The Exhumation Histoy Of The Gangdese Batholith From Low Temperature Thermochronology And Sedimentay Response

The lower temperature thermochronometric systems have closure temperatures ranging from 60-300 ?C, making them sensitive to exhumation through crustal depths of about one to several kilometers. Thus, thermochronology can constrai erosion rates and evolution of landscape with orognic growth and decay cycles and possibe climate-tectonic feedback response times. I present the new Fission track and helium data from broad areas with different landscape features and tectonic background in the central Gangdese batholith to reveal their cooling histories and corresponding controls. Combining the new and published low-temperature thermochronometric data and sedimentary basin analysis of Gangdese conglomerate constrain the coupling of exhumation and deposition in the southmost of Gangdese batholith.These new data and thermal modeling, in combination with the regional geological data, suggest that the distinct parts of Gangdese batholith underwent different cooling histories resulted from various dynamic mechanisms. The Late Eocene-Early Oligocene exhumation of northern Gangdese batholith, coeval with the magmatic gap, might be triggered by crust thickening; while this stage of exhumation in southern Gangdese batholith cannot be clearly elucidated, because the most of plutonic rocks with the information of this cooling event were probably eroded away. Since then, the northern Gangdese batholith experienced a slow and stable exhumation, while the southern Gangdese batholith underwent two more stages of exhumation. The late Oligocene-early Miocene rapid cooling might be a response to denudation caused by the Gangdese Thrust or related to the regional uplift and exhumation in extensional background. By the early Miocene, the rapid exhumation was associated with localized river incision or intensification of Asian monsoon, or north-south normal fault.Gangdese conglomerate cropping out ubiquitously along >1300 km length southernmost boundary of Gangdese batholith preserves processes governing basin and topographic development. The new and published low-temperature thermochronometric data from Gangdese batholith and Gangdese conglomerate indicate a period of rapid exhumation initiated around 17-15 Ma in southern margin of Gangdese batholith, while the regional uplift commenced during the deposition of Gangdese conglomerate based on an abrupt facies change from deep-water lacustrine deposits to red alluvial fan or fluvial deposits. The initiation of rapid exhumation probably had lagged behind increased rock uplift, but the change of depositional environment would have shown immediately in the basin with the regional uplift. Gangdese conglomerate was buried associated with development of the north-directed Great Counter thrust followed by rapid exhumation by efficient incision of the paleo-Yarlung river around 17-15 Ma.