地质学报（英文版）2003，Vol.77Issue(2)：155-168,14.
40Ar/39Ar Dating of Deformation Events and Reconstruction of Exhumation of Ultrahigh-Pressure Metamorphic Rocks in Donghai,East China
40Ar/39Ar Dating of Deformation Events and Reconstruction of Exhumation of Ultrahigh-Pressure Metamorphic Rocks in Donghai,East China
摘要
Abstract
Recent investigations reveal that the ultrahigh-pressure metamorphic (UHPM) rocks in the Donghai regionof East China underwent ductile and transitional ductile-brittle structural events during their exhumation. The earlierductile deformation took place under the condition of amphibolite facies and the later transitional ductile-brittledeformation under the condition of greenschist facies. The hanging walls moved southeastward during both of these twoevents. The 40Ar/39Ar dating of muscovites from muscovite-plagioclase schists in the Haizhou phosphorous mine, whichare structurally overlain by UHPM rocks, yields a plateau age of 218.0±2.9 Ma and isochron age of 219.8Ma, indicatingthat the earlier event of the ampibolite-facies deformation probably took place about 220 Ma ago. The 40Ar/39Ar dating oforiented amphiboles parallel to the movement direction of the hanging wall on a decollement plane yields a plateau age of213.1 ±0.3 Ma and isochron age of 213.4±4.1 Ma, probably representing the age of the later event. The dating of pegmatiticbiotites and K-feldspars near the decollement plane from the eastern Fangshan area yield plateau ages of 203.4±0.3 Ma,203.6±0.4 Ma and 204.8±2.2 Ma, and isochron ages of 204.0±2.0 Ma, 200.6±3.1 Ma and 204.0±5.0 Ma, respectively,implying that the rocks in the studied area had not been cooled down to closing temperature of the dated biotites and K-feldspars until the beginning of the Jurassic (about 204 Ma). The integration of these data with previous chronological ageson the ultrahigh-pressure metamorphism lead to a new inference on the exhumation of the UHPM rocks. The UHPM rocksin the area were exhumed at the rate of 3-4 km/Ma from the mantle (about 80-100 km below the earth's surface at about240 Ma) to the lower crust (at the depth of about 20-30km at 220 Ma), and at the rate of 1-2 km/Ma to the middle crust (atthe depth of about 15 km at 213 Ma), and then at the rate of less than 1 km/Ma to the upper crust about 10 km deep at about204 Ma.关键词
ultrahigh-pressure metamorphic rocks, structural deformation, 40Ar/39Ar dating, exhumation, Donghai, East ChinaKey words
ultrahigh-pressure metamorphic rocks, structural deformation, 40Ar/39Ar dating, exhumation, Donghai, East China分类
天文与地球科学引用本文复制引用
LI Jinyi,YANG Tiannan,CHEN Wen,ZHANG Sihong..40Ar/39Ar Dating of Deformation Events and Reconstruction of Exhumation of Ultrahigh-Pressure Metamorphic Rocks in Donghai,East China[J].地质学报（英文版）,2003,77(2):155-168,14.基金项目
This study was financially supported by the former Ministry of Geology and Mineral Resources of China (grant No. 9501102). （grant No. 9501102）
