Betwixt and Between: Structure and Evolution of Central Mongolia

Tuesday, 15 December 2015: 11:30
304 (Moscone South)
Anne Meltzer1, Leonard D Ancuta2, Richard W Carlson3, Jeremy K Caves4, C Page Chamberlain5, John C Gosse6, Bruce D Idleman2, Dmitri A Ionov7, Kalin T McDannell2, Mendelson Tamra8, Hari Mix9, Ulziibat Munkhuu10, Ray Russo11, Mark Sabaj-Perez12, Dork L Sahagian2, Derek J Sjostrom13, Stephen G Smith14, Josh C Stachnik1, Baasanbat Tsagaan10, Karl W Wegmann15, Matthew J Winnick4, Peter K Zeitler2 and Alex Prousevitch16, (1)Lehigh University, Earth and Environmental Sciences, Bethlehem, PA, United States, (2)Lehigh University, Bethlehem, PA, United States, (3)Carnegie Institution for Science Washington, Washington, DC, United States, (4)Stanford University, Stanford, CA, United States, (5)Stanford University, Environmental Earth System Science, Stanford, CA, United States, (6)Dalhousie University, Halifax, NS, Canada, (7)University of Montpellier II, Montpellier Cedex 05, France, (8)University of Maryland, Baltimore County, Department of Biological Sciences, Baltimore, MD, United States, (9)Santa Clara University, Santa Clara, CA, United States, (10)Institute of Astronomy and Geophysics, Ulaanbaatar, Mongolia, (11)University of Florida, Gainesville, FL, United States, (12)Academy of Natural Sciences Drexel University, Philadelphia, PA, United States, (13)Rocky Mountain College, Billings, MT, United States, (14)North Carolina State University at Raleigh, Marine, Earth, and Atmospheric Sciences, Raleigh, NC, United States, (15)North Carolina State Univ., Raleigh, NC, United States, (16)University of New Hampshire Main Campus, Durham, NH, United States
Central Mongolia sits deep in the Asian continental interior between the Siberian craton to the north, the edge of the India-Asia collision to the south, and far-field subduction of the Pacific plate to the east. It has a complex geologic history comprising Archean to Early Proterozoic crystalline rocks modified by accretionary events in the Paleozoic, and Cenozoic deformation and basalt volcanism that continues today.

Within central Mongolia, the broad domal Hangay upland is embedded in the greater Mongolian Plateau. Elevations within the dome average ~1.5 km above the regional trend and locally reach ~4000 m. This elevated landscape hosts a low-relief surface cut into crystalline basement, and a 30 Ma record of intermittent basalt magmatism. Here we integrate observations from geomorphology, geochronology, paleoaltimetry, biogeography, petrology, geochemistry, and seismology to document the timing, rate, and pattern of surface uplift in the Hangay and more broadly to understand the geodynamics of the Mongolian plateau.

Results from mantle and crustal xenoliths, seismology, thermochronology, and basalt geochemistry are consistent with: a high geothermal gradient with temperatures reaching ~900°C at 60 km depth, intercepting the mantle adiabat at ~90 km depth; an uppermost mantle composed mostly of fertile peridotites; low-volume Cenozoic basaltic magmatism sourced below the lithosphere, with isotopic characteristics similar to much east-Asian Cenozoic mafic volcanism; a 42-57 km-thick crust of island-arc affinity formed during accretion of the Central Asia Orogenic Belt; elevations supported primarily by crustal isostasy; slow exhumation (30-100 m/My) over hundreds of millions of years; and long-term thermal stability of the upper crust and relief lowering since the Mesozoic. Results from geomorphology, paleoaltimetry, fish genetics, and basalt geochronology imply that drainage divides are stable since the mid-Miocene with modest surface uplift (up to 1 km) and topographic relief up to 800 m remaining largely unchanged since ~10 Ma. Surprisingly, this area of remarkable stability over significant time and space sits above a shallow convecting mantle and hosts some of the largest recorded intracontinental earthquakes.