O Camp nas bacias dos Solimões, Amazonas, Parnaíba e Parecis, Norte do Brasil: implicações geotectônicas e deposicionais para o jurássico do Gondwana Ocidental.

Abstract

Geological studies in conjunction with applications of geophysical techniques are being widely used to highlight and characterize CAMP gravimetric anomalies throughout Northern Brazil, including the Solimões, Parecis, Amazonas and Parnaíba basins. Interpretations of a residual gravimetric anomaly from these basins were used to expand the understanding of the distribution of CAMP throughout the subsurface. This study was carried out through qualitative and quantitative interpretations of gravimetric data, supported by surface geological information, mainly stratigraphic data based on outcrops. From direct gravimetric modeling, based on available crustal gravitational structure models to separate a residual gravity signal from observed gravity data, realistically detailed geological and tectonic features were interpreted, providing useful information for a geophysical interpretation of geological sources. With the residual gravity anomaly, a map of the elastic thickness (Te) of the basins was obtained, using a new procedure, presumably allowing some gaps presented in the current literature on the CAMP to be filled. For each Te value, the residual gravimetric signal was calculated, considering the surfaces described by topography and Moho for a regional model with standard density and discretized into prisms. The cross-correlation between the observed gravity signal and calculated gravity signal made it possible to obtain a map of the elastic thickness of the studied areas. The highest correlation value is directly related to the best value of elastic thickness and Moho depth associated with crustal deformation. Our study used a combination of these techniques to presumably define the possible extent of Jurassic magmatism, the basin rheology of igneous body intrusion and history of thermal subsidence that largely controlled depositional control during and after the CAMP. The presence of low gravity values is closely related to the less dense lithological units of the upper crust, while the high gravity values are related to high-density rocks correlated to the continental tholeiitic flood basalts of the CAMP. The use of residual gravity anomaly based on crustal modeling combined with previous geological data was effective in identifying the CAMP record in these Amazonian sedimentary basins. Furthermore, some gravimetric signatures correlate well with the main structural discontinuities, particularly with the Monte Alegre Dome and Xambioá, Serra Formosa and Vilhena arches, respectively, in the Amazon, Parnaíba and Parecis basins. This interpretation provides a reasonable explanation for understanding structural lineaments without exclusively tectonic connotations, assuming a new interpretation for the gravitational field related to intracrustal density contrast or residual gravity field for these basins. Eastern Gondwana was gradually uplifted by subvolcanic bodies of the Penatecaua magmatism in the Amazon and Solimões basins. In contrast, extrusive volcanism characterizes Mosquito magmatism in the Parnaíba basin interspersed with intertrap sediments. Information obtained from the elastic thickness map, Moho depth and residual gravity signal indicate a thinner crust in the Parnaíba basin favoring the magmatic eruption induced by a hot spot installed on the western edge of the basin. On the other hand, in basins with denser and thicker crust, magma accumulates mainly as sills, providing greater resistance to rupture due to the swelling of the CAMP. The Parnaíba Basin experienced three magmatic pulses at intervals of approximately 1 Myr, alternating with the development of aeolian-fluvial-lacustrine systems (intertrap sediments) during non-magmatic periods, indicating short intervals of magmatic resump-tion and cooling in the CAMP, contrasting with the longer and continuous magmatism in the Amazon and Solimões basins, which lack intertrap deposits. These results are important for a new disposition of the tectonomagmatic, structural and stratigraphic history for these basins, since from a new context or geological evolution for the area it will allow a better understanding of the studied basins in lava-sediment interaction, preserved from the Jurassic and related to the CAMP events, which preceded the main continental rupture in northwestern Pangea.