Lithosphere structure in Madagascar: Implications for the geodynamic processes that have shaped Madagascar

Crustal structure in the southern part of Madagascar obtained from receiver function analysis and joint inversion of receiver function and Rayleigh wave group velocity. (top) Moho depths and VP∕VS ratios from the H-K stacking with estimated errors. The tectonic units refer to the different tectonometamorphic domains in the southern part of Madagascar. (bottom) S wave velocity obtained from the joint inversion of receiver functions and surface wave dispersion curves. The single station models were shifted according to station elevation such that the depths shown are with respect to sea level. Dash-dotted, dashed, dotted, and solid lines show the sediment to upper crust, upper to middle crust, middle to lower crust, and crust-mantle boundaries, respectively. The observed crustal structure in the Precambrian shield in southern Madagascar differs from that for a typical Archean-Proterozoic crust. The archean crust (Antananarivo domain) is thicker than the Proterozoic crust (Androyen, Anosyen, Ikalamavony domains). A mafic lithology forms the bottom of the archean crust, whereas it is either missing or has only minor contribution in the Proterozoic. In the Morondava basin, a sediment layer with thickness between 3 and 10 km is observed at the top layer and the lower crust has been thinned or removed.

Georg Foster-Research Fellowship (HERMES), Alexander von Humboldt

The assembly and separation of supercontinents during the Wilson cycle (during which a continents rift and later converge, reassembling the fragments) are key geological processes to understand the long-term plate tectonic evolution of the Earth's surface. Madagascar is an ideal place to study the multistage assembly and break up of Gondwanaland, the supercontinent whose break-up also gave rise to many present-day continental regions (South America, Africa, Antarctica, Australia, Arabia and India). The surface traces of assembly and breakup processes have been studied extensively using geological methods in Madagascar and elsewhere, but the imprint on the deep structure has so far not been studied in much detail because of the relative sparsity of seismological studies in Madagascar. In this project we aim to determine the detailed Earth structure associated with the different geological domains of Madagascar based on new temporary seismic experiments that were carried out in Madagascar between 2011 and 2014. The results will not only shed light on the geodynamic processes that have shaped Madagascar, including more recent modifications to the lithospheric fabric, but will also have practical implications for improving knowledge of the seismotectonics.

Contact

  • F. Tilmann (GFZ Potsdam)

Funding

  • Georg Foster-Forschungsstipendium (HERMES), Alexander von Humboldt
    • Elisa Rindraharisaona
Frederik Tilmann
Head
Prof. Frederik Tilmann
Seismology
Albert-Einstein-Straße 42-46
Building A 46, Room 103
14473 Potsdam
+49 331 288-1240
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