摘要
大悟杂岩位于大别山西段,主体为花岗质片麻岩。为了限定其形成与变形过程,本文综合运用锆石U-Pb法和白云母^(40) Ar/^(39) Ar法进行年代学研究。锆石U-Pb LA-ICP-MS法对这些花岗质片麻岩定年结果显示:锆石的Th/U值为0.79~4.29,属于典型的岩浆锆石特征;206Pb/238 U的加权平均年龄为(810±63)Ma(n=12,MSWD=0.021),代表这些花岗质片麻岩的形成时代。大悟杂岩核部花岗质片麻岩的白云母坪年龄为(210.5±1.4)Ma,相应的等时线年龄为(211.6±2.5)Ma。这些新的研究结果支持以下两点认识:大悟杂岩中的花岗质片麻岩形成于新元古代,而不是白垩纪;这些前寒武纪岩石的构造抬升过程发生在三叠纪晚期(211 Ma)。由于西大别晚三叠世构造与高压—超高压变质岩的出露过程有关,因此,大悟杂岩的变形与高压—超高压变质岩的抬升之间的关系就成为一个耐人寻味的科学问题。同时,由于大悟杂岩中的多数构造面理和线理形成于区域高压—超高压变质作用之后,据此推断西大别三叠纪晚期的变形发生在造山晚期-后造山背景下,伴随着地壳和岩石圈的大规模伸展与减薄。
Dawu complex is located in the western part of the Dabie orogenic belt.The complex is mainly composed of gneissic granite.To constrain the timing of the formation and deformation processes of the complex,a set of integrated zircon U-Pb and muscovite ^40 Ar-^39 Ar dating were carried out.The conducted zircon U-Pb LA-ICP-MS isotopic dating of the gneissic granites from the complex showed Th/U ratios in the range of 0.79-4.29 indicating the zircon is a typical magmatic mineral.The weighted mean-^206Pb/^238 U age is（810±63）Ma（n=12,MSWD=0.021）,which is considered to be the formation age of the gneiss.The ^40 Ar/39 Ar dating of muscovite from the gneissic granites in the central part of Dawu complex yields a plateau age of（210.5 ± 1.4）Ma and an isochron age of（211.6 ± 2.5）Ma.The new dating results support that：（1）The strongly deformed magmatic rocks in the Dawu complex were formed in the Neoproterozoic rather than Cretaceous,（2）Large scale crustal deformation and exhumation of the Precambrian rocks mainly occurred in Late Triassic（211Ma）.Since the Late Triassic tectonic processes were related to exhumation of the HP-UHP metamorphic rocks in western Dabie orogen,it is worth investigating the relationship between the formation of the Dawu complex and the exhumation of the HP-UHP metamorphic rock in the study area.Meanwhile,most of the foliations and lineations in the Dawu complex formed after the regional HP-UHP metamorphism,we therefore infer that the Late Triassic deformation occurred in the geodynamic settings of late to post-orogeny,and might be accompanied by large scale crustal extension and lithospheric thinning.
作者
崔建军
王艳红
郑光高
施炜
马立成
Cui Jianjun Wang Yanhong Zheng Guanggao Shi Wei Ma Licheng(Institute of Geomechanics , Chinese Academy of Geological Sciences, Beijing 100081, China School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China)
出处
《吉林大学学报（地球科学版）》
EI
CAS
CSCD
北大核心
2017年第1期139-153,共15页
Journal of Jilin University：Earth Science Edition
基金
国家科技专项(SinoProbe-08-1)
地质力学研究所基本科研经费(DZLXJK201302)~~
