Seismotectonics of Madagascar

Bertil, Didier; Regnoult, Jean Marc

doi:10.1016/s0040-1951(98)00088-2

Cited by 57 publications

(63 citation statements)

References 24 publications

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“…In Madagascar, it is believed that Late Neoproterozoic/Cambrian shear zones were reactivated and controlled the opening of the Late Paleozoic basins and the later drift evolution of Madagascar (Montenat et al, 1996;Piqu e et al, 1999a). Likewise, a present day extensional regime is inferred from Recent reactivation of these former zones of weaknesses (Bertil and Regnoult, 1998;Piqu e et al, 1999b). Up to now, limited numbers of low temperature geochronological data exists from southern Madagascar (e.g.…”

Section: Introductionmentioning

confidence: 99%

Titanite and apatite fission track analyses on basement rocks of central-southern Madagascar: constraints on exhumation and denudation rates along the eastern rift shoulder of the Morondava basin

Emmel

Jacobs

Razakamanana

2004

Journal of African Earth Sciences

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Section: Introductionmentioning

confidence: 99%

Titanite and apatite fission track analyses on basement rocks of central-southern Madagascar: constraints on exhumation and denudation rates along the eastern rift shoulder of the Morondava basin

Emmel

Jacobs

Razakamanana

2004

Journal of African Earth Sciences

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“…The sediments consist of laterized sandstones and sandy shales with intercalated layers of calcareous shales (Razafimanantsoa et al 1972). Madagascar is presently seismically active with most seismicity confined to the crust (Rambolamanana et al 1997;Bertil and Regnoult 1998). Seismicity is most frequent beneath the Ankaratra volcanic field in central Madagascar (Bertil and Regnoult 1998).…”

Section: Regional Settingmentioning

confidence: 99%

“…Madagascar is presently seismically active with most seismicity confined to the crust (Rambolamanana et al 1997;Bertil and Regnoult 1998). Seismicity is most frequent beneath the Ankaratra volcanic field in central Madagascar (Bertil and Regnoult 1998). The ongoing extension in Madagascar has been tentatively linked to the East African rift system (Bertil and Regnoult 1998;Laville et al 1998;Kusky et al 2007).…”

Section: Regional Settingmentioning

confidence: 99%

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A new perspective on the significance of the Ranotsara shear zone in Madagascar

Schreurs

Giese

Berger³

et al. 2009

Int J Earth Sci (Geol Rundsch)

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The Ranotsara shear zone in Madagascar has been considered in previous studies to be a [350-km-long, intracrustal strike-slip shear zone of Precambrian/Cambrian age. Because of its oblique strike to the east and west coast of Madagascar, the Ranotsara shear zone has been correlated with shear zones in southern India and eastern Africa in Gondwana reconstructions. Our assessment using remote sensing data and field-based investigations, however, reveals that what previously has been interpreted as the Ranotsara shear zone is in fact a composite structure with a ductile deflection zone confined to its central segment and prominent NW-SE trending brittle faulting along most of its length. We therefore prefer the more neutral term ''Ranotsara Zone''. Lithologies, tectonic foliations, and axial trace trajectories of major folds can be followed from south to north across most of the Ranotsara Zone and show only a marked deflection along its central segment. The ductile deflection zone is interpreted as a result of E-W indentation of the Antananarivo Block into the less rigid, predominantly metasedimentary rocks of the Southwestern Madagascar Block during a late phase of the Neoproterozoic/Cambrian East African Orogeny (c. 550-520 Ma). The Ranotsara Zone shows significant NW-SE striking brittle faulting that reactivates part of the NW-SE striking ductile structures in the flexure zone, but also extends along strike toward the NW and toward the SE. Brittle reactivation of ductile structures along the central segment of the Ranotsara Zone, confirmed by apatite-fission track results, may have led to the formation of a shallow Neogene basin underlying the Ranotsara plain. The present-day drainage pattern suggests on-going normal fault activity along the central segment. The Ranotsara Zone is not a megascale intracrustal strike-slip shear zone that crosscuts the entire basement of southern Madagascar. It can therefore not be used as a piercing point in Gondwana reconstructions.

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“…1). The Cenozoic magmatism is thought to be related to extensional tectonics like that in eastern Africa characterized by NNE-SSW normal fault systems (Bertil and Regnoult 1998;Rakotondraompiana et al 1999;Piqué et al 1999), but the rocks of the Ampasindava province closely follow a NW-SE regional elongation towards the Antongil Bay ( Fig. 1).…”

Section: Introductionmentioning

confidence: 97%

The age and petrogenesis of alkaline magmatism in the Ampasindava Peninsula and Nosy Be archipelago, northern Madagascar

Cucciniello

Tucker²,

Jourdan

et al. 2015

Miner Petrol

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The Ampasindava alkaline province consists of a series of circular and elliptical intrusions, lava flows, dyke swarms and plugs of Cenozoic age emplaced into the Mesozoic-Cenozoic sedimentary rocks of the Antsiranana basin (NW Madagascar) and above the crystalline basement. The magmatism in the Ampasindava region is linked to a NW-SE trending extensional tectonic setting. New 40Ar/39Ar age determinations on feldspar separate of alkali granites and basaltic dykes yielded ages of 18.01 ± 0.36 Ma and 26 ± 7 Ma, respectively. Alkali basalts and basanites, nepheline syenites and phonolites, and silica saturated-to-oversaturated syenites, trachytes, granites and rhyolites are the main outcropping lithologies. These rocks have sodic affinity. The felsic rocks are dominant, and range from peraluminous to peralkaline. The mantle-normalized incompatible element patterns of the mafic lavas match those of Na-alkaline lavas in within-plate rift settings. The patterns are identical in shape and absolute concentrations to those of the Bobaomby (Cap d’Ambre) and Massif d’Ambre primitive volcanic rocks. These geochemical features are broadly compatible with variable degrees of partial melting of incompatible element-enriched mantle sources. The mineralogical and geochemical variations are consistent with fractional crystallization processes involving removal of olivine, feldspar, clinopyroxene, amphibole, Fe-Ti oxides and apatite. Removal of small amount of titanite explains the concave upward lanthanide pattern in the evolved nepheline syenites and phonolites, which are additionally rich in exotic silicates typical of agpaitic magmas (eudialyte, F-disilicates)

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Seismotectonics of Madagascar

Cited by 57 publications

References 24 publications

Titanite and apatite fission track analyses on basement rocks of central-southern Madagascar: constraints on exhumation and denudation rates along the eastern rift shoulder of the Morondava basin

Titanite and apatite fission track analyses on basement rocks of central-southern Madagascar: constraints on exhumation and denudation rates along the eastern rift shoulder of the Morondava basin

A new perspective on the significance of the Ranotsara shear zone in Madagascar

The age and petrogenesis of alkaline magmatism in the Ampasindava Peninsula and Nosy Be archipelago, northern Madagascar

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