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Early Carboniferous magmatism of the southern West Junggar (SWJ) region is essential for understanding the accretionary processes and crustal growth in the southwestern segment of the Central Asian Orogenic Belt. A comprehensive study of geochronological, geochemical, and Sr-Nd-Pb-Hf isotopic compositions was carried out in this study for basalts from the Baogutu Formation in Sulushuoke region, aiming to provide constraints on the Early Carboniferous tectonic evolution of the SWJ, NW China. LA-ICP-MS zircon U-Pb dating of four basalt samples yielded crystallization ages ranging from 339 Ma to 347 Ma, indicating the presence of early Carboniferous volcanic rocks in West Junggar. The studied tholeiitic basalts are geochemically characterized by nearly flat REE patterns, enriched large iron lithosphere elements (e.g. K) and depleted high field strength elements (e.g. Nb, Ta, Zr, Hf) relative to those in N-MORB, resembling those of modern Mariana Trough back-arc basin basalts. In addition, they have high positive εNd(t) values (+5.86 to +6.59) with initial 87Sr/86Sr ratios in the range of 0.704783–0.705315 and variable εHf(t) values (+3.99 to +15.6). The rocks cover restricted ranges in initial Pb isotope ratios with (206Pb/204Pb)i from 17.529 to 18.289, (207Pb/204Pb)i from 15.509 to 15.627, and (208Pb/204Pb)i from 37.628 to 38.397. These signatures indicate that the tholeiitic basalts were derived from 10% to 20% partial melting of a spinel-lherzolitic N-MORB-like depleted mantle source modified by fluids released from the subducted lithosphere in a back-arc extensional setting. From our new data presented in this study and in conjunction with those from previous works, we, therefore, suggest that a back-arc basin related to the northwestward subduction of the Junggar oceanic crust was developed in the Hatu-Baogutu region during the early Carboniferous time. [ABSTRACT FROM AUTHOR]

The Devonian volcanic rocks are widely distributed in the East Junggar (Xinjiang, NW China), preserving important magmatic records for investigating Palaeozoic tectonic evolution. The Beitashan Formation is mainly composed of pyroclastic rocks and sedimentary rocks in the lower section and intermediate–basic volcanic lava and pyroclastic rocks in the upper section. In this paper, we present geochronological, geochemical, and in situ Lu–Hf isotopic data for Beitashan Formation volcanic rocks from the East Junggar. Zircon U–Pb analyses from a basalt sample by laser ablation inductively coupled plasma mass spectrometry yielded a weighted mean age of 387.8 ± 4.5 Ma, indicating that it was generated in the Middle Devonian. The basic–intermediate volcanic rocks are tholeiitic to calc‐alkalic and are characterized by MgO (2.29–5.91 wt.%), low TiO2 (0.75–1.36 wt.%), and relatively high Al2O3 (15.82–16.73 wt.%). Furthermore, they display enrichment in light rare‐earth elements and large‐ion lithophile elements (such as Ba and Sr) and depletion in Nb, Ta, and Ti, along with slightly positive Eu anomalies (δEu = 0.83–1.15) and Ce anomalies (δCe = 1.00–1.11). In addition, in situ zircon Hf isotopic analyses from basalt samples show εHf(t) values ranging from +4.33 to +15.2, indicating a depleted mantle source with minor crustal contamination. They also show relatively low Nb/Zr (0.04–0.06), Th/Yb (0.67–3.83), and Ba/La (6.79–67.53) and high Ce/Th (7.71–18.94), Ba/Rb (21.39–294.28), and Ba/Th (31.42–486.58). The geochemical data suggest these rocks were likely derived from 10% to 30% partial melting of a garnet‐rich with minor spinel‐bearing Iherzolite depleted mantle metasomatized by slab‐derived fluids, with crustal contamination. Combined with the geological setting and previous studies, we suggest that the northern East Junggar was in a northward‐subducted island‐arc setting in the Devonian. [ABSTRACT FROM AUTHOR]

