Heintz et al. 2005lateral resolution : 700 - 1000km 300 - 500 km T > 40s, long paths T > 15s, shorter paths

Surface-wave tomography studies: Vs at 100 km depth

High velocities in the Amazon craton

Feng et al. 2005

S-wave anomalies at 150km (Heintz et al., 2005)

%

Note low-velocities beneath the Chaco/Pantanal basins.

100km 150km

250km

Upper Mantle Shear Velocity ModelN.ShapiroUniv.Colorado

SDT (diffraction tomography model).

200km

Global tomography (Univ. Colorado)

Few stations in South America, very long paths

-> low resolution (does not isolate Amazon craton

Note low-velocities beneath the Chaco/Pantanal basins.

Joint inversion results:

Vs 100 km

Generally high velocitiesIn the Amazon craton.No clear separation between the Guyana and Guaporé shields.

Separate high-velocity block in Southern S.Francisco craton.

Possible cratonic block beneath the Paraná basin?

resolution 300-600km

Vs 150 km

thickest lithosphere in oldest block A

TransBrasilian Lineament:generally low velocities orlimits high velocity blocks.

oldest rocks

Vs 200 km

resolution 500-800km

2.9-3.0 Gagranitoids/greenstonesCarajás Iron Province

150 km

Guyana shield Guaporé shield S.Francisco craton

NW SE

station

cratonintrusion 85-60 Ma

intrusions 130-120 Ma, Atlantic rift

P-wave tomography

geochemistry(Gibson et al., 1997)

tomography (BLSP, 2004)effect of ray paths

Note striking similarity of lithospheric thicknesses (geochemistry model) with P-wave anomalies along the white line (200km depth)

Seismicity

Earthquakes tend to occur above low-velocity areas (thinner lithosphere?)

600.

500.

400.

300.

200.

100.

0 .

Dep

th (

km)

A A '

Number of earthquakes along NW-SE profile (+- 100km width)

Iporá APIP SFC S.Mar/plat.

mag>3,5

lithosphere/asthenosphere limit?

Teresina station

Vp/Vs = 1,71

Crustal thickness= 40 km(assuming Vp=6.4km/s)

Crustal thicknesses from receiver functions. Note thick crust in the low-topography Paraná basin.

46 km

33 km

46 km

33 km

35 km

Crustal thickness

constrained by 1- Rayleigh waves2- receiver functions3- isostasy

Feng et al.(2005)

1.74

1.76

1.74

1.711.70

Average crustal Vp/VSratio

Archean is generally more felsic, consistent with low Vp/Vs (<1.73).Mafic rocks, in general, have Vp/Vs >1.75, consistent with Magmatic Arc.

1.73

1.71 Assumpção et al., 2004)