Mapping the continental lithosphere
Abstract
We combine results from seismology, petrology and geochemistry to define the thermal structure of the lithosphere beneath the continents. This procedure involves first deriving laterally-varying upper mantle shear-wavespeed models from multi-mode surface wave tomography. Our upper mantle model now results from the analysis of more 850,000 surface wave seismograms that have provided more than 20 million constraints on the upper mantle shear wavespeed structure, giving an upper mantle wavespeed model with an average lateral resolution of about 250 km and an average vertical resolution of about 25 km. We relate seismic wave speed (Vs) and temperature (T) by combining the shear wave velocity structure of the oceanic plate determined from the surface-wave tomography with a temperature model of the oceanic plate to define a relationship between Vs and T. This relationship is then calibrated for the continents using a large, global upper mantle nodule data set. We use this Vs-T relationship to create temperature-depth profiles for the continents from the seismic tomography models and identify the base of the lithosphere as the change from conducting to convecting geotherms. Our recent efforts have significantly reduced the errors in the Vs-T relationship and significantly increased the lateral resolution in the lithospheric maps over our earlier effort. In addition to the upper mantle temperature, our new procedure, which parametrizes the behavior in terms of a Maxwell relaxation time, allows us to map the upper mantle attenuation and viscosity structure. The resulting lithospheric thickness maps of the continents provide new insight into the role the lithosphere plays in controlling mountain building, volcanism, earthquakes, continental rifting and our understanding of the large-scale evolution of the continents.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.V51D..02P
- Keywords:
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- 1000 GEOCHEMISTRY;
- 3600 MINERALOGY AND PETROLOGY;
- 7218 SEISMOLOGY / Lithosphere;
- 8103 TECTONOPHYSICS / Continental cratons