Heintz et al. 2005 lateral resolution : 700 - 1000km 300 - 500 km T > 40s, long paths T > 15s, shorter paths Surface-wave tomography studies: Vs at 100.

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Presentation transcript:

Heintz et al lateral resolution : km 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 Model N.Shapiro Univ.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 velocities In 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 km Vs 150 km thickest lithosphere in oldest block A TransBrasilian Lineament: generally low velocities or limits high velocity blocks.

oldest rocks Vs 200 km resolution km Ga granitoids/greenstones Carajás Iron Province

150 km Guyana shield Guaporé shield S.Francisco craton NWSE

station craton intrusion Ma intrusions 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?)

Number of earthquakes along NW-SE profile (+- 100km width) Iporá APIP SFC S.Mar/plat. mag>3,5 lithosphere/asthenosphere limit?

Receiver Function R Z FR(w) = R(w)/Z(w) fr(t) = response from an incident pulse consisting of all P-to-S conversions at crustal interfaces

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 waves 2- receiver functions 3- isostasy Feng et al.(2005)

Average crustal Vp/VS ratio 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 Assumpção et al., 2004)