Subduction system in the Qilian orogenic belt experienced the variability of an active continental arc in space and time related to the subduction of the Proto‐Tethys Ocean. Zircon U–Pb geochronology and whole‐rock chemical and Sr–Nd isotopic data of mafic to intermediate dykes in the western part of the Central Qilian belt (WCQB) are used to track magma provenance from compositionally variable reservoirs in the sub‐arc mantle and constrain the magmatic evolution of the rear‐arc at 450–445 Ma. Petrological, whole‐rock chemical and zircon U–Pb dating results reveal that the studied dykes mainly comprise calc‐alkaline lamprophyre (CAL), high Mg # andesitic porphyrite (HMA) and high FeO hornblende gabbro (HFG) with crystallization ages of 447, 453 and 448 Ma, respectively. Among them, CAL and HMA have affinities in high‐K calc‐alkaline suites, high REE contents (∑REE = 131.1–202.3 ppm) with high La N /Yb N values (6.77–17.99), enriched in large‐ion lithophile elements (LILE, e.g., Rb and U), and depleted in high‐field‐strength elements (HFSE, e.g., Nb, Ta, and Ti). They also have high Th/La (0.20–0.46), Th/Nb (0.67–1.64) and Th/Yb (3.88–14.11) ratios, and relatively high whole‐rock initial 87 Sr/ 86 Sr ratios (0.707469–0.708493) and ε Nd ( t ) values (−4.7 to −3.1). Whereas, HFG is affinities in medium to high‐K calc‐alkaline suites, and has moderate rare earth elements (∑REE = 70.1–112.5 ppm) with flat REE patterns (La N /Yb N = 2.12–3.05) and exhibits enriched LILE, and Sr–Nd isotopes (( 87 Sr/ 86 Sr) i = 0.713496–0.729216, ε Nd ( t ) = −2.93 to +2.04). Such typical “continental” geochemical features of the different K‐rich dykes do not result from crustal assimilation but reflect an enriched mantle source resulting from their mantle heterogeneity due to recycling of different subducted sediments. The temporal evolution of the geochemical characteristics of mafic‐intermediate dykes is consistent with an extension setting triggered by removing the thickened arc crust root in the WCQB.

The U-Pb ages and Hf isotopic composition of detrital zircons provide important constraints on basin evolution and paleogeography. The Qaidam block, a continental fragment along the northeastern margin of the Tibetan Plateau, has been suggested to have been either in an internal or a peripheral position in Rodinia. We present a systematic study of late Mesoproterozoic to Ediacaran sedimentary sequences from the Altyn Tagh belt, a part of the Qaidam block displaced by the Altyn Tagh fault, in an effort to establish its position within Rodinia. The (meta-)sedimentary rocks of the Altyn Complex of South Altyn can be correlated with the Taxidaban Group, the part of the basement (meta-) sedimentary sequence of Central Altyn, on the basis of lithological and geochronological similarities. Both of these were deposited in the late Mesoproterozoic to early Neoproterozoic. The early Neoproterozoic Suoerkuli Group of Central Altyn and its coeval magmatism formed in an extensional setting. This extensional episode facilitated thinning of the lithosphere during the late Tonian-Ediacaran when the sedimentary protoliths of the Hongliuquan Complex were deposited. Detrital zircon grains from late Mesoproterozoic to Ediacaran sedimentary sequences in the Altyn Tagh orogenic belt show a wide distribution of Meso- and Paleoproterozoic ages between 1800 and 1000 Ma, which match well with contemporaneous supracrustal sequences in northeastern Laurentia. In combination with the similarity in late Mesoproterozoic to Ediacaran tectono-thermal events, we propose the Qaidam block was located along the northeast Laurentian margin during the late Meso- to Neoproterozoic assembly of Rodinia.& COPY; 2023 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

碱性系列岩浆岩和埃达克岩是通常产生于汇聚板块边缘的特殊岩石类型,记录了俯冲物质与地幔橄榄岩相互作用的过程.笔者对中祁连南缘党河南山地区贾公台杂岩体和鸡叫沟岩体进行了岩石学、地球化学和锆石U-Pb年代学研究.LA-ICP-MS锆石U-Pb定年表明,鸡叫沟岩体中的二长闪长岩形成于(467±4.7)Ma,贾公台岩体花岗闪长岩形成于(445±4.3)Ma.地球化学分析结果表明,鸡叫沟杂岩体中角闪辉石岩、辉长岩和二长闪长岩整体上具有富K、富Na的特征,均属于碱性系列岩浆岩,具有钾玄岩特征;岩体中不同岩石类型具有相似的微量元素配分型式,富集Sr、Nb、LILE和LREE等,岩浆源区存在金红石残留,其形成过程与弧地幔楔底部富碱的俯冲沉积物和地幔橄榄岩混合、熔融有关.贾公台花岗闪长岩属于中钾钙碱性系列,Na2O/K2O值大于2.5,样品具有高Sr(＞400X10-6)、低Y(＜7×10-6)的特征,高Sr/Y值(＞70)和La/Yb值(＞22)具有高硅埃达克岩特征,与俯冲洋壳的榴辉岩相部分熔融有关,源区存在石榴子石残留特征.党河南山碱性岩浆岩-埃达克岩组合指示了俯冲物质深部熔融的特点(大于50～100 km),揭示了该地区强烈的壳幔相互作用过程,表明俯冲沉积物和俯冲洋壳可以为弧岩浆侵入体形成提供直接的物质来源,进一步说明俯冲物质和地幔橄榄岩相互作用可能是岛弧地壳生长的方式之一.

