Evolving marginal terranes during Neoproterozoic supercontinent reorganisation: constraints from the Bemarivo Belt in northern Madagascar

Contributors:
  1. Justin Payne
  2. Andrew Merdith
  3. John Foden
  4. Theodore Razakamanana
  5. Bert De Waele

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Description: Madagascar is important for unravelling the geodynamic evolution of the transition between the Rodinia and Gondwana supercontinents as it contains several suites of c. 850–700 Ma magmatic rocks that have been postulated to correlate with other ex-Rodinia terranes. The Bemarivo Belt of northern Madagascar contains the youngest suite of these magmatic rocks that date to c. 750–700 Ma. We present zircon Hf and O isotope data from the Bemarivo Belt to understand its place in the Neoproterozoic plate tectonic reconfiguration. We demonstrate that the northern Bemarivo Belt is distinctly different from the southern Bemarivo Belt. Magmatic rocks of the southern Bemarivo Belt and Anaboriana Belt are characterised by evolved εHf(t) signatures and a range of δ18O values, similar to the Imorona-Itsindro Suite of central Madagascar. Magmatic rocks from the