When continents drip: Exploring surface geologic records of a dynamic lower lithosphere

The sinking of gravitationally unstable lithosphere beneath high-elevation plateaus is proposed to be a key driver of their uplift and is proposed to have occurred across our planet including beneath the Andes Tibet Anatolia Colorado Plateau and Nevadaplano. Where the lithosphere is actively sinking geophysical imaging affords a snapshot of this process. However the transience of these events leaves faint imprints on the surface. Once unstable lithosphere has sunk little evidence of this process remains besides (in some cases) low-volume magmatism that typically has low preservation potential. This talk will explore an alternative archive: the surface sedimentary record. Basin-filling strata form casts of the surface topography, preserving records of tectonic events that are the foundation of our understanding of orogen dynamics today. Yet the persistence of high-elevation hinterland depocenters for millions of years with “phantom" tectonic subsidence presents a sedimentological conundrum. Numerical geodynamic models predict that lithosphere removal could lead to transient topographic changes that could be preserved in the surface record particularly in deposits of lakes or playas that are subsequently inverted. The question is, can we find evidence in the geologic record of such a dynamic topographic response to lithospheric dripping? And could such relatively small-scale mantle dynamics drive major continental scale changes in the surface geology?

Speaker: John He, UC Los Angeles

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