Earth structure and instrumental seismicity of Madagascar: Implications on the seismotectonics

Rindraharisaona, E. J.; Guidarelli, M.; Aoudia, Abdelkrim; Rambolamanana, G.

doi:10.1016/j.tecto.2013.03.033

Cited by 29 publications

(40 citation statements)

References 47 publications

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“…S4, in this study), a clear phase, presumably the Ps wave converted from the Moho discontinuity, is observed at ∼4 s. This indicates thinner crust (∼36 km) as reported in this study and earlier ones using receiver functions (e.g. Rindraharisaona et al 2013Rindraharisaona et al , 2017, which used more than one station along the eastern coast and considered broader back azimuth ranges. In support of this interpretation, crustal thickness estimates from gravimetry imply that the crust thins towards the eastern coast (Fourno & Roussel 1994;Rakotondraompiana et al 1999).…”

Section: Discussionsupporting

confidence: 82%

“…In the same region, Rambolamanana et al (1997) used a simultaneous inversion of hypocentral parameters and crustal velocities to obtain a thickness of 42 km, and Rai et al (2009) inferred a thickness of 38 km from receiver functions. A more recent study by Rindraharisaona et al (2013), using a joint inversion of receiver functions and surface wave dispersion measurements from the four permanent broad-band seismic stations in Madagascar, found crustal thicknesses of 35 km beneath station SBV (in the north) and FOMA (in the south), 42 km beneath station ABPO (centre), and 39 km beneath station VOI (southcentral). The surface-wave tomography study of Pasyanos & Nyblade (2007) found crustal thicknesses in Madagascar to vary between 25 and 35 km, and the global CRUST 1.0 model shows crustal thicknesses ranging from 36 to 45 km (Laske et al 2013).…”

Section: Previous Studies Of the Crust Of Madagascarmentioning

confidence: 98%

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The structure of the crust and uppermost mantle beneath Madagascar

Andriampenomanana

Nyblade

Wysession

et al. 2017

Geophysical Journal International

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S U M M A R YThe lithosphere of Madagascar was initially amalgamated during the Pan-African events in the Neoproterozoic. It has subsequently been reshaped by extensional processes associated with the separation from Africa and India in the Jurassic and Cretaceous, respectively, and been subjected to several magmatic events in the late Cretaceous and the Cenozoic. In this study, the crust and uppermost mantle have been investigated to gain insights into the present-day structure and tectonic evolution of Madagascar. We analysed receiver functions, computed from data recorded on 37 broad-band seismic stations, using the H-κ stacking method and a joint inversion with Rayleigh-wave phase-velocity measurements. The thickness of the Malagasy crust ranges between 18 and 46 km. It is generally thick beneath the spine of mountains in the centre part (up to 46 km thick) and decreases in thickness towards the edges of the island. The shallowest Moho is found beneath the western sedimentary basins (18 km thick), which formed during both the Permo-Triassic Karro rifting in Gondwana and the Jurassic rifting of Madagascar from eastern Africa. The crust below the sedimentary basin thickens towards the north and east, reflecting the progressive development of the basins. In contrast, in the east there was no major rifting episode. Instead, the slight thinning of the crust along the east coast (31-36 km thick) may have been caused by crustal uplift and erosion when Madagascar moved over the Marion hotspot and India broke away from it. The parameters describing the crustal structure of Archean and Proterozoic terranes, including average thickness (40 km versus 35 km), Poisson's ratio (0.25 versus 0.26), average shear-wave velocity (both 3.7 km s -1 ), and thickness of mafic lower crust (7 km versus 4 km), show weak evidence of secular variation. The uppermost mantle beneath Madagascar is generally characterized by shear-wave velocities typical of stable lithosphere (∼4.5 km s -1 ). However, markedly slow shear-wave velocities (4.2-4.3 km s -1 ) are observed beneath the northern tip, central part and southwestern region of the island where the major Cenozoic volcanic provinces are located, implying the lithosphere has been significantly modified in these places.

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Section: Discussionsupporting

confidence: 82%

Section: Previous Studies Of the Crust Of Madagascarmentioning

confidence: 98%

The structure of the crust and uppermost mantle beneath Madagascar

Andriampenomanana

Nyblade

Wysession

et al. 2017

Geophysical Journal International

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“…All of the four permanent stations in Madagascar are located in Precambrian basement units. Receiver functions of these stations indicate a crustal thickness between 38 and 42 km [ Rai et al , ; Rindraharisaona et al , ]. Inversion of local earthquake arrival times for the national network in central Madagascar revealed a similar crustal thickness [ Rambolamanana et al , ].…”

