian) tectonothermal event in the Southeastern China has a great tectonic implication for the evolutionary history of the Cathaysia Block. [ABSTRACT FROM AUTHOR]

• The volcanic rocks formed in an arc setting at 756-740 Ma. • The late Tonian arc in the Wuyi domain was part of a major arc system in the West Cathaysia terrane. • The Wuyi arc system was different from the arc system along the western margin of the Yangtze Block at the late Tonian. • The West Cathaysia terrane was distinct from the southeastern margin of the Yangtze Block and they were not amalgamated until after the late Tonian. The late Tonian tectonic setting of the West Cathaysia terrane in South China is highly controversial and is key to better understanding the timing of amalgamation between the Yangtze Block and the West Cathaysia terrane and the positions of these two terranes in Rodinia and Gondwana. A detailed field-based study was conducted on the petrology, zircon U-Pb geochronology and Lu-Hf isotopes, and whole-rock geochemistry of a series of Neoproterozoic meta-volcanic and meta-sedimentary rocks in the Wuyi domain in the northeastern West Cathaysia terrane. The results indicate that the meta-volcanic rocks formed in an arc setting at 756-740 Ma, and the meta-sedimentary rocks were developed in an arc-related basin with single zircon age peaks of 765-728 Ma. We propose that the late Tonian arc in the Wuyi domain was part of a major arc system in the West Cathaysia terrane. An arc setting for the West Cathaysia terrane is distinct from the continental rift setting for the southeastern margin of the Yangtze Block at the time, supporting an interpretation that the two terranes were not amalgamated until after the late Tonian and occupied separate positions in Rodinia. [ABSTRACT FROM AUTHOR]

• SJC experienced multiple magmatism of ~2.78, ~2.69 and ~2.55 Ga. • Neoarchean magma derived from episodic juvenile crust growth and crustal reworking. • Recycling of sediments was not intense or extensive in SJC during Neoarchean. • A bottom-up tectonic regime related to plume activity is favored for NCC in Neoarchean. Recent advances in high-precision in-situ analysis of zircon U-Pb-Hf-O isotopes have significantly improved our approach to studying the origin and evolution of Archean crust. This study presents high-precision in-situ zircon U-Pb-Hf-O isotopes for the Southern Jilin Complex (SJC) on the northeastern margin of the North China Craton (NCC) and explores the potential of such an integrated approach in understanding the Archean crust evolution and its tectonic implications. The SJC consists mainly of Archean granitoid gneisses hosting minor supracrustal rock xenoliths. Zircon U-Pb data from representative lithologies reveal three episodes of magmatism at ~2.78, ~2.69 and ~2.55 Ga, respectively. The former two granitoid magmatic events are recognized for the first time in NE NCC, while the latest one is widespread over the NCC. All metamorphic zircon domains document similar metamorphic ages of 2.51–2.48 Ga, consistent with the widespread metamorphism of ~2.50 Ga in the NCC. Most concordant magmatic zircons preserve "mantle-like" O isotopic signatures, indicating the magma sources were not contaminated by large amounts of high δ18O supracrustal sediments. Hf depleted mantle model ages of magmatic zircons display one predominant peak at 2.9–2.8 Ga and two subordinate peaks at 3.3–3.2 Ga and 2.7–2.6 Ga, indicating possible episodic crust-mantle differentiation in Southern Jilin. Integrated zircon U-Pb-O-Hf data from the SJC suggest that magma sources were mainly derived from multiple episodes of reworking of juvenile or ancient crust with mantle component addition, while recycling of sediments was trivial during the Neoarchean in this region. The spatial–temporal relations of magmatism, lack of supracrustal addition to magma sources, and other geological evidence from the NCC are in favor of a bottom-up geodynamic regime possibly related to plume activities, arguing against a widespread top-down mechanism involving modern-style subduction in the NCC during the Neoarchean. [ABSTRACT FROM AUTHOR]

