Evolution of high-pressure mafic granulites and pelitic gneisses from NE Madagascar: Tectonic implications

Ishwar-Kumar, C.; Sajeev, K.; Windley, Brian F.; Kusky, Timothy M.; Feng, Peng; Ratheesh-Kumar, R.T.; Huang, Yan; Zhang, Y.; Jiang, Xingfu; Razakamanana, Théodore; Yagi, Koshi; Itaya, Tetsumaru

doi:10.1016/j.tecto.2015.07.019

Cited by 15 publications

(3 citation statements)

References 106 publications

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“…Collectively called the Malagasy suture, but known as the Betsimisaraka suture in Madagascar (Kröner et al, 2000;Collins and Windley, 2002;Collins et al, 2003;Key et al, 2011) and Palghat-Cauvery shear zone in India (Collins et al, 2007a;Clark et al, 2009;Santosh et al, 2012), this highly-deformed schist belt contains detrital zircons as young as 0.70 Ga and abundant mafic-ultramafic lenses. It is interpreted as a second strand of the Mozambique Ocean that subducted westwards under the inferred continental arc in southern India and Madagascar (Collins and Pisarevsky, 2005;Ishwar-Kumar et al, 2015), although others have argued that both 0.85-0.70 Ga plutons and ultramafic-decorated schist belt formed in a rift and not at a convergent margin (Tucker et al, 2011a;Brandt et al, 2014).…”

Section: Cryogenian Magmatic Arcs and Ophiolitementioning

confidence: 99%

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: Cryogenian Magmatic Arcs and Ophiolitementioning

confidence: 99%

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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“…The general fit of these continents is well accepted, but precise correlations among these continental fragments are still debated. The Madagascar-India correlation has been widely discussed in several recent publications (e.g., Tucker et al, 2011aTucker et al, , 2011bIshwar-Kumar et al, 2013;Rekha et al, 2013Rekha et al, , 2014Tucker et al, 2014;Ishwar-Kumar et al, 2015). This discussion has been driven by the increased use of sophisticated analytical techniques leading to an improved understanding of the chronology and evolution of various rock-types.…”

Section: Tectonic Implicationsmentioning

confidence: 99%

UHT granulites of the Highland Complex, Sri Lanka II: Geochronological constraints and implications for Gondwana correlation

Osanai

Sajeev²,

Nakano

et al. 2016

Journal of Mineralogical and Petrological Sciences

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The regional ultrahigh-temperature (UHT) metamorphism of the Highland Complex, Sri Lanka is well established and has an important role in our understanding of the tectonic history of the Gondwana supercontinent. U-Pb zircon dating of sapphirine-bearing Mg-Al granulites yielded two major metamorphic age populations at approximately 620-590 and 563-525 Ma with no evidence of older zircon cores. Pelitic granulite samples with a Grt-Sil-Spl-Crd assemblage have similar metamorphic ages with concordant data clusters at~602, 563, and 526 Ma and inherited zircon cores aged from 2040 to 1600 Ma. The pelitic granulites also underwent two stages of metamorphism (565-520 and 622-580 Ma). Some of these pelitic granulite samples have inherited zircon cores ranging from 3060 to 760 Ma. Zircons in mafic granulite samples have age ranges of 566-533 and 620-578 Ma. A calc-silicate granulite sample also has similar age populations at 591, 541, and 524 Ma. Combining these new results with previously published ages from Sri Lanka and formerly adjacent continental fragments of Gondwana, we propose that the terranes in southern Madagascar (south of Ranotsara Shear Zone), Northern and Southern Madurai and the Trivandrum Blocks of southern India, the Highland Complex of Sri Lanka, and the Skallen Group in the Lützow-Holm Complex of East Antarctica represent a unique metamorphic belt that regionally experienced the Ediacaran-Cambrian UHT event during the amalgamation of the Gondwana supercontinent.

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“…The Betsimisaraka suture zone consists predominantly of paragneisses and mica-schists that dip shallowly to the west. In recent studies, the existence and exact position, shape and age of the Betsimisaraka suture has become controversial (Tucker et al 1999, 2011, 2014; Key et al 2011; Ishwar-Kumar et al 2013, 2015,2016 b ; Rekha et al 2013; Rekha, Bhattacharya & Prabhakar, 2014; Ratheesh-Kumar et al 2015). The Ranomena complex consists of layered gabbro, harzburgite, orthopyroxenite, clinopyroxenite, garnet websterite and chromitite-layered harzburgite (Hottin, 1969; Bauer & Key, 2005; Grieco, Merlini & Cazzaniga, 2012; Grieco et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Chromite chemistry as an indicator of petrogenesis and tectonic setting of the Ranomena ultramafic complex in north-eastern Madagascar

et al. 2016

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The Ranomena ultramafic complex in NE Madagascar consists of layered gabbro, harzburgite, orthopyroxenite, clinopyroxenite, garnet websterite and chromitite-layered peridotite. This study of the Ranomena chromite chemistry aims to better understand the petrogenesis and palaeotectonic environment of the complex. The chromite from the Ranomena chromitite is unzoned/weakly zoned and has a Cr# (Cr/(Cr + Al)) of 0.59–0.69, a Mg# (Mg/(Fe + Mg)) of 0.37–0.44, and low Al2O3 (15–23 wt %) suggesting derivation from a supra-subduction zone arc setting. Calculation of parental melt composition suggests that the parental magma composition of the Ranomena chromitite was similar to that of a primitive tholeiitic basalt formed at a high degree of mantle melting, suggesting the parental melt composition was equivalent to that of an island-arc tholeiite (IAT). The parental magma of the Ranomena chromite had a FeO/MgO ratio of 0.9 to 1.8, suggesting arc derivation. The parental magma was Al- and Fe-rich, similar to a tholeiitic basaltic magma. The composition of orthopyroxene from the chromitite indicates a crystallization temperature range of 1250–1300°C at 1.0 GPa. The chemistry of the chromite in the Ranomena chromitite further suggests that the complex formed in a supra-subduction zone arc tectonic setting.

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Evolution of high-pressure mafic granulites and pelitic gneisses from NE Madagascar: Tectonic implications

Cited by 15 publications

References 106 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

UHT granulites of the Highland Complex, Sri Lanka II: Geochronological constraints and implications for Gondwana correlation

Chromite chemistry as an indicator of petrogenesis and tectonic setting of the Ranomena ultramafic complex in north-eastern Madagascar

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