Citation: | ZENG Xiangwu, ZHAO Jun, NIE Xiaoyong. LA-ICP-MS zircon U-Pb age, geochemistry and genesis of Neoproterozoic granitoids in the Biezhentao Mountain of Wenquan County, Xinjiang[J]. Geological Bulletin of China, 2020, 39(2-3): 177-193. |
The Neoproterozoic granites of the Biezhentao Mountain in Wenquan County of Xinjang were studied in this paper.Four LA-ICP-MS zircon U-Pb ages of 910~950 Ma were obtained for granitic gneisses in the Biezhentao Mountain of Wenquan County of Xinjiang.These new zircon LA-ICP MS U-Pb ages, together with previously published data, indicate that the granites were emplaced during 910~950 Ma.A few inherited old zircons U-Pb ages of >1000 Ma were found in all dated samples; they may have derived from the source rocks. These granitoids are characterized by a very coarse grained and huge augen gneiss texture. Major element data indicate that they belong to peraluminous monzogranite, with SiO2 (≥ 70%), K2O+Na2O (6.5%~8.9%), and K2O > Na2O, thus defined as calc-alkaline to shoshonitic rocks. These rocks show nearly parallel REE patterns with different abundances and distinct negative Eu anomalies. All the granitoids display similar spider diagrams with obvious negative anomalies of Ba, Nb, Ta, Sr, P and Ti, and obvious enrichment of Rb, Th, U, K. Sr-Nd data suggest that the protoliths of Neoproterozoic granitoids belong to peraluminous S-type granites. Zircon εHf (t) values range from +1.7 to +5.7, with model ages (tDM1) of 883~1351 Ma and model ages (tDM2) of 891~1588 Ma. Furthermore, with the age information on the ancient terranes of Tarim basin, the authors hold that the Tianshan ancient block probably formed a part of Rodina supercontinent during Early Neoproterozoic period and these granitoid rocks were linked to lithospheric thickening.
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Simplified intrusive rock map of the Wenquan area in West Tianshan
Simplified geological map for the Biezhentao Mountain of Wenquan County
Simplified geological map for theBiezhentao Mountain of Wenquan County
CL images, analytical points for U-Pb(solid circles), analytical points for Lu-Hf isotope(dashed circles)and 206Pb/238U ages of zircons
U-Pb concordia diagrams and weighted average 206Pb/238U ages of zircons for the granitic gneiss
The K2O versus SiO2 diagram(a) and Shand's index Al/(Na + K) versus Al/(Ca + Na + K)plots(b)
Chondrite-normalized REE patterns(a)and multi-element variation diagrams(b)
Diagrams of (87Sr/86Sr)i-εNd(t)(a)and age-εHf(t)(b)for the granitic gneiss
Tectonic implications for granite R1-R2(a)and Rb/30-Hf-3Ta(b) diagrams