The Paleozoic metamorphic history of the Central Orogenic Belt of China from 40Ar/ 39Ar geochronology of eclogite garnet fluid inclusions

Abstract

The pressure–temperature–time evolution of the UHP eclogites of Dabie–Sulu, in the eastern sector of the Central Orogenic Belt of China shows a complex pattern of predominantly Triassic, and to a lesser extent Early Paleozoic ages. 40Ar/ 39Ar stepwise-crushing analysis of eclogitic garnets yielded consistently Paleozoic ages. Because our initial results from the Bixiling eclogite were of limited areal extent, their significance required further testing. Data for garnet-bearing gneiss and eclogites from new locations in northern and southern Dabieshan (Shuanghe, Ganghe and Hongmiao), confirm the Paleozoic garnet results obtained from Bixiling eclogite. We also tested the technique on a garnet sample of known Paleozoic age from Altyn Tagh in the western Central Orogenic Belt. These new results indicate that light-colored garnets from Dabieshan and Altyn Tagh yield concordant 40Ar/ 39Ar ages ranging from 445–465 Ma by in vacuo crushing, and confirm that a Paleozoic (U)HP metamorphic event took place in the Central Orogenic Belt from Altyn Tagh in western China to Dabieshan in eastern China. In contrast, dark-colored garnets from mafic metavolcanics do not yield 40Ar/ 39Ar plateaux or isochrons ages.