The São Francisco cratonic root beneath the Neoproterozoic Brasilia belt (Brazil): Petrophysical data from kimberlite xenoliths

Petrostructural analysis of 31 mantle xenoliths from three kimberlitic pipes intruding the Neoproterozoic Brasilia belt close to southwestern margin São Francisco craton (SFC) reveals microstructures and compositions similar those observed in cratonic roots worldwide. (1) The spinel-peridotites sampling upper section lithospheric have dominantly refractory modal mineral compositions, whereas garnet-peridotites deep more fertile consistent with (2) present a variation microstructure coarse-granular coarse-porphyroclastic, but olivine crystallographic preferred orientations (CPO). (3) fine-porphyroclastic microstructures. (4) Many coarse-porphyroclastic display Fe-enrichment pyroxenes, often associated Ti-enrichment pyroxenes or spinel occurrence phlogopite. (5) Equilibrium temperatures pressures are geotherm, equilibrium conditions require warmer geotherm. We interpret these observations as indicating that sample SFC root, which extends beneath belt, was modified by reactive transport magmas forming Alto Parnaiba Igneous Province (APIP) between 120 90 Ma. APIP magmatism resulted heterogeneous metasomatism, Fe enrichment, development peridotites garnet-peridotites, moderate heating root. These changes may produce decrease seismic velocities explaining local weak negative anomaly APIP, contrasts positive velocity anomalies characterizing root P-wave tomography models. However, magma did not erase CPO. Comparison average properties seismological data implies subhorizontal fossil flow directions non-negligible contribution teleseismic S-waves splitting.