U-Pb zircon geochronology of basaltic pyroclastic rocks from the basement beneath the Xisha Islands in the northwestern South China Sea and its geological significance

IF 1.4 3区 地球科学 Q3 OCEANOGRAPHY Acta Oceanologica Sinica Pub Date : 2024-04-15 DOI:10.1007/s13131-023-2198-2
Yu Zhang, Kefu Yu, Shiying Li
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Abstract

As one of the micro-blocks dispersed in the South China Sea (SCS), the basement of the Xisha Islands has rarely been drilled because of the thick overlying Cenozoic sediments, which has led to a confused understanding of the pre-Cenozoic basement of the Xisha Islands. Well CK-1, a kilometer-scale major scientific drill in the Xisha Islands in the northwestern SCS, penetrated thick reefal limestone (0–888.4 m) and the underlying basement rocks (888.4–901.4 m). In this study, we present the zircon U-Pb ages of basement basaltic pyroclastic rocks from Well CK-1 in the Xisha Islands of the northwestern SCS to investigate the basement nature of the Xisha micro-block. The basement of Well CK-1 consists of basaltic pyroclastic rocks on the seamount. The zircon grains yielded apparent ages ranging from ca. 2 138.9 Ma to ca. 36 Ma. The old group of zircon grains from Well CK-1 was considered to be inherited zircons. Two Cenozoic zircons gave a weighted mean 206pb/238U age of (36.3 ± 1.1) Ma, Mean Squared Weighted Deviations (MSWD) = 1.2, which may represent the maximum age of the volcano eruption. The Yanshanian inherited zircons (116.9–105.7 Ma and 146.1–130.2 Ma) from Well CK-1 are consistent with the zircons from Well XK-1, indicating that the basement of Chenhang Island may be similar to that of Well XK-1. We propose that the Xisha micro-block may have developed on a uniform Late Jurassic metamorphic crystalline basement, intruded by Cretaceous granitic magma.

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南海西北部西沙群岛基底玄武质火成岩的U-Pb锆石地质年代及其地质意义
作为分散在中国南海(SCS)的微型区块之一,西沙群岛的基底由于上覆厚厚的新生代沉积物而很少被钻探,这导致对西沙群岛前新生代基底的认识混乱。CK-1井是南中国海西北部西沙群岛的一个千米级大科学钻井,穿透了厚厚的礁状灰岩(0-888.4米)和下伏基底岩(888.4-901.4米)。本研究介绍了南中国海西北部西沙群岛CK-1井基底玄武质火成岩的锆石U-Pb年龄,以研究西沙微块的基底性质。CK-1井的基底由海山上的玄武质火成岩组成。锆石颗粒的表观年龄从约 2 138.9 Ma 到约 36 Ma 不等。CK-1井的老锆石被认为是继承锆石。两块新生代锆石的加权平均 206pb/238U 年龄为 (36.3 ± 1.1) Ma,平均平方加权偏差 (MSWD) = 1.2,这可能代表了火山爆发的最大年龄。CK-1井的燕山期继承锆石(116.9-105.7 Ma和146.1-130.2 Ma)与XK-1井的锆石一致,表明陈行岛的基底可能与XK-1井的基底相似。我们认为,西沙微地块可能发育在均匀的晚侏罗世变质结晶基底上,并由白垩纪花岗岩岩浆侵入。
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来源期刊
Acta Oceanologica Sinica
Acta Oceanologica Sinica 地学-海洋学
CiteScore
2.50
自引率
7.10%
发文量
3884
审稿时长
9 months
期刊介绍: Founded in 1982, Acta Oceanologica Sinica is the official bi-monthly journal of the Chinese Society of Oceanography. It seeks to provide a forum for research papers in the field of oceanography from all over the world. In working to advance scholarly communication it has made the fast publication of high-quality research papers within this field its primary goal. The journal encourages submissions from all branches of oceanography, including marine physics, marine chemistry, marine geology, marine biology, marine hydrology, marine meteorology, ocean engineering, marine remote sensing and marine environment sciences. It publishes original research papers, review articles as well as research notes covering the whole spectrum of oceanography. Special issues emanating from related conferences and meetings are also considered. All papers are subject to peer review and are published online at SpringerLink.
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