胶东—苏北石榴石二辉橄榄岩形成条件及年代  

Formation Conditions and Age for Garnet Lherzolite from Eastern Shandong and Northern Jiangsu,China

作　　者：白文吉[1] 胡旭峰[1] 周美付 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]加拿大萨斯堪彻温大学地质系

出　　处：《岩石矿物学杂志》1992年第4期299-305,共7页Acta Petrologica et Mineralogica

基　　金：国家自然科学基金资助项目的部分研究内容

摘　　要：在胶东—苏北地区,由石榴石二辉橄榄岩、尖晶石二辉橄榄岩、石榴石辉石岩、榴辉岩、斜辉辉橄岩和纯橄岩组成的杂岩成群和成带分布,延长590km。该岩带越过郯庐断裂带延伸至大别山,全长约1200km。岩带内石榴石二辉橄榄岩与尖晶石橄榄岩伴生,组成较大的岩块,并且与榴辉岩伴生,曾被作者确定为一种有层序的岩套。石榴石二辉橄榄岩的Sm-Nd同位素年龄为925±53Ma,矿物地质温度计和压力计表明其形成于115—160km深部,温度为800—1371℃。该石榴石二辉橄榄岩平衡温度和压力符合大陆地温线,而不同于中国东部沿海地区玄武岩中包体石榴石二辉橄榄岩,后者的平衡温度压力符合于大洋地温线。A zone of eclogite-garnet lherzolite-spinel lherzolite complex occurs in.the Archean basement, running from the east seacoast in Shandong throughnorthern Jiangsu into the Dabie Mountains for about 1200 km. The complexsuite has a sequence consisting of garnet lherzolite, spinel lherzolite andduuite in the lower part, and eclogite and garnet pyroxenite in the upperpart. The garnet lherzolite, spinel lherzolite and dunite are of interbeddedlayer. Over 1000 of the complex blocks are exposed as boudins resulting fromstretching and shearing, which have formed a specific 'melange'with theircountry rocks including gneiss, amphibolite and granulite. The garnet lherzolite is similar in main chemical composition to thexenoliths from the basalts in eastern China, is characterized by a highcontent of MgO for the olivine, clinopyroxene, orthopyroxene and garnet. The fresh garnet lherzolite has a total REE content of 2.41--14.23 ppm,and shows much the same REE patterns which are similar to those of pyro-lite. The equilibrium temperatures and the pressures of the minerals rangefrom 800 to 1371℃, and from 35 to 49.8×10~8 Pa respectively. The paleo-geotherm is essentially coincident with the continental geotherm. The age of the garnet lherzolite determined by Sm-Nd methodt is 925±53 Ma. The authors suggest that the garnet lherzolite represents essentially Paleo-pyrolite of South China.

关 键 词：石榴石 二辉橄榄岩 成因 年代 

分 类 号：P578.947[天文地球—矿物学]