摘要
本次研究运用岩相学和碎屑锆石U-Pb年龄物源分析方法获得北海涠洲岛海滩砂的物源特征,从而揭示北部湾大陆边缘“源-汇”系统及其沉积搬运过程。涠洲岛海滩砂以棱角状-次圆状石英为主(70%~75%),生物碎屑次之(20%~25%),含少量玄武岩岩屑和橄榄石碎屑颗粒(约5%),反映碎屑沉积物经历了较短距离的搬运且沉积时间较短。涠洲岛海滩砂碎屑锆石U-Pb年龄集中在288~210 Ma(峰值为236 Ma)和435~380 Ma,表明涠洲岛海滩砂主要来源于桂东南地区印支期花岗岩体以及加里东期和燕山期岩体。花岗岩来源的陆源碎屑经南流江、九洲江等河流快速地搬运至合浦-北海三角洲,在风暴作用下再扩散至北部湾中部海域。这一过程很好地记录了大陆边缘从陆到洋区域性“源-汇”系统。同时,涠洲岛是第四纪火山岛,是北部湾中部海域的隆起剥蚀区之一,其为海滩沉积物提供近源的基性岩碎屑组分,即存在盆地局部“源-汇”系统。因此,涠洲岛海滩砂沉积是大陆边缘区域性“源-汇”系统与盆地局部“源-汇”系统相互叠加的产物。本研究为理解大陆边缘从陆到洋“源-汇”系统与盆地局部“源-汇”系统的相互作用提供范例。
This study applied grain-size and lithological and detrital zircon U-Pb provenance analyses to identify depositional facies and the provenance of intertidal beach sands on the Weizhou Island,Beibu Bay;these help constrain the“Source to Sink”sedimentary system and associated sediment transport processes on the continental margin of the Beibu Bay.The lithological study shows that beach sands are predominantly angular to subrounded quartz(70%–75%),with subordinary bioclasts(20%–25%)and minor basaltic fragment and olivine(5%),indicating that the grains have undergone short-distance transport and short residence time.Laser Ablation ICPMS U-Pb zircon geochronology shows the zircon age-spectrum is dominated by modal ages of 288–210 Ma(peaking at 236 Ma)and 435–380 Ma,as well as containing minor zircon grains of Precambrian age.The modal ages of detrital zircon imply that the beach sediments were mainly derived from Indosinian granites to the north in the southeastern Guangxi.Granites of Caledonian(467–420 Ma)and Yanshanian(160–90 Ma)age in the southeastern Guangxi contributed minor detritus to the beach on the Weizhou Island.Granite-derived sediment was first transported through the Nanliu and Jiuzhou rivers into the Hepu-Beihai delta and then redistributed through the central part of the Beibu Bay by frequent storms.This series of source weathering,transportation and sedimentation processes preserved by these exotic sediments on the Weizhou Island accurately documents a regional(first-order)“Source to Sink”system from land to sea on a continental margin.Weizhou Island is a Quaternary basaltic island and is a part of the denudation area in central Beibu Bay.Mafic grains such as olivine,clinopyroxene,and basaltic rock fragments are physically weathered components of the olivine-bearing basalts and volcaniclastics on the Weizhou Island,namely local sediments.This implies that Weizhou Island itself is a local,but apparently minor,source of the beach sands,reflecting a local“Source to Sink”system in the Beibu Bay.Therefore,beach sands on Weizhou Island are products of the interaction between a continental margin“Source to Sink”system and a local“Source to Sink”system.Our provenance analyses complicate a straightforward application of the“Source to Sink”paradigm because the local source is inferior to the distant source.
作者
郑昊
温淑女
庞崇进
Bryan Krapez
何平
ZHENG Hao;WEN Shu-nü;PANG Chong-jin;Bryan Krapez;HE Ping(Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration,Collaborative Innovation Center for Exploration of Hidden Nonferrous Metal Deposits and Development of New Materials in Guangxi,Guilin University of Technology,Guilin 541004,China;State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China)
出处
《地球化学》
CAS
CSCD
北大核心
2020年第5期563-580,共18页
Geochimica
基金
国家自然科学基金(41803020,41703039)
同位素国家重点实验室开放基金(SKLIG-KF-14-06)
有色及贵金属隐伏矿床勘查教育部工程研究中心项目(2018GCZX001)。
关键词
从源到汇
海滩砂
物源分析
火山岛
北部湾
source to sink
beach sand
detrital zircon provenance analysis
volcanic island
Beibu Bay
作者简介
郑昊(1997–),男,本科在读,资源勘查工程专业。E-mail:771195167@qq.com;通讯作者:温淑女,E-mail:wenshunv@glut.edu.cn,Tel:+86-773-3675177。
