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Considerable controversy concerns the consumption and closure processes of the North and South Altyn Oceans resulting in the formation of the North Altyn Tagh subduction-accretion belt and the South Altyn Tagh subduction-collision belt in the Altyn Tagh orogen in southeastern Tarim. This study focused on U–Pb ages and Hf isotopes of detrital zircons from early Paleozoic sedimentary rocks in the Central Altyn Tagh terrane. Our dating results revealed that the studied sedimentary rocks were deposited at ca. 467–429 Ma. The predominant early Paleozoic detrital zircons demonstrate negative εHf(t) values, highlighting their derivation from the coeval intermediate-felsic magmatic rocks sourced from ancient supracrustal materials with enriched isotopes. These inferred, enriched intermediate-felsic magmatic rocks were probably generated in different consumption and closure processes of the North and South Altyn Oceans, based on geochronology and geochemistry of the early-middle Paleozoic intermediate-felsic magmatic rocks in the Altyn Tagh orogen. A number of ca. 520–490 Ma detrital zircons were primarily derived from the coeval, enriched intermediate-felsic magmatic rocks in the local Central Altyn Tagh terrane and the adjacent North Altyn Tagh subduction-accretion belt associated with the advancing subduction of the North Altyn Ocean. The ca. 490–470 Ma detrital zircons are most prominent and suggest a derivation from the coeval, enriched magmatic rocks subject to the rollback of the North Altyn Ocean. These inferred magmatic rocks might have once existed in the region but have been intensely exhumed to be source material for the studied sedimentary rocks. A few ca. 450 Ma detrital zircons indicate a provenance from the North Altyn Tagh subduction-accretion belt during collision after the final closure of the North Altyn Ocean. In contrast, some ca. 470–460 Ma detrital zircons were probably derived from the coeval intermediate- to felsic-magmatic rocks in the Central Altyn Tagh terrane during the exhumation stage of the deep continental collision after the final closure of the South Altyn Ocean. Combination of provenance study and magmatic record provides potential to establish complicated orogenic evolution. [ABSTRACT FROM AUTHOR]

The porphyritic monzogranite of Laojunshan (eastern Qinling in central China) forms a W–E elongated pluton characterized by a varying abundance of cm-scale potassium-feldspar (Kfs) megacrysts (with or without plagioclase mantles), mafic microgranular enclaves (MMEs) and associated mafic dykes. The measurements of the shape preferred orientation of Kfs megacrysts and the tiling of megacrystic pairs throughout the pluton suggest that these megacrysts constitute magmatic foliations subparallel to the pluton's margin, possibly resulting from eastward non-coaxial magmatic flow. Felsic-mafic magma mixing and mingling were important during magma emplacement, as indicated by abundant MMEs, coeval mafic dykes and disequilibrium textures within Kfs megacrysts. Quantitative analyses of the crystal size distribution and the in-situ chemistry of Kfs megacrysts revealed that the temperature fluctuation in the deep magma chamber and the resultant textural coarsening are the most likely important mechanisms for the growth of Kfs megacrysts. The syn-tectonic and two-main-stage emplacement of the pluton in a sinistral transtensional regime is inferred by the mechanical coupling between magmatic–submagmatic–solid-state fabrics in the pluton and wall-rock deformations, as well as zircon U–Pb dating results, which produce eastward younging emplacement ages spanning from ∼122 Ma to ∼119 Ma. Combined with other studies, our work supports the idea that the Qinling-Dabie orogen was in a sinistral transtensional regime during the Early Cretaceous, which may correspond to the eastward extrusion tectonics in eastern China. [ABSTRACT FROM AUTHOR]

