西沙群岛东岛浮岩矿物地球化学特征及成因探讨  

Research on Geochemical Characteristics and Genesis of Mineral of Dongdao in the Xisha Island

作　　者：吕迎秋 韩宗珠[1,2] 许红[3] 来志庆[1,2] 刘明[1,2] LV Yingqiu;HAN Zongzhu;XU Hong;LAI Zhiqing;LIU Ming(College of Marine Geosciences;The key Lab of Geosciences and Prospecting Techniques, Ministry of Education,Ocean University of China,Qingdao 266100,China;China Geological Servey-Qingdao Institute of Marine Geology,Qingdao 266071,China)

机构地区：[1]中国海洋大学海洋地球科学学院,山东青岛266100 [2]中国海洋大学海底科学与探测教育部重点实验室,山东青岛266100 [3]中国地质调查局青岛海洋地质研究所,山东青岛266071

出　　处：《海洋湖沼通报》2018年第5期138-146,共9页Transactions of Oceanology and Limnology

摘　　要：本文对采自西沙群岛东岛的2件浮岩样品进行了岩石学和矿物地球化学研究,研究表明,东岛浮岩样品属于中性火山岩,SiO_2含量在60%左右,化学组成相当于粗面岩,斑状结构,斑晶主要为斜长石、单斜辉石和少量橄榄石,基质为玻璃质。斜长石及辉石斑晶矿物具有中心熔蚀结构,斜长石形成温度为1030℃-1080℃;单斜辉石属均为普通辉石,斑晶Al_2O_3含量较低;橄榄石属于透铁橄榄石,橄榄石斑晶Fo值为55.40-60.53,从核部到边部各化学成分略有降低,且具有轻微的化学成分环带。从核部到边部Fo值略有降低。东岛浮岩岩浆是西沙地块受到拉张作用,中地壳物质减压熔融形成粗面质岩浆,并经历短暂的岩浆房冷凝时期,拉张减薄作用形成裂谷后,由于压力突然释放,粗面质岩浆沿裂谷快速上升在水下喷发形成浮岩。In this paper,the petrochemistry and mineral geochemistry of two pumice samples collected from the Xisha Islands are studied.The results show that the Dongdao pumice samples belong to the neutral volcanic rocks,the SiO2 content is about 60%,the chemical composition is equivalent to the trachyte and porphyritic-structures.The phanerocryst is mainly composed of plagioclase,clinopyroxene and a small amount of olivine,with vitreous matrix.Plagioclase and pyroxene porphyry minerals have a central corrosion structure,with the plagioclase formation temperature of 1030℃-1070℃.Clinopyxene is all augite,and Al2O3 content is low.Olivine belongs to hyalosiderite,with the Fo value 55.40-60.53.From the core to the edge,the chemical composition is slightly lower,and has a slight chemicalcomposition ring.From the core to the edge,the Fo value is slightly lower.The pumice magma of Dongdao is the Xisha block by the role of tensile effect.The middle crustal material decompression melting forms trachyte magma,and experienced a brief period of the slurry chamber condensation.After the formation of the rift,the pressure is suddenly released,the trachyte magma rises rapidly along the rift to form the pumice.

关 键 词：西沙群岛 浮岩 矿物 地球化学 岩浆活动 

分 类 号：P574.2[天文地球—矿物学]