UPPER MANTLE STRUCTURE: HANGAY DOME, CENTRAL MONGOLIA

Mongolia is part of the Central Asian Orogenic Belt and contains various regions of juvenile and reworked pre-Paleozoic crust, a reflection of a complex accretionary history. The Hangay Dome, a region of high topography located in central Mongolia, spans an area of ~200,000 km², and reaches elevations of ~4,000 m. This domal feature is bound to the north and south by two active strike-slip faults, the Bulnay and Gobi-Altay. A northwest-southeast right-lateral strike-slip system also exists to the west of the region in the Mongolian Altay. Since 1905, these faults systems have been home to four of the largest intracontinental earthquakes with magnitudes reaching ≥ 8. The extent to which the accretionary history controls present day deformation or contributes to present day topography remain open questions. Geodynamic processes potentially in play include Pacific Plate subduction, effects of the India-Asia collision, rifting stemming from the Lake Baikal region, mantle-plume activity, upwelling of the asthenospheric mantle, lithospheric delamination, and/or the underplating of magmatic rocks at the base of the crust. Looking at the structure of the upper mantle can help to determine which of these processes may be important.

A seismic array, comprised of 72 broadband seismic stations, was installed in 2012 covering the Hangay region to record data over a two-year period. We use over 300 teleseismic events, magnitudes 5.5 and above with epicentral distances between 30 and 60 degrees, to calculate P-wave travel time residuals. These travel time residuals range between +/- 1 second and initial analysis of their spatial distribution reveals a low-velocity anomaly beneath the region with high-velocity areas surrounding the dome. Three-dimensional finite-frequency teleseismic tomography, using these events, will provide a better understanding of the velocity structure beneath the Hangay including the depth and lateral extent of the velocity anomalies in the region. This will provide additional insight into the origin of the high topography and deformation seen in central Mongolia.