海南岛雷鸣盆地鹿母湾组碎屑岩地球化学特征、锆石U-Pb年龄和Hf同位素组成:对物源及构造环境的启示

Geochemical Characteristics,Zircon U-Pb Ages and Hf Isotopic Compositions of the Lumuwan Formation in the Leiming Basin,Hainan Island:Implications for Its Provenance and Tectonic Environment

海南岛雷鸣盆地鹿母湾组的确切沉积时限和沉积物来源是研究的空白区域。本文选取雷鸣盆地鹿母湾组作为研究对象,通过全岩地球化学、碎屑锆石U-Pb年代学和Lu-Hf同位素分析,旨在限定其沉积时限及物质来源,并探讨其沉积构造环境。鹿母湾组碎屑沉积岩的最年轻碎屑锆石年龄峰(113.3 Ma)与侵入其中的花岗闪长岩岩体年龄(~107 Ma)限定鹿母湾组沉积时限为109.9~113.3 Ma。全岩地球化学研究表明,鹿母湾组碎屑沉积岩的分异指数(ICV)为0.78~1.52(平均值0.96)、化学风化指数(CIA)为51.11~73.45(平均值65.27),反映其源区岩石具有中等成熟度并经历了弱的化学风化作用。结合微量元素、稀土元素含量及相关比值(如La、Th、Sc、Zr、Hf、∑REE及δEu)、源区判别图和构造环境判别图解,本文认为鹿母湾组碎屑沉积岩可能沉积于活动大陆边缘相关的盆地,主要来源于同时代的长英质火山岩或火山物质,少量碎屑来自华南内陆和海南岛早古生代岩浆岩。

Few studies have focused on the age and provenance of the Lumuwan Formation in the Leiming Basin.Here,we present whole-rock geochemistry,zircon U-Pb chronology,and Lu-Hf isotopic compositions of the Lumuwan Formation and discuss the sedimentation time,provenance,and sedimentary tectonic environment.The deposition time of the Lumuwan Formation is 109.9-113.3 Ma constrained by the youngest detrital zircon age peaks(113.3 Ma)and the age of the intruded rock masses(ca.107 Ma).The ICV and CIA of the detrital sedimentary rocks in the Lumuwan Formation range from 0.78 to 1.52 and 51.11 to 73.45,with average values of 0.96 and 65.27,respectively,indicating that the protolith with medium maturity had undergone weak chemical weathering.Combined with the contents and ratios of trace elements(e.g.,La,Th,Sc,Zr,Hf,∑REE andδEu),source discriminant diagrams,and tectonic discriminant diagrams,we conclude that the detrital rocks of the Lumuwan Formation are typical continental-crust-derived sedimentary rocks,which had been likely to be deposited in basins related to active continental margins.This comprehensive study showed that the Lumuwan Formation was mainly sourced from felsic volcanic rocks or volcanic materials contemporaneous with the sedimentation,with a small amount of debris originating from the early Paleozoic magmatic rocks of the South China plate and Hainan Island.