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)