The Chaco-Paraná Basin from GOCE and Integrated Terrestrial/Satellite Gravity Data: Unraveling Major Lithosphere Discontinuities Gabriel N
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The Chaco-Paraná Basin from GOCE and Integrated Terrestrial/Satellite Gravity Data: Unraveling Major Lithosphere Discontinuities Gabriel N. Dragone ([email protected]), Naomi Ussami and Carlos A. M. Chaves Universidade de São Paulo Department of Geophysics, Institute of Astronomy, Geophysics and Atmospheric Sciences. Abstract Vertical derivative of upward continued field The Chaco-Paraná basin (CPB) is located in the South American plate, mainly in the northeast of Figure 6: Upward continuation to 15 km of the BAM (white Argentina. Its oldest sediments are related to the Eopaleozoic and, from the Late Carboniferous rectangle in Figs. 2 and 3) from EGM2008 field. A NE-SW trend to the Early Cretaceous, it shares a common sedimentation history with the Paraná Basin (PB) and negative anomalies can be observed in the PB, whereas in (southeastern of Brazil). The Asunción High separates these two basins, and a lithosphere with the CPB the anomalies are scattered, tending to be more distinct characteristics for each of them has been distinguished through both seismological and positive. Thus, a major suture zone between both basins can be deep magnetotelluric (MT) studies. Crustal thicknesses of roughly 32 km and 42 km have been inferred (white curve). determined for the CPB and PB, respectively. These changes are discussed herein through the analysis of two global potential field models, the EGM2008 model, which encompasses both terrestrial and satellite data, and an entirely satellite one, derived from GOCE data. The results, Seismological and deep MT studies in accordance to those aforementioned, suggest a crustal, and possibly a lithospheric scale, suture zone. Introduction Figure 1: Topographic map of part of South America. The contour of the basins as well as the geological structures which separate them (in blue) are from Milani (2000). The CPB covers an area of Figure 8: MT vertical session along the approximately 700,000 km² and it is Paraná and Pantanal basins (Bologna et al., limited to the east by the PB, with the submitted). Asunción High separating them; to the Figure 7: Crustal thickness map from receiver function (Bianchi, 2008). Snoke and James (1997) west by the Sierras Pampeanas. Its suggest crustal thicknesses of 32 km for the CPB and 42 km for the PB. geomorphology is characterized by a low- land (~100 m a.s.l.). Depth of Moho derived from Gravity data Geopotential field models Figure 9: Total sedimentary package of both basins digitized from Milani et al. (2000) Figure 10: a) Gravity Effect owing to Sedimentary thickness (GES) calculated from rectangular prisms algorithm (Chaves, 2010); b) GOCE data in the study area; c) GOCE data minus GES; d) Figures 2 and 3: Bouguer Anomaly Maps (BAM) from the EGM20008 (degree 2159, Pavlis et al., Depth of Moho estimated using a density contrast of 300 kg/m³ and a mean depth of 38 km 2008) and GOCE (degree 250, Pail et al., 2011) models. according to the Parker-Oldenburg method (Gómez-Ortiz and Agarwal, 2004). Conclusions The change in the crustal thickness estimated from the inversion of the gravity data derived from the GOCE mission (~35 km for the CPB, ~42 km for the PB), jointed to the analysis aforementioned, the MT vertical session and the seismological studies, indicates a major lithosphere discontinuity which suggests the existence of a suture zone between the basins. Figure 4: Profiles along the white References dotted lines in Figs. 2 and 3. We Bianchi, M.B. Variations in the crustal, lithosphere and mantle structure for the South American platform using P- and S-waves highlight that from intermediate- to receiver functions. 2008. 133 p. Thesis (PhD) – IAG/USP, São Paulo, 2008. Bologna et al., Mapping lithospheric sutures and amalgamated terranes within the Parana basin integrating EM induction and gravity data. Submitted to J. S. American Earth Sciences. long-wavelengths the geopotential Chaves, C. A. M. Inversão linear de anomalias do geóide da Província Borborema : variação composicional ou perturbação térmica no manto? Master’s Thesis – IAG/USP, São Paulo, 2010. models agree, predicting the same Gomez-Ortis, D.; Agarwal, B.N.P. 3DINVER.m: a MATLAB program to invert the gravity anomaly over a 3D horizontal density interface by Parker-Oldenburg's algorithm. Computer & Geosciences, v. 31, pp. 513-520, 2005. anomalies. It is also possible to Milani, E.J.; Thomaz Filho, A. Sedimentary Basins of South America. In: CORDANI, U. G. (Org.). Tectonic Evolution of South Figure 5: Upward continuation of the Bouguer America. Rio de Janeiro: 31st International Geological Congress, 2000. v. 1, pp. 389-399. observe an abrupt change in the anomaly map derived from GOCE. The steep Pail, R.; Bruinsma, S.; Migliaccio, F.; Föerste, C.; Goiginger, H.; Schuh, W.D.; Hoeck, E.; Reguzzoni, M.; Brockmann, J.M.; Abrikosov, O.; Veicherts, M.; Fecher, T., Mayrhofer, R.; Krasbutter, I.; Sanso, F.; Tscherning, C.C. First GOCE gravity field models derived by three amplitude of the regional gravity gradient that separates the two basins continues different approaches. Jounal of Geodesy, in review, 2011. northwards, separating the PB from the Pantanal Pavlis, N.K.; Holmes, S.A.; Kenyon, S.C.; Factor, J.K. An Earth Gravitational Model to Degree 2160: EGM2008. In: The 2008 which varies from 10-20 mGal over General Assembly of The European Geosciences Union, 13-14 abr. 2008, Vienna, Austria, 2008. basin, where a deep magnetotelluric session (red Snoke, J.A.; James, D.E. Lithospheric structure of the Chaco and Paraná basins of South America from surface‐wave inversion. the CPB to -80 mGal in the PB. line) has been carried out (Fig. 8). Journal of Geophysical Research, v. 102, n. B2, pp. 2939–2951, Feb., 1997. .