Broadband Seismic Deployments for Imaging the Upper Mantle Structure in the Lützow-Holm Bay Region, East Antarctica

Broadband seismic deployments have been carried out in the Lützow-Holm Bay region (LHB), Dronning Maud Land, East Antarctica. The recorded teleseismic and local events are of sufficient quality to image the structure and dynamics of the crust and mantle of the terrain. Passive seismic studies by receiver functions and shear wave splitting suggest a heterogeneous upper mantle. Depth variations in topography for upper mantle discontinuities were derived from long period receiver function, indicating a shallow depth discontinuity at 660 km beneath the continental area of LHB. These results provide evidence of paleo upwelling of the mantle plume associated with Gondwana break-up. SKS splitting analysis anticipated a relationship between “fossil” anisotropy in lithospheric mantle and past tectonics. Moreover, active source surveys (DSSs) imaged lithospheric mantle reflections involving regional tectonic stress during Pan-African and succeeding extension regime at the break-up. By combining the active and passive source studies of the mantle structure, we propose an evolution model of LHB for constructing the present mantle structure.

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Lithospheric and sublithospheric deformation under the Borborema Province of northeastern Brazil from receiver function harmonic stripping

Solid Earth ◽

10.5194/se-10-893-2019 ◽

2019 ◽

Vol 10 (3) ◽

pp. 893-905 ◽

Cited By ~ 3

Author(s):

Gaelle Lamarque ◽

Jordi Julià

Keyword(s):

Lithospheric Mantle ◽

Seismic Anisotropy ◽

Receiver Function ◽

Seismic Station ◽

Atlantic Coast ◽

Shear Zones ◽

Receiver Functions ◽

Azimuthal Anisotropy ◽

Northeastern Brazil ◽

Borborema Province

Abstract. The depth-dependent anisotropic structure of the lithosphere under the Borborema Province in northeast Brazil has been investigated via harmonic stripping of receiver functions developed at 39 stations in the region. This method retrieves the first (k=1) and second (k=2) degree harmonics of a receiver function dataset, which characterize seismic anisotropy beneath a seismic station. Anisotropic fabrics are in turn directly related to the deformation of the lithosphere from past and current tectonic processes. Our results reveal the presence of anisotropy within the crust and the lithospheric mantle throughout the entire province. Most stations in the continental interior report consistent anisotropic orientations in the crust and lithospheric mantle, suggesting a dominant northeast–southwest pervasive deformation along lithospheric-scale shear zones developed during the Brasiliano–Pan-African orogeny. Several stations aligned along a northeast–southwest trend located above the (now aborted) Mesozoic Cariri–Potiguar rift display large uncertainties for the fast-axis direction. This non-azimuthal anisotropy may be related to a complex anisotropic fabric resulting from a combination of deformation along the ancient collision between Precambrian blocks, Mesozoic extension and thermomechanical erosion dragging by sublithospheric flow. Finally, several stations along the Atlantic coast reveal depth-dependent anisotropic orientations roughly (sub)perpendicular to the margin. These results suggest a more recent overprint, probably related to the presence of frozen anisotropy in the lithosphere due to stretching and rifting during the opening of the South Atlantic.

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