CRUSTAL STRUCTURE BENEATH THE EASTERN EDGE OF THE RIO GRANDE RIFT

A 2D array of broadband seismographs (SIEDCAR) was deployed on the eastern flank of the Rio Grande Rift to confirm and constrain quantitatively features associated with mantle downwelling observed by a previous seismic study (Gao et al., 2004). The SIEDCAR project consisted of a deployment of a total of 71 broadband seismic stations interspersed with 25 Transportable Array stations, aimed to determine the seismic structure and thickness of the continental crust, as well as the upper mantle structure beneath the eastern edge of the Rio Grande Rift.

We will present results from receiver functions computed with SIEDCAR data to determine crustal and lithospheric structure beneath the east flank of Rio Grande Rift. Crustal and lithosphere thickness are estimated using P-to-S and S-to-P receiver function modes, respectively. Receiver function migration method was applied to produce images of the crust and lithosphere. The results show variable crustal thickness through the region with an average thickness of 45 km. The crust achieves its maximum thickness of 60km at 105W longitude, between 33.5N and 32.2N latitude. This observation confirms previous receiver function results from Wilson et al., 2005. Meanwhile, body wave tomography (Rockett et al., 2011) using the same data shows a mantle downwelling closely associated with the thickened crust. We believe that the thickened crust might be due to lower crustal flow associated with mantle downwelling or mantle delamination. In this model the sinking mantle pulls the crust downward causing a pressure gradient within the crust thus causing the flow. Our S-P images show signal from the lithosphere-asthenosphere boundary (LAB) with an average LAB thickness of 100 km thickening from west to east. The region with abnormally thick crust overlies a region where the LAB appears to have a discontinuity, providing further evidence for a crust-mantle connection.