Exhumation of the ultrahigh-pressure continental crust in east central China: Cretaceous and Cenozoic unroofing and the Tan-Lu fault

The orogenic architecture of the world's largest ultrahigh-pressure exposur e, the Hong'an-Dabie Mountains of the Triassic Qinling-Dabie orogenic belt, is dominated by Cretaceous and Cenozoic structures that contributed to its exhumation from less than or equal to 30 km depth. Cretaceous magmatic cru stal recycling (greater than or equal to 50% for the entire Dabie) and heat ing (>250 degrees to >700 degrees C) were most prominent in Dabie, and exhu mation, magmatism, and cooling were all controlled by Cretaceous transtensi on. Exhumation was accomplished principally by an asymmetric Cordilleran-ty pe extensional complex in the northern Dabie (Northem Orthogneiss unit) bet ween 140 and 120 Ma, at rates as fast as 2 mm/yr and average horizontal str etching rates of up to 6 mm/yr. Cretaceous reactivation occurred within a r egional transtensional strain field as a result of far-field collisions and Pacific subduction. The onset of crustal extension was preceded and possib ly facilitated by a reheating of the Hong'an-Dabie crust (similar to 140 Ma ) coeval with the onset of voluminous magmatism in eastern China (similar t o 145 Ma), which resulted from a change in Pacific subduction from highly o blique to orthogonal. The Tan-Lu continental-scale fault was a normal fault zone in the mid-Cretaceous (similar to 110-90 Ma) and underwent greater th an or equal to 5.4 km dip slip and greater than or equal to 4 km throw in t he Cenozoic. During the India-Asia collision the Qinling-Dabie belt acted a s the structural discontinuity between the strike-slip-dominated escape tec tonics south of the Qilian-Qinling-Dabie belt and the rifting-dominated tec tonism north of it. The most prominent Cretaceous and Cenozoic structures o f the Hong'an-Dabie, the Xiaotian-Mozitang and the Jinzhai fault zones, res pectively, reactivated major lithospheric structures of the Triassic orogen , i.e., the Huwan detachment zone and the suture.