Structural evolution and medium-temperature thermochronology of central Madagascar: implications for Gondwana amalgamation

Published on 2020-02-03T14:17:56Z (GMT) by
Madagascar occupied an important place in the amalgamation of Gondwana and preserves a record of several Neoproterozoic events that are linked to orogenesis of the East African Orogen. In this study, we integrate remote sensing, field data and thermochronology to unravel complex deformation in the Ikalamavony and Itremo domains of central Madagascar. The deformation sequence comprises a gneissic foliation (S1), followed by south to south-west directed, tight to isoclinal, recumbent folding (D2). These are overprinted by north-trending upright folds that formed during an ~E–W shortening event (D3). Together these produced type 1 and type 2 fold interference patterns throughout the Itremo and Ikalamavony domains. We show that the Itremo and Ikalamavony domains were deformed together in the same orogenic system, which we interpret as the <i>c.</i> 630 Ma collision of Azania with Africa along the Vohibory Suture in southwestern Madagascar. In eastern Madagascar, deformation is syn- to post-550 Ma, which likely formed in response to final closure of the Mozambique Ocean along the Betsimisaraka Suture that amalgamated Madagascar with the Dharwar Craton of India. Apatite U–Pb and novel LA–QQQ-ICP–MS muscovite and biotite Rb–Sr thermochronology indicate that much of central Madagascar cooled through ~500°C at <i>c.</i> 500 Ma.

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Armistead, Sheree E.; Collins, Alan S.; Redaa, Ahmad; Jepson, Gilby; Gillespie, Jack; Gilbert, Sarah; et al. (2020): Structural evolution and medium-temperature thermochronology of central Madagascar: implications for Gondwana amalgamation. Geological Society of London. Collection. https://doi.org/10.6084/m9.figshare.c.4840575.v1