Regional-Scale Extensional Tectonic Pattern of Ultrahigh-Pressure and High-Pressure Metamorphic Belts from the Dabie Massif, China

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Abstract
Recently, regional structural studies and detailed mapping at a scale of 1:10,000 in several key areas in the Dabie massif have revealed that the present regional tectonic pattern of ultrahigh-pressure and high-pressure metamorphic belts was formed mainly by extensional processes that postdate the Triassic collision between the Sino-Korean and Yangtze cratons. The tectonic pattern is characterized by an ancient metamorphic core complex, in which the most prominent feature is the development of multilayered extensional detachment zones on a crustal scale. This pattern controls the present spatial distribution of the ultrahigh-pressure metamorphic (UHPM) and high-pressure metamorphic (HPM) rocks, and obviously records large-scale subhorizontal extensional flow under amphibolite-facies conditions when the UHPM and HPM rocks were returned to lower-middle crustal levels. Based mainly on the crustal-scale tectonic scenario and combined with previous petrological and geochronological studies, the Dabie Mountains can be subdivided into six main tectonometamorphic units—the Northern Huaiyang (NHY) tectonic belt, Dabie complex, UHPM unit, HPM unit, epidote-blueschist (EBM) unit, and weakly metamorphosed sedimentary cover (SC). All units are tectonically separated by detachment ductile shear or fault zones. The Balifan-Mozi-tan-Xiaotian fault (BMXF), separating the NHY tectonic belt to the north from the Dabie massif (DM) to the south, is considered as the suture zone between the Sino-Korean and Yangtze cratons during the Triassic intracontinental collision. The geodynamic implications of this extensional tectonic pattern for the exhumation process of the UHPM and HPM rocks also are briefly discussed. It appears that recognition of the extensional tectonic pattern is of paramount importance for an understanding of the kinematics and dynamics of the Dabie-Sulu collisional orogen.

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