海南岛早古生代大地构造格局:来自志留纪早期碎屑锆石年代学的约束

Early aleozoic ectonics f ainan sland:Constraints rom he etrital ircons U-Pb Geochronology on Early Silurian Sandstones

北东向乐东-定安断裂的具体位置及演化对海南岛大地构造单元划分及构造演化研究意义重大。本文采用碎屑锆石年代学方法,分析了乐东-定安断裂南西段两侧志留纪兰多维列世沉积物物源的特征及其差异,并讨论其中蕴含的大地构造意义。研究结果表明东方江边娜姆河地区志留纪兰多维列世陀烈组中碎屑锆石年龄介于1457~3124 Ma之间,显示1个主峰年龄约1840 Ma,大多数锆石年龄介于1624~2046 Ma之间。保亭南好地区志留纪兰多维列世足赛岭组中碎屑锆石年龄介于417~2937 Ma之间,其中最年轻一组锆石年龄介于417~501 Ma之间,形成了一个449 Ma的主峰,其余锆石年龄多介于1300~1800 Ma之间。东方江边娜姆河地区陀烈组和保亭南好地区足赛岭组沉积特征和物源的差异性暗示它们形成的沉积背景与物源区不同,结合其他相关地质资料,认为以乐东-定安断裂为界可将海南岛划分为琼西北地块与琼东南地块,二者拼合形成统一的海南地块,拼合时间应晚于早志留世。

Constraining the location and formation age of the NE-Trending Ledong-Dingan fault is crucial to better understand the tectonic unit division and tectonic evolution of Hainan island.In this contribution,detrital zircon geochronology is used to analyze the characteristics and differences of the lower Silurian sediment sources on both sides of the southwestern segment of the Ledong-Dingan fault,and to interpret the tectonic significance indicated by the provenance differences.The dating results show that the detrital zircon ages from the early Silurian Tuolie Formation in the Jiangbian area(Dongfan County)which located at the northwest of Ledong-Dingan fault range from 1457 Ma to 3124 Ma,and most zircon ages range from 1624 Ma to 2046 Ma,with the main peak at about 1840 Ma.And the detrital zircon ages from the early Silurian Zusailing Formation in Nanhao area(Baoting county)which is located at the southeast of Ledong-Dingan fault range from 417 Ma to 2937 Ma,in which the youngest group of zircons is from 417 Ma to 501 Ma,forming the main peak of 449Ma,while the rest mostly range from 1300 Ma to 1800 Ma.The differences of the sedimentary characteristics and source between the two Formation suggest the different sedimentary background and provenance area.Together with other relevant geological data,Hainan island should be subdivided into the Qiongxibei block(northwest Hainan Island)and the Qiongdongnan block(southeast Hainan Island)with the fault as boundary which are combined to form a unified Hainan block during the time later than the Early Silurian.