A T-t cooling path for UHPM rocks and their country rock from Dabie mountains reveals that the cooling history of the UHPM rocks from 800 degrees C to 300 degrees C can be subdivided into three stages: two rapid cooling stages ( the initial rapid cooling from 800 degrees C to 500 degrees C during 226 +/- 3Ma to 219 +/- 7Ma and the second rapid cooling from 450 degrees C to 300 degrees C during 180Ma to 170Ma) and one isothermal stage in between them (Li S. et al., 2000). This T-t path with two rapid cooling processes has been confirmed by the recent geochronological results including a precise U-Pb age of 218 +/- 1.2Ma (with T-c = 460 degrees C) for rutile from the coesite-bearing eclogite (Li Q. et al., 2003), the Th-Pb monazite core age of 223 +/- 1 Ma (with T-c = 675 +/- 25 degrees C) and monazite rim age of 209 3Ma (corresponding to retrograde amphiblite facies metamorphism T-c = 500 degrees C similar to 450 degrees C) for the jadeite quartzite (Ayers et al. 2000) and Rb-Sr age of 182.7 +/- 3.6Ma for the secondary phengite from an intensive foliated eclogite (Li S. et al., 2001). The two rapid cooling events may reflect two rapid uplift processes of the UHPM rocks during the exhumation history. The U-Pb zircon ages of 225 similar to 205Ma for the syncollisional granites developed in eastern Qinling and eastern Sulu terrane coincide with the first rapid cooling time of the Dabie UHPM rocks. Because syncollisional granite is suggested to be result of slab break off during continental subduction (Davies and Blanckenburg, 1995), the time consistency between the syncollisional granite formation and the first rapid cooling of the UHPM rocks indicates that the slab break off could be one of the important mechanisms for the initial uplifting and cooling of the UHPM rocks,. The Pb isotopic mapping in Dabie mountains reveals that the UHPM rocks characterized by relative higher radiogenic Ph (Pb-206/Pb-204 = 17.026 similar to 20.781) in South Dabie zone were derived from subducted upper continental crust, while the UHPM rocks characterized by relative lower radiogenic Pb (Pb-206/Pb-204 = 15.844 similar to 17.204) in North Dabic zone were derived from subducted lower continental crust. This observation indicates that a detachment or a decoupling in between the subducted upper and lower continental crusts must be occurred during continental subduction. It has been demonstrated by a physical modeling that the decoupled upper crust can be uplifted by thrust along the detachment surface during the continental subduction process. Similarly, it can be referred that a detachment or a decoupling in between the felsic and mafic subducted lower continental crust could be also occurred, because no subducted mafic lower continental crust has been exhumed in Dabic orogen. Several low-viscosity zones occurred at different depths in continental lithosphere (Meissner and Mooney, 1998) provide the conditions for such detachment or decoupling in subducted continental crust. Therefore, the first rapid uplifting of the subducted upper crust and/or part of felsic lower crust is a result of the both detachment or decoupling in subducted continental crust and slab breakoff. These processes can only cause the uplifting and exhumation of the decoupled upper and felsic lower continental crust, while the undecoupled mafic lower continental crust could be subducted continuously after slab breakoff. After slab breakoff, the continuing convergence of two continental blocks in the later Triassic and earlier-middle Jurassic might indue the lithosphere splitting of the SCB and lithospheric-wedging between the south margin of the NCB and north margin of the SCB. This process caused the over-thrust of the mid-upper continental crust with exhumed UHPM rocks and underthrust of the deep lithosphere of the SCB. It could be an important mechanism responsible for the second rapid cooling and uplifting of the UHPM rocks. The Rb-Sr age of 182.7 +/- 3.6Ma for the secondary phengite from an intensive foliated eclogite may indicates the lithospheric-wedging time. Geochronology study of the Huilanshan mafic granulite from the Luotian Dome reveal a fast uplifting in the early Cretaceous. An intense magmatism was occurred simultaneously in the Dabie orogen. The coupling of the mountain fast uplifting and intense magmatism in the Dabie orogen suggests that a mountain root remove or lithospheric delamination event was occurred in the early Cretaceous. Consequently, the UHPM rocks in the Dabie orogen must be further exhumed in a large area with this fast mountain uplifting.
