The Dabieshan Coesite‐bearing Eclogite Terrain—A Late Archaean Ultra ‐ high‐ Pressure Metamorphic Belt

Abstract A U ‐Pb zircon age of 2774±24 Ma for eclogite from the Bixiling rock body of Anhui Province, central China, indicates that the Dabieshan coesite‐bearing eclogite was probably formed in the Late Archaean. A phengite Ar‐Ar isochron age of 662±13 Ma for the eclogite confines also an upper limit age of its subsequent retrograde metamorphism in the Precambrian. The results of isotopic dating for such type of eclogite coincide with the geological features of its restricted occurrence within the Archaean metamaorphic terrain composed of the Dabie Group. It is believed that the Dabieshan coesite‐bearing eclogite terrain might be a Late Archaean ultra‐high‐pressure metamorphic belt. The Dabie Mountains area was the eastward extension of the southern Qinling structural belt during the Triassic. Both the Dabie Group and the coesite‐bearing eclogite host,ed therein underwent a late‐stage dynamic metamorphic event. The present authors have obtained a muscovite Ar‐Ar isochron age of 192.6± 2.8 Ma from plagioclase gneiss and a hornblende Ar‐Ar plateau age of 230.7±4.6 Ma for the low amphibolite in eclogite respectively, which represent the Indosinian reworking ages of the original metamorphic rocks of the Dabie Group gneiss and coesite‐bearing eclogite.