As a micro-continent lying at the junction of the North China, Yangtze, and Tarim Cratons in northwest China, the composition and tectonic-thermal history of the Qaidam Block not only are crucial for determining its tectonic attribute and relationships with surrounding cratons, but also can provide key constraints on convergence, fragmentation, and paleogeographic reconstruction of Columbia and Rodinia. In this study, systematic petrology, geochemistry, and zircon U–Pb–Hf isotope analyses were conducted on newly discovered Meso-Neoproterozoic granitic rocks from drill cores in the Qaidam basin and three stages granitic magmatism at ca. 1420 Ma, ca. 900 Ma and 780–750 Ma are yielded. The ca. 1420 Ma granitic rocks exhibit characteristics of highly fractionated I-type granites, with high Yb but low Sr contents, low Sr/Y and La/Yb ratios, high zircon saturation temperatures (774–831 ℃), and positive εHf(t) values (–0.04 to +11.35) with TDM2 values of 2178–1468 Ma, suggesting that they were mainly derived from the ancient crust with mantle magma input under an extensional setting. The ca. 900 Ma granitic rocks have high A/CNK values (1.01–1.21) and variable zircon εHf(t) values (–1.93 to + 6.58) with TDM2 ages between 1402 and 1910 Ma, indicating they are S-type granites formed by partial melting of sedimentary rocks in thickened crust. The ca. 780–750 Ma granites have high Zr + Nb + Ce + Y contents, 10000* Ga/Al ratios, and crystallization temperatures (mean = 808 ℃), belonging to the A1-type granite formed in a continental rift setting. Combined with the previous researches, the Meso-Neoproterozoic tectonic-thermal events in the Qaidam Block can be divided into three stages, 1.8–1.1 Ga, 1.0–0.9 Ga and 850–750 Ma, corresponding to the fragmentation of Columbia, and the assembly and breakup of Rodinia, respectively. Comparing the Qaidam Block with the surrounding blocks and the major cratons in Columbia and Rodinia, it is considered that the Qaidam Block was splited from the Tarim Craton and they may have occupied an interior position in Columbia but a peripheral position in Rodinia, connecting to the India and East Antarctica. 

Meso-Neoproterozoic tectonic-thermal events in the Qaidam Block, NW China and their geological significance: Constraints from drill cores geochronology and geochemistry studies

ABSTRACT The South Altyn Tagh (SAT) is renowned for hosting high‐pressure to ultrahigh‐pressure (HP–UHP) rocks indicative of continental deep subduction. Nevertheless, its geodynamic evolution remains enigmatic due to uncertainty regarding protolith origins and the intricate relationships between HP–UHP rocks and their coeval, unmetamorphosed or low‐grade metamorphic counterparts. This study presents novel LA–ICP–MS zircon U–Pb ages, zircon Lu–Hf isotopic compositions and whole‐rock geochemical analyses of both HP–UHP felsic gneiss and unmetamorphosed to low‐grade metamorphic Neoproterozoic granite samples from the SAT, northwestern China. Our findings indicate that both felsic gneiss and granite samples share protolith ages ranging from 920 to 898 Ma, displaying a high K 2 O content and low CaO and Na 2 O contents, characteristic of S‐type granites. The presence of inherited zircons with ages of 1.79–1.40 Ga, along with ε Hf ( t ) values of –5.32 to +4.03 and T DM2 ages of 2.00–1.54 Ga for ~900 Ma zircons, suggests that both felsic gneisses and granite samples originated from the partial melting of Mesoproterozoic metasedimentary rocks. Zircon grains of felsic gneiss samples exhibit a metamorphic age cluster at 505–498 Ma, consistent with the ~500 Ma continental deep subduction event in the SAT. Conversely, granite samples lack ~500 Ma metamorphic age records; a few granite samples record a younger anatectic age cluster at 455–452 Ma, indicating the influence of a ~450 Ma post‐collisional extension event in the SAT. Integrating petrological and geochemical investigations of both felsic gneisses and Neoproterozoic granite samples in the SAT and adjacent orogens, we propose that: (1) both the felsic gneisses and Neoproterozoic granites in the region formed during the late syn‐collision to extensional collapse of the Rodinia supercontinent, (2) the rifting of Rodinia (860–623 Ma) resulted in the development of the Proto‐Tethys ocean and the isolation of granite plutons along margins of different continental blocks, (3) the early‐Palaeozoic continental collision (~500 Ma) subjected the Neoproterozoic granite in the subduction plate to continental deep subduction and led to the coexistence of HP–UHP felsic gneiss and non‐subducted Neoproterozoic granite in the SAT after the exhumation process. These results demonstrate that HP–UHP felsic gneisses and Neoproterozoic granites preserve a complex tectono‐metamorphic history spanning Rodinia's fragmentation, the Proto‐Tethys ocean's evolution and the Early Palaeozoic orogeny. 

Two Types of Neoproterozoic Granitoids Reveal the Multi‐Stage Tectonic Evolution of the South Altyn Tagh, Spanning From Rodinia's Disintegration to Palaeozoic Continental Deep Subduction

Reconstructing Tarim within Rodinia: Constraints from early Tonian accretionary and collisional records in the Altyn belt

Grenvillian evolution of the Qaidam block and its position in Rodinia constrained by U–Pb–Hf composition of detrital zircons from the Altyn Tagh, Northern Tibet

Episodic Neoproterozoic magmatic suites in the Altyn Tagh, NW China, are thought to be related break-up of the Rodinia supercontinent. These suites resulted from long-term extension of the lithosph...

Episodic Neoproterozoic extension-related magmatism in the Altyn Tagh, NW China: implications for extension and breakup processes of Rodinia supercontinent

Newly discovered Neoproterozoic A-type granite in the Altun orogenic belt: A record of the initial breakup of Rodinia

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Newly discovered Neoproterozoic A-type granite in the Altun orogenic belt: A record of the initial breakup of Rodinia