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Academic Report on 2018-5-11: Paleoelevation of the Tibetan Plateau relative to plate convergence, crustal shortening, volcanism and conservation of crustal mass
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Academic Report on 2018-5-11 

Subject: Paleoelevation  of  the Tibetan Plateau relative to plate convergence, crustal shortening, volcanism and conservation of crustal mass 

ReporterProf. Marin K. Clark 

Abstract: Mounting evidence from the structural record across northern and eastern Tibet calls for the onset of crustal thickening to either precede or closely follow the ~ 50 Ma collision of India with Eurasia. However, and much to our surprise, flat-lying basalts and extensive lake sediments constrain the end of upper crustal shortening to soon after ~ 30 Ma, still young in the orogen’s history. Further, the total amount of upper crustal shortening is insufficient to account for the total thickness of crust unless the pre-collisional crustal thickness was in excess of 50 km. This suggests some redistribution of crust from the south by lower crustal flow, regardless of whether or not coeval changes to mantle lithosphere thickness also altered plateau altitude. We compiled new and published geochemical and geochronologic data from across Tibet from high MgO volcanic rocks that indicate that lithospheric mantle melting has been present beneath the central plateau since nearly the time of collision, and completely encompasses the plateau between 30-20 Ma. The presence of mantle lithosphere melting post-dates the cessation of crustal shortening, but also occurs long before extensional faulting. Thus the volcanic record is consistent with a scenario of lithospheric thickening in tandem with crustal shortening, followed by mantle lithosphere removal and attendant melting. But importantly, this process occurs much earlier in the orogen’s history than previously thought. 

  

Time10:00, May, 11th, 2018  

VenueRoom  300   

  

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