修淳, 张道军, 翟世奎, 刘新宇, 毕东杰. 西沙岛礁基底花岗质岩石的锆石U-Pb年龄及其地质意义[J]. 海洋地质与第四纪地质, 2016, 36(3): 115-126. DOI: 10.16562/j.cnki.0256-1492.2016.03.011
引用本文: 修淳, 张道军, 翟世奎, 刘新宇, 毕东杰. 西沙岛礁基底花岗质岩石的锆石U-Pb年龄及其地质意义[J]. 海洋地质与第四纪地质, 2016, 36(3): 115-126. DOI: 10.16562/j.cnki.0256-1492.2016.03.011
XIU Chun, ZHANG Daojun, ZHAI Shikui, LIU Xinyu, BI Dongjie. ZRICON U-Pb AGE OF GRANITIC ROCKS FROM THE BASEMENT BENEATH THE SHI ISLAND, XISHA ISLANDS AND ITS GEOLOGICAL SIGNIFICANCE[J]. Marine Geology & Quaternary Geology, 2016, 36(3): 115-126. DOI: 10.16562/j.cnki.0256-1492.2016.03.011
Citation: XIU Chun, ZHANG Daojun, ZHAI Shikui, LIU Xinyu, BI Dongjie. ZRICON U-Pb AGE OF GRANITIC ROCKS FROM THE BASEMENT BENEATH THE SHI ISLAND, XISHA ISLANDS AND ITS GEOLOGICAL SIGNIFICANCE[J]. Marine Geology & Quaternary Geology, 2016, 36(3): 115-126. DOI: 10.16562/j.cnki.0256-1492.2016.03.011

西沙岛礁基底花岗质岩石的锆石U-Pb年龄及其地质意义

ZRICON U-Pb AGE OF GRANITIC ROCKS FROM THE BASEMENT BENEATH THE SHI ISLAND, XISHA ISLANDS AND ITS GEOLOGICAL SIGNIFICANCE

  • 摘要: 西沙地块作为南海中散布的微地块之一,迄今尚缺乏有关中生代构造-岩浆活动的岩石学资料或证据。在2012-2013年,中海石油(中国)有限公司湛江分公司在西沙岛礁上设计实施了"西科1井"科学钻探,成功钻取了长达1 268.02 m的岩心,并在井深1 257.52 m处钻遇由变质岩和侵入岩组成的结晶基底。利用LA-ICP-MS分析测试技术,对取自岛礁基底的花岗质岩石进行了锆石U-Pb年龄测定,结合邻区和华南地区花岗质岩石的形成年代,探讨了与岩浆作用相关的大地构造环境。结果表明:西沙花岗质岩石在岩性上属碱长花岗岩和二长花岗岩,与南沙地块的花岗质岩石同为I型花岗岩,形成于活动陆缘构造环境下,其岩浆源区可能在一定程度上受到了幔源组分的影响;西沙岛礁基底花岗质岩石形成年龄在144~158 Ma之间,是晚侏罗世构造-岩浆作用的产物,在成岩时代上可与华南燕山期花岗岩进行对比,反映出由古太平洋板块俯冲机制诱发的燕山期岩浆活动对华南大陆和南海地区产生了广泛的影响;岩石学证据表明,西沙-中沙和南沙地块经历了燕山期多期次岩浆活动的改造,在基底构造上属华南大陆的延伸部分。

     

    Abstract: The petrological evidence of the Mesozoic tectonic-magmatic activity in the Xisha block, one of micro-blocks dispersed in the South China Sea, remains deficient. In 2012-2013, the Zhanjiang Branch of CNOOC successfully drilled the Well XK-1 with a core length of 1 268.02 m in the Shi Island, Xisha Islands, and met the crystalline basement composed of metamorphic and intrusive rocks at core depth of 1 257.52 m. In this paper, zircon U-Pb ages of granitic basement rocks from the Well XK-1 were measured with LA-ICP-MS technique. These granitic rock samples, identified as alkali-feldspar granite and monzogranite in lithology, belong to I-type granites and are formed under the geotectonic setting of active continental margin, same as those from the Nansha block. The geochemical characteristics of zircon trace elements indicate that the magma source is possibly influenced to some extent by mantle-derived components. The granitic rocks in the Xisha block with zircon U-Pb age ranging from 144 to 158 Ma are the product of the Late Jurassic tectonic-magmatic activity and comparable to the Yanshanian granites in the South China, which reveals that the Yanshanian magmatism occurred widely in both South China and the South China Sea. The petrological data show that both the Xisha-Zhongsha block and Nansha block are transformed by the Yanshanian multi-stage magmatic activities and belong to the extension of basement structure of the South China Continent.

     

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