Crustal assembly of the Antananarivo and Masora domains, central–eastern Madagascar: constraints from U–Pb zircon geochronology and whole–rock geochemistry of meta–granitoids

Ichiki, Takashi; Ishikawa, Masahiro; Kimura, Jun–Ichi; Senda, Ryoko; Rakotondrazafy, Raymond

doi:10.2465/jmps.141225

Cited by 9 publications

(8 citation statements)

References 63 publications

(107 reference statements)

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“…The existence of pre‐600 Ma metamorphic dates in the Anosyen domain contradicts the tectonic model proposed by GAF‐BGR [] in which the final suturing of East and West Gondwana occurred along the contact between the Androyen and Anosyen domains after 600 Ma. Furthermore, it is difficult to reconcile the existence of a west facing ~850–700 Ma continental arc that produced the Imorona‐Itsindro suite [ Müller , 2000; GAF‐BGR , ; Moine et al ., ; Ichiki et al ., ] with a model in which outboard terranes (i.e., Androyen and Anosyen domains) were contiguous with older cratonic portions of East Gondwana since the Paleoproterozoic [e.g., Tucker et al ., ]. Rather, the inferences that the Vohibory arc was oceanic until ~630 Ma and that the Imorona‐Itsindro magmatism (until ~700 Ma) represents an east directed subduction of oceanic crust necessitate that there were oceans on both sides of an Androyen‐Anosyen microcontinent prior to final Gondwana assembly.…”

Section: Discussionmentioning

confidence: 99%

“…The Antananarivo domain was either the western margin of East Gondwana [ Muller , ; GAF‐BGR , (GAF‐BGR is sponsored by the Projet de Gouvernance des Ressources Minerales, Madagascar (a program funded by the World Bank), an international consortium of scientists conducted four years of research across Madagascar, the results of which were compiled into a final report by the German firms GAF‐AG and BGR, and then published by Madagascar's Ministry of Energy and Mines in . ); Tucker et al ., , ; Ichiki et al ., ] or part of a microcontinent (Azania) that collided first with West Gondwana and later with East Gondwana [ Collins and Pisarevsky , ; Collins et al ., ]. Prior to the final assembly of Gondwana, much of central Madagascar, including the Antananarivo domain, was intruded by the ~850–700 Ma Imorona‐Itsindro suite that has been attributed to either intracontinental extension [ Tucker et al ., , ], a west facing continental magmatic arc on the western margin of East Gondwana [ Muller , ; GAF‐BGR , ; Moine et al ., ; Ichiki et al ., ], or an east facing continental arc on the eastern margin of Azania [ Collins and Pisarevsky , ]; these plutonic rocks are notably absent in southern Madagascar.…”

Section: Geologic Backgroundmentioning

confidence: 99%

“…); Tucker et al ., , ; Ichiki et al ., ] or part of a microcontinent (Azania) that collided first with West Gondwana and later with East Gondwana [ Collins and Pisarevsky , ; Collins et al ., ]. Prior to the final assembly of Gondwana, much of central Madagascar, including the Antananarivo domain, was intruded by the ~850–700 Ma Imorona‐Itsindro suite that has been attributed to either intracontinental extension [ Tucker et al ., , ], a west facing continental magmatic arc on the western margin of East Gondwana [ Muller , ; GAF‐BGR , ; Moine et al ., ; Ichiki et al ., ], or an east facing continental arc on the eastern margin of Azania [ Collins and Pisarevsky , ]; these plutonic rocks are notably absent in southern Madagascar. During continent‐continent collision, Mesoproterozoic and Neoproterozoic sedimentary rocks deposited on the Archean and Paleoproterozoic crust became folded into and intercalated with the older crust [ Tucker et al ., ].…”

Section: Geologic Backgroundmentioning

confidence: 99%

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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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Section: Discussionmentioning

confidence: 99%

Section: Geologic Backgroundmentioning

confidence: 99%

Section: Geologic Backgroundmentioning

confidence: 99%

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

et al. 2016

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“…Equivalent units in Madagascar are the Antongil Domain, with 3.3-3.1 Ga tonalite intruded by 2.6-2.5 Ga granite (Tucker et al,Figure 3. Cratons (>0.9 Ga) and Pan-African orogens (0.7-0.5 Ga) of Gondwana (modified from Gray et al, 2008;Meert and Lieberman, 2008;Harley et al, 2013 1999; Schofield et al, 2010), and the Masora Domain with similar protoliths but a stronger Pan-African overprint discussed further below (Tucker et al, 2011a;Key et al, 2011;Ichiki et al, 2015). Although Indian and African sides of the orogen both record 2.6-2.5 Ga magmatism, they are set apart by major magmatic events at 3.5-3.0 Ga in the former, and at 2.1-1.8 Ga and~1.0 Ga in the latter.…”

Section: Cratonic Margins Of the East African Orogenmentioning

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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“…The rocks from the Antananarivo Block of Madagascar also show geochemical characteristics that vary from calcic to alkali-calcic and ferroan to magnesian (Collins et al, 2003;Ichiki et al, 2015). In this study, an attempt is made to compare and correlate the geochemical features of granulites of the Madurai Block in the SGT and the Antananarivo Block of Madagascar, to better understand the tectonic connections between the two.…”

Section: Introductionmentioning

confidence: 99%

Geochemistry of granulitic rocks from the western Madurai Block, Southern Granulite Terrain, India and its Madagascar linkage

P. Anu-Sha,

R. Baiju,

A. Justine

2024

Journal of Mineralogical and Petrological Sciences

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The Southern Granulite Terrain of peninsular India consists of a wide range of metamorphic rocks with formation ages that span the late Archean Era to the Cambrian Period. It consists of numerous tectonic blocks dissected by deep crustal-scale shear zones. The Madurai Block is the largest crustal block, comprising Neoarchean to Ediacaran-Cambrian gneisses that include charnockite, hornblende-biotite gneiss, mafic granulite and metapelite, amongst other lesser rock types. This study focuses on the geochemistry of granulite-facies rocks from the western part of the Madurai Block, how these rocks correlate with similar types in other tectonic blocks of the Southern Granulite Terrain, and the implication of such correlations for East Gondwana tectonics. The geochemistry of the various granulite-facies rocks from the western Madurai Block reveals metaluminous to slightly peraluminous, calcic to alkalic, and ferroan to magnesian signatures. Geochemical tectonic discrimination diagrams indicate both A-type granitoid and Cordilleran affinities, consistent with petrogenesis in active continental margin and extensional tectonic settings, with chemical variation also generated through magmatic differentiation. Similar lithological, geochronological and geochemical features have been reported from granulites of the Antananarivo Block of Madagascar, based on which a correlation can be made with the western Madurai Block that predates Gondwana assembly.

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Crustal assembly of the Antananarivo and Masora domains, central–eastern Madagascar: constraints from U–Pb zircon geochronology and whole–rock geochemistry of meta–granitoids

Cited by 9 publications

References 63 publications

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

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

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

Geochemistry of granulitic rocks from the western Madurai Block, Southern Granulite Terrain, India and its Madagascar linkage

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