Linking deep Earth and surface processes across convergent domains: from mantle flow to glacial erosion
IPGP - Îlot Cuvier
Séminaires Tectonique et Mécanique de la Lithosphère
University of Cambridge
A long-term cooling trend, eventually leading to the onset of glaciation, characterized the late-Cenozoic Climate. Thus, in depth understanding of the surface evolution of an orogen requires assessments as to the common ground between the solid Earth and climate-modulated erosion. Here, I will address the couplings between the mantle and lithospheric forcing on the strain and topography across convergent domains and show how the surface evolution may be conditioned by glacial processes. I will also provide evidence of a link between glacial erosion and the magma productivity, which further demonstrates the tight coupling between the deep Earth and surface dynamics. The relative contributions of the mantle and crustal dynamics to the strain and topography of the Aegean-Anatolian and eastern Indian-Eurasian systems is still elusive. Numerical experiments calibrated on the available observations suggest that the non-convective mantle return flow associated with differential along-strike slab kinematics can affect the surface strain and topography across the upper plate through basal drag and vertical tractions. These results imply that the Earth’s surface is conditioned not only by large-scale mantle convection, but also by more local mantle flow in response to slab tearing or differential rollback/descent. A similar forcing from local mantle dynamics may also be seen in the Alps, where a change in regional isostatic support in the west, possibly associated with detachment of the European slab, seems established. The recent evolution of the Alps, however, is conditioned by glacial processes, which affects the overall geomorphology and the isostatic balance by erosional unloading. The Alps are uplifting fast but, because crustal tectonics is moderate, the most serious contributor to vertical motion is ruled out and alternative mechanisms may be either «deep processes» or surface unloading. A review of the observations, with particular emphasis on dynamic topography or isostatic adjustment to erosion during the Quaternary suggests that the current vertical motion in the Alps is unlikely to be related to a single process. Through lithsopheric loading/unloading, glacial processes affect not only the surface uplift or subsidence history but also the magma productivity. Several studies suggest that lithospheric unloading due to ice melting during the transition to interglacials leads to increased subaerial magmatic and volcanic activity. Such a climatic forcing on the magma productivity, however, has always been evaluated regardless of continental unloading by glacial erosion, albeit the density of rock exceeds that of ice by three times. I will present and discuss numerical results suggesting that erosion may be as important as deglaciation in affecting continental unloading and associated volcanic and magmatic activity.