SHRIMP Single Zircon U-Pb Geochronology of Eclogites from Yingshan and Xiongdian

Abstract

Zircons of eclogites from Xiongdian (Luoshan, Henan) and Mifengjian (Yingshan, Hubei) are dated by the SHRIMP U Pb method. The Yingshan coesite bearing ultrahigh pressure eclogite shows four age groups: (773±20) Ma, (730±16) Ma, (461±7) Ma and (262±6) Ma, with the dominance of the (461±7) Ma group. The Xiongdian high pressure eclogite shows three age groups of (449±14) Ma, (307±14) Ma and (216±4) Ma. The ca. 450 Ma age is present in eclogites from both localities. They have extremely low Zr (9×10 -6 -19×10 -6 ). Together with the MORB like trace element characteristics and e Nd (+6.56 at 450 Ma), the age suggests an early Paleozoic high and ultrahigh pressure metamorphic event probably related to the subduction of oceanic crust and associated arc materials. The coexisting Ordovician and Triassic ages in the Xiongdian eclogite also suggest that the northern boundary of the Dabie high and ultrahigh pressure metamorphic belt, regardless of time, is to the north of Xiongdian.