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Tectonic evolution of the South Atlantic passive continental margin based on onshore structural data.

Principal Investigators: Dr. Daniel Köhn, Prof. Dr. Ulrich A. Glasmacher, Prof. Dr. Cees Passchier

KöhnIIThis work will deal with the opening of the South Atlantic and the tectonic development of its margins with special emphasis on the Parána LIP’s (Large Igneous Province) in Brazil and the Etendeka LIP’s in Namibia. We will study the effects of deep-seated mantle processes, far-field plate stresses and local margin dynamics on the passive margin. Our first hypothesis is that the margins on both sides of the South Atlantic experienced a very different development following LIP extrusion, since hot-spot activities on both margins vary and the Brazilian margin is influenced by the Andean orogeny (being currently under compression in an E-W direction). Our second hypothesis states that the passive continental margin is segmented onshore along the large Florianopolis/Rio Grande Fracture Zone and associated faults and experiences different block movements through time. The second hypothesis is based on new thermochronologic data assembled in the first SAMPLE phase, which shows margin segmentation. Our third hypothesis is that reactivation of basement faults plays an important role in the margin dynamics. The Parána and Etendeka LIP’S and their contact to the basement rocks are an ideal archive of the post-rift development of the margin. Detailed field-work on reactivation of basement faults will be followed by a fault slip analysis in order to determine local paleo-stress states (directions of principal stresses and relative ratios of differential stresses). We will use a new powerful method (SVS-method, Sippel et al. 2009) that allows us to separate different stress states and test them thoroughly. Finally we will try to fit the determined stress states in time frames using relative fault intersections, fault dyke relations where we will date important volcanics and thermochronological data from the accompanying project. We aim to produce a new tectonicthermochronologic model of the dynamics of the South Atlantic margins, their differences and segmentation. Our work tackles important SAMPLE questions, will be compared and adjusted to offshore studies and builds an ideal basis for large-scale numerical models.