• The central Dunhuang Orogenic belt (DOB) can be split into two contrasting terranes. • The granitoid rocks were emplaced in two phases: ca. 284–275 Ma and ca. 255–238 Ma. • The two phases of granitoids are arc-related and post-collisional rocks, respectively. The Dunhuang orogenic belt (DOB), located in the southern Central Asian Orogenic Belt (CAOB), exposes Precambrian and Paleozoic intrusive-metamorphic rocks. To better understand its evolution, we carried out detailed petrological and geochronological investigations on the major lithologies of the central DOB. The central DOB can be divided into two terranes, the north and the south, with contrasting geological history. The north is characterized by Precambrian crystalline rocks (ca. 3.1–1.6 Ga) overprinted by Devonian tectono-thermal events. The Precambrian rocks show evidence for major juvenile crust growth with additions of older crustal materials at 2.7–2.5 Ga, a major crustal reworking event at 2.0–1.9 Ga, and juvenile additions with minor crustal reworking at 1.8–1.7 Ga. In contrast, the south is characterized by early Devonian (ca. 406 Ma) TTG-gneiss and amphibolite gneiss, and some Late Paleozoic–early Mesozoic granitoid rocks (ca. 284–238 Ma). The Late Paleozoic–early Mesozoic granitoid rocks from the south were emplaced in two phases: early Permian (ca. 284–275 Ma) and late Permian–middle Triassic (ca. 255–238 Ma). They belong to the high-K calc-alkaline I-type series which were generated from mixing juvenile materials with Mesoproterozoic continental crust. The early Permian and the late Permian–middle Triassic granitoid rocks are considered as arc/subduction-related and post-collisional rocks, respectively. These suggest that the final assembly of the DOB with the Beishan or final assembly within the DOB happened in the middle Permian (ca. 275–255 Ma). The DOB formed by accretion/collision of multiple terranes/microcontinents, similar to other areas in the CAOB. [ABSTRACT FROM AUTHOR]

A Neoproterozoic subduction-accretion complex have been identified along the Zhenghe-Dapu fault (ZDF) zone in the inner Cathaysia Block, South China. The serpentinites are characterized by low 187Os/188Os ratios of 0.11621 to 0.12008 and very low 187Re/188Os values of 0.031-0.129, which are similar to those from highly refractory mantle residues, indicating that they are tectonic rather than igneous origin. The meta-ultramafic rocks, including pyroxene hornblende schist and hornblende schist, are characterized by high Ni, Cr and low K2O content. Their convex upward REE partterns, along with lower concentrations of highly incompatible elements indicate that their protolith were cumulate origin. Low initial 87Sr/86Sr and high 143Nd/144Nd ratios suggest that they were derived from partial melting of an depleted mantle source. Low Nb/Yb, Th/Yb and Ti/V imply they have IAT-like geochemical features which occurred in oceanic island arc setting. The associated metasedimentary rocks have low chemical index of alteration (CIA) values (34.7-58.2) and relatively high index of compositional variability (ICV) values (0.98-3.22) suggested weak chemical weathering and an immature source. Low K2O/Al2O3 (0.01-0.03), low zirconδ18O values (4.4 to 5.3‰) and high zircon ɛHf (t) values (+13.5 to +16) of the metasedimentary rocks point to mantle-derived material supply for their protolith. TDM1 (616-719 Ma) of the zircons reflect the source material was derived from a mantle source with Neoproterozoic model ages. Low La/Sc and Th/Sc values infer that their source material were derived from an ocean island arc setting. These rocks have experienced strong mylonitization. Shear-sense indicators show that the mylonitized rocks experienced sinistral strike-slip motion parallel to the ZDF zone. Metamorphic zircons from the mylonitized rocks yield SIMS U-Pb age of ca.522-520 Ma, suggesting that the subduction-accretion complex experienced intensive Pan-African metamorphic event. All these features prefer that there was a Pan-African accretionary orogeny in the South China Block. The ZDF zone probably marks the collisional belt between the west Cathaysia Block and the west Australia, corresponding to the assembly of the Gondwanaland. [ABSTRACT FROM AUTHOR]

Includes a supportive view of Zheng-xiang Li's tectonic model for continent-continent collision between the North and South China blocks. Requirements for a nonsynchronous collision; Conflicting views on the need for a promontory for the South China block.

