Crustal and lithospheric complexity beneath the North Tanzanian Divergence from seismological and geochemical analyses.

We present a joint analysis of seismological images and petrophysical data in the North Tanzanian Divergence, where the lithospheric break-up is at its earliest stage. In this part of the East African Rift, the current surface deformation is related to complex interaction between tectonic (active fault, pre-rift lithospheric structure) and magmatic processes within the mantle and the crust. We present here the compilation of seismological results such as receiver function, local tomography, regional tomography on datasets collected during CRAFTI-CoLiBrEA and HaTARi projects, in a region with clearly opposite seismological and magmatic behaviours: near Natron the seismicity is well located within the upper crust and linked to present day magmatism (Lengai edifice), whereas Manyara area is characterized by a deep seismicity and no evidence of present magmatic activity at the surface. First, these different approaches deliver Vp, Vs and deduced Vp/Vs images with both different resolution and different depth investigation. The combined images of crustal and lithospheric structure provide the appropriate scale to point out the interactions between melt, gas, faults, and inherited fabrics in specific areas. We then compare those geophysical observations with magma composition, magma storage (depth of reservoir, magma volume) and ascent as well as partial melts content at depth obtained from petrophysical and geochemical analysis of lava samples. We will analyze if this combination of seismological approaches constrained with petrological and geochemical data produce accurate images of the entire current magma plumbing system.  Finally, we will discuss the results in terms of magmatic processes and how they interact with the rifting in a cratonic lithosphere.