MULTISTAGE METAMORPHISM OF THE HUANGTULING GRANULITE, NORTHERN DABIE OROGEN, EASTERN CHINA: IMPLICATIONS FOR THE TECTONOMETAMORPHIC EVOLUTION OF SUBDUCTED LOWER CONTINENTAL CRUST

Abstract

Granulites from Huangtuling in the North Dabie metamorphic core complex in eastern China preserve rare mineralogical and mineral chemical evidence for multistage metamorphism related to Palaeoproterozoic metamorphic processes, Triassic continental subduction-collision and Cretaceous collapse of the Dabie Orogen. Six stages of metamorphism are resolved, based on detailed mineralogical and petrological studies: (I) amphibolite facies (6.3-7.0 kbar, 520-550 °C); (II) high-pressure/ high-temperature granulite facies (12-15.5 kbar, 920-980 °C); (III) cooling and decompression (4.8-6.0 kbar, 630-700 °C); (IV) medium-pressure granulite facies (7.7-9.0 kbar, 690-790 °C); (V) low-pressure/high-temperature granulite facies (4.0-4.7kbar, 860-920 °C); (VI) retrograde greenschist facies overprint (1-2 kbar, 340-370 °C). The P-T history derived in this study and existing geochronological data indicate that the Huangtuling granulite records two cycles of orogenic crustal thickening events. The earlier three stages of metamorphism define a clockwise P-T path, implying crustal thickening and thinning events, possibly related to the assembly and breakup of the Columbia Supercontinent at c. 2000 Ma. Stage IV metamorphism indicates another crustal thickening event, which is attributed to Triassic subduction/collision between the Yangtze and Sino-Korean Cratons. The dry lower crustal granulite persisted metastably during the Triassic subduction/collision because of the lack of hydrous fluid and deformation. Stage V metamorphism records the Cretaceous collapse of the Dabie Orogen, possibly due to asthenosphere upwelling or removal of the lithospheric mantle resulting in heating of the granulite and partial melting of the North Dabie metamorphic core complex. Comparison of the Huangtuling granulite in North Dabie and the high-pressure-ultrahigh-pressure metamorphic rocks in South Dabie indicates that the subducted upper (South Dabie) and lower (North Dabie) continental crusts underwent contrasting tectonometamorphic evolution during continental subduction-collision and orogenic collapse. © 2006 Blackwell Publishing Ltd.