Geochemical Characteristic of the Xungba Formation Sandstones in the Xungba Basin, Tibet, and its Constraints on Provenance and Tectonic Setting
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    Abstract:

    The Xungba Basin, located in the Gangdese boron bearing mineralization region of the Alpine Himalayan tectonic volcanic metallogenic belt, contains a set of variegated volcanic rocks and clastic sedimentary rocks resulting from the second play of the Himalayan movement in the Miocene. This study carried out element geochemical analysis for clastic sedimentary rocks of the Xungba Formation. The results show that clastic sedimentary rocks of the Xungba Formation occur as angular to sub angular, indicating a proximal deposition. The clastic sedimentary rocks are characterized by medium SiO2, high Na2O, and low TFe2O3 and MaO, indicating they are felsic rocks in source rocks. The Chemical Index of Alteration (CIA) is 5741 in average, and Chemical Index of Weathering (CIW) is high around 6681, illustrating source rocks underwent weak to middle degree of chemical weathering. Chondrite normalized REE patterns and trace elements spider diagrams display LREE rich but HREE depletion, with Eu negative anomaly, an average (La/Sm)N of 428、(La/Yb)N of around 273, ∑LREE/∑HREE of 825, (Gd/Yb)N of 289 and Eu/Eu* of 069. Our study indicates that sedimentary structure occurs in an active continental margin with several samples found likely in island arc environment and passive continental margin. The rocks derived mainly from felsic igneous rocks of upper crust, with a minor addition of andesitic rocks and ancient crustal material.Based on the regional geological background and previous research result, this study suggests that the source rocks of the Xiongba Formation clastic sandstone were distributed mainly around the volcanic edifice zonation in northwest of the Xungba Basin, and confirms that the study area is also characterized by tectonic volcanic sedimentary setting. Therefore, the comprehensive information reveals that the study area is a favorable metallogenic prospect area.

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WANG Congshan, CHEN Wenxi, SHAN Fulong.2016. Geochemical Characteristic of the Xungba Formation Sandstones in the Xungba Basin, Tibet, and its Constraints on Provenance and Tectonic Setting[J]. Acta Geologica Sinica,90(6):1195-1207

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History
  • Received:December 05,2014
  • Revised:April 16,2015
  • Adopted:June 28,2016
  • Online: June 28,2016
  • Published: