Abstract:From south to north, three parallel metamorphic imbricated slices compose the Sulu high to ultrahigh pressure metamorphic terrane. They are high pressure (HP) slice, very high pressure (VHP) slice, and ultrahigh pressure (UHP) slice, separated by ductile shear zones. Using 40Ar/39Ar and whole rock Rb-Sr techniques, the authors analyzed micas from amphibolite facies rocks in the UHP slice and from greenschist facies rocks in the HP slice to constrain the timing of exhumation of the Sulu HP-UHP metamorphic belt. Together with previous results from zircon U/Pb, whole rock Sm-Nd and Rb-Sr measurements, the data obtained show that peak metamorphism and subsequent exhumation in the UHP zone occurred in 240～220 Ma and 220～200 Ma, respectively. In the HP zone, however, peak metamorphism and the onset of exhumation occurred earlier than 258 Ma and in 258～240 Ma, respectively. These data have led us to propose a newmodel for the formation and exhumation of the Sulu HP-UHP rocks. In this model,sequential subduction and exhumation of different parts of the Yangtze slab occurred in different periods, depending upon vertical variations in the physical properties of the subducted continental crust.
