摘要
本文报道了冀东青龙地区新太古代朱杖子群和单塔子群变质岩的锆石SHRIMP U-Pb定年结果。朱杖子群底部张家沟组砾岩中的TTG砾石、花岗岩砾石和基质的岩浆锆石207Pb/206Pb加权平均年龄分别为2515±9Ma(MSWD=1.9)、2510±10Ma(MSWD=1.6)和2512±7Ma(MSWD=1.0),朱杖子群底部张家沟组黑云斜长片麻岩碎屑锆石207Pb/206Pb加权平均年龄为2540±6Ma(MSWD=1.6),朱杖子群桲罗台组变质酸性火山岩岩浆锆石207Pb/206Pb加权平均年龄为2516±8Ma(MSWD=1.1),单塔子群鲁杖子组黑云变粒岩碎屑锆石207Pb/206Pb加权平均年龄为2504±7Ma(MSWD=1.8),另有一个数据点的207Pb/206Pb年龄为3.04Ga。根据本文定年结果和前人资料,获得主要结论如下:朱杖子群和单塔子群形成于新太古代晚期,很可能为岛弧环境的产物;朱杖子群与下伏单塔子群之间虽存在角度不整合关系,但时间间断不长,朱杖子群底部张家沟组砾岩不具有底砾岩性质;③绿片岩相—角闪岩相的朱杖子群和单塔子群与角闪岩相—麻粒岩相的遵化深变质绿岩带—三屯营—太平寨—迁安岩浆杂岩区变质程度差异很大,但形成时代相同,是后期构造作用把它们置于同一地壳平面。
In this paper are reported the SHRIMP U-Pb zircon ages of the Neoarchean Zhuzhangzi and Dantazi Groups in the Qinglong area, eastern Hebei Province. Weighted mean 207Pb/206Pb ages of magmatic zircons from TTG and granite pebbles and matrix of the Zhangjiagou Formation of the lowest Zhuzhangzi Group are 2515±9 Ma （MSWD=1.9）, 2510±10 Ma （MSWD=1.6） and 2512±7 Ma （MSWD=1.0）, respectively. Detrital zircons from biotite plagioclase gneiss of the Zhangjiagou Formation of the lowest Zhuzhangzi Group have a weighted mean 207Pb/206Pb age of 2540±6 Ma （MSWD=1.6）. A weighted mean 207Pb/206Pb age for magmatic zircon from meta-felsic volcanic rock of the Buloutai Formation of the Zhuzhangzi Group is 2516±8 Ma （MSWD=1.1）. The majority of detrital zircons from fine-grained biotite gneiss of the Luzhangzi Formation of the Dantazi Group have a weighted mean 207Pb/206Pb age of 2504±7 Ma （MSWD=1.8）, with a spot being 3044 Ma in 207Pb/206Pb age. Based on data obtained in this study and by others, some conclusions can be drawn as follows： （1） The Zhuzhangzi and Dantazi Groups were formed in an arc environment at the end of Neoarchean; （2） The age gap between deposition of the Zhuzhangzi and Dantazi Groups was very short although there indeed was a unconformity between them; （3） The Zhuzhangzi and Dantazi Groups of greenschist—amphibolite facies and the Santunyun—Taipingzhai—Qianxi magmatic complex of amphibolite—granulite facies are different in metamorphic grade but were formed almost at the same time, being a result of late crustal movement which overthrust these deep-seated rocks to the same crustal level.
出处
《地质论评》
CAS
CSCD
北大核心
2010年第6期888-898,共11页
Geological Review
基金
中国地质构造区划与区域地质调查综合集成项目(编号1212010811033)
国土资源部重点项目(编号1212010711815)的成果
