Earth Science Frontiers ›› 2021, Vol. 28 ›› Issue (3): 355-378.DOI: 10.13745/j.esf.sf.2021.1.9

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Estimation of the extend of granitoid exhumation in the Weiya-Tianhu area: Insight into ore prospecting in the Central Tianshan region, Xinjiang

LI Jilin1,2(), CHEN Zhengle1,3,*(), ZHOU Taofa2, HAN Fengbin1, ZHANG Wengao1, HUO Hailong1, LIU Bo1,2, ZHAO Tongyang4, HAN Qiong4, LI Ping4, ZHENG Jiaxing4, CHEN Guimin5   

  1. 1. Ministry of Land and Resources Key Laboratory of Paleomagnetism and Tectonic Reconstruction, Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China
    2. School of Resources and Environmental Engineering, Hefei University of Technology, Hefei 230009, China
    3. State Key Laboratory of Nuclear Resources and Environment, East China University of Technology, Nanchang 330013, China
    4. Xinjiang Institute of Geological Survey, Ürümqi 830000, China
    5. No.6 Geological Survey Team, Bureau of Xinjiang Geology and Mineral Resources Development, Hami 839000, China
  • Received:2021-01-20 Revised:2021-02-18 Online:2021-05-20 Published:2021-05-23
  • Contact: CHEN Zhengle

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Abstract:

The Weiya-Tianhu granitoid area is located on the Central Tianshan Terrane, Xinjiang, southeast of the Central Asian Orogenic Belt (CAOB), where Late Paleozoic-Early Mesozoic magmatic activities were widespread and the strategic key mineral Weiya V-Ti magnetite is produced. This paper reports the detailed petrographic observations of the region. Based on these observations, the compositions of amphiboles and biotites from the Weiya, Tianhu, and Shaquanzinan granitoids were obtained by electron microprobe analysis (EMPA) to constrain the crystallization controlling factors for the three granitoids. The constrained controlling factors such as temperature, pressure, oxygen fugacity, water content and Fe provide references for analyzing the physicochemical conditions of magmatic mineralization and ore prospecting in the region. The EMPA data show that the amphiboles are rich in Mg, Ca and Na, poor in K, and belong to calcic amphiboles. The biotites have the characteristics of high Mg, Ti, Al and K contents and low Si and Na contents, which suggests a magnesia origin. The chemical compositions of amphiboles and biotites revealed their host magma to be the calc-alkaline orogenic rock series from a hybrid crustal-mantle source, attributed probably to partial melting of mantle wedge and continental crust under the tectonic setting of plate subduction. The crystallization temperature and pressure of the Shaquanzinan quartz diorite, Weiya monzonitic granites and moyites, and Tianhu granodiorites, calculated by geothermometric method, were 651-753 ℃ and 31-79 MPa, 762-833 ℃ and 85-215 MPa, 668-812 ℃ and 31-117 MPa, respectively. The magmatic oxygen fugacity lgf(O2) in the three granitoids at crystallization varied from -15.7 to -9.4, with high water content in the melt during amphibole crystallization. Therefore, it is suggested that the granitoids in the region have the characteristics of high temperature, low pressure, high oxygen fugacity, water-rich and high Fe index, which are beneficial to elemental enrichment in ore-forming fluid and hence favoring Fe mineralization. The intrusive depth of these granitoids was further assessed by Al-in-hornblende barometry. The results show that the extend of granitoid exhumation is between 2.2-5.5 kilometers in the region, where the rates of uplifting and exhumation differ significantly. Together with the known ore distribution on land surface, it is proposed that Fe prospectivity is highly favorable at depth in the Tianhu granodiorite area.

Key words: mineralogical characteristics, physicochemical conditions, Al-in-hornblende barometry, uplifting-exhumation extend, Weiya-Tianhu area in the Central Tianshan Terrane

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