Multi-isotopic system geochronology of low temperature eclogite from Huangzhen, Southern Dabie Terrain

Abstract

Zircon U-Pb thermal ionization mass-spectrometer (TIMS) and secondary ion mass-spectrometer (SIMS) dating, mica and amphibole 40 Ar- 39 Ar dating and mineral Sm-Nd isotopic compositions of Huangzhen low temperature eclogite and country granitic gneiss are carried out. The zircon U-Pb weighted average SIMS age is (231.6±9.7) Ma for one eclogite. The mica 40 Ar- 39 Ar isochron age is (232.6±2.1) Ma and the lowest plateau age is (221.7±2.4) Ma from same sample. U-Pb TIMS concordant ages from other eclogite zircons are from (221.3±1.4) Ma to (222.5±2.3) Ma. U-Pb SIMS low intercept age from country granitic gneiss is (221±35) Ma. The retrograde amphibole 40 Ar- 39 Ar isochron age is (205.9±1.0) Ma. Except for mica, which may contain excess 40 Ar, all the ages represent peak and retrograde metamorphism of low temperature eclogites. It is indicated that the Huangzhen low temperature eclogites differ from Xiongdian low temperature eclogites of north of the Northern Dabie Terrain in metamorphic ages. Huangzhen low temperature eclogites share one coherent HP-UHP terrain with high temperature eclogites from Southern Dabie Terrain and they may have differences in subduction depth and cooling rates during exhumation.