West Junggar is located at the southwest margin of the Central Asian Orogenic Belt and includes Silurian pillow basalts of the Mayilashan Formation. The petrogenesis and tectonic setting of these pillow basalts are important for the understanding of the tectonic evolution and metallogeny of the West Junggar area. This paper presents geochronological, geochemical, and whole‐rock Sr–Nd–Pb isotope data from the pillow basalts of the Mayilashan Formation. Zircon LA‐ICP‐MS U–Pb dating of a pillow basalt, which is in conformable contact with the chert, suggests that they were erupted at 437.2 ± 2.2 Ma marking the timing of generation of these rocks as Middle Silurian. Geochemically, all the pillow basalts bear the signature of ocean island basalt (OIB), and are characterized by alkaline affinity with high concentrations of TiO2 (3.28–4.12 wt.%), LILE and LREE enrichment and HREE depletion ((La/Yb)N = 5.5–7.3), with very weak Eu anomalies (Eu/Eu* = 0.96–1.06), and no obvious Nb, Ta, or Ti negative anomalies. Their Sr–Nd–Pb isotopic compositions ((87Sr/86Sr)I = 0.7037–0.7051, εNd(t) = 1.9–2.9, 206Pb/204Pbi = 17.74–18.22, 207Pb/204Pbi = 15.48–15.52, and 208Pb/204Pbi = 36.49–37.86) show Dupal‐like isotopic signature of ophiolites in the southern Paleo‐Asian Ocean. These characteristics indicate that the magmas were derived from a deep OIB reservoir, that is, a depleted but slightly heterogeneous asthenospheric mantle source with ~5–15% partial melting of garnet and spinel lherzolite. Our obtained results, in conjunction with previous published data, allow us to suggest that the alkaline pillow basalts formed in a seamount within an intraoceanic setting, where a larger number of seamounts with different ages occurred in the Paleo‐Asian Ocean. [ABSTRACT FROM AUTHOR]

The Zoige Depression is an important depocenter zone within the northeast of the Songpan-Ganzi Flysch Basin, which is bounded by the South China, North China, and Qiangtang blocks, and also forms the northeastern margin of Tibetan Plateau. This paper discusses the provenance of Middle to Late Triassic sedimentary rocks in the Zoige Depression using petrography, heavy mineral assemblages, and zircon U-Pb geochronology. The results demonstrate that the detritus is derived from multiple source regions. Four distinct parent rocks can be distinguished based on the heavy mineral assemblages and lithic fragments: Provenance 1 predominantly comprises intermediate-acidic volcanic rocks; Provenance 2 includes high-grade metamorphic rocks; Provenance 3 contains a mixture of various detrital components; and Provenance 4 primarily consists of mafic volcanic rocks. The different U-Pb ages of the zircons from the Middle to Late Triassic ranging from 260 to 280, 429-480, 792-974, and 1,800-2,500 Ma represent distinct source regions, which are comparable to the 4 provenances mentioned above: Provenance 1 (260-280 Ma), Eastern Kunlun Orogen; Provenance 2 (429-480 and/or 1,800-2,500 Ma), Qinling orogeny (mainly in North Qinling); Provenance 3 (1,800-2,500 Ma), the North China Block; and Provenance 4 (792-974 Ma), the Yangtze Block. Overall, the detritus in the Middle Triassic (Ladinian, T2zg) primarily originates from the Eastern Kunlun Orogen and North Qinling. During the Late Triassic (Early Carnian, T3z), the southern margin of the North China Block was likely transported westward to the basin by a river network between the North China and South China blocks flowing through the Qinling region, because of the predominance of the detrital zircon age ranging from 1,800 to 2,500 Ma and the occurrence of quartz sandstone with visible enlargement texture. Since the Late Triassic (Middle Carnian, T3zh), great changes have occurred in the source terrains, such as the absence of sources of the Eastern Kunlun Orogen and North China Block and the predominance of Yangtze Block. This drastic change can be explained by the Triassic collision between the South China and North China blocks, and the clockwise rotation of the South China Block progressively closed the basin and uplifted the Qinling orogeny. [ABSTRACT FROM AUTHOR]