• ∼785 Ma mafic-ultramafic cumulates in West Cathaysia formed from hydrous basaltic magmas. • Their geochemical data are consistent with arc-related cumulate petrogenesis. • They were probably formed at a crustal depth in a subduction setting. • Yangtze and West Cathaysia were not amalgamated in the Tonian, but more likely in the early Paleozoic. The Neoproterozoic tectonic setting of the West Cathaysia terrane and its relationship with the Yangtze Block are critical to understanding the formation and tectonic evolution of South China. A detailed study of late Tonian mafic-ultramafic cumulate slivers embedded in the Shenshan tectonic mélange along the northwest margin of West Cathaysia is presented here with the aim of elucidating its Neoproterozoic tectonic history. These partly-altered mafic-ultramafic rocks include olivine-bearing cumulates (olivine pyroxene hornblendite or olivine hornblende pyroxenite), pyroxene hornblendite, and gabbroic cumulates. The early crystallization of clinopyroxene and the abundance of hornblende indicate that they formed from hydrous magmas. The rocks have similar geochemical distribution patterns and show variable initial 87Sr/86Sr ratios of 0.702679 to 0.709742 and positive εNd(t) values of +2.10 to +4.52. The mineral compositions of the clinopyroxene and hornblende and their whole-rock extended normalized trace element patterns show features (e.g., negative Nb anomalies, LILE enrichment) typical of rocks with an arc affinity. The high calculated Mg# values (58–77, average 71) of the equilibrium magmas are close to those of primary mantle-derived basalts. We conclude that these mafic and ultramafic cumulates were derived from a subduction-related, hydrous, magnesian basalt in a subduction setting. The estimated crystallization temperature and pressure, based on the composition of the amphiboles, suggest that the minerals accumulated in magma chambers at middle to lower crustal depths. LA-ICP-MS U-Pb dating of zircon from the gabbroic cumulate indicates crystallization at ca. 785 Ma. A previous interpretation for West Cathaysia at this time involved a continental rift basin (the Nanhua basin) that straddled the southeastern margin of the Yangtze Block and the northwestern margin of West Cathaysia. In contrast, our results suggest that West Cathaysia was an arc at ca. 785 Ma, which supports the interpretation that the amalgamation between Yangtze and West Cathaysia did not occur in the Tonian, but more likely in the early Paleozoic. [ABSTRACT FROM AUTHOR]

To better reveal the early Neoproterozoic tectonic process of South China with respect to the assembly of the Rodinia supercontinent, an integrated dataset of geochronology, whole-rock geochemistry, and Sr-Nd-Hf isotopic compositions for diabases that intruded the Kunyang Group in the southwestern Yangtze Block is herein presented. Zircon U-Pb dating gives four weighted mean 206Pb/238U ages of 946 ± 4 Ma, 948 ± 6 Ma, 939 ± 4 Ma, and 918 ± 7 Ma, suggesting mafic magmatism in the earliest Neoproterozoic. The diabases possess Nb = 12.3–30.5 ppm, Nb/U = 19.99–37.06, Nb/La = 0.78–1.05, (Nb/Th) PM = 0.44–0.80, and (Nb/La) PM = 0.75–1.02, geochemically resembling those of typical Nb-enriched basalts. They are tholeiitic in composition with low SiO 2 (49.49–51.95 wt%), high TiO 2 (2.03–4.65 wt%), MgO (2.50–6.14 wt%), and Fe 2 O 3 T (15.38–18.84 wt%) contents. They are enriched in light rare earth elements (LREEs) with weak negative Eu anomalies (Eu/Eu* = 0.75–0.96) and show E-MORB-like characteristics with slight to moderate Nb-Ta depletion. The samples show zircon ε Hf (t) values ranging from + 5.8 to + 10.3 and whole-rock ε Nd (t) values from + 0.5 to + 0.9. These elemental and isotopic characteristics suggest that the 0.95–0.92 Ga diabases may have derived from an E-MORB-like magma source with the injection of metasomatized slab melts. Integrating previous studies with our results, we propose that the southwestern Yangtze Block evolved from an intracontinental rift to a passive continental margin in the late Mesoproterozoic, followed by the development of an earliest Neoproterozoic continental arc-back-arc basin system analogous to the Northern Okinawa Trough. The distinct tectonic processes between the southern and northern parts of the Yangtze Block at ca. 1.0–0.9 Ga favour the hypothesis that the final cratonization of the present-day Yangtze Block occurred slightly later than ∼ 0.9 Ga in response to the Rodinia supercontinent assembly. [ABSTRACT FROM AUTHOR]

