北祁连西段熬油沟辉长岩的锆石SHRIMP U-Pb年龄及地质意义  

SHRIMP U-Pb zircon age of gabbro in Aoyougou in the western segment of the North Qilian Mountains,China and its geological implications.

作　　者：相振群[1] 陆松年[1] 李怀坤[1] 李惠民[1] 宋彪[2] 郑健康 

机构地区：[1]中国地质调查局天津地质矿产研究所,天津300170 [2]北京离子探针中心,北京100037 [3]青海省区域地质调查研究院,青海西宁810012

出　　处：《地质通报》2007年第12期1686-1691,共6页Geological Bulletin of China

基　　金：国家自然科学基金项目(编号:40032010-C;40373032);国土资源调查项目(编号:200313000060;1212010560801-04)成果

摘　　要：从北祁连熬油沟辉长岩中选出的锆石的外部形态、内部结构单一。SHRIMP测年共测定8个点,每个点的Th/U值都非常高,大都在0.8以上。8个点的206Pb/238U表面年龄在误差范围内完全一致,加权平均值为503.7Ma±6.4Ma,这一结果与前人在同一地点采集的辉绿岩墙样品的锆石SHRIMP U-Pb测年结果有较大的差异。结合研究区内已有的研究成果认为:①熬油沟地区的辉长辉绿岩形成于早古生代,并不是中元古代早期。②辉长岩中的锆石成因单一,其测试年龄结果的地质意义明确;而同源岩浆侵入体的辉绿岩往往容易从围岩中捕获大量锆石,使得锆石成因复杂,年龄测试结果复杂。因此,与辉绿岩相比,辉长岩锆石SHRIMP U-Pb年代学研究可以获得更为可靠的、地质意义明确的年龄信息。SHRIMP U-Pb zircon ages of gabbro at Aoyougou in the western segment of the North Qilian Mountains are reported in this paper. The zircon crystals separated from the gabbro have a euhedral-subhedral shape and a loosely striped inner structure on cathodoluminescence （CL） images. A total of eight spots were analyzed by SHRIMP U-Pb dating and the Th/U ratios at all the analyzed spots are very high, mosdy 〉0.8. The apparent ^206Pb/^238U ages of all the eight analyses are consistent within errors, with a weighted mean ^206Pb/^238U age of 503.7 ± 6.4 Ma. The results are significandy different from the SHRIMP U-Pb zircon age data of diabase dike samples collected from the same site reported by previous researchers. Based on the available research results obtained in the area, the authors conclude that： （1） gabbro and diabase in the Aoyougou area were formed in the early Paleozoic rather than the early Mesoproterozoic; and （2） the zircons separated from diabase are usually very complex in origin and much caution is needed in the interpretation of their age data, but, on the contrary, zircons from gabbro are generally of simple and unequivocal origin and consequently their U-Pb ages are more reliable with unambiguous geological significance.

关 键 词：北祁连山 熬油沟 辉长岩 锆石SHRIMP U-PB年龄 

分 类 号：P588.124[天文地球—岩石学] P597.3[天文地球—地质学]