Asthenospheric imprints on the lithosphere in Central Mongolia and Southern Siberia from a joint inversion of gravity and seismology (MOBAL experiment)

Details Asthenospheric imprints on the lithosphere in Central Mongolia and Southern Siberia from a joint inversion of gravity and seismology (MOBAL experiment) Asthenospheric imprints on the lithosphere in Central Mongolia and Southern Siberia from a joint inversion of gravity and seismology (MOBAL experiment)

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008geoji.175.1283t&link_type=abstract

Geophysical Journal International, Volume 175, Issue 6, pp. 1283-1297.

Astronomy and Astrophysics

Astronomy

Gravity Anomalies And Earth Structure, Seismic Tomography, Continental Tectonics: Extensional, Dynamics Of Lithosphere And Mantle, Dynamics: Gravity And Tectonics, Asia

Scientific paper

We present a joint inversion of gravity and teleseismic data to enlighten the lithospheric structures of the Baikal-Mongolia region, an area characterized by high topographic contrasts, sporadic Cenozoic volcanism, extension and large transcurrent faulting in the vicinity of the Baikal Rift, Central Asia. The study uses a 1000km long seismic transect that cross-cuts the main tectonic structures from north to south (namely, the Siberian platform, Tunka basin, Hangay Dome and Gobi-Altai belt).
The Siberian platform depicts a high-velocity lithosphere down to about 150km. We evidence strong velocity contrasts within the crust below the Hangay Dome and the Tunka depression, interpreted as a thickened crust. A low-velocity/density region is located at various depths below the Hangay Dome. Thanks to the dense spatial coverage of gravity data, we are able to define the 3-D geometry of this particular low-velocity/density anomaly. The Hangay Dome anomalous body extends from 60 to 225km depth at his largest point and slightly thins to no more than 40km at its easternmost end. A deep low-velocity zone (below 150km) with only a weak negative density contrast is observed on the eastern part of the transect.
We propose that the late Cenozoic uplift of the whole Mongolian Plateau and associated rifting, magmatism, high heat flow and lithospheric thinning are not externally driven by the India-Asia collision, but results from the interaction of two mantle plumes with the overlying lithosphere. Conversely, recent faulting may be the major expression of the India-Asia collision in this region, as well as N-S striking rift basins that connect and interact with major strike-slip faults, such as the Bolnai fault.
The comparison between time residuals of this experiment and the Baikal Rift seismic data shows an undeniable disproportion for the Hangay anomaly. The Hangay time residuals are far more positive than through the Baikal, arguing for an asthenospheric signature that is not seen beneath the Baikal Rift. Furthermore, the southern edge of the thick Siberian cratonic lithosphere may favour the rise of a sublithospheric mantle flow at the contact with the Baikal-Mongolia lithosphere.

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