摘要
陕西安康的瓦房店、紫阳、岚皋、镇坪和湖北竹溪一带的早古生代地层中广泛出露具双峰式岩浆岩组合的岩墙群。本文通过紫阳高滩辉长岩锆石LA-ICP-MS U-Pb年代学研究,获得其侵位年龄为410±4.5Ma。高滩辉长岩具有类似OIB的稀土元素和微量元素分配特征,Th/Nb比值小于0.11,Nb/Zr大于0.15,显示其形成于与地幔柱活动相关的富集地幔源区。Nb/U、Ce/Pb比值及U、Th、Pb和Ni含量特征显示岩浆演化早期经历橄榄石和辉石的弱分离结晶作用,岩浆上升过程中几乎未受到地壳物质混染作用。高滩辉长岩年代学、微量元素地球化学特征及区域地质特征表明,早古生代晚期扬子陆块北缘地幔柱作用使得该区软流圈地幔上涌,导致扬子板块北缘陆内裂解,引发紫阳、岚皋一带早古生代晚期的基性岩浆作用。由于地幔深部热动力条件制约,这次大陆裂解事件未能持续。高滩辉长岩锆石年龄是对扬子板块北缘陆内裂解事件的响应。
Nb/U, Ce/Pb and concentration of U, Th, Pb and Ni in the gabbro dikes indicate that the pyroxenes and olivines were main fractional minerals in the fractional crystallization during the magma evolution, and they were not affected by contamination of continental crust from the mantle to crust. These helps to infer that the extensional tectonics developed constrainedly in the Early Paleozoic by the mantle plume activities that happened at the boundary of paleocontinent on the northern margin of Yangtze Plate,thus producing the large group of basic dike swarms in these areas. The deep thermodynamic condition is responsible for the crustal extension and end. Thus the age of 410±4.5 Ma not only represents the magma emplacement, but also the extension evolution history of this continent crust rift from beginning to end in Silurian.
出处
《地质科学》
CAS
CSCD
北大核心
2014年第2期456-471,共16页
Chinese Journal of Geology(Scientia Geologica Sinica)
基金
中国地质调查局地质调查项目(编号:1212011121116)资助
关键词
扬子板块北缘
辉长岩
锆石U-PB定年
大陆裂解
Northtern margin of the Yangtze Plate, Gabbro, Zircon U-Pb LA-ICP-MSdating, Continental rifting