Abstract: The Machaoying fault zone extends along the southern margin of the North China Craton (NCC) and controlled the regional structures and hydrothermal mineral systems in this area. The fault underwent at least two major deformational phases, as revealed by macro- and micro-structural observations from a well-developed segment of the fault in the Hongzhuang–Baitu area, located south of the Xiong''er Mountains. Early ductile deformation is characterized by thrusting from north to south, which was subsequently overprinted by late brittle faulting. Syntectonic strain shadows of biotite are preserved around rotated porphyroclasts of quartz amygdales in mylonite. The biotite yields a 40Ar–39Ar plateau age of 524.9±1.9 Ma, which is interpreted as the time of regional thrusting along the Machaoying fault zone. The thrusting may be temporally correlated with an Early Cambrian discontinuity in sedimentation observed in the rocks sequences of the NCC, suggesting a compressional regime in this area and a craton-wide tectonic event. Many 540–500 Ma tectonic events have been previously identified in the Qinling–Qilian–Kunlun Orogenic Belt of central China and in massifs in northeastern China, both of which surround the NCC, and some of these were interpreted to be associated with assembly of Gondwana. However, paleomagnetic data indicate that the NCC was unlikely to have been connected with Gondwana in the Early Cambrian and thus our new biotite date cannot record deformation along the Gondwanan margin. Dating of K-feldspar from a quartz–K-feldspar vein formed along one of the brittle faults of the Machaoying fault zone yields a much younger 40Ar–39Ar plateau age of 119.5±0.7 Ma. This is a minimum age for the brittle deformation along the southern margin of the NCC, which also overlaps the age of widespread gold and molybdenum mineralization in the region. [Copyright &y& Elsevier]

Abstract: We report SHRIMP U–Pb zircon ages from K-bentonite beds from different locations in the Xiamaling Formation near Beijing at the northern margin of the North China Craton (NCC). The 1379±12 Ma and 1380±36 Ma ages obtained in our study correlate with similar data (1368±12 Ma) obtained from recent studies and assign a Mid-Mesoproterozoic (Ectasian Period) age for the formation. In addition, a detailed bed-by-bed study of the K-bentonite sequence indicates that the present dated successions northwest of Beijing can be correlated fairly well with that of the well-known Meso- to Neoproterozoic standard section in Jixian to the east of Beijing. The new data call for a major revision of the previous Meso- to Neoproterozoic chronostratigraphic subdivision of the northern NCC, with a revised calibration into the early to middle Mesoproterozoic Era. Our data suggest that the Tawuia-bearing assemblage in the lower part of the Xiamaling Formation in the NCC could be older than ~1380 Ma, and is not limited to a representative feature of the Neoproterozoic Little-Dal-Group-type macroalgal biota. Combined with other similar discoveries, we conclude that the macro-evolution of Proterozoic eukaryotic biotas, represented by macroalgal assemblages, would have probably been a long, protracted, and somewhat monotonous process. On the other hand, reassessment of the paleomagnetic database for these successions, combined with stratigraphic correlations and similarities in the macroalgal assemblages on the NCC and Laurentia, support a configuration in which the NCC was in close proximity to the Laurentia–Siberia–Baltica grouping during much of the Mesoproterozoic to Neoproterozoic time. Furthermore, our study suggests recent assumptions linking δ 34SCAS and δ 13Ccarbonate fluctuations in the Jixian section with the assembly and breakup of Rodinia must now be reconsidered, as these fluctuations may correlate better with the tectonics associated with the Columbia supercontinent cycle. [Copyright &y& Elsevier]