Detrital provenance analysis is an effective way to understand paleogeographic change and geodynamics. In this paper, we present petrological, whole-rock geochemical and detrital zircon U–Pb geochronological analysis of Early and Middle Jurassic terrestrial clastic rocks in the Jingdezhen Basin and the Huangshan Basin in the Jiangnan domain, South China. Petrology and whole-rock geochemistry show that the source rocks are dominated by intermediate to acid component. The Chemical Index of Alteration ranges from 69 to 86, suggesting a moderate weathering history for the source rocks. The Early–Middle Jurassic sediments in the Jingdezhen and Huangshan basins were mostly sourced from magmatogenic greywackes and felsic magmatic rocks, respectively. Detrital zircons have seven age peaks at ~ 240 Ma, ~ 430 Ma, ~ 1390 Ma, ~ 1880 Ma, ~ 2500 Ma, –3200 Ma and 788–999 Ma (a wide peak). Provenance analysis indicates that the source rocks are in the Jiangnan domain, the Northwest Zhejiang Basin and the Wuyishan domain. Combining these with previous results and paleocurrent directions, we infer that the NE-trending Wuyishan and Xuefengshan domains and the nearly E–W-Jiangnan domain and Nanling tectonic belt were orogenic uplifts and watersheds during the Late Triassic to Middle Jurassic. The Early Mesozoic geodynamics in the South China Block was related to the westward subduction of the Paleo-Pacific Plate and the northward continent–continent collision following the closure of the Paleo-Tethys Ocean. [ABSTRACT FROM AUTHOR]

[Display omitted] • Arc-related mafic magmatism occurred at the latest Mesoproterozoic (1.03–1.01 Ga); • An arc–back-arc system may have developed in the southwestern Yangtze Block; • Amalgamation of the Yangtze Block at 0.9 Ga linked to the Rodinia assembly. Although the latest Mesoproterozoic tectonics of the southwestern Yangtze Block have been the focus of many recent studies, the paleogeographic configuration and related processes that controlled the South China Block with respect to the Rodinia assembly are still poorly understood. Here, an integrated dataset of zircon U–Pb geochronology, whole–rock geochemistry, and Sr–Nd–Hf isotopes of mafic intrusions from the Yonglang and Luji areas in the southwestern Yangtze Block is presented. Zircon U–Pb dating reveals that the mafic intrusions were emplaced at 1.03–1.01 Ga. These samples are divided into three groups based on mineralogical and geochemical characteristics. Group 1 meta -diabase samples exhibits calc-alkaline features and have obvious negative Nb-Ta-Ti anomalies and low zircon ε Hf (t) and whole-rock ε Nd (t) values. They may have been derived from an enriched lithospheric mantle source in an arc-related setting. Group 2 amphibolites are characterized by higher Nb contents (8.3–12.8 ppm), Nb/U, (Nb/Th) N , and (Nb/La) N ratios, resembling those of Nb-enriched basalt derived from a metasomatized mantle wedge. Group 3 meta -diabase samples have higher TiO 2 (1.7–2.8 wt%), MgO (5.4–6.5 wt%), and Fe 2 O 3 t (13.1–17.4 wt%), with obvious negative Nb-Ta anomalies and high positive zircon ε Hf (t) values, indicative of derivation from a depleted mantle affected by subducted components. Integrating previous studies with our new results, an arc–back-arc system, with northward subduction (current coordinates), is suggested to have been developed in the southwestern Yangtze Block during the latest Mesoproterozoic. Furthermore, we suggest that the amalgamation of the current united Yangtze Block may occur at ca. 0.9 Ga, which is more likely linked to the assembly of the Rodinia supercontinent. [ABSTRACT FROM AUTHOR]

