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• Recognition of middle Mesoproterozoic sedimentary rocks in the northeastern Altyn Tagh orogen, southeast of the Tarim craton. • Detrital zircon U-Pb ages and Hf isotopes in the Altyn Tagh resemble those from the southern Central Asian orogenic belt. • Mesoproterozoic basements in the southern Central Asian orogenic belt show an affinity with western Amazonia associated with the peripheral accretion of Supercontinent Nuna. The Central Asian orogenic belt (CAOB) is one of the largest Phanerozoic accretionary orogens in Earth's history with myriad metal deposits. Mesoproterozoic basements are sporadically preserved along the southern CAOB. Their tectonic affinity remains controversial, which hampers us from better understanding the basic architecture and Phanerozoic tectonic evolution of the CAOB. This study identified Mesoproterozoic sedimentary rocks in the northeastern Altyn Tagh, southeast of the Tarim craton, from which detrital zircons have remarkable U-Pb age peaks at ca. 1.7 and 1.4 Ga and highly variable ε Hf (t) values from −9 to + 14, resembling those from the southern CAOB. Based on provenance tracing and comparison of available geological records, the Mesoproterozoic basements in the southern CAOB show an affinity with the Rondonian-San Ignacio Province in western Amazonia associated with the peripheral accretion of the Nuna supercontinent and were subsequently fragmented and dispersed over 3000 km in distance. Predominately juvenile 1.8–1.3 Ga magmatic rocks with a scarcity of ca. 1.4 Ga ones in southern Laurentia and southwestern Baltica preclude a possible link. Likewise, a paucity of ca. 1.4 Ga zircons and incomparable isotope signatures in North China, India, and Australia challenge their affinities with the CAOB's basements. This work focuses on the tectonic attribution of the Mesoproterozoic basements in the southern CAOB and highlights the energetic Mesoproterozoic era, during which the accretionary orogeny was intensely operative along the periphery of the Nuna supercontinent. [ABSTRACT FROM AUTHOR]

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]

This article reports new geochemical data from Permian sandstones, most probably deposited during a period of postcollisional extension, from the Yamansu, Shaquanzi, and Xingxingxia areas in the Eastern Tianshan, northwestern China, to determine and characterize their provenance and source nature. The medium- to coarse-grained sandstones are composed mainly of angular to subangular quartz and volcanic fragments, with minor plagioclase and/or microcline, suggesting proximal deposition. Although the samples show relatively large variations in SiO2 (59.7-70.8 wt%), Al2O3 (9.0-14.9 wt%), and Fe2O3T + MgO (2.3-5.2 wt%) contents, they yield low chemical index of alteration values (41-55) but high index of compositional variability values (1.06-1.78), suggestive of their derivation mainly from compositionally immature sources with weak chemical weathering. Their relatively low Zr concentrations (99-225 ppm) and GdN/YbN ratios (1.20-1.53) manifest insignificant zircon and monazite enrichments. Most of the samples are characterized by upper continental crust-like rare earth element (REE) patterns with δEu values of 0.63-0.99, reflecting dominant contributions from intermediate to felsic rocks. In particular, the Xingxingxia and Shaquanzi samples have relatively low SiO2/Al2O3 (4.51-5.82) and Th/U (2.67-3.77) ratios but high ΣREE (total REE) contents (71.8-141.1 ppm), indicative of a low degree of sedimentary sorting/recycling, whereas the Yamansu samples have higher SiO2/Al2O3 (6.30-6.57) and Th/U (3.93-5.16) ratios but low ΣREE contents (77.1-86.8 ppm), probably indicative of a higher degree of sedimentary recycling or more involvement of recycled materials. Tectonic-setting discrimination using geochemical data from the samples yielded inconsistent results, with the Xingxingxia and Shaquanzi samples dominantly plotted in or adjacent to the active continentalmargin or continental island arc field, while the Yamansu samplesmostly plotted in or adjacent to the passive margin field. Combining our findings with those of previous detrital zircon studies, we suggest that the inconsistent tectonic discriminations of the Permian sandstones most likely resulted from their receiving different proportions of source rocks that have distinct geochemical compositions. This study provides ample evidence that the geochemical compositions of sedimentary rocks within a continuous sequence or in the same depositional tectonic setting can vary significantly as a result of changes in contents of different source materials and thus that the use of tectonic-setting discrimination diagrams requires great caution. [ABSTRACT FROM AUTHOR]