Connecting the North China Craton to the east and the Tarim Craton to the west, the Alxa Terrane is a key place in investigating the timing of the final closure of the Paleo-Asian Ocean (PAO). New LA-ICPMS zircon U–Pb dating results reveal ca. 300–268 Ma gabbros and diorites in the Bayan Nuru area in the eastern part of the Alxa Terrane. The ~ 300 Ma gabbros show plagioclase accumulations with anorthite compositions, arc-like geochemical affinities with relative enrichment in large ionic lithophile elements and depletion in high field strength elements (e.g., Ti, Nb and Ta), as well as negative ε Hf (t) and ε Nd (t) values and high initial 87 Sr/ 86 Sr ratios. These features indicate a magma source of an enriched lithospheric mantle metasomatized by high fluid activities. In comparison, the 280–268 Ma gabbros and diorites also have arc-like geochemical affinities but show increasingly evolved isotope compositions, implying more sediment inputs. Compiled zircon ε Hf (t) and whole-rock ε Nd (t) values of the magmatic rocks in the Alxa Terrane decrease from the Late Carboniferous to the Early Permian, and increase from the Middle Permian to the Triassic. The significantly large variation in zircon ε Hf (t) and whole-rock ε Nd (t) values at ca. 280–265 Ma likely reflects a tectonic switch from a subduction setting to a post-collisional setting, corresponding to the timing of the final closure of the PAO in the Alxa Terrane. Thus, the PAO progressively closed from west to east along the northern margin of the Tarim Craton, the Alxa Terrane, and then the northern margin of the North China Craton during Late Carboniferous to Middle Triassic time. [ABSTRACT FROM AUTHOR]

• Late Neoproterozoic gabbro was first found in the northeastern margin of the Yangtze Block. • The gabbro originated from enriched lithospheric mantle in the setting of intracontinental rift. • The discovery of gabbro indicates that the breakup of Rodinia lasted until the late Neoproterozoic. Late Neoproterozoic tectonic evolution of the Yangtze Block is crucial for better understanding the breakup of Rodinia. The reported mafic magmatism related to the breakup event mainly distributed in the northwestern margin of the Yangtze Block. For the first time this study found a Late Neoproterozoic meta -gabbro pluton in the northeastern margin of the Yangtze Block. By means of petrography, zircon U–Pb geochronology, geochemistry and zircon Hf isotope, the formation age, petrogenesis and tectonic setting of the meta -gabbro pluton were determined and discussed. Dating results show that the pluton was formed at 642–636 Ma, reflecting an important magmatic event during the late Neoproterozoic. Geochemical characteristics indicate a tholeiite series for the meta -gabbro rocks, with positive anomalies of Th, La, Pb, Nd and negative anomalies of Nb, Ta, Zr, which are similar to intraplate basalts contaminated by the crust. The zircon 176Hf/177Hf ratios range from 0.282356 to 0.282563, with εHf(t) values ranging from + 0.74 to + 1.44. The two-stage Hf model ages range from 1289 Ma to 1748 Ma. Magma source of the meta -gabbro was mainly derived from an enriched mantle, which was evolved from the lithospheric mantle metasomatized by slab-derived melts and contaminated by a small amount of lower crust materials during magma ascent. Together with regional tectonics, we inferred that the meta -gabbro pluton was formed under the setting of intracontinental rift. Our result not only enriches the late Neoproterozoic magmatic activity events in the northern margin of the Yangtze Block, but also provides new evidence for the block involved in the late breakup of the Rodinia. [ABSTRACT FROM AUTHOR]

