南海西北部内陆架表层沉积物的重矿物分布及其控制因素

DISTRIBUTION PATTERN OF HEAVY MINERALS IN THE SURFACE SEDIMENTS ON INNER SHELF,NORTHWEST SOUTH CHINA SEA AND ITS CONTROLLING FACTORS

对2008年取自于南海西北部内陆架408个站位表层沉积物样品进行了重矿物研究。结果表明:本区重矿物可划分为3个重矿物组合区,各分区的优势重矿物组合分别为锆石-钛铁矿-赤铁矿,白钛矿-锐钛矿-绿帘石以及辉石-角闪石-绿帘石。3个区域在沉积环境、水动力状况、沉积物粒度、氧化还原条件方面都存着明显的差异,反映重矿物的分布受到物源和水动力条件的共同控制。受水动力影响,研究区重矿物分布的总体趋势表现为:从水动力强的Ⅰ区到水动力相对弱的Ⅲ区,重矿物组合由河口三角洲高密度、强稳定性矿物组合逐步向浅海内陆架和半封闭海湾低密度、弱稳定的矿物组合转变。研究区重矿物具有多源性,分为陆源、近源和自生三大类。海南岛和粤西的云开地块是研究区重矿物的主要来源。另外,珠江的碎屑物质以及广东沿岸海岛的风化剥蚀物也是重要的物源。

The heavy minerals of 408 surface sediment samples collected from the inner shelf of the northwest South China Sea were analyzed in 2008.The results suggested that there are three heavy mineral provinces in this region,dominated by Zircon-Ilmenite-Hematite assemblage,Anatase-White Titanium-Epidote assemblage,and Pyroxene-Hornblende-Epidote assemblage respectively.The three provinces have conspicuous differences in depositional environment,hydrodynamic condition,grain size and redox environment,suggesting that the distribution pattern of heavy minerals is controlled by both provenance and hydraulic conditions.From the provinceⅠwith high hydrodynamic condition to the province Ⅲ with relatively low hydrodynamic condition,or from the river estuary and deltas to the inner shelf and semiclosed bays,the stable heavy minerals of high density gradually decrease and those with less density and lower stability increase.The heavy minerals in the study area came from three major sources,i.e.terrestrial,nearshore and autogenetic sources.Terrestrial heavy minerals were mainly from the Hainan island and Yunkai massif.The heavy minerals from erosion of the coastal islands and surrounding lands are mainly distributed by the Pearl River.