FN Archimer Export Format PT J TI Lithospheric low-velocity zones associated with a magmatic segment of the Tanzanian Rift, East Africa BT AF PLASMAN, M. TIBERI, C. EBINGER, C. GAUTIER, S ALBARIC, J. PEYRAT, S. DEVERCHERE, Jacques LE GALL, B. TARITS, Pascal ROECKER, S. WAMBURA, F. MUZUKA, A. MULIBO, G. MTELELA, K. MSABI, M. KIANJI, G. HAUTOT, S. PERROT, J. GAMA, R. AS 1:1;2:2;3:3;4:2;5:4;6:2;7:1;8:1;9:1;10:5;11:6;12:7;13:6;14:6;15:6;16:8;17:9;18:1;19:6; FF 1:;2:;3:;4:;5:;6:;7:;8:;9:;10:;11:;12:;13:;14:;15:;16:;17:;18:;19:; C1 IUEM, UMR Geosci Ocean, Plouzane, France. Univ Montpellier, UMR5243, Geosci Montpellier, Montpellier 5, France. Univ Rochester, Rochester, NY USA. Univ Franche Comte, Besancon, France. Rensselaer Polytech Inst, Troy, NY USA. Univ Dar Es Salaam, Dar Es Salaam, Tanzania. Nelson Mandela Inst, Arusha, Tanzania. Uppsala Univ, Uppsala, Sweden. IMAGIR Sarl, Brest, France. C2 UBO, FRANCE UNIV MONTPELLIER, FRANCE UNIV ROCHESTER, USA UNIV FRANCHE COMTE, FRANCE RENSSELAER POLYTECH INST, USA UNIV DAR ES SALAAM, TANZANIA NELSON MANDELA INST, TANZANIA UNIV UPPSALA, SWEDEN IMAGIR SARL, FRANCE UM LGO IF 2.528 TC 28 UR https://archimer.ifremer.fr/doc/00638/75026/75673.pdf LA English DT Article DE ;Time-series analysis;Continental tectonics: extensional;Africa;Crustal imaging AB Rifting in a cratonic lithosphere is strongly controlled by several interacting processes including crust/mantle rheology, magmatism, inherited structure and stress regime. In order to better understand how these physical parameters interact, a 2 yr long seismological experiment has been carried out in the North Tanzanian Divergence (NTD), at the southern tip of the eastern magmatic branch of the East African rift, where the southward-propagating continental rift is at its earliest stage. We analyse teleseismic data from 38 broad-band stations ca. 25 km spaced and present here results from their receiver function (RF) analysis. The crustal thickness and Vp/Vs ratio are retrieved over a ca. 200 x 200 km(2) area encompassing the South Kenya magmatic rift, the NTD and the Ngorongoro-Kilimanjaro transverse volcanic chain. Cratonic nature of the lithosphere is clearly evinced through thick (up to ca. 40 km) homogeneous crust beneath the rift shoulders. Where rifting is present, Moho rises up to 27 km depth and the crust is strongly layered with clear velocity contrasts in the RF signal. The Vp/Vs ratio reaches its highest values (ca. 1.9) beneath volcanic edifices location and thinner crust, advocating for melting within the crust. We also clearly identify two major low-velocity zones (LVZs) within the NTD, one in the lower crust and the second in the upper part of the mantle. The first one starts at 15-18 km depth and correlates well with recent tomographic models. This LVZ does not always coexist with high Vp/Vs ratio, pleading for a supplementary source of velocity decrease, such as temperature or composition. At a greater depth of ca. 60 km, a midlithospheric discontinuity roughly mimics the step-like and symmetrically outward-dipping geometry of the Moho butwith a more slanting direction (NE-SW) compared to theNS rift. By comparison with synthetic RF, we estimate the associated velocity reduction to be 8-9 per cent. We relate this interface to melt ponding, possibly favouring here deformation process such as grain-boundary sliding (EAGBS) due to lithospheric strain. Its geometry might have been controlled by inherited lithospheric fabrics and heterogeneous upper mantle structure. We evidence that crustal and mantle magmatic processes represent first order mechanisms to ease and locate the deformation during the first stage of a cratonic lithospheric breakup. PY 2017 PD JUN SO Geophysical Journal International SN 0956-540X PU Oxford Univ Press VL 210 IS 1 UT 000409281300034 BP 465 EP 481 DI 10.1093/gji/ggx177 ID 75026 ER EF