Section: Geological and Tectonic Settingmentioning

confidence: 99%

Crustal structure of southern Madagascar from receiver functions and ambient noise correlation: Implications for crustal evolution

et al. 2017

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The Precambrian rocks of Madagascar were formed and/or modified during continental collision known as the Pan‐African orogeny. Aborted Permo‐Triassic Karoo rifting and the subsequent separation from Africa and India resulted in the formation of sedimentary basins in the west and volcanic activity predominantly along the margins. Many geological studies have documented the imprint of these processes, but little was known about the deeper structure. We therefore deployed seismic stations along an SE‐NW trending profile spanning nearly all geological domains of southern Madagascar. Here we focus on the crustal structure, which we determined based on joint analysis of receiver functions and surface waves derived from ambient noise measurements. For the sedimentary basin we document a thinning of the underlying crystalline basement by up to ∼60% to 13 km. The crustal velocity structure demonstrates that the thinning was accomplished by removal or exhumation of the lower crust. Both the Proterozoic and Archean crust have a 10 km thick upper crust and 10–12 km thick midcrust. However, in contrast to the typical structure of Proterozoic and Archean aged crust, the Archean lower crust is thicker and faster than the Proterozoic one, indicating possible magmatic intrusions; an underplated layer of 2–8 km thickness is present only below the Archean crust. The Proterozoic mafic lower crust might have been lost during continental collision by delamination or subduction or thinned as a result of extensional collapse. Finally, the Cretaceous volcanics along the east coast are characterized by thin crust (30 km) and very large VP/VS ratios.

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“…Madagascar (Figure ) is an ideal natural laboratory to study the sources of anisotropy beneath continental regions and the rheological implications for the lithosphere‐asthenosphere system because (1) active volcanism is minimal or absent across most of the continental island, thus limiting the effect of melt lenses (Michon, ), (2) there are well‐exposed tectonic fabrics for comparison (Collins & Windley, ; Schreurs et al, ), and (3) numerous geological and geophysical observations provide evidence of present‐day tectonic activities potentially linked to viscous coupling to asthenospheric flow (Bertil & Regnoult, ; Kusky et al, ; Rambolamanana et al, ; Rindraharisaona et al, ).…”

Section: Introductionmentioning

confidence: 99%

“…Madagascar (Figure 1) is an ideal natural laboratory to study the sources of anisotropy beneath continental regions and the rheological implications for the lithosphere-asthenosphere system because (1) active volcanism is minimal or absent across most of the continental island, thus limiting the effect of melt lenses (Michon, 2016), (2) there are well-exposed tectonic fabrics for comparison (Collins & Windley, 2002;Schreurs et al, 2010), and (3) numerous geological and geophysical observations provide evidence of present-day tectonic activities potentially linked to viscous coupling to asthenospheric flow (Bertil & Regnoult, 1998;Kusky et al, 2010;Rambolamanana et al, 1997;Rindraharisaona et al, 2013). Reiss et al (2016) produced the first SKS splitting observations along the SELASOMA seismic profile (SEismological signatures in the Lithosphere/Asthenosphere System Of Southern Madagascar) that spans southern Madagascar in a NE-SW orientation, while Ramirez et al (2018) provided additional SKS splitting measurements across the entire continental island (Figure 1).…”

Section: Introductionmentioning

confidence: 99%

Numerical Modeling of Mantle Flow Beneath Madagascar to Constrain Upper Mantle Rheology Beneath Continental Regions

et al. 2020

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Over the past few decades, azimuthal seismic anisotropy measurements have been widely used proxy to study past and present‐day deformation of the lithosphere and to characterize convection in the mantle. Beneath continental regions, distinguishing between shallow and deep sources of anisotropy remains difficult due to poor depth constraints of measurements and a lack of regional‐scale geodynamic modeling. Here, we constrain the sources of seismic anisotropy beneath Madagascar where a complex pattern cannot be explained by a single process such as absolute plate motion, global mantle flow, or geology. We test the hypotheses that either Edge‐Driven Convection (EDC) or mantle flow derived from mantle wind interactions with lithospheric topography is the dominant source of anisotropy beneath Madagascar. We, therefore, simulate two sets of mantle convection models using regional‐scale 3‐D computational modeling. We then calculate Lattice Preferred Orientation that develops along pathlines of the mantle flow models and use them to calculate synthetic splitting parameters. Comparison of predicted with observed seismic anisotropy shows a good fit in northern and southern Madagascar for the EDC model, but the mantle wind case only fits well in northern Madagascar. This result suggests the dominant control of the measured anisotropy may be from EDC, but the role of localized fossil anisotropy in narrow shear zones cannot be ruled out in southern Madagascar. Our results suggest that the asthenosphere beneath northern and southern Madagascar is dominated by dislocation creep. Dislocation creep rheology may be dominant in the upper asthenosphere beneath other regions of continental lithosphere.

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Earth structure and instrumental seismicity of Madagascar: Implications on the seismotectonics

Cited by 29 publications

References 47 publications

The structure of the crust and uppermost mantle beneath Madagascar

The structure of the crust and uppermost mantle beneath Madagascar

Crustal structure of southern Madagascar from receiver functions and ambient noise correlation: Implications for crustal evolution

Numerical Modeling of Mantle Flow Beneath Madagascar to Constrain Upper Mantle Rheology Beneath Continental Regions

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