Geochemistry and Zircon U-Pb age of Volcanic Rocks from the Chagangnuoer and Zhibo Iron Deposits, Western Tianshan, and their Geological Significance

详细信息   

• 责任者：Jiang ZongSheng(MRL Key Laboratory of Metallogeny and Mineral Assessment ; Institute of Mineral Resources ; Chinese Academy of Geological Sciences ; Beijing 100037 ; China) ; Zhang ZuoHeng
• 刊名：Acta Petrologica Sinica
• 出版年：2012
• 卷期：28(7)
• 关键词：铁矿 ; iron ores ; 火山成矿作用 ; volcanogenic mineralization ; 天山 ; Tianshan Mountains
• 页码：p.2074-2088
• 图表：illus.,2 tables,54 refs.
• 分类号：1001
• issnNo：ISSN1000-0569
• isbnNo：CN11-1922/P

摘要

The Chagangnuoer and Zhibo iron deposits occurring in eastern segment of western Tianshan, were hosted primarily by the Late Carboniferous volcanic rocks, which mainly contain basalt, basaltic andesite, trachyte and andesitic tuff. The tectonic setting and age of the volcanic rocks are key elements in the reconstruction of ore genesis. In this paper, representative samples of volcanic rocks from the Chagangnuoer and Zhibo iron deposits were analyzed for major, trace elements and zircon U-Pb dating to validate their tectonic setting and formation ages. Geochemical data indicate that most of the volcanic rocks range in composition from calc-alkaline, high-K calc-alkaline to shoshonitic, with light rare earth element(LREE)and large ion lithophile element(LILE; e. g. , Rb, Th, K)enrichment and almost flat heavy rare earth element(HREE)patterns as well as strongly negative Nb, Ta and Ti anomalies, similar to features of arc volcanic rocks. In the plots of tectonic discrimination, the basaltic volcanic rocks are mainly projected in arc setting regions. LA-ICP-MS U-Pb dating of magmatic zircons from the rhyolite and dacite yield weighted average ²⁰⁶Pb/²³⁸U ages of 301.8±0.9Ma and 300.3±1.1Ma, respectively. In addition, weighted average ²⁰⁶Pb/²³⁸U ages from 303.8Ma to 305Ma were

    

obtained for two diorites. The similar geochemical characteristics and formation ages of volcanic rocks and diorites indicated that they were sourced from the same parent magma and may formed in the same tectonic setting. Combined with the regional geological data, we therefore suggest that the high-K calc-alkaline to shoshonitic volcanic rocks were probably the products of continental island-arc magmatism during the late stage of subduction.