Lithospheric Structure of a Transitional Magmatic to Amagmatic Continental Rift System-Insights from Magnetotelluric and Local Tomography Studies in the North Tanzanian Divergence, East African Rift
|Author(s)||Plasman Matthieu1, Hautot Sophie2, Tarits Pascal3, Gautier Stephanie1, Tiberi Christel1, Le Gall Bernard3, Mtelela Khalfan4, Gama Remigius5|
|Affiliation(s)||1 : Univ Montpellier, UMR5243, Geosci Montpellier, F-34000 Montpellier, France.
2 : IMAGIR Sarl, F-29290 St Renan, France.
3 : Inst Univ Europeen Mer, Lab Geosci Ocean, F-29280 Plouzane, France.
4 : Univ Dar Es Salaam, Dept Phys, Dar Es Salaam 35091, Tanzania.
5 : Univ Dar Es Salaam, Dept Geol, Dar Es Salaam 35091, Tanzania.
|Source||Geosciences (Mdpi), 2019-11 , Vol. 9 , N. 11 , P. 462 (30p.)|
|Note||This article belongs to the Special Issue The East African Rift: Tectonics, Magmatism and Natural Hazards|
|Keyword(s)||magnetotellurics, 3-D inversion, North Tanzanian Divergence, East African rift, lithospheric structure, CO2 content, seismology, joint interpretation|
Continental break-up is controlled by several parameters and processes (rheology, inherited structures, magmatism, etc). Their impact, chronology and interactions are still poorly known and debated, particularly when rifting interacts with cratons. In order to better understand the rifting initiation in a cratonic lithosphere, we analysed 22 magnetotelluric (MT) soundings collected along two East-West profiles in two different rift segments of the North Tanzanian Divergence. The North Tanzanian Divergence, where the East African Rift is at its earliest stage, is a remarkable example of the transition between magmatic to amagmatic rifting with two clearly identified segments. Only separated by a hundred kilometers, these segments, Natron (North) and Manyara (South), display contrasted morphological (wide versus narrow), volcanic (many versus a few edifices) and seismic (shallow versus deep activity) signatures. Magnetotelluric profiles across the two segments were inverted with a three-dimensional approach and supplied the resistive structure of the upper lithosphere (down to about 70 km). The Natron segment has a rather conductive lithosphere containing several resistive features (Proterozoic Belt), whereas the Manyara segment displays highly resistive blocks probably of cratonic nature encompassing a conductive structure under the axial valley. The joint interpretation of these models with recent local and regional seismological studies highlights totally different structures and processes involved in the two segments of the North Tanzanian Divergence. We identified contrasted CO2 content, magma upwelling or trapping, in depth regarding the Manyara or the Natron branch and the influence of inherited cratonic structures in the rifting dynamics.