本文選題：南海 + 西沙�。� 參考：《中國科學(xué):地球科學(xué)》2017年12期

【摘要】：基底年齡對重建海洋區(qū)域的構(gòu)造演化歷史具有重要意義.南海西沙隆起盆地基底方面的研究主要局限在重磁和地震資料以及20世紀(jì)70年代西永一井的分析資料上,長期沒有新的突破.本文針對新獲取的西科一井兩個基底樣品開展了巖石學(xué)分析和鋯石U-Pb同位素測年,來研究西沙群島基底的形成時間及構(gòu)造屬性.結(jié)果表明,基底成分為晚侏羅世角閃斜長片麻巖,鋯石~(206)Pb/~(238)U平均年齡為(152.9±1.7)Ma,但是最年輕年齡為(137±1)Ma,說明變質(zhì)作用結(jié)束時間大致在早白堊世.變質(zhì)巖底部與二長花崗巖突變接觸,為早白堊世晚期((107.8±3.6)Ma)巖漿侵入的結(jié)果,與西永一井早期測得的前寒武紀(jì)基底年齡(全巖Rb-Sr法,627Ma)明顯不同,西科一井的基底鋯石都屬于晚中生代巖漿活動的產(chǎn)物.晚侏羅世-早白堊世的區(qū)域變質(zhì)作用和花崗質(zhì)巖漿侵入不僅出現(xiàn)于西沙,在南海的珠江口盆地和南沙群島等區(qū)域都有報道,與東亞陸緣受到古太平洋板塊大規(guī)模、長時間的俯沖密切相關(guān),其可能導(dǎo)致了中特提斯洋在南海的關(guān)閉.對于南海是否發(fā)育有統(tǒng)一的前寒武紀(jì)變質(zhì)結(jié)晶基底仍存在爭議,但是可以肯定的是,中生代板塊俯沖擠壓與新生代裂陷拉張已經(jīng)顯著改造了南海地區(qū)的原始基底
[Abstract]:The basement age is of great significance for the reconstruction of the tectonic evolution history of the marine area. The research on the basement of Xisha uplift basin in the South China Sea is mainly confined to the gravity and magnetic data and seismic data and the analysis data of Xiyong Yiyi well in the 1970s. There has been no new breakthrough for a long time. In this paper, petrological analysis and zircon U-Pb isotopic dating have been carried out for two basement samples obtained from Xichiyi well to study the formation time and tectonic properties of the basement of Xisha Islands. The results show that the basement composition is a late Jurassic hornblende gneiss with an average age of 152.9 鹵1.7 Ma for zircon Zircon 206Pb / L / 238U, but the youngest age is 137 鹵1 Ma, indicating that the end time of metamorphism was probably in the early Cretaceous. The metamorphic rock bottom is in contact with the monzomorphic granite, which is the result of magmatic intrusion in late early Cretaceous (107.8 鹵3.6 Ma), which is obviously different from the Precambrian basement age (whole-rock Rb-Sr method 627Ma), which was obtained in the early stage of Xiyong first well. The basement zircon of Xiceyi well is the product of late Mesozoic magmatic activity. The late Jurassic-early Cretaceous regional metamorphism and granitic magmatic intrusion occurred not only in Xisha, but also in the Pearl River mouth basin and Nansha Islands in the South China Sea. Long-term subduction may have led to the closure of the Middle Tethys in the South China Sea. It is still controversial whether there is a unified Precambrian metamorphic crystalline basement in the South China Sea, but it is certain that the Mesozoic plate subduction and Cenozoic rift extension have significantly altered the primitive basement in the South China Sea.
【作者單位】： 同濟大學(xué)海洋地質(zhì)國家重點實驗室;中國地質(zhì)大學(xué)構(gòu)造與油氣資源教育部重點實驗室;中海石油中國有限公司湛江分公司;西北大學(xué)地質(zhì)學(xué)系;
【基金】：國家科技重大專項項目(編號:2017ZX05-26-005) 國家自然科學(xué)基金項目(批準(zhǔn)號:91128207、41576059)資助
【分類號】：P736.1
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本文編號：1981092