Towards unravelling the Mozambique Ocean conundrum using a triumvirate of zircon isotopic proxies on the Ambatolampy Group, central Madagascar

Madagascar occupies an important location within the East African Orogen (EAO), which involves a collection of Neoproterozoic microcontinents and arc terranes lodged between older cratonic units during the final assembly of the supercontinent Gondwana. The detrital zircon record of Proterozoic metasedimentary rock packages within the Antananarivo Domain (the Ambatolampy, Manampotsy, Vondrozo, Item and Ikalamavony Groups) is used to identify pre-orogenic tectonic affiliations of the region-affiliations that control interpretations of the evolution of the Mozambique Ocean and the formation of this part of central Gondwana. Here we focus on the Ambatolampy Group, a previously poorly known group of high-grade siliciclastic metasedimentary rocks, and compare these data to similar data from the other sedimentary packages in central Madagascar (the Vondrozo, Sofia, Manampotsy, Itremo, Mob, Ikalamavony, Androyen, Ambodiriana, lakora and Maha Groups). New U-Pb (SHRIMP) zircon data for the Ambatolampy Group yield detrital age maxima of similar to 3000 Ma, similar to 2800-2700 Ma, similar to 2500 Ma, similar to 2200-2100 Ma and similar to 1800 Ma. The youngest near-concordant detrital zircon age is 1836 +/- 25 Ma, which we suggest represents the maximum depositional age of the Ambatolampy Group, in contrast to younger ages reported elsewhere. The detrital spectra are very similar to those from the Itremo Group and we suggest that they correlate with each other. Metamorphic zircons and zircon rims constrain the minimum depositional age to be similar to 540 Ma; the interpreted age of metamorphism. New delta O-18 data (SHRIMP-SI) and hafnium (MC-LA-ICP-MS) isotopic data complement the U-Pb data and provide new constraints on the age, geochemistry and provenance of the metasedimentary rocks. We suggest that central Madagascar contained a Mesoproterozoic (to possibly Tonian) siliciclastic sedimentary basin, within which the Ambatolampy Group, and the Item and Maha Groups (and possibly part of the Iakora Groups) were deposited. Later sedimentary systems are represented by the Ikalamavony, Ambodiriana, Manampotsy and Moto Groups. (C) 2015 Elsevier B.V. All rights reserved.