A-type stratoid granites of Madagascar revisited: Age, source and links with the breakup of Rodinia

摘要: The stratoid granites of Madagascar are sheet-like granite sills emplaced conformably to the schistosity Antananarivo and Ikalamavony domains Precambrian basement. Most them fine-grained rocks with A-type affinities. They belong two different plutonic suites: Kiangara Suite north Imorona–Itsindro recognized in whole central Madagascar. Stratoid everywhere characterized by same structural pattern evidencing deformation events. first event (D1 foliations mildly dipping west lineations trending WSW) was coeval synkinematic magma emplacement. second one, responsible for local reworking ductile conditions, is regarded as result late Pan-African transcurrent tectonics along N–S striking shear zones. New situ U–Pb zircon dating from both suites yields similar results group ages: upper intercept ages 790–780 Ma crystallization ages, younger ca. 555 corresponding a metamorphic overprint. These new data suggest that were at Ma. Sm–Nd isotopic support existence groups. has eNd(t) −15 likely derived partial melting Archaean crust. made more pronounced nature comagmatic syenites −12 contribution mantle melts. Mafic enclaves ranging −5 −11 encompass Nd signature Itsindro gabbros, which subcontinental lithospheric source. interpretation consistent crustal thinning extension during Cryogenian Rodinia rifting stage Ma, left major imprint Separation conjugage margin represented North China craton suggested. influence limited reheating, tectonic fluid transfer vicinity late-Neoproterozoic (∼550 Ma)