Heintz%20et%20al.%202005

1
Surface-wave tomography studies Vs at 100 km
depth
High velocities in the Amazon craton
Heintz et al. 2005
Feng et al. 2005
lateral resolution 700 - 1000km
300 - 500 km T gt 40s, long paths
T gt 15s, shorter paths
2
Note low-velocities beneath the Chaco/Pantanal
basins.

S-wave anomalies at 150km (Heintz et al., 2005)
3
150km
100km
Global tomography (Univ. Colorado) Few stations
in South America, very long paths -gt low
resolution (does not isolate Amazon craton
Note low-velocities beneath the Chaco/Pantanal
basins.
250km
200km
Upper Mantle Shear Velocity Model N.Shapiro Univ.C
olorado SDT (diffraction tomography model).
4
Vs 100 km
Joint inversion results
Generally high velocities In the Amazon
craton. No clear separation between the Guyana
and Guaporé shields.
Possible cratonic block beneath the Paraná basin?
5
Vs 150 km
resolution 300-600km
thickest lithosphere in oldest block A
TransBrasilian Lineament generally low
velocities or limits high velocity blocks.
6
Vs 200 km
oldest rocks
resolution 500-800km
2.9-3.0 Ga granitoids/greenstones Carajás Iron
Province
7
150 km
Guaporé shield
NW
SE
Guyana shield
S.Francisco craton
8
P-wave tomography
station
craton
intrusion 85-60 Ma
intrusions 130-120 Ma, Atlantic rift
9
geochemistry (Gibson et al., 1997)
Note striking similarity of lithospheric
thicknesses (geochemistry model) with P-wave
anomalies along the white line (200km depth)
effect of ray paths
tomography (BLSP, 2004)
10
Seismicity
Earthquakes tend to occur above low-velocity
areas (thinner lithosphere?)
11
Number of earthquakes along NW-SE profile
(- 100km width)
maggt3,5
Iporá
S.Mar/plat.
SFC
APIP
12
Z
R
FR(w) R(w)/Z(w) fr(t) response from an
incident pulse consisting of
all P-to-S conversions at
crustal interfaces
Receiver Function
13
Teresina station Vp/Vs 1,71 Crustal
thickness 40 km (assuming Vp6.4km/s)
14
33 km
46 km
46 km
33 km
35 km
Crustal thicknesses from receiver functions.
Note thick crust in the low-topography Paraná
basin.
15
Crustal thickness constrained by 1- Rayleigh
waves 2- receiver functions 3- isostasy
Feng et al.(2005)
16
Average crustal Vp/VS ratio
1.74
1.76
Archean is generally more felsic, consistent with
low Vp/Vs (lt1.73). Mafic rocks, in general, have
Vp/Vs gt1.75, consistent with Magmatic Arc.
1.71
1.70
1.74
1.73
1.71
Assumpção et al., 2004)