摘要
红石山-百合山蛇绿混杂岩带是北山造山带最北部的一条蛇绿混杂岩带,前人对百合山蛇绿岩的研究很少涉及。百合山蛇绿岩主要由变质橄榄岩、辉石橄榄岩、堆晶辉石岩、辉长岩、玄武岩等组成,对其中的辉长岩进行地球化学和锆石U-Pb年龄测试,以了解洋盆性质和形成时间。研究结果显示:辉长岩具有Al 2O 3、MgO含量高,P 2O 5含量低,富集大离子亲石元素、亏损高场强元素的特征,岩石初始87 Sr/86 Sr值为0.70418~0.70711,(143 Nd/144 Nd)i为0.512392~0.512568,εNd(t)值为+4.61^+7.28,反映岩浆物质来源于亏损地幔源区,形成过程受到俯冲消减流体的影响。辉长岩LA-MC-ICP-MS锆石U-Pb定年结果为344.6±1.8 Ma,岩石地球化学分析显示其属SSZ型(俯冲带型)蛇绿岩,形成于俯冲板片之上的不成熟弧后盆地环境,应为北侧雀儿山-圆包山岛弧基础上发育的早石炭世有限洋盆,代表了古亚洲洋在北山北部的分支洋盆。结合区域上广泛分布于百合山蛇绿混杂岩带南侧的晚石炭世—早二叠世白山岩浆弧特征,指示古亚洲洋在北山北部的演化至少持续到晚古生代晚期。
The Hongshishan-Baiheshan ophiolite mélanges belt is the northernmost ophiolite mélanges belt in the Beishan area.However,most of the researchers have been focused on the Hongshishan ophiolite mélanges but paid very insufficient attention to the Baiheshan ophiolite.The authors analyzed geochemistry and zircon U-Pb chronology of gabbros in order to understand the ocean basin tectonic environment and formation time.The results show that gabbro has high content of Al 2 O 3,MgO and LILE but poor content of P 2 O 5 and HFSE.Meanwhile,the gabbro have bulk Sr-Nd isotope composition of(87 Sr/86 Sr)i=0.70418~0.70711,(143 Nd/144 Nd)i=0.512392~0.512568,andεNd(t)=+4.61^+7.28.These data show that the magma of gabbro might have come from depleted mantle source area and the formation process of gabbro was affected by the subduction fluid.The LA-MC-ICP-MS zircon U-Pb dating yielded a 206 Pb/238 U age of 344.6±1.8 Ma for the Baiheshan ophiolite.The petrogeochemical analysis shows that gabbro formed SSZ type ophiolites in the subducting plate above the immature back-arc basin.The result suggests that Baiheshan ophiolite mélanges belt might have been a Carboniferous limited ocean formed in the Queershan-Yuanbaoshan arc and may have been the branch ocean basin of the Paleo-Asian Ocean in the Beishan area.According to the studies of the Late Carboniferous-Early Permian Baishan magmatic arc located in the southern part of the Hongshishan-Baiheshan ophiolite mélanges belt,the authors hold that the evolution of the Paleo-Asian Ocean lasted at least to the end of the Late Paleozoic.
作者
牛文超
辛后田
段连峰
赵泽霖
张国震
任邦方
张永
NIU Wenchao;XIN Houtian;DUAN Lianfeng;ZHAO Zelin;ZHANG Guozhen;REN Bangfang;ZHANG Yong(Tianjin Center,China Geological Survey,Tianjin 300170,China;Notth China Center for Geoscience Innovation,Tianjin 300170,China)
出处
《地质通报》
CAS
CSCD
北大核心
2020年第9期1317-1329,共13页
Geological Bulletin of China
基金
中国地质调查局项目《阴山成矿带小狐狸山和雅布赖地区地质矿产调查》(编号:DD20160039)
《内蒙古15万清河沟、红柳峡等两幅区域地质调查》(编号:DD20160039-17)。