[Display omitted] During Carboniferous time, tremendous juvenile arc crust was formed in the southern Central Asian Orogenic Belt (CAOB), although its origin remains unclear. Herein, we presented zircon U-Pb-Hf and whole-rock geochemical and Sr-Nd isotopic data for a suite of volcanic and pyroclastic rocks from the Khan-Bogd area in southern Mongolia. These Carboniferous pyroclastic rocks generally have some early Paleozoic zircons, probably derived from the granitic and sedimentary rocks of the Lake Zone and the Gobi-Altai Zone to the north, indicative of a continental arc nature. In addition, they have a main zircon U-Pb age of ca. 370–330 Ma, positive Hf and Nd isotopes, and mafic-intermediate arc affinity, similar to the coeval arc magmatism. Moreover, the pyroclastic rocks of the northern area have more mafic and older volcanic components with depositional time (ca. 350–370 Ma; Visean and Bashkirian stages) earlier than that in the southern area (mainly ca. 350–315 Ma; Serpukhovian and Bashkirian stages). Combining a preexisting northward subduction supported by the available magnetotelluric data with a slab rollback model of the main oceanic basin of the Paleo-Asian Ocean (PAO) during Carboniferous and Triassic times, we infer that the Carboniferous arc magmatism was probably derived from a backarc ocean triggered by slab rollback. Thus, the juvenile arc volcanism of Mongolia, together with other areas (e.g., Junggar) in the southern CAOB, represented a significant lateral accretion that terminated after the Carboniferous due to a significant contraction of the PAO. [ABSTRACT FROM AUTHOR]

In Northeast China, oceanic subduction between the Jiamusi and Songliao blocks remains topic of hot debate. The Heilongjiang Complex has been regarded as an accretionary belt resulting from the subduction of an intervening ocean between the two blocks. In this study, we carry out extensive geological, geochemical and geochronological investigations on the sedimentary rocks, amphibolites and blueschists from the Heilongjiang Complex. The detrital zircons from meta-sedimentary rocks yield U-Pb age spams ranging from 268 to 780 Ma. Whereas the interlayered amphibolites show negative Nb-Ta-Ti and positive Pb anomalies and have a protolithic age of 188.2 ± 1.0 Ma, suggesting a subduction zone or magmatic arc origin in the Jurassic. The elevated initial Sr isotopic ratios (0.708–0.711) and negative ε Nd (t) values (− 4.3 to − 1.3) provide further evidence of the modification by upper continental crust during the magma ascending. LREE/HREE and MREE/HREE ratios suggest that the magma was likely derived from the mixing of lithospheric and asthenospheric melts. The presence of low Th/Ce (0.04–0.12) and Hf/Sm (0.35–0.55), but high Zr/Hf (35.4–43.4) and Pb/Ce (0.25–0.49) ratios strongly implies a contribution from subducted sediments. The identification of active continental margin type magmas of Early Jurassic age suggests that the subduction of the oceanic plate between the Jiamusi and Songliao blocks may have started around Early Jurassic time. In addition, the blueschists have a protolithic age of 186 ± 1.1 Ma and display geochemical affinities of oceanic island basalts, suggesting that the ocean between the Jiamusi and Songliao blocks closed sometime after 186 Ma. Mineral 40 Ar/ 39 Ar dating results from the Heilongjiang Complex further indicate that blueschist- to greenschist-facies metamorphism occurred in the Middle to Late Jurassic (158–175 Ma), marking the onset of termination of the oceanic subduction. [ABSTRACT FROM AUTHOR]

