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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS011 Oral Presentation 2098
Mantle convection beneath Mongolian-Baikal Rift zone and its geodynamic
implications
Dr. Xiong Xiong
Key Laboratory of Dynamic Geodesy Institute of Geodesy and Geophysics, CAS IASPEI
Jiye Wang, Rongshan Fu
Mongolia occupies a peculiar place in Asia, which is characterized by very complicated tectonics under
the impact of the India-Asia collision to the south and the subduction of Pacific Plate to the east. It
recently became clear that Mongolia, which is one of the least studied and poorly understood of the
tectonically active regions of the world, plays a key role in deciphering the intracontinental deformation
processes. Although it is generally agreed upon that Mongolia is a direct consequence of the India-Asia
collision and the subsequent compression between Asia and the northward advancing Indian continent,
the collision and compression model alone cannot account for all regional tectonic features of Mongolia.
Therefore, other mechanisms may superimpose upon the India-Asia collision and compression, and the
small-scale convection within upper mantle is believed to be one of the candidates, which is responsible
for intraplate and regional tectonic processes. Relating regional gravity anomalies and mantle
convection, we calculated the small-scale mantle convection pattern and resulted stress at the
lithospheric base beneath Mongolia by using isostatic gravity anomalies. The numerical results indicate
that the Mongolia and its adjacent areas are characterized by a very complicated pattern of mantle flow
and convection-generated stress field in deep. The low activity of the mantle flow and small magnitude
of the convection-generated stress suggest that the Siberia Platform is a stable tectonic unit, which is
short of active dynamic process in deep. The eastern Mongolia is another area where mantle convection
and its impact are weak. This is consistent with the present-day low tectonic activity in these areas.
Beneath the Baikal Rift Zone exists an upwelling mantle plume, which is identical to the low-velocity
anomalies originated from the 670km discontinuity imaged by seismic tomography. The Hangay-Hővsgől
Plateau is underlain by mantle upwellings, resulting in extension stress regime. A complicated pattern of
mantle flow and convection-generated stress is exhibited in the western Mongolia. The consistency
between the surface tectonic features and the mantle flow pattern, as well as the resulted stress field,
suggests that the small-scale convection within upper mantle may be one of the main mechanisms
which control the regional tectonics in Mongolia.
Keywords: mantle convection, mongolia, geodynamic implication