Hallo! I’m
Lavinia Tunini, and I’m in the last year of my PhD in the Institute of Earth
Sciences Jaume Almera. Since almost two years I’m studying the lithospheric
structure in the Himalaya-Tibetan Plateau, which is the largest orogenic system
on Earth. The dramatic global-scale geologic event occurred around 55 million
years ago when the northward drifting Indian sub-continent collided against the
southern margin of Eurasia plate. Today, India plate is still advancing towards
the north-east, bulldozing Eurasia plate at a rate of ~4cm/yr and the Indian
lower crust continues to be pushed underneath the Tibetan Plateau. Beside the compressive
regime related to the tectonic convergence, stress data show also extensional features
in the middle of the Tibetan Plateau and to the east of the eastern Himalaya
syntaxis (i.e. India’s eastern indentation). Why? The mechanism is still hotly
debated in the scientific community. The removal of the lithospheric root in
the north-eastern Tibetan Plateau and changes in the mechanical properties of
the lithosphere have been proposed to explain the current deformation patterns
and the outstanding elevation of the plateau (around 5000 m). By using a
geophysical-petrological method I also find that the north-eastern Tibetan
Plateau is underlined by a thinner lithosphere (lithospheric base at ~120 km depth) with respect to its southern
sector (lithospheric base at ~280
km depth) (Fig. 1).
Now, I’m investigating which is the relation between the deep lithospheric structure and the deformation patterns at surface. I’m modelling the whole Central Asia but with a special focus on the eastern and south-eastern sector of the Himalaya-Tibetan region (Fig. 2), which is one of the most active intra-continental areas on Earth. Velocity vectors from GPS data image a sort of glacier-like flow of material around the eastern Himalaya syntaxis, and stress data indicate compression and strike-slip regimes in Burma and Yunnan provinces. In addition, the region is densely populated and the level of seismicity is very high, therefore the study of the present-day deformation is of extreme importance for the area! By using a finite-element method which simulates the Earth’s lithosphere as a thin shell, I’m investigating the mechanism responsible for the observed deformation. The results, so far, suggest that a strong lithosphere can explain the eastward extrusion of material from the eastern Tibetan Plateau. However, the clockwise rotation of the velocity vectors around the syntaxis can be realistically explained only by imposing a weak rheology for the lithospheric mantle, and southward and/or south-westward velocities at the boundary nodes of Sunda-Eurasia border. Is the observed deformation related to a retreat of the suducting slab or to a lower crust channel flow? Work is still in progress...
Now, I’m investigating which is the relation between the deep lithospheric structure and the deformation patterns at surface. I’m modelling the whole Central Asia but with a special focus on the eastern and south-eastern sector of the Himalaya-Tibetan region (Fig. 2), which is one of the most active intra-continental areas on Earth. Velocity vectors from GPS data image a sort of glacier-like flow of material around the eastern Himalaya syntaxis, and stress data indicate compression and strike-slip regimes in Burma and Yunnan provinces. In addition, the region is densely populated and the level of seismicity is very high, therefore the study of the present-day deformation is of extreme importance for the area! By using a finite-element method which simulates the Earth’s lithosphere as a thin shell, I’m investigating the mechanism responsible for the observed deformation. The results, so far, suggest that a strong lithosphere can explain the eastward extrusion of material from the eastern Tibetan Plateau. However, the clockwise rotation of the velocity vectors around the syntaxis can be realistically explained only by imposing a weak rheology for the lithospheric mantle, and southward and/or south-westward velocities at the boundary nodes of Sunda-Eurasia border. Is the observed deformation related to a retreat of the suducting slab or to a lower crust channel flow? Work is still in progress...
Figure 1. Location and
lithospheric structure of the C-D profile crossing the eastern Himalaya and
Tibetan Plateau.
Figure 2. The study region of Central Asia. The
numerical model, from the lithospheric (crust + lithospheric mantle) and thermal
structure, and by assigning a ductile or brittle behaviour to the lithosphere
depending on the temperature, provides surface velocities (green arrows) which
are compared with GPS data (blue arrows). We’re trying to explain the clockwise
motion of material around the eastern syntaxis in the south-eastern sector of
the Himalaya-Tibetan orogen (black squared region).
The study has been supported by
ATIZA (CGL2009-09662-BTE), TECLA (CGL2011–26670), Topo-Iberia CSD2006-0004 and
TopoMed/GASAM (CGL2008-03474-E/BTE/07-TOPO-EUROPE-FP-006) projects.
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