Early Miocene Exhumation History in the Eastern Gangdese Porphyry Copper Belt and Its Influence on the Spatiotemporal Distribution of Oligocene-Miocene Porphyry Deposits

Gangdese Oligocene-Miocene porphyry copper belt is the important component of Tethys metallogenic domain, where numerous giant and large porphyry-skarn Cu-Mo-Au deposits have been discovered. However, the Tibetan Plateau that hosts this copper belt has suffered intense and rapid uplifting and erosion since Oligocene. How these Oligocene-Miocene deposits preserved in that environment suffering rapid uplifting and erosion remains as mystery and how the temporal and spatial distribution of erosion dominate the Oligocene-Miocene deposits in the belt remains unsettled. Basing on the zircon and apatite (U-Th)/He dating on the vertical section inner Gangdese arc 40km north of Zedong area, the author discovered an early Miocene (17.3~15.1 Ma) intense and rapid erosion event in the Gangdese porphyry Cu belt, during which the average erosion rate was >1.82 km/Ma, the erosion amount was 4 km. And then the erosion rate decreased to 0.14~0.19 km/Ma with the erosion amount from 15.1 Ma to present of ~2.5 km. Integrating the previous thermo-chronological data, the author reveals that the early Miocene intense erosion zone in the Gangdese porphyry Cu belt was E-W trending and controlled by the southward thrusting of Xietongmen-Oiga shear zone. Even though the contemporaneous erosional event was also developed on the southern and northern sides, the intensities were significantly lower than the shear zone area, indicating that the uplifting and erosion in the plateau has varied temporally and spatially since Miocene. Besides, the Oligocene and Miocene porphyry deposits are distributed in the weak erosion zones on the southern and northern sides of the early Miocene E-W trending intense erosional belt respectively, indicating that the differential erosion is one of the restrictive factors for the temporal and spatial distribution of Oligocene-Miocene deposits in the belt.