The closure time of the Karamaili Ocean is the key to understand the accretionary history of the East Junggar at the southern Central Asian Orogenic Belt in the Paleozoic. In this study, we report geochronology, whole-rock elemental and Sr-Nd isotopic data and zircon Lu-Hf isotopic data of four Late Carboniferous to Early Permian I- and A-type granitic plutons in the Karamaili region in East Junggar, NW China. The Carboniferous Hongliuxia gneissic granite and the Hongliugou granodiorite yield zircon 206Pb/238U ages of 324 ± 1 Ma and 306 ± 1 Ma, respectively, and both of them are high-K calc-alkaline and belong to I-type granitoids. These granites show (87Sr/86Sr) i values from 0.7034 to 0.7046, ɛ Nd (t) values from 4.4 to 6.3, with Nd T DM2 model ages of 559–727 Ma; and ɛ Hf (t) values from 9.4 to 12.8, with Hf T DM2 model ages of 481–710 Ma. The variable positive Nd-Hf isotopic signature and young T DM2 model ages suggest that the I-type granitoids were derived from partial melting of juvenile crustal source, probably earlier arc intrusion. The Early Permian Daliugou and Mawangmiao plutons have 206Pb/238U ages of 297 ± 1 Ma and 284 ± 2 Ma, respectively, show high-K calc-alkaline to shoshonitic characteristics and belong to A 2 -type granite. They exhibit (87Sr/86Sr) i values from 0.7040 to 0.7065, ɛ Nd (t) values from 2.1 to 5.4, with Nd T DM2 model ages of 612–887 Ma; and ɛ Hf (t) values from 5.2 to 11.5, with Hf T DM2 model ages ranging from 548 Ma to 955 Ma, and the Nd-Hf isotope data also suggest that they were derived from juvenile crustal source. Mafic microgranular enclaves in the Daliugou pluton yield zircon 206Pb/238U age of 299 ± 2 Ma, and show similar geochemistry affinity with the granite host. The presence of enclaves and reverse zoning K-feldspars indicate that the magma mixing may have played an important role in the evolution of the Daliugou pluton. In this study, only the Hongliuxia gneissic granite was deformed, and a Nd-Hf isotopic transition occurred at ~300 Ma. Furthermore, the Late Carboniferous I-type granitoids from the Hongliuxia and the Hongliugou plutons show an arc affinity, and the Early Permian A-type granitoids from the Mawangmiao and the Daliugou plutons show post-collisional affinity. These lines of evidence enable us to argue that the Karamaili Ocean probably closed at a period between 324 Ma and 306 Ma. The post-collisional Early Permian magmatism in East Junggar was independent from the Tarim mantle plume. [Display omitted] • The Late Carboniferous granitic magmatism along the Karamaili ophiolite belt is I-type. • The Early Permian granitic magmatism along the Karamaili ophiolite belt is A-type. • Magma mixing may have played an important role in the East Permian A-type magmatism. • The closure of the Karamaili Ocean probably occurred between 324 Ma and 306 Ma. • The Early Permian magmatism was independent from the Tarim mantle plume. [ABSTRACT FROM AUTHOR]

The closure of the Junggar Ocean between the Central Tianshan and Junggar terranes is essential in understanding the final assembly of the southern Central Asian Orogenic Belt. This study presents new whole-rock geochemical, Sr–Nd and zircon U–Pb–Hf isotopic data for mafic–intermediate intrusions from the Central Tianshan block to provide robust constraints on the final closure of the ocean. LA-ICP-MS U–Pb dating on magmatic-type zircons yields weighted mean 206 Pb/ 238 U ages of ca. 310 Ma and ca. 290 Ma, which are interpreted as the crystallization ages of the intrusions. Petrographic and geochemical analyses of the Late Carboniferous mafic–intermediate rocks, characterized by typical subduction-related signatures, low Sm/Yb (< 2.0) but high Lu/Hf (≥ 0.2) ratios and positive ε Nd (t) (+ 1.2 to + 3.1) and zircon ε Hf (t) (+ 4.1 to + 7.8) values, suggest that their parental magmas were most likely generated by the partial melting of a metasomatized lithospheric mantle wedge in the spinel stability field and emplaced in a continental arc setting. This consideration is consistent with the occurrence of Carboniferous ophiolitic and arc-related granitoids in the region, probably as a result of the southward subduction of the Junggar oceanic plate. In contrast, the Early Permian mafic magmatism exhibits typical within-plate basalt affinities, such as high TiO 2 (2.7–3.2 wt.%) contents, elevated Ti/V (86.0–115.1) and Zr/Y (4.9–9.3) ratios, OIB-like trace element patterns and high ε Nd (t) (+ 1.1 to + 4.5) and zircon ε Hf (t) (+ 3.0 to + 9.8) values. In association with previous investigations, we suggest that their protoliths were most probably derived from the partial melting of an asthenospheric mantle source in the garnet stability field, plausibly induced by asthenosphere upwelling during the slab break-off of the Junggar oceanic plate, which agrees well with the linear distributions of Permian mafic–ultramafic rocks in the Eastern Tianshan. Collectively, our data pinpoint a tectonic transition from oceanic subduction to post-collisional extension during Late Carboniferous to Early Permian time, probably triggered by the closure of the Junggar Ocean and subsequent arc–continent collision between the Central Tianshan and Junggar terranes that gave rise to the final assembly of the Eastern Tianshan. [ABSTRACT FROM AUTHOR]

