Zircon U-Pb dating of the metamorphic rocks of different grades from the southern part of the Dabie terrain in China

Zircon U-Pb dating was carried out for a number of the metamorphic rocks of different grades in the southern part of the Dabie terrain. They include r egional orthogneisses and enclosed phyllite in South Dabie unit as well as schist and amphibolite in Susong metamorphic belt. The ages of one orthogne iss sample indicate an emplacement time of its protolith at Neoproterozoic (576 +/- 49Ma) and a metamorphic event at 245 +/- 33Ma. Ages of 400 to 500M a were obtained for the samples of the orthogneiss and phyllite in South Da bie ultrahigh pressure terrain as well as schist and amphibolite in Susong metamorphic belt suggesting that these rocks were affected by a tectono-the rmal event at Early Palaeozoic. This implies that the rocks were not subduc ted to mantle depths by plate subduction and did to suffer resetting of U-P b isotopic system by ultrahigh pressure metamorphism at Triassic. (C) 2001 Elsevier Science Ltd. All rights reserved.