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AGU: Tectonics

 

Keywords

  • Gondwana break-up
  • Indian Ocean
  • Karroo
  • Madagascar
  • Morondava basin
  • apatite fission-track

Index Terms

  • 1140 - Thermochronology
  • 8105 - Continental margins: divergent
  • 8106 - Continental margins: transform
  • 8109 - Continental tectonics: extensional
  • 8175 - Tectonics and landscape evolution

Paper in Press

TECTONICS, doi:10.1029/2011TC002921

Low-temperature evolution of the Morondava rift basin shoulder in western Madagascar - an apatite fission-track study

Key Points
  • Tectonic evolution of the Morondava rift basin shoulder
  • Thermal evolution during failed rifting, rifting, drifting and exhumation
  • Implications for geodynamic evolution of the Indian Ocean region

Authors:

Jörg Giese

Diane Seward

Guido Schreurs

The evolution of the rift shoulder and the sedimentary sequence of the Morondava basin in western Madagascar was mainly influenced by a Permo-Triassic continental failed rift (Karroo rift), and the early Jurassic separation of Madagascar from Africa. Karroo deposits are restricted to a narrow corridor along the basement-basin contact and parts of this contact feature a steep escarpment. Here, apatite fission-track (AFT) analysis of a series of both basement and sediment samples across the escarpment reveals the low-temperature evolution of the exhuming Precambrian basement in the rift basin shoulder and the associated thermal evolution of the sedimentary succession. Seven basement and four Karroo sediment samples yield apparent AFT ages between ~330 and ~215 Ma and ~260 and ~95 Ma, respectively. Partially annealed fission-tracks and thermal modeling indicate post-depositional thermal overprinting of both basement and Karroo sediment. Rocks presently exposed in the rift shoulder indicate temperatures of >60 {degree sign}C associated with this reheating whereby the westernmost sample in the sedimentary plain experienced almost complete resetting of the detrital apatite grains at temperatures of about ~90-100 {degree sign}C. The younging of AFT ages westwards indicates activity of faults, re-activating inherited Precambrian structures during Karroo sedimentation. Furthermore, our data suggest onset of final cooling/exhumation linked to (I) the end of Madagascar's drift southward relative to Africa during the Early Cretaceous, (II) activity of the Marion hotspot and associated Late Cretaceous break-up between Madagascar and India, and (III) the collision of India with Eurasia and subsequent re-organization of spreading systems in the Indian Ocean.

Received 13 April 2011; accepted 9 January 2012.

Citation: Giese, J., D. Seward, and G. Schreurs (2012), Low-temperature evolution of the Morondava rift basin shoulder in western Madagascar - an apatite fission-track study, Tectonics, doi:10.1029/2011TC002921, in press.