• A phase equilibrium model study of garnet mica schists in the northern Tarim reveals two clockwise P-T paths. • The Barrovian metamorphic series developed in the northern Tarim, represented by the Upper Xingditage Group (high T/P) and the Lower Xingditage Group (low T/P). • The northern Tarim became a part of the Columbia supercontinent at ∼ 1.91 Ga. • The northern Tarim has an affinity with southwest Siberia during the assembly of the Columbia supercontinent. The Tarim Craton has been considered a part of the Columbia supercontinent. However, the paleogeographic location of the Tarim Craton remains ambiguous or has not been considered in the reconstruction model. This problem is partly due to the dispute over the collisional time between northern Tarim and major Columbia blocks. The Xingditage Group in the Kuluketage area records important information on the Paleoproterozoic evolution of northern Tarim during the Columbia supercontinent convergence, in which the garnet mica schist unit is key to constraining the collision time. We carried out petrographic, phase equilibrium modeling, and zircon U-Pb chronological studies for two garnet mica schist samples (LJS-1 and LJS-2) from the Lower Xingditage Group. This study attempted to constrain the collision time of the northern Tarim in the late Paleoproterozoic from the metamorphic evolution perspective. Petrography shows that both samples are rutile-kyanite-garnet mica schist. The phase equilibrium modeling reveals two clockwise P-T paths. For the sample LJS-1, the peak stage was constrained at ∼ 780 °C/12 kbar and subsequently decompressed to ∼ 760 °C/4 kbar. For sample LJS-2, the peak pressure is relatively higher, reaching ∼ 790 °C/16 kbar, followed by decompression to ∼ 796 °C/3 kbar. Both P-T paths have a near isothermal decompression path, indicating a rapid exhumation process. Zircons in this study record a metamorphic age of 1907 ± 8 Ma, which can represent the collision age of northern Tarim in the late Paleoproterozoic. We propose that the northern Tarim experienced a long-lived orogenic event in the late Paleoproterozoic, and the northern Tarim became a part of the Columbia supercontinent at ∼ 1.91 Ga. In comparison with orogenic belt evolution, an affinity with southwest Siberia was established for northern Tarim during the assembly of the Columbia supercontinent. [ABSTRACT FROM AUTHOR]

The geological attraction of the Heilongjiang Complex, extending along a suture zone between the Jiamusi and Songliao blocks in Northeast China, resides in excellent exposures of blueschists, which occur in association with granitic gneisses, marbles, meta-ultramafic rocks, greenschists, quartzites, muscovite–albite schists and two-mica schists from the complex. However, controversy has long surrounded the ages and tectonic settings of mafic protoliths of the blueschists from the complex. The lithological association and major and trace element compositions indicate that the ultramafic–mafic protoliths of the Yilan blueschists can be subdivided into the tholeiitic and alkali groups, both of which were derived from partial melting of garnet-facies peridotites, but at different degrees of melting. Magmatic zircons from a tholeiitic blueschist sample yield a 206 Pb/ 238 U age of 275 ± 2 Ma, interpreted as its protolithic age. The sample also contains large amounts of older inherited zircons up to 1200 Ma, which, together with the geochemical features of the sample, indicate that the tholeiitic basalts were generated in a continental rift. The further development of the rift led to the formation of an ocean between the Jiamusi and Songliao blocks, in which some ocean islands developed, represented by the alkali mafic protoliths of the Yilan blueschists, as supported by geochemical data. Magmatic zircons from an alkaline mafic blueschist sample yield a 206 Pb/ 238 U age of 141.8 ± 1 Ma, indicating that the ocean between the Jiamusi and Songliao blocks had not been closed by ~ 141 Ma, not at 210–180 Ma as previously considered. [ABSTRACT FROM AUTHOR]