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

Fernandes, Priscila Rezende ; Tommasi, Andréa ; Vauchez, Alain ; Neves, Sérgio Pacheco ; Nannini, Felix

Tectonophysics, 2021-10, Vol.816, p.229011, Article 229011 [Periódico revisado por pares]

Amsterdam: Elsevier B.V

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  • Título:
    The São Francisco cratonic root beneath the Neoproterozoic Brasilia belt (Brazil): Petrophysical data from kimberlite xenoliths
  • Autor: Fernandes, Priscila Rezende ; Tommasi, Andréa ; Vauchez, Alain ; Neves, Sérgio Pacheco ; Nannini, Felix
  • Assuntos: Annealing ; Anomalies ; Belt conveyors ; Biotite ; Composition ; Craton ; Cratons ; Crystallography ; Deformation ; Earth Sciences ; Enrichment ; Equilibrium conditions ; Fertility ; Fossils ; Garnet ; Geophysics ; Iron ; Isotopes ; Lava ; Magma ; Mantle ; Melt-rock reaction ; Metasomatism ; Microstructure ; Mineral composition ; Mineralogy ; Olivine ; P waves ; Pyroxenes ; Roots ; S waves ; Sampling ; Sciences of the Universe ; Seismic anisotropy ; Seismic properties ; Seismic velocities ; Seismological data ; Seismology ; Spinel ; Tectonics ; Titanium ; Tomography ; Transport
  • É parte de: Tectonophysics, 2021-10, Vol.816, p.229011, Article 229011
  • Descrição: Petrostructural analysis of 31 mantle xenoliths from three kimberlitic pipes intruding the Neoproterozoic Brasilia belt close to the southwestern margin of the São Francisco craton (SFC) reveals microstructures and compositions similar to those observed in cratonic roots worldwide. (1) The spinel-peridotites sampling the upper section of the lithospheric mantle have dominantly refractory modal and mineral compositions, whereas garnet-peridotites sampling the deep lithospheric mantle have more fertile compositions, consistent with those observed in cratonic roots worldwide. (2) The spinel-peridotites present a variation in microstructure from coarse-granular to coarse-porphyroclastic, but similar olivine crystallographic preferred orientations (CPO). (3) The garnet-peridotites have fine-porphyroclastic microstructures. (4) Many coarse-porphyroclastic spinel-peridotites display Fe-enrichment in olivine and pyroxenes, often associated with Ti-enrichment in pyroxenes or spinel and occurrence of modal phlogopite. (5) Equilibrium temperatures and pressures of garnet-peridotites are consistent with a cratonic geotherm, but equilibrium conditions of spinel-peridotites require a warmer geotherm. We interpret these observations as indicating that the xenoliths sample the SFC mantle root, which extends beneath the Brasilia belt, but was modified by reactive transport of the magmas forming the Alto Parnaiba Igneous Province (APIP) between 120 and 90 Ma. The APIP magmatism resulted in heterogeneous modal metasomatism, Fe enrichment, development of coarse-porphyroclastic microstructures in spinel peridotites and fine-porphyroclastic microstructures in garnet-peridotites, and moderate heating of the cratonic mantle root. These changes may produce a decrease in seismic velocities explaining the local weak negative anomaly observed in the lithospheric mantle beneath the APIP, which contrasts with the positive velocity anomalies characterizing the SFC mantle root in P-wave tomography models. However, reactive magma transport did not erase the olivine CPO. Comparison of the average seismic properties of the xenoliths with seismological data implies dominantly subhorizontal fossil flow directions and a non-negligible contribution of the cratonic root to teleseismic S-waves splitting. •The xenoliths sample the São Francisco craton root below the Neoproterozoic Brasilia Belt.•Refractory compositions and coarse-granular microstructures, typical of cratons, predominate.•Cretaceous kimberlitic magmatism changed microstructures, compositions, and moderately heated the cratonic root.•Reactive melt percolation locally reduced seismic velocities, but did not erase seismic anisotropy.
  • Editor: Amsterdam: Elsevier B.V
  • Idioma: Inglês
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  • Realização: ABCD-USP USP   Logos de Redes Sociais: Freepik

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