• Three episodes of magmatism are firstly recognized in the Qianlishan Complex. • Initiation subduction contributed to the formation of the Ordos arc at 2.3–2.0 Ga. • HP metamorphism and syn -collisional magmatism occurred at 1.97–1.95 Ga. • The post-collisional extension caused UHT metamorphism and magmatism at 1.93–1.91 Ga. This study presents detailed petrology, major and trace element chemistry, Sr-Nd isotope, and in-situ zircon U-Pb dating and Hf-O isotopes on granites from the Qianlishan Complex of the Khondalite Belt in North China. Zircon SIMS U-Pb data indicate three episodes of Paleoproterozoic magmatism at ca. 2.06 Ga, 1.95 Ga and 1.92 Ga. Of those, the ca. 2.06 Ga hornblende monzogranites and fine-grained potassic granites display typical features of A-type granite, represented by metaluminous affinity, high FeOT/MgO ratios (3.29–5.63), and high Ga/Al and Zr + Nb + Ce + Y values with high zircon saturation temperatures (916–1000 °C). Moreover, they have positive zircon εHf values of +0.29 to +5.01 and homogenous δ18O values of 5.11–5.87 ‰, probably derived from the partial melting of calc-alkaline granitoids without addition of supracrustal rocks. The ca. 1.95 Ga garnet-bearing granites contain peraluminous minerals of garnet and muscovite and have high ASI index (>1.1) and δ18O values (7.14–9.18 ‰), indicating S-type granite. Their negative whole-rock εNd(t) values (−2.87 to −2.81) and zircon εHf(t) values (−4.06 to +1.29) suggest a source of ancient supracrustal rocks. The ca. 1.92 Ga coarse-grained potassic granites present metaluminous and magnesian signatures of I-type granite, including low A/CNK and FeOT/MgO ratios. Their negative εHf(t) values (−5.00 to −1.64) and homogenous δ18O values (5.20–6.00%) suggest that the original magma was derived primarily from enriched lower crust. The results, combined with regional geology and previous studies, establish a prolonged magmatic-metamorphic evolution of the Khondalite Belt from subduction to collision, involving ca. 2.3–2.0 Ga subduction-related arc magmatism, ca. 1.95 Ga syn -collisional high-pressure high-temperature crustal anatexis, and ca. 1.92 Ga post-collisional magmatism and synchronous ultrahigh temperature metamorphism. [ABSTRACT FROM AUTHOR]

[Display omitted] • 1.18–1.14 Ga A-type monzogranites were identified in the SW Yangtze Block. • The A-type monzogranites formed by partial melting of ancient granitic sources. • Continental rifting took place extensively in the Yangtze Block at ca. 1.2–1.1 Ga. • The Yangtze Block was not yet part of the Rodinia in the late Mesoproterozoic. The late Mesoproterozoic tectonic history of the Yangtze Block, South China in the context of the supercontinent cycles remains poorly understood due to the scarce preservation of geological records of this age. In this study, we report petrology, whole-rock geochemistry, zircon U-Pb ages and Hf-Nd isotopes for newly identified late Mesoproterozoic monzogranites from the southwestern Yangtze Block. SHRIMP and LA-ICP-MS zircon U-Pb dating results reveal that these monzogranites crystallized at ca. 1.18–1.14 Ga. All the studied samples possess typical geochemical signatures of A 1 -type granite, such as relatively high SiO 2 (73.31–77.50 wt.%), Na 2 O + K 2 O (7.14–8.09 wt.%) and Zr + Nb + Ce + Y (362–445 ppm) contents, zircon saturation temperatures (825–851 °C), and low Y/Nb ratios (0.78–1.04). They have negative whole-rock ε Nd (t) values from −6.9 to −5.7 and zircon ε Hf (t) values from −7.4 to −2.5, with consistent Nd and Hf model ages of 2.4–2.1 Ga. The parental magmas for these monzogranites were generated by partial melting of the early Paleoproterozoic crustal materials at low pressure and high temperature. Taking into account of the coeval within-plate mafic magmatism in the southwestern Yangtze Block, these ca. 1.18–1.14 Ga A 1 -type monzogranites were most likely emplaced in a continental rift setting. Available data indicate continental rifting may have occurred extensively in the Yangtze Block at 1.2–1.1 Ga, followed by oceanic plate subduction starting at 1.1 Ga. We propose the Yangtze Block was an isolated plate during 1.2–1.1 Ga and started to drift toward the Rodinia supercontinent at ca. 1.1 Ga, favoring the proposal that a coherent supercontinent did not yet exist in the late Mesoproterozoic. [ABSTRACT FROM AUTHOR]