We present an overview of the internal structure of the 10 ophiolitic mélanges in the Central China Orogen (CCO) with a focus on the geochemical character and tectonic evolution of the ophiolitic mélange-related ocean island basalt (OIB) and mafic rock assemblages. The ophiolitic mélanges in CCO are generally complicated and usually consist of metamorphic peridotites (serpentinite), cumulates, gabbros, basaltic lavas (pillows), and abyssal radiolarian cherts. The ages of ophiolitic mélanges range from Mesoproterozoic to Carboniferous. The OIB-type basalts and mafic rocks in CCO occur as tectonic blocks within the mélanges that are composed of limestones, radiolarian cherts, and turbidites, possessing formation characteristics of seamounts (oceanic islands/plateau). The mafic rocks in ophiolitic mélanges of CCO display uniform chondrite-normalized rare earth element (REE) patterns with light REE enrichment and heavy REE depletion, no obvious Eu anomalies or negative Nb, Ta, and Ti anomalies, and primitive mantle-normalized trace element patterns with significant large-ion lithophile element enrichment, similar to those of modern OIB and the Hawaiian alkaline basalts. The OIB-type basalts and mafic rocks are considered as accreted seamount fragments in an accretionary complex of CCO and may represent plume-related magmatism within the Proto-Tethys Ocean and Paleo-Tethys Ocean. Our study provides further insights into the processes of multiple subduction and long-lasting accretionary histories with seamounts in the CCO. [ABSTRACT FROM AUTHOR]

Zircon U–Pb geochronological and geochemical analyses are reported for a suite of the early Carboniferous volcanic rocks from West Junggar (Northwest China), southern Central Asian Orogenic Belt (CAOB), with the aim to investigate the sources, petrogenesis, and tectonic implications. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb analysis from an andesite yielded concordant weighted mean206Pb/238U age of 345 ± 3 Ma, indicating the presence of early Carboniferous volcanic rocks in West Junggar. The early Carboniferous volcanic rocks consist of basalt, basaltic andesite, and andesite. Geochemically, all the samples bear the signature of ocean island basalt (OIB), and are characterized by alkaline affinity with minor variations in SiO2compositions (45.13–53.05 wt.%), high concentrations of Na2O + K2O (5.08–8.89 wt.%) and TiO2(1.71–3.35 wt.%), and LREE enrichment and HREE depletion ((La/Yb)N = 7.1–12.4), with weak Eu anomalies (Eu/Eu* = 0.9–1.1) and no obvious Nb, Ta, and Ti negative anomalies. These features suggest that the early Carboniferous volcanic rocks were derived from an OIB-related source that consists of oceanic lithosphere with ~1–3% degree partial melting of garnet lherzolite. From these observations, in combination with previous work, we conclude that the early Carboniferous alkaline volcanic rocks in Karamay region formed by upwelling of asthenospheric mantle through a slab window in a forearc setting during consumption of the West Junggar Ocean. Meanwhile, seamounts, which formed in the Late Devonian and were accreted and subducted in Karamay arc, also brought geological effects in the subduction zone. [ABSTRACT FROM AUTHOR]

