Timing of orogenic exhumation processes of the Qinling Orogen: evidence from 40Ar/39Ar dating

The Qinling Orogenic Belt was formed by long-lived subduction and collision between the North and South China blocks. Our Ar-40/Ar-39 geochronological data of amphibole, white mica, and biotite reveal different exhumation and cooling histories of the major units in the North Qinling Belt and South Qinling Belt (SQB), constraining the multiple orogenic processes. The exhumation of the Qinling Group in the North Qinling Belt started before 432Ma, through about 500 degrees C during 432.3-405Ma, followed by rapid cooling below 425 degrees C at 388.9 +/- 1.1Ma and slow cooling through about 300 degrees C during 333.3-329.5Ma. A similar exhumation history of the Kuanping Group started from about 383Ma, cooled below 425 degrees C at 364.9 +/- 1.2 Ma and 300 degrees C at 341.8 +/- 1.3 Ma. The metamorphic fore-arc sedimentary wedge cooled below 500 degrees C during 322-311.2Ma, below 425 degrees C at 306.3 +/- 2.8Ma, and 300 degrees C at 249 +/- 2.8Ma. However, the white mica Ar-40/Ar-39 ages of 349.4 +/- 5.1 and 363.2 +/- 2.5Ma constrain the syntectonic metamorphic crystallization age of the Devonian Liuling Group in the northern SQB, whereas 228.2 +/- 0.7Ma indicates either a delayed cooling of the Wudang Group in the southern SQB or a second stage of low-temperature thermal overprint. Together with previous cooling ages and regional geology, our new data support a tectonic model of Early Paleozoic Andean-type orogeny with subsequent Late Paleozoic continental subduction in the Qinling Orogenic Belt.