[Display omitted] • Metavolcanic rocks of the Tonghua area were formed at ca. 2.60 and 2.52 Ga, and metamorphosed at 2.53–2.47 Ga. • The SJB and NLB experienced two episodes of crustal growth at ∼ 2.7 Ga and ∼ 2.6–2.5 Ga, and were reworked at 2.53–2.47 Ga. • The Northern Liaoning Block and Southern Jilin Block have different tectonic setting. • Metavolcanic rocks formed in a transitional inner-oceanic arc to active continental margin geodynamic setting. The Tonghua area is located on the northeastern edge of the Eastern Block of the North China Craton (NCC), and connects the Northern Liaoning Block (NLB) in the west and Southern Jilin Block (SJB) in the north. The greenstone sequences in this region are voluminous metavolcanic rocks, which mainly comprise amphibolite, pyroxene amphibolite, pyroxene/amphibole–plagioclase gneiss, and biotite–plagioclase gneiss. Here we present zircon cathodoluminescence images, U–Pb dates, and Lu–Hf isotope data, as well as whole-rock geochemical data for these rocks, in order to constrain the geodynamic evolution of the Neoarchean crust and mantle and define the crustal evolution process of the northeastern NCC. Zircons from these metavolcanic rocks can be divided into two groups, with one having a typical magmatic origin and the other a metamorphic recrystallization origin. Zircon U–Pb dating and Lu–Hf isotopic results show that the magmatic zircons have two peak ages, dated at ca. 2.60 Ga and ca. 2.52 Ga, with the former have ε Hf =+3.04 to + 9.24 and single-stage model ages (T DM) of 2.80–2.54 Ga, the younger group have ε Hf values of + 2.41 to + 7.05 and T DM values of 2.73–2.56 Ga. While the metamorphic zircons document consistent metamorphic ages at 2.47–2.53 Ga, suggesting a regional metamorphic event. Their framing into the regional background has allowed us to explore the complete Neoarchean tectonic-thermal event and further contrast the NLB and SJB in the chronology, as well as to reveal crustal growth (∼2.7 Ga, ∼2.6–2.5 Ga) and reworking (∼2.53–2.47 Ga) history in the Neoarchean. The geochemical data indicate that the rocks were divided into three types, with affinities to mid-ocean ridge basalt (N-MORB), island arc tholeiites (IATs), and continental arc basalts (CABs). Taking into account the arc-related magmatism and the distribution of ancient crystalline basement (≥2.7 Ga), it is proposed that a long-lived, active continental-margin setting may have evolved along the northeastern margin of the NCC during the late Neoarchean (∼2.5–2.6 Ga), which distinguishes the NLB and SJB. Moreover, the geochemical and Lu–Hf isotope mapping results also indicate that the NLB and SJB have different tectonic setting. We consider that the metavolcanic rocks from the Tonghua area are related to an arc–continent collision, and formed in a transitional inner-oceanic arc to active continental margin geodynamic setting during the late Neoarchean (2.6–2.5 Ga). [ABSTRACT FROM AUTHOR]