Zircon U–Pb geochronological and geochemical analyses are reported for a suite of the middle Silurian volcanic rocks from northern West Junggar (NW China), southern Central Asian Orogenic Belt (CAOB), with the aim to investigate the sources, petrogenesis, and tectonic implications. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb analysis from an andesite yielded a concordant weighted mean206Pb/238U age of 429 ± 3 Ma, indicating the presence of middle Silurian volcanic rocks in northern West Junggar. The andesite is tholeiite series and characterized by minor variations in compositions (SiO2 = 55.68–59.17 wt.%, Al2O3 = 14.56–17.7 wt.%, TiO2 = 0.55–1.23 wt.%, Na2O + K2O = 3.46–7.16 wt.%, and P2O5 = 0.15–0.37 wt.%), with wider MgO content (2.18–6.48 wt.%) and Mg# (57.4–77.9). All andesitic rocks are enriched in large-ion lithophile elements (LILEs; e.g. Rb, Ba, K, and Th) and light rare earth elements (LREEs), but strongly depleted in some high field strength elements (HFSEs; e.g. Nb, Ta and Ti), with slight negative Eu anomalies (Eu/Eu* = 0.8–1). These features suggest that the andesitic magmas were derived from 2–8% partial melting of a garnet lherzolite depleted mantle source with subducted sediments metasomatized by slab-derived fluids. Combining the current study with those data in existing literature, we conclude that the middle Silurian volcanic rocks formed in an intra-oceanic subduction setting during consumption of the Irtysh–Zaysan Ocean, and further confirm the eastern extension of the early Palaeozoic Boshchekul–Chingiz volcanic arc of East Kazakhstan in China. [ABSTRACT FROM AUTHOR]

The paper presents new U–Pb zircon ages and geochemical data from early Carboniferous volcanic rocks of the Wuerkashier Mountains in the northern West Junggar region, NW China, and of the Char suture–shear zone in East Kazakhstan. The study included analysis of geological setting, major and trace elements, and rock petrogenesis. Both localities host early Carboniferous volcanic units dominated by plagioclase-porphyry andesites and dacites. A West Junggar dacite yielded a206Pb/238U age of 331 ± 3 Ma. The Junggar volcanic rocks are tholeiitic, and the Char samples are intermediate between tholeiitic and calc-alkaline. Both the Junggar and Char volcanic units are characterized by LREE enriched rare-earth spectra (La/Smn = 1.1–2.4) with Eu negative anomalies (Eu/Eu* = 0.12–1.0) and Nb-Ta minimums (Nb/Thpm = 0.15–0.35; Nb/Lapm = 0.3–0.7) on multi-element spectra. The Junggar andesites and dacites have higher REE and HFSE (Ti, Nb, Zr, Y, and Th) compared with the Char rocks, suggesting their derivation from a different mantle source. The melting modelling in the Nb-Yb system showed that the Junggar volcanic rocks formed by low- to medium- (2–5%) degree melting of depleted mantle harzburgite and spinel lherzolite. The Char volcanic rocks formed by high-degree melting (15–20%) of spinel lherzolite and garnet-bearing peridotite. The regional geology of West Junggar and East Kazakhstan and the geochemical features of the rocks under study (i.e. depletion in Nb, Ta, and Ti and enrichment in Th, and combination of LREE enrichment and HFSE depletion) all suggest a subduction-related origin of both Junggar and Char volcanic rocks. The early Carboniferous volcanic rocks of West Junggar possibly formed by subduction of the Junggar-Balkhash ocean beneath an active margin of the Kazakhstan continent, whereas those of East Kazakhstan formed by subduction of the Irtysh-Zaisan Ocean beneath an intra-oceanic arc at the active margin of the Siberian continent. [ABSTRACT FROM AUTHOR]

U–Pb zircon geochronological, geochemical, and whole-rock Sr–Nd isotopic analyses are reported for a suite of Karamay A-type granites from the Central Asian Orogenic Belt (CAOB) in the western Junggar region of northern Xinjiang, Northwest China, with the aim of investigating the sources and petrogenesis of A-type granites. The Karamay pluton includes monzogranite and syenogranite. Laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb dating yielded a concordant weighted mean206Pb/238U age of 304 ± 5 Ma (n = 11), defining a late Carboniferous magmatic event. Geochemically, the rock suite is characterized by high SiO2, FeOt/MgO, total alkalies (K2O + Na2O), Zr, Nb, Y, Ta, Ga/Al, and rare earth elements (REEs) (except for Eu), and low contents of MgO, CaO, and P2O5, with negative Ba, Sr, P, Eu, and Ti anomalies. These features indicate an A-type affinity for the Karamay granitic intrusions. Isotopically, they display consistently depleted Sr–Nd isotopic compositions (initial87Sr/86Sr = 0.7014–0.7022, ϵNd(t) = +5.6–+7.0). Geochronological, geochemical, and isotopic data suggest that the Karamay A-type granites were derived from remelting juvenile lower crust, followed by fractional crystallization. The Karamay A-type granites as well as widespread late Carboniferous magmatism in the western Junggar region of the southwestern CAOB may have been related to ridge subduction and a resultant slab window. This further demonstrates the importance of the late Palaeozoic granitic magmatism in terms of vertical crustal growth in northern Xinjiang. [ABSTRACT FROM AUTHOR]

