Sr-Nd isotopes of Early and Late Carboniferous volcanic rocks in Yining Massif (Xinjiang, NW China): Implications for petrogenesis and tectonic evolution of Western Tianshan

2018 ◽  
Vol 53 ◽  
pp. 137-147 ◽  
Author(s):  
Lili Tong ◽  
Yongjun Li ◽  
Ganyu Li ◽  
Zhucang Li ◽  
Gaoxue Yang ◽  
...  
Keyword(s):  
Tectonic Evolution ◽  
Volcanic Rocks ◽  
Late Carboniferous ◽  
Nd Isotopes ◽  
Nw China ◽  
Western Tianshan

Bimodal magmatism produced by delamination: geochemical evidence from late Palaeozoic volcanic rocks from the Yili Block, Western Tianshan, Northwestern China

2020 ◽  
pp. 1-15
Author(s):  
Genwen Chen ◽  
Rui Liu ◽  
Teng Deng ◽  
Lixing Wang
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Volcanic Rocks ◽  
Orogenic Belt ◽  
Late Carboniferous ◽  
Early Permian ◽  
Asthenospheric Mantle ◽  
Late Palaeozoic ◽  
Depleted Mantle ◽  
Western Tianshan

Abstract The Western Tianshan orogenic belt is essential for understanding the evolution of the Central Asian orogenic belt. However, no agreement exists among geologists about its tectonic environment during the Late Palaeozoic. The volcanic rocks of the Yishijilike and Wulang Formation in the Yili Block, Western Tianshan, formed in the Late Carboniferous to Early Permian, mainly consist of a bimodal suite of basalts – basaltic andesites and rhyolites, with only some intermediate rocks. Mafic rocks are slightly enriched in light rare earth elements (LREE) and depleted in Nb, Ta, Zr and Hf, suggesting a subduction-modified depleted mantle source. Some mafic samples in the Early Permian bimodal volcanic rocks have high Ti contents with relatively high concentrations of Nb and high field strength elements (HFSE) and low contents of heavy rare earth elements (HREE). These rocks are similar to the continental flood basalts, which suggests that they formed from an asthenospheric mantle. This paper indicates that mafic members were created by the partial melting of the asthenospheric mantle material and subduction-modified lithospheric mantle mixture. Some rhyolites and dacites in the Wulang formation were enriched in Ga, Nb, Zr, Ce and Y and depleted in Sr and Eu. Additionally, they showed fractionation of rare earth elements (REE) with negative Eu anomalies, which is indicative of an A-type affinity of felsic rocks. The genesis of mafic members and an A-type affinity of felsic members indicate that the Late Carboniferous – Early Permian magmatism in the Western Tianshan area formed as a result of an extensional setting. This study also reveals bimodal magmatism produced by delamination in an extensional tectonic setting.

scholarly journals Cooling and exhumation of the Late Paleozoic Tulasu epithermal gold system, Western Tianshan, NW China: implications for preservation of Pre-Mesozoic epithermal deposits

2020 ◽  
pp. jgs2020-099
Author(s):  
Xiao-Bo Zhao ◽  
Chun-Ji Xue ◽  
Wei-Ce Zhao ◽  
Reimar Seltmann ◽  
David T.A. Symons ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Gold Deposits ◽  
Late Paleozoic ◽  
Epithermal Gold ◽  
Nw China ◽  
Epithermal Deposits ◽  
Tectonic Events ◽  
Western Tianshan ◽  
Shallow Crust ◽  
Exhumation History

Epithermal gold deposits are rarely well preserved in pre-Mesozoic terranes because of their low-temperature mineralization at shallow crust levels, and they are easily destroyed by subsequent erosion or depleted by tectonic events. However, several significant Late Paleozoic epithermal gold deposits have been found in the Tulasu volcanic basin in NW China, forming one of the largest gold districts in the western Tianshan Orogen. Here, we report a new 40Ar/39Ar age from a monzonite porphyry enclave hosted in andesite and apatite fission track data for 10 volcanic rocks from the Tulasu basin. These data, combined with the previous dataset, are used to perform inverse thermal modelling to quantify the district's cooling and exhumation history. Our modelling indicates a phase of burial reheating during Late Paleozoic sedimentation following mineralization, a subsequent rapid exhumation in the Jurassic to Early Cretaceous (c. 196–128 Ma), and a slow exhumation to the present. The Mesozoic exhumation is likely related to the far-field effects of the Cimmerian orogeny along the southern Eurasian margin. Therefore, we suggest that the rapid burial by thick sediments and the slow protracted exhumation after mineralization were crucial for the preservation of the Paleozoic epithermal gold system at Tulasu.

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