Author(s)

Victor F. Velázquez, Claudio Riccomini, José M. Azevedo Sobrinho, Mikhaela A. J. S. Pletsch, Alethéa E. Martins Sallun, William Sallun Filho, Jorge Hachiro

Escola de Artes, Ciências e Humanidades, Universidade de S?o Paulo, S?o Paulo, Brasil.
Instituto de Geociências, Universidade de S?o Paulo, S?o Paulo, Brasil.
Instituto Geológico, Secretaria do Meio Ambiente, S?o Paulo, Brasil.

The 3.6 km-diameter Colonia impact crater, centred at 2352'03"S and 4642'27"W, lies 40 km to the south-west of the S?o Paulo city. The structure was formed on the crystalline basement rocks and displays a bowl-shaped with steeper slope near the top that decreases gently toward the centre of the crater. Over recent years were drilled two boreholes inside the crater, which reached a maximum depth of 142 m and 197 m. Geological profile suggests four different lithological associations: 1) unshocked crystalline basement rocks (197 - 140 m); 2) fractured/brecciated basement rocks (140 - 110 m); 3) polymictic allochthonous breccia deposits (110 - 40 m); and 4) post-impact deposits (40 - 0 m). Petrographic characterisation of the polymictic allochthonous breccia reveals a series of distinctive shock-metamorphic features, including, among others, planar deformation features in quartz, feldspar and mica, ballen silica, granular texture in zircon and melt-bearing impact rocks. The occurrence of melt particles and very high-pressure phase transformation in suevite breccia suggest a shock pressure regime higher than 60 GPa.

Colônia Crater; Polymictic Allochthonous Breccia; Shock Metamorphism Effects

V. Velázquez, C. Riccomini, J. Sobrinho, M. Pletsch, A. Sallun, W. Filho and J. Hachiro, "Evidence of Shock Metamorphism Effects in Allochthonous Breccia Deposits from the Colônia Crater, São Paulo, Brazil," International Journal of Geosciences, Vol. 4 No. 1A, 2013, pp. 274-282. doi: 10.4236/ijg.2013.41A025.