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

Sheree E. Armistead, Alan S. Collins, Ahmad Redaa, Gilby Jepson, Jack Gillespie, Sarah Gilbert, Morgan L. Blades, John D. Foden and Theodore Razakamanana
Structural evolution and medium-temperature thermochronology of central Madagascar; implications for Gondwana amalgamation
Journal of the Geological Society of London (March 2020) 177 (4): 784-798

Abstract

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 (S (sub 1) ), followed by south- to SW-directed, tight to isoclinal, recumbent folding (D (sub 2) ). These are overprinted by north-trending upright folds that formed during an approximately east-west shortening event (D (sub 3) ). 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 degrees C at c. 500 Ma. Supplementary material: A detailed geological map of central Madagascar (Supplementary A), detailed methods and geo- and thermochronology results (Supplementary B), isotopic data for geo- and thermochronology (Supplementary C) and Landsat images and structural interpretation examples (Supplementary D) are available at https://doi.org/10.6084/m9.figshare.c.4840575


ISSN: 0016-7649
EISSN: 2041-479X
Coden: JGSLAS
Serial Title: Journal of the Geological Society of London
Serial Volume: 177
Serial Issue: 4
Title: Structural evolution and medium-temperature thermochronology of central Madagascar; implications for Gondwana amalgamation
Affiliation: University of Adelaide, Department of Earth Sciences, Adelaide, South Aust., Australia
Pages: 784-798
Published: 20200303
Text Language: English
Publisher: Geological Society of London, London, United Kingdom
References: 62
Accession Number: 2020-047072
Categories: Structural geologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., 1 table, geol. sketch maps
S20°00'00" - S19°00'00", E04°52'60" - E48°00'00"
Secondary Affiliation: Universite de Toliara, MDG, Madagascar
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data from The Geological Society, London, London, United Kingdom
Update Code: 202029
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