南大西洋洋中脊玄武岩中斜长石特征及其岩石学意义  

Characteristics and Petrogenesis Significance of Plagioclases in Basalt from the South Mid-Atlantic Ridge

作　　者：祁奇[1,2] 来志庆[1,2] 龙晓军[1,2] 冷传旭 赵广涛[1,2] 

机构地区：[1]中国海洋大学海底科学与探测技术教育部重点实验室,山东青岛266100 [2]中国海洋大学海洋地球科学学院,山东青岛266100

出　　处：《中国海洋大学学报（自然科学版）》2016年第3期105-112,共8页Periodical of Ocean University of China

基　　金：国家自然科学基金项目(41376053)资助~~

摘　　要：本文利用电子探针技术分析了南大西洋洋中脊玄武岩中斜长石的结构构造和物质组成特征,讨论了该区岩浆过程在斜长石中的记录。按粒径大小可将研究区玄武岩中的斜长石分为斑晶、微晶和基质三类,斑晶斜长石核部平均An值为74,属于培长石,而边部平均An值为69,属于拉长石,呈正环带构造,微晶斜长石平均An值为67,与斑晶斜长石边部成分近似,且其粒径与斑晶斜长石边部宽度接近,约在30μm,极可能是同一时期形成。基质斜长石平均An值为63,略小于微晶斜长石。利用马西兹修改后的斜长石结晶温度计算公式,估算出斑晶斜长石核部结晶温度约为1 214℃,斑晶斜长石边部结晶温度约为1 085℃,微晶斜长石的结晶温度约为1 081℃,而基质斜长石的结晶温度约为1 056℃。由此推测,高An值（78~80）的斑晶斜长石的核部可能是形成于岩浆源区的捕掳晶。斑晶斜长石的边部、微晶斜长石及基质斜长石的结晶温度相近,说明三者可能近乎同时结晶;但由于它们的颗粒大小变化范围较大,很可能分别形成于岩浆房、岩浆通道及喷出洋壳表面后等环境中。与冲绳海槽玄武岩中斜长石比较,本区斜长石平均An值跨度以及结晶温度跨度均比冲绳海槽小,本区An值为74~63,结晶温度为1 214~1 056℃,而冲绳海槽An值为86~47,结晶温度为1 250~950℃。这表明相对于岩浆物理化学环境曾经历快速变化的弧后盆地来说,慢速洋中脊的岩浆活动的物理化学环境则相对稳定。In this paper,electronic probe technology is applied for analyzing structure,composition and ingredient features of plagioclases of mid-ocean ridge basalt in South Atlantic.It is a very important way to understand magmatic process in Mid-Atlantic Ridge area.Records of magmatic process in this area in the plagioclases are discussed.According to size,basalt in the research area as same as the Okinawa Trough can be divided into three categories：phenocryst,microphenocryst and groundmass.It means there are three different generations of plagiclases in this area.The mean An value of core of phenocryst plagioclases is 74,which means they belong to bytownite;on the other hand,the mean An value of their marginal parts is 69,which means they belong to labradorite and have a construction of positive band and the An value declines sharply from their core to edge.The mean An value of microlite plagioclases is 67 and microlite plagioclases are close to marginal parts of phenocryst plagioclases with regard to ingredient and particle size（about 30μm）.Therefore,there is a high probability that they have been formed during a same period.The mean An value of substrate plagioclases is 63,which is a little smaller than that of microlite plagioclases.When calculating with the formula for calculating crystallizing temperature of plagioclases which has been modified by Mansiz,the crystallizing temperature for core of phenocryst plagioclases is1 214℃ while that for edge is 1 085℃;the crystallizing temperature for microlite plagioclases is 1 081℃while that for substrate plagioclases is 1 056℃.Hence,we infer that core of phenocryst plagioclases with high An（78~80）may have formed from magmatic hearth area and their crystallizing temperatures decline sharply from core to edge,which means magma may have experiences a rapid-cooling process.The edge parts of phenocryst plagioclases are close to microlite plagioclases and substrate plagioclases with regard to crystallizing temperature,which means the three types may have been

关 键 词：玄武岩 斜长石 结晶温度 大西洋洋中脊 

分 类 号：TM619[电气工程—电力系统及自动化]