Abstract: The Darbut Ophiolitic Complex consists of ultramafic rocks, cumulates, pillow lavas and abyssal radiolarian cherts, and occurs in the Sartuohai–Suluqiaoke area which is situated in the eastern part of the West Junggar (NW China), Southern Altaids. In the present study, we report new geochronological and geochemical data obtained for gabbro and basalt blocks embedded in the Darbut Ophiolitic Complex. Zircon U–Pb analyses from one representative gabbro sample by LA-ICP-MS yielded a weighted mean age of 391±6Ma, showing that it was emplaced in the Middle Devonian. The samples bear N-MORB, E-MORB, and arc-like geochemical signatures. They are tholeiitic in composition with low concentrations of Na2O+K2O varying from 1.36 to 4.09wt.%, Mg and Ti depleted, large ion lithophile elements (LILEs) enriched, with insignificant negative Eu. They also show negative Nb–Ta anomalies and high positive ε Nd(t) values, with relative high La/Nb, Ba/Nb, Ba/La, Ba/Th and Zr/Nb ratios. We interpret that these volcanic rocks were derived from a slightly metasomatized depleted mantle source in a back-arc basin setting, which corresponds to 10–30% partial melting of a depleted spinel lherzolite mantle. The data presented here in combination with previously published data suggest a northwestward subduction model for the West Junggar. During the period of the Early Devonian to Early Carboniferous, the West Junggar was dominated by normal northwestward subduction, and the ridge subduction commenced in the Late Carboniferous. [Copyright &y& Elsevier]

Highlights from the article: The cover image, by Gaoxue Yang et al., is based on the Research Article I Petrogenesis of pillow basalts in West Junggar, NW China: Constraints from geochronology, geochemistry, and Sr-Nd-Pb isotopes i . https://doi.org/10.1002/gj.3078. GRAPH.

Alkaline basalts are common constituents in many ophiolite belts and accretionary complexes. Here we report geological, geochronological, geochemical, and whole-rock Sr–Nd isotopic data for alkaline basalts from the Karamay ophiolitic mélange of West Junggar, southern Central Asian Orogenic Belt (CAOB). In the ophiolitic mélange, imbricate thrusts, duplexes, “web” structures, pinch-and-swell structures, tilted structures in pillow metabasalts, and shear band cleavages are widely developed. U–Pb analyses of zircon grains from a representative basalt by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) yielded crystallization age of ca. 395 ± 3 Ma, suggesting formation during the Middle Devonian. Geochemically, all the samples bear the signature of ocean island basalt (OIB), and are characterized by alkaline affinity with high concentrations of Na 2 O + K 2 O (4.22–7.28 wt.%) and TiO 2 (1.72–2.89 wt.%), LILE and LREE enrichment and HREE depletion ((La/Yb) N = 8.4–15.6), with very strong or no Eu anomalies (Eu/Eu * = 0.6–1.1), and no obvious Nb, Ta or Ti negative anomalies. The rocks display consistent Sr–Nd isotopic compositions (initial 87 Sr/ 86 Sr ratios = 0.70326–0.70453, ε Nd( t ) = + 3.1–+7.6). The results suggest that all the alkaline basalts were derived from a mantle plume-related source in an intra-oceanic setting with ca. 1–3% degree partial melting of garnet lherzolite. These observations, in combination with previous work, indicate that the alkaline basalts from Karamay ophiolitic mélange can be correlated to a Middle Devonian mantle plume-related magmatism within Paleo-Asian Ocean. We further suggest that the plume-related activity in the CAOB was generally continuous during the development of the Paleo-Asian Ocean. [ABSTRACT FROM AUTHOR]

