FAPESP Thematic Project 2013/24214-6
Pantanal-Chaco-Paraná Basins (PCPB): Crust and Upper Mantle Seismic Structure and Evolution
Figure 1. S-wave anomalies at 100km depth, (Assumpção, Feng, Julià & Tassara, 2013). TBL = TransBrasiliano Lineament. Very low velocities (orange, red) are seen in the asthenospheric wedge of Bolivia and northern Argentina and beneath the Pantanal. The high-velocities (green, blue) indicate thick lithosphere beneath the northern and southern parts of the Paraná Basin.
Open squares are temporary stations; colored triangles and circles are
permanent stations of the Brazilian Network.
Introduction - Previous Studies
Since 1992, the deep crustal and upper mantle structure of SE Brazil has been studied by deployment of over 50 temporary stations, mainly in the northern Paraná Basin and surrounding areas, in several projects run by USP with collaboration from IPT (Technological Research Institute, SP), Carnegie Institution, UnB (Brasilia University), Northwestern University (NWU, USA), UNESP (Univ. of the State of São Paulo) and lately ON (National Observatory, RJ).
Seismological methods (receiver functions, tomography, SKS splitting, etc.) have mapped important features (Fig. 1 above), like: a) thick crust and thick lithosphere beneath the Paraná basin, possibly associated with a cratonic block; b) low-velocities in the upper mantle and thin lithosphere in the Pantanal Basin, possibly explaining the local seismicity; c) thick root beneath the São Francisco Craton. However, the Pantanal and Chaco Basins and the southern part of the Paraná Basin have not been adequately sampled yet, so their deep structures are not known with good resolution.
Goals of this Project
We will advance our knowledge of the deep structure in the western part of Brazil (and neighbouring countries) to investigate several open questions about the crustal evolution of the Pantanal, Chaco and Paraná Basins and the present geodynamics in this part of the South American plate. In particular, we want to study the:
Crustal and upper mantle structure of the Pantanal Basin, to better delimit the belt of thin crust that seems to exist along the TransBrasiliano Lineament. We will also better characterize the low seismic velocities in the upper mantle, which may influence upper mantle flow. We will test if the Pantanal subsidence is caused by downwelling of upper mantle flow.
Crustal structure of the Paraná and Chaco Basins, to help resolve the pending issue of the extent of mafic underplating, usually required by gravity modeling, but not seen as a significant feature in seismic models.
Geometry of the Nazca Plate, beneath SE Brazil, to help model upper mantle flow and estimate the effects in the upper lithosphere (crustal stresses and dynamic topography).
Intraplate seismicity using the small events likely to be recorded during the 4-year project.
Crustal deformation, measured by a high-precision geodetic GNSS network. This will allow new data on rheological properties of the lithosphere to be correlated with seismicity-derived crustal stresses and seismic properties.
Upper mantle flow, studied by numerical methods using upper mantle properties derived from the tomography models. Of special interest is the effect of upper mantle flow on the lithosphere, such as basin subsidence, and crustal stresses correlatable with seismicity.
- Deep structure along the SW continuation of the TransBrasiliano Lineament, to contribute to the debate on the possible existence/extension of the Clymene Ocean in the Early Paleozoic just before the Gondwanaland Assembly.
To achieve these goals, 40 temporary stations will be installed for three years. 20 stations have been loaned by the Pool of Geophysical Equipment (National Observatory, Rio de Janeiro) and 20 have been purchased by the Project. University of Liverpool will also lend 10 additional temporary stations. From the set to be purchased, 10 will be on stand-by for aftershock deployments. Fig. 2 shows a map of the planned station distribution.
Several seismological techniques will be used, such as receiver functions (both P- and S-RFs), body- and surface-wave tomography, SKS splitting, and focal mechanism studies. Collaboration from several institutions, both in Brazil (INPE, UNESP, IPT, UnB, UFRN, UFMS and Unipampa) and in neighboring countries (Bolivia, Paraguay, Argentina and Uruguay) will ensure successful field campaigns as well as integrated interpretation of the results. Collaboration from Northwestern University and Liverpool in tomography studies and from Royal-Holloway, London University (RHWL, UK), in numerical modeling of upper mantle flow, will strengthen the project.
Figure 2. Seismic stations and crustal thickness in SE Brazil. a) Current permanent station (colored symbols) and proposed temporary deployments (open squares) covering the regions of the Pantanal Basin (Pt, dark yellow area) and the Chaco (CH) and Paraná (PR) basins (pale yellow). Blue and green triangles are the permanent stations of the Brazilian Seismographic Network (RSBR) deployed by USP and UnB. Orange circles are the RSBR stations installed by the National Observatory. Gray squares are global permanent stations (BDFB, CPUP). Light blue triangles are newly planned RSBR stations. Open squares are the temporary stations being deployed for the proposed passive experiment starting in 2015. b) contours of crustal thickness from the compilation of Assumpção et al.(2013). Red dots in the continent denote crustal measurements at seismic stations (onshore); green lines are limits of the main geological provinces as shown by the colors in (a).
- IAG/IEE-USP (Univ. of São Paulo, Brazil) coordination, Marcelo Assumpção (coordinator), Marcelo Bianchi, Hans Agurto, Victor Sacek.
- INPE, São José dos Campos, SP: Ícaro Vitorello (vice-coordinator), Marcelo B. de Pádua.
- UFMS, Campo Grande/Aquidauana: Edna Facincani, Toni Paranhos, José Marcato Jr.
- UnB, Brasília, DF: Marcelo Rocha
- IPT, São Paulo: Luis Carlos Ribotta
- Unipampa, RS: Marcus Vinicius Lima
- UNESP, Rio Claro, SP: João Carlos Dourado, Mario Luis Assine
- UFRN, Natal: Jordi Julià
Latin Americam Institutitions:
- Observatorio San Calixto, Bolivia: Estela Minaya
- Univ. Nacional, Paraguay: Juan Carlos Velasquez
- INPRES, Argentina: Mario Araujo, Gerardo Sanchez, Mario Bufaliza
- U.N. de la Plata, Argentina: María Laura Rosa, Nora Sabbione
- Univ. de la República, Uruguay, Observ. Geofísico de Aiguá: Leda Sanchez, Oscar Castro
- North American and European Institutions:
- CSIC, Barcelona, Spain: Martin Schimmel
- Liverpool University, Liverpool: Andreas Rietbrock
- Northwestern University, USA: Suzan van der Lee
- Royal Holloway, London: Jason Morgan, Marta Pérez-Gussinyè
Purchase of 20 new stations (done)
January-June: Installation of 5 initial GNSS stations.
January to June: Deployment of 20 temporary stations in Brazil (loaned from Brazilian Geophysical Equipment Pool, National Observatory, Rio de Janeiro).
July to December: Deployment of stations in Bolivia, Paraguay, Argentina and Uruguay, after proper paper work for temporary export/import licences. Start of maintenance visits to temporary stations deployed in Brazil.
Initial results to be presented at the AGU Fall meeting (December, 2016)
First preliminary results on crustal thicknesses from RF studies and anisotropy from SKS splitting.
First preliminary models of upper mantle tomography from body-wave and surface-wave tomography.
Presentation of initial results at AAGG meeting, La Plata, Argentina.
Implementation of parameters of the numerical model for mantle flow.
Installation of remaining GNSS stations and initial processing of GNSS data for quality control.
2016 - 2017 - 2018:
Visit to all temporary and permanent stations on a 6-months basis
More complete results of the project presented at meetings.
São Paulo, 13-April-2016.