• The bimodal volcanic rocks in the western Jiangnan Orogenic Belt were formed at 820–806 Ma in a back-arc extension environment. • The final formation of the Jiangnan Orogenic Belt along the southeastern margin of the Yangtze Block occurred later than ca. 806 Ma. • Preliminary scenario for the tectonic evolution of the Jiangnan Orogenic Belt and the southeastern margin of the Yangtze Block is constructed. This study presents zircon SIMS U-Pb ages, whole-rock geochemistry and Nd-Hf-O isotope data of Neoproterozoic meta-volcanic rocks discovered from the Longsheng area of the western Jiangnan Orogenic Belt. Zircon SIMS U-Pb dating reveals that these rocks were emplaced during 820–806 Ma. The basaltic rocks are enriched in light rare earth element (LREE; [La/Yb] N = 3.38–8.40), slight negative Nb and Ta anomalies, and positive ε Nd (t) (+4.39 to +4.75) values. In addition, they possess relatively high zircon δ18O values of 7.24–10.78‰. These features, together with the SiO 2 contents (41.26–51.76 wt%), and high Mg# of 54–68, Ti/V and Ti/Y ratios of 49–68 and 415–570, suggest that they could derived from a depleted mantle source metasomatized by subduction-related melts. The dacitic rocks are high-K calc-alkaline and exhibit the characteristics of A1-type granite: typical enrichment in alkaline element, LREE ([La/Yb] N = 5.74–15.16) and large ion lithophile element (LILE), and depletion in Nb, Ta, Sr and Ti. Coupled with their different and negative ε Nd (t) (−8.75 to −9.16) compared with the basaltic rocks. This indicates that the dacitic rocks were probably generated by partial melting of crust as a result of magma underplating. The geochemical and Nd-Hf-O isotopic characteristics, together with regional geology, imply that the formation of the Longsheng bimodal volcanic rocks involves an extensional regime associated with a subduction-related environment. These new data, combined with previous results, indicate a preliminary scenario for the tectonic evolution of the Jiangnan Orogenic Belt and the southeastern margin of the Yangtze Block, which can provide significant insight into the understanding the evolution of South China. [ABSTRACT FROM AUTHOR]

• The emplacement of diabases in the Cuoke area occurred at ca. 1.14 Ga. • The SW Yangtze Block was dominated by continental rift during 1.2–1.1 Ga. • Intraplate magmatism occurred over the Yangtze Block prior to its involvement in the Rodinia assembly. The late Mesoproterozoic geodynamic setting of the Yangtze Block, South China remains largely unknown due to the scarce geological records of this age. This study presents a new dataset consisting of petrology, whole-rock geochemistry, zircon U-Pb geochronology and Hf isotopes of newly identified late Mesoproterozoic diabases in the southwestern Yangtze Block. Two diabase samples give zircon U-Pb ages of 1138 ± 4 Ma and 1141 ± 4 Ma. The diabases are tholeiitic in composition and have consistent high TiO 2 contents (2.18–2.93 wt%) but low Mg# values (41–47). They are slightly enriched in LREEs with (La/Yb) N ratios of 2.87–3.99 and show E-MORB-like trace element patterns with positive Nb-Ta anomalies. The diabase samples exhibit positive zircon ε Hf (t) values from + 9.4 to + 13.7 and whole-rock ε Nd (t) values from + 3.4 to + 4.0. These results suggest that they may have undergone negligible crustal contamination during the magma evolution and were most likely generated from partial melting of a depleted asthenosphere mantle source. The diabases possess consistent Nb/Yb (4.87–5.91) and Th/Yb (0.031–0.59) ratios, ruling out the possibility of interaction with subduction-related materials. They have high Ti/V (38–46) and Zr/Y (3.36–5.23) ratios, typical of within-plate basalts. Considering the contemporary A-type granites and alkaline basalts in the same region, intense continental rifting most likely occurred in the southwestern Yangtze Block during the late Mesoproterozoic. Widespread intraplate magmatism of 1.2–1.1 Ga in the Yangtze Block indicates that it may not have been involved in the Rodinia assembly at the time. [ABSTRACT FROM AUTHOR]

