A geological synthesis of the Precambrian shield in Madagascar

Tucker, Robert D.; Roig, Jean-Yves; Moine, B.; Delor, Claude; Peters, Stephen G.

doi:10.1016/j.jafrearsci.2014.02.001

Cited by 125 publications

(166 citation statements)

References 86 publications

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“…5), beginning with the cratonic margins in Africa and India, before discussing juvenile arcs, oceanic sutures, and reworked cratonic rocks within the orogen itself. Fritz et al (2013), Tucker et al (2014) and Collins et al (2014) provided detailed reviews of these relationships, with a focus on east Africa, Madagascar and India respectively, although some of their explanations for these relationships differ from those proposed here.…”

Section: Tectonic Architecture Of the East African Orogenmentioning

confidence: 81%

“…Color version is available online from http://doi.org/ 10.2465/jmps.151117. though exposed rocks yield metamorphic ages of 0.56-0.54 Ga,~0.63 Ga granite sheets in these rocks (Paquette and Nédélec, 1998;Tucker et al, 2014) suggest a similar total time span of metamorphism to southern Madagascar.…”

Section: Metamorphism Between the Suturesmentioning

confidence: 81%

“…Nor can it explain why the hottest thermal gradients are recorded in the Azania microcontinental block dominated by reworked Archean to Paleoproterozoic material, while adjacent arc terranes have cooler gradients. Jöns and Schenk (2011) suggested that UHT metamorphism in southern Madagascar was driven by charnockite plutons, which are most abundant in the Anosyen Domain where peak T is highest, but these 0.58-0.52 Ga syn-to late-tectonic plutons (now called the Ambalavao Suite; Boger et al, 2014;Tucker et al, 2014;Boger et al, 2015) are more likely a crustal re-sponse to high-T conditions than the cause of UHT metamorphism. Nicollet (1990) similarly used anorthosite and mafic-ultramafic complexes in southern Madagascar to argue that UHT conditions were driven by extension and delamination of mantle lithosphere, but these high-T magmatic rocks are now known to be much older than the UHT event.…”

Section: Discussionmentioning

confidence: 99%

“…Reworked crust between the Mozambique and Malagasy sutures includes orthogneiss with 2.6-2.4 Ga protoliths in the Antananarivo Domain of central Madagascar (Tucker et al, , 2011a(Tucker et al, , 2014 and northwestern Madurai Block of India (Ghosh et al, 2004;Plavsa et al, 2012;Brandt et al, 2014). Other igneous protoliths include~2.0, 1.7-1.6, and 1.0 Ga granite in the Nagercoil and northeastern and southern Madurai blocks of India (Plavsa et al, 2012;Brandt et al, 2014;Kröner et al, 2015), local 2.2-1.8 and~1.0 Ga mafic and felsic rocks in south-central Madagascar (Tucker et al, 2011b), and 0.94-0.90 Ga alkali granite and anorthosite in southern Madagascar (Boger et al, 2015).…”

Section: Reworked Crust Of the Southern East African Orogenmentioning

confidence: 99%

“…Tucker et al (1999Tucker et al ( , 2011aTucker et al ( , 2014 and Brandt et al (2014) emphasised the similarity of 2.6-2.4 Ga orthogneiss protoliths to the Dharwar Craton, arguing that much of Madagascar and southern India was part of a greater Dharwar Craton reworked by 0.65-0.50 Ga collision. In this model the Mozambique suture joins rocks of African and Indian origin and is the only site of Neoproterozoic ocean closure, whereas the Malagasy suture is a Neoproterozoic rift that reactivated an intracratonic Archean boundary.…”

Section: Reworked Crust Of the Southern East African Orogenmentioning

confidence: 99%

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Pan–African granulites of Madagascar and southern India: Gondwana assembly and parallels with modern Tibet

Fitzsimons

2016

Journal of Mineralogical and Petrological Sciences

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Granulites of the southern East African Orogen formed by continental collision during Gondwana assembly. The highest metamorphic gradients of 25-50°C km −1 were attained at 0.58-0.53 Ga in a microcontinental block that was sandwiched between two collisional sutures and is now exposed in Madagascar and southern India. The 50 Myr duration of extreme pressure-temperature (P-T) conditions and lack of coeval mantle magmatism suggest that metamorphism was driven by radiogenic heat accumulation beneath a long-lived orogenic plateau. Bounding sutures most likely record transfer of this microcontinent across the Neoproterozoic Mozambique Ocean, analogous to Gondwanan terranes that crossed Tethys before final India-Asia collision and, like Tibet, these sutures mark the edges of a plateau that formed following terminal ocean closure and collision. Both sutures record moderate metamorphic gradients of 15-25°C km −1 but with quite different ages. Metamorphism along the western suture at 0.65-0.61 Ga followed the end of magmatism in an adjacent 0.85-0.65 Ga ocean-arc terrane. It has an anti-clockwise P-T path that reflects preferential thickening of the hot arc during early stages of collision, and dates ocean closure at the western suture. Metamorphism along the eastern suture at 0.53-0.51 Ga has a clockwise P-T path and is widely assumed to date terminal collision in the East African Orogen. However, this event was coeval with rapid exhumation of granulites in the adjacent plateau and is more likely to reflect reactivation of a much older eastern suture during plateau collapse. Great care should be taken when using metamorphism to date ocean closure in ancient orogens. Rocks with hot metamorphic gradients give poor age constraints on initial collision because peak T is attained >50 Myr after ocean closure if radioactivity is a major part of the heat budget. Suture zone rocks with moderate metamorphic gradients can provide more reliable estimates for the time of ocean closure but are also prone to later reactivation in orogens with protracted histories.