The Heilongjiang Complex is a blueschist facies metamorphic belt located within the Zhangguangcailing Orogen between the Jiamusi and Songliao blocks in Northeast China. This complex has been regarded as an accretionary belt related to the subduction of an intervening oceanic domain between the two blocks. However, the timing of ocean closure and final amalgamation has not been well constrained, with different models arguing for a period of 210–180 Ma or sometime after ~ 140 Ma. This work reports in-situ detrital zircon U–Pb and Hf isotopic analyses of meta-sedimentary rocks from the Heilongjiang Complex. Detrital zircons from seven meta-sedimentary rocks samples yield U–Pb ages spanning from 1690 to 167 Ma, with main populations matching those of multi-phase magmatism in the Jiamusi and Songliao blocks. Several Precambrian age groups (600 Ma, 700 Ma, 900 Ma, 960 Ma, 1200 Ma, and 1300 Ma) are consistent with the inherited zircons from the mafic rocks in the Heilongjiang Complex. A comparison with compiled data of magmatic rocks suggests that the two blocks may have been connected to each other during Permian time. Detrital zircon dating of all siliciclastic rocks yielded the youngest age component of ~ 170 Ma, suggesting that the latest deposition of the mica schists happened at some time after ~ 170 Ma. We propose that the Jiamusi and Songliao blocks once existed as a single block around Late Permian, which underwent a rifting event in the Permian to form a rifting basin that was subsequently evolved into an oceanic domain (Heilongjiang Ocean). The closure of the Heilongjiang Ocean occurred after ~ 170 Ma. [ABSTRACT FROM AUTHOR]

In the Trans-North China Orogen (TNCO) of the North China Craton, low-grade supracrustal successions extensively occur in the Wutai, Lüliang, Zanhuang, Zhongtiao and Dengfeng Complexes from north to south. Meta-sedimentary samples from the Wutai and Zhongtiao Complexes were collected for geochemical and Nd isotopic studies and several samples from the Zanhuang and Dengfeng Complexes were also analyzed for Nd isotopic studies for comparative purpose. Most of the meta-siltstones and meta-sandstones from the Wutai and Zhongtiao Complexes are characterized by depletions in mobile elements like CaO, Sr and Na 2 O, high Chemical Index of Weathering (CIW) values and strong positive correlation between Al 2 O 3 and TiO 2 , indicating intense weathering conditions. Significant post-depositional K-metasomatism is indicated in the A–CN–K diagrams for most of the analyzed samples and the relatively high pre-metasomatized Chemical Index of Alteration (CIA) values (43–87) also imply a high degree of source weathering. Depleted transitional trace elements (Ni, Cr, Co and Sc), fractionated light rare earth elements patterns, mild negative Eu anomalies in the majority of these meta-sedimentary samples point toward felsic source rocks, including the ∼2.5 Ga granitics, TTG gneisses and the Paleoproterozoic granitics in the TNCO. Minor contribution from mafic rocks is evidenced from relative high contents of MgO, Fe 2 O 3 T , Sc and lower La/Yb N ratios in some older sequence-set samples from the Zhongtiao Complex. Our geochemical and Nd isotopic data, combined with previous studies in the lithostratigraphic sequence, provenance and depositional age, suggest that the older and younger sequence-sets of the low-grade supracrustal successions in the TNCO were deposited in the different depositional environments. The older sequence-set was deposited in a back-arc basin between the “Andean-type” continental margin arc and the Eastern Block after ∼2.1 Ga, whereas the younger sequence-set formed in a foreland basin between ∼1.88 and ∼1.80 Ga, which is consistent with the model that the collision between the Eastern and Western Blocks to form the Trans-North China Orogen occurred at ∼1.85 Ga. [ABSTRACT FROM AUTHOR]