The Qianlishan Complex is a multiply deformed granulite terrane of the Khondalite Belt that represents a Paleoproterozoic continent-continent collisional orogen in the Western Block of the North China Craton. Two major stages of deformation (D 1 and D 2) were identified in the Qianlishan Complex. D 1 mainly produced NWW-trending overturned to recumbent intrafolial isoclinal folds F 1 , sub-horizontal penetrative foliations S 1 , NNE-SSW mineral lineations L 1 associated with top-to-the-SSW thrust shear, reflecting crustal thickening due to the NNE-SSW compression. D 1 was developed with the prograde (M 1) and peak (M 2) granulite-facies metamorphism. D 2 successively superposed the D 1 structures and was characterized by NWW-SEE-trending doubly plunging open to tight upright folds F 2 and minor sub-vertical axial planar foliations/cleavages S 2. D 2 was accompanied by post-peak near-isothermal decompression (M 3), probably related to exhumation following the crustal thickening. SIMS U–Pb zircon ages of deformation-related leucocratic dykes demonstrate that D 1 broadly occurred at 1976–1936 Ma and D 2 subsequently happened at 1936–1854 Ma. These results indicate that the Khondalite Belt underwent long-term (~100 Myr) polyphase deformation and high-grade metamorphism associated with magmatism. Timing constraints and kinematic compatibility suggest that the deformation sequence resulted from the NNE-SSW collision between the Yinshan and Ordos Blocks to form the Western Block at ~1.95 Ga. fx1 [ABSTRACT FROM AUTHOR]

South China is the largest block of Rodinia in southeastern Asia. It consists of the Yangtze and Cathaysia blocks, separated by the Jiangshan-Shaoxing-Pingxiang Fault. Most studies suggest that the two blocks were amalgamated in the early Neoproterozoic, and the middle Neoproterozoic vocano-sedimentary sequences on both blocks were deposited in a post-collisional rift basin (the Nanhua rift basin). Here, we conducted a geochemical and geochronological study of a turbidite sequence at the western margin of the Cathaysia Block that was previously considered to have been deposited in the Nanhua rift basin. The sedimentary rocks are characterized by bathypelagic to bathyal facies. They are composed of siliciclastic sedimentary rocks interlayered with tuffaceous materials and have geochemical compositions between felsic to intermediate arc igneous rocks. Abundant euhedral detrital zircons define a major age peak at ca. 790–770 Ma, indicating that the detrital grains were derived mostly from locally distributed syn-sedimentary middle Neoproterozoic arc igneous rocks. Predominance of zircons with ages close to the time of deposition and the whole-rock trace element compositions of the turbidite sequence also imply a convergent plate margin setting for the turbidite. The Hf isotopic compositions of the Neoproterozoic detrital zircons suggest that their provenance consisted of largely reworked crustal materials, inconsistent with a potential interpretation that similarly aged igneous rocks in the Jiangnan Orogen were the provenance. These lines of evidence, combined with other available data, suggest that the western margin of the Cathaysia Block (the West Cathaysia terrane) bears more similarities to the western and northern margins of the Yangtze Block and northern India and formed part of a Neoproterozoic subduction-accretion system located along the margin of Rodinia. We suggest that early Paleozoic strike-slip movement along the Jiangshan-Shaoxing-Pingxiang Fault played a significant role in shaping the current tectonic framework of South China by bringing the West Cathaysia terrane to its present position with respect to the Yangtze Block. [ABSTRACT FROM AUTHOR]

This paper summarizes available lithostratigraphic, tectonothermal, geochronological and geophysical data to investigate the formation and evolution of the Yinshan Block, the tectonic nature of the Ordos Block, and the subduction to collision history of the Khondalite Belt, and establishes Paleoproterozoic accretion and assembly of the Western Block of the North China Craton. New critical evidence indicates that a magmatic arc developed in the Ordos Block caused by the initiation of northward slab subduction beneath the southern margin of the Ordos Block during 2.3–2.0 Ga, which contributed to the opening of the back-arc basin between the Ordos and Yinshan blocks. And then, the north margin of the Ordos Block was then transformed into a passive-type continental margin and collided with the Yinshan Block along the Khondalite Belt to form the Western Block after final closure of the back-arc basin during 1.97–1.91 Ga. Seismic data across the Western Block including a 300-km-long south-north-trending receiver function profile and a common conversion point stacking image in depth domain obviously show its crustal structure, in which the relics of two subduction slabs were preserved beneath the Ordos Block and the Khondalite Belt, respectively. Therefore, we propose a new tectonic model to help to better constrain Paleoproterozoic accretion and assembly of the Western Block in North China. [ABSTRACT FROM AUTHOR]