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Section: Tectonic Architecture Of the East African Orogenmentioning

confidence: 81%

Section: Metamorphism Between the Suturesmentioning

confidence: 81%

Section: Discussionmentioning

confidence: 99%

Section: Reworked Crust Of the Southern East African Orogenmentioning

confidence: 99%

Section: Reworked Crust Of the Southern East African Orogenmentioning

confidence: 99%

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Pan–African granulites of Madagascar and southern India: Gondwana assembly and parallels with modern Tibet

Fitzsimons

2016

Journal of Mineralogical and Petrological Sciences

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Focused radiogenic heating of middle crust caused ultrahigh temperatures in southern Madagascar

et al. 2016

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Internal heating can cause melting, metamorphism, and crustal weakening in convergent orogens.This study evaluates the role of radiogenic heat production (RHP) in a Neoproterozoic ultrahigh-temperature metamorphic (UHTM) terrane exposed in southern Madagascar. Monazite and zircon geochronology indicates that the Paleoproterozoic Androyen and Anosyen domains (i) collided with the oceanic Vohibory Arc at~630 Ma, (ii) became incorporated into the Gondwanan collisional orogen by~580 Ma, and (iii) were exhumed during crustal thinning at 525-510 Ma. Ti-in-quartz and Zr-in-rutile thermometry reveals that UHTM occurred over >20,000 km 2 , mostly within the Anosyen domain. Assuming that U, Th, and K contents of samples from the field area are representative of the middle to lower crust during orogenesis, RHP was high enough-locally >5 μW/m 3 -to cause regional UHTM in <60 Myr. We conclude that, due in large part to the stability and insolubility of monazite at high crustal temperatures, RHP was the principal heat source responsible for UHTM, obviating the need to evoke external heat sources. Focused RHP probably thermally weakened portions of the middle crust, gravitationally destabilizing the orogen and facilitating thinning via lateral extrusion of hot crustal sections.

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Seismic anisotropy of the lithosphere and asthenosphere beneath southern Madagascar from teleseismic shear wave splitting analysis and waveform modeling

et al. 2016

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Madagascar occupies a key position in the assembly and breakup of the supercontinent Gondwana. It has been used in numerous geological studies to reconstruct its original position within Gondwana and to derive plate kinematics. Seismological observations in Madagascar to date have been sparse. Using a temporary, dense seismic profile across southern Madagascar, we present the first published study of seismic anisotropy from shear wave splitting analyses of teleseismic phases. The splitting parameters obtained show significant small‐scale variation of fast polarization directions and delay times across the profile, with fast polarization rotating from NW in the center to NE in the east and west of the profile. The delay times range between 0.4 and 1.5 s. A joint inversion of waveforms at each station is applied to derive hypothetical one‐layer splitting parameters. We use finite‐difference, full‐waveform modeling to test several hypotheses about the origin and extent of seismic anisotropy. Our observations can be explained by asthenospheric anisotropy with a fast polarization direction of 50°, approximately parallel to the absolute plate motion direction, in combination with blocks of crustal anisotropy. Predictions of seismic anisotropy as inferred from global mantle flow models or global anisotropic surface wave tomography are not in agreement with the observations. Small‐scale variations of splitting parameters require significant crustal anisotropy. Considering the complex geology of Madagascar, we interpret the change in fast‐axis directions as a ~150 km wide zone of ductile deformation in the crust as a result of the intense reworking of lithospheric material during the Pan‐African orogeny. This fossil anisotropic pattern is underlain by asthenospheric anisotropy induced by plate motion.

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A geological synthesis of the Precambrian shield in Madagascar

Cited by 125 publications

References 86 publications

Pan–African granulites of Madagascar and southern India: Gondwana assembly and parallels with modern Tibet

Pan–African granulites of Madagascar and southern India: Gondwana assembly and parallels with modern Tibet

Focused radiogenic heating of middle crust caused ultrahigh temperatures in southern Madagascar

Seismic anisotropy of the lithosphere and asthenosphere beneath southern Madagascar from teleseismic shear wave splitting analysis and waveform modeling

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