March 8, 2018 @ 4:00 pm - 5:00 pm CST
Current Research in EEPS Seminar: David Rowley, University of Chicago
Negative buoyancy associated with subduction of cold, dense oceanic lithosphere has for the past 45 years been considered to be the dominant driver of Earth’s tectonic plates. In this framework, mid-ocean ridges are viewed as passive plate boundaries whose divergence accommodates flow driven by subduction of oceanic slabs at trenches. Using global plate kinematic reconstructions we show that over the past 80 Myr the East Pacific Rise (EPR), Earth’s dominant mid-ocean ridge, has been characterized by limited ridge-perpendicular migration and by persistent, asymmetric ridge accretion that are anomalous relative to other mid-ocean ridges. We reconstruct the subduction-related torques of plates on either side of the EPR since 80 Ma based on published paleo-age grid (Müller et al. 2008) and corresponding plate boundary reconstructions (Gurnis et al. 2012). Slab-pull-related torques retrodict that the EPR should have been characterized by significant (~3800 km) eastward migration in the NNR frame of reference, with ~2000 km in the past 40Ma. In a passive upwelling system there is no reason for systematic asymmetric accretion along the EPR. In contrast to these retrodictions, plate reconstructions retrodict 0 km of eastward migration in that same 40 Myr interval, and an ~60:40% split in accretion to the Nazca/Farallon versus Pacific plate over the past 53 Ma.
We account for these observations of EPR stability using mantle flow calculations based on globally integrated buoyancy distributions derived from jointly inverted seismic velocity, geodynamic and mineral physics data that require core-mantle boundary (CMB) heat flux that may be as high as 20TW. The time-dependent mantle flow predictions, which extend both backwards and forwards in time, yield a long-lived deep-seated upwelling that has its highest radial velocity under the EPR, and is inferred to control its observed kinematics. The mantle-wide upwelling beneath the EPR drives horizontal components of asthenospheric flows beneath the plates that are also asymmetric, but faster than the overlying surface plate motions, thereby contributing to surface plate motions through viscous tractions in the Pacific region.