Abstract: The West Junggar domain in NW China is a distinct tectonic unit of the Central Asian Orogenic Belt (CAOB). It is composed of Paleozoic ophiolitic mélanges, arcs and accretionary complexes. The Sartuohai ophiolitic mélange in the eastern West Junggar forms the northeastern part of the Darbut ophiolitic mélange, which contains serpentinized harzburgite, pyroxenite, dunite, cumulate, pillow lava, abyssal radiolarian chert and podiform chromite, overlain by the Early Carboniferous volcano-sedimentary rocks. In this paper we report new geochronological and geochemical data from basaltic and gabbroic blocks embedded within the Sartuohai ophiolitic mélange, to assess the possible presence of a Devonian mantle plume in the West Junggar, and evaluate the petrogenesis and implications for understanding of the Paleozoic continental accretion of CAOB. Zircon U–Pb analyses from the alkali basalt and gabbro by laser ablation inductively coupled plasma mass spectrometry yielded weighted mean ages of 375±2Ma and 368±11Ma. Geochemically, the Sartuohai ophiolitic mélange includes at least two distinct magmatic units: (1) a Late Devonian fragmented ophiolite, which were produced by ca. 2–10% spinel lherzolite partial melting in arc-related setting, and (2) contemporary alkali lavas, which were derived from 5% to 10% garnet+minor spinel lherzolite partial melting in an oceanic plateau or a seamount. Based on detailed zircon U–Pb dating and geochemical data for basalts and gabbros from the Sartuohai ophiolitic mélange, in combination with previous work, indicate a complex evolution by subduction–accretion processes from the Devonian to the Carboniferous. Furthermore, the alkali basalts from the Sartuohai ophiolitic mélange might be correlated to a Devonian mantle plume-related magmatism within the Junggar Ocean. If the plume model as proposed here is correct, it would suggest that mantle plume activity significantly contributed to the crustal growth in the CAOB. [Copyright &y& Elsevier]

Abstract: The Mayile ophiolitic mélange (MOM) is located in the southwestern part of the West Junggar (NW China) and forms part of the Southern Altaids. The MOM comprises ultramafic rocks, gabbro, pillow and massive lavas, abyssal radiolarian cherts and volcaniclastic rocks. Zircons with magmatic crystallization features including oscillatory zoning and high Th/U values from the isotropic gabbro within the MOM yield LA-ICP-MS U–Pb age of 572±9Ma (MSWD=1.0) marking the timing of crystallization of these rocks as late Neoproterozoic. Geochemically, the basalts of the corresponding gabbros from MOM display OIB-type alkali basalt and E-MORB-type tholeiitic basalt features. Both of these groups are characterized by LILE and LREE enrichment and HREE depletion, very weak or no Eu anomalies (Eu/Eu*=0.9–1), and no obvious Nb, Ta and Ti negative anomalies, suggesting a typical OIB affinity. We propose that these volcanic rocks were derived from a mantle plume-related magmatism associated with the evolution of the Paleoasian Oceanic system, with the mantle source containing 2%–5% garnet, ∼2% spinel and ∼2% amphibole. The basalts show within-plate affinity marked geochemical similarities with those from Hawaii and Xigaze seamount, suggestive of their intra-oceanic setting. Subduction of the oceanic lithosphere commenced during late Cambrian to early Ordovician, with the eventual accretion of the seamounts in the fore-arc together with oceanic fragments forming the Mayile ophiolitic mélange. [Copyright &y& Elsevier]