Structural evolution and medium-temperature thermochronology of central Madagascar: implications for Gondwana amalgamation
journal contribution
posted on 2023-05-21, 07:52authored bySheree ArmisteadSheree Armistead, Collins, AS, Redaa, A, Jepson, G, Gillespie, J, Gilbert, S, Blades, ML, Foden, D, Razakamanana, T
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 SW-directed, tight to isoclinal, recumbent folding (D2). These are overprinted by north-trending upright folds that formed during an approximately east–west 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 c. 630 Ma collision of Azania with Africa along the Vohibory Suture in southwestern Madagascar. In eastern Madagascar, deformation is syn- to post-550 Ma, and probably 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 laser ablation triple quadrupole inductively coupled plasma mass spectrometry (LA-QQQ-ICP-MS) muscovite and biotite Rb-Sr thermochronology indicates that much of central Madagascar cooled through c. 500°C at c. 500 Ma.
History
Publication title
Journal of the Geological Society
Volume
177
Issue
4
Pagination
784-798
ISSN
0016-7649
Department/School
School of Natural Sciences
Publisher
Geological Soc Publ House
Place of publication
Unit 7, Brassmill Enterprise Centre, Brassmill Lane, Bath, England, Avon, Ba1 3Jn