The Qilian orogen at the northeastern margin of the Tibetan Plateau records a complete history from continental breakup to oceanic basin evolution and back to continental collision during the Neoproterozoic to Paleozoic interval. The Qilian Ocean, as a branch of the Proto-Tethys Ocean, was connected to the Iapetus Ocean but is lesser known than its two more famous counterparts. This paper presents zircon U-Pb and biotite-muscovite 40Ar/39Ar isotope data from the Yemananshan Complex in the western Central Qilian belt to assess the age and provenance of late Mesoproterozoic-early Paleozoic successions in the Qilian orogen. The results indicate the Central Qilian belt is characterized by Late Mesoproterozoic-early Neoproterozoic orogenesis with magmatism from 1200 Ma to 900 Ma and clastic metasedimentary rocks deposited between 1050 and 920 Ma. Statistical analysis of detrital zircon data and auxiliary temporal information from the Qilian orogen affirms the notion that sedimentation occurred in four distinct megasequences: (1) 1950-1850 Ma, the oldest known strata, (2) 1250-920 Ma, during Grenvillian-Sveconorwegian orogenesis, (3) 840-760 Ma, the disintegration of Rodinia, and (4) 650-550 Ma, which is typical of the orogenic belts that sutured the Gondwana continental blocks. Metamorphic zircon and 40Ar/39Ar isotope data indicate early Paleozoic metamorphism at ca. 475 Ma, which overlaps with magmatic activity associated with arc-back-arc basin development in the Central Qilian belt, which was associated with subduction of the Proto-Tethys in eastern Gondwana.

Neoproterozoic granitoids are widely distributed in the Altyn Tagh, and provide indispensable information on the pre-Cenozoic tectonics and evolutionary history at the northeastern margin of Tibetan Plateau. In this study, zircon U-Pb geochronological results show that the granitoids were emplaced during the interval between 997 Ma and 901 Ma. Petrological studies reveal that these granitoids have high Al2O3 and K2O, low CaO and Na2O contents with Al-rich minerals, such as muscovite, which show typical S-type properties. These Neoproterozoic granitoids contain abundant inherited cores of Mesoproterozoic age with epsilon(Hf) (t) values between 9.43 to 4.60. We interpret this to indicate magma generation via partial melting of Mesoproterozoic metasedimentary rocks. Based on a comparison to similar Neoproterozoic magmatic and metamorphic events described in the East Kunlun and North Qaidam, we suggest that the Altyn Tagh, East Kunlun and North Qaidam were part of the same terrane (Qadiam block) during the early Neoproterozoic. Petrogenetic data when combined with other geological and tectonic information suggest a late syn- to post-collisional setting rather than a syn-collisional setting. The Qaidam block was probably located adjacent to Laurentia, Baltica and Amazonia, during Neoproterozoic time.

Arc magma differentiation in deep arc crust is a fundamental process for the generation of continental crust. Here we focus on field geological, geochemical, geochronological, and thermodynamic simulation of the Hamardaban Complex in Yanchiwan, western part of the Central Qilian belt. Two rock types in the Hamardaban Complex are identified : mafic-ultramafic cumulates ( includes pyroxene hornblendite, hornblende gabbro and hornblendite) and diorites ( includes diorite and quartz diorite). Zircon U-Pb dating yield 473 +/- 1 Ma for the formation of pyroxene hornblendite, which is consistent with the age of adjacent high-K to shoshonitic volcanic rocks (HKSV ). The Hamardaban Complex and HKSV display uniform whole rock Sr-Nd-Hf isotopic composition : (Sr-87/Sr-86)(i) =0. 7035 similar to 0. 7053, epsilon(Nd) ( t) = + 3. 9 similar to + 5. 1, epsilon(Hf)( t) = + 10.8 similar to + 13. 1. These features indicate that they were formed from an identical parental magma source. Petrological and geochemical characteristics show diorite is sourced from the melt formed by partial melting of mantle peridotites metasomatized by sediment melt in the subduction zone, with crystallization differentiation dominated by hornblende in the middle and lower crust. Mafic ultramafic rocks have cumulate structure and residual cumulate geochemical composition characterized by high Fe, MgO (6. 19%similar to 14. 29% , Mg-# =52.3 similar to 74. 6) and low Si. Combining thermodynamic modeling and previous experimental data, it is suggested that diorite of the Hamardaban Complex is the product of 50% similar to 67% fractional crystallization of hydrous mantle derived basaltic melt under the conditions of medium pressure ( ca. 0. 7GPa) and oxygen fugacity at NNO +1. These correlations imply that diorite and mafic-ultramafic cumulate represent counterpart melt and cumulate of single mantlederived basaltic magma, respectively. This study further shows hornblende fractionation plays a key role in arc magma differentiation, which leads to the formation of andesitic arc crust.