Reconstruction of the Phanerozoic tectono-thermal history of central and southern Madagascar, based on fission track thermochronology
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Madagascar, Gondwana, thermochronology. - Titanite and apatite fission track (FT) thermochronology on 127 basement and 18 sedimentary rock samples from central and southern Madagascar record a complex cooling and denudation history since the Early Palaeozoic. Titanite FT analyses gave ages ranging between 483 Ma and 266 Ma. Apatite FT ages vary between 460 Ma and 79 Ma. Samples from Late Carboniferous to Jurassic sediments from the Morondava basin gave apatite FT ages ranging between 462 Ma and 184 Ma. FT data argues for reactivation of several Late Neoproterozoic/Early Cambrian ductile shear zones pre-dating the initial opening of the Morondava basin during the Late Carboniferous. Apatite FT data indicate that the subsequent Mesozoic rift evolution was accompanied with an eastward migration of areas of fast cooling. During Mesozoic times the Morondava basin had a greater eastward extension. Detrital apatite FT data derived from the outcropping Sakoa Group imply that after the Late Carboniferous deposition these rocks were covered by 2-4 km of sedimentary rocks. The final separation of Madagascar and East Africa during the Jurassic influenced mainly samples in southwest Madagascar, where basement regions and also former basin regions were exhumed. Combined Titanite FT and structural data argue for a minor tectono-thermal influence of the Marion hot spot during the Madagascar-India separation. However, apatite FT ages and modelled cooling paths indicate that the break-up during the Cretaceous was associated with a denudation amount of ~4 km crustal section along a narrow stripe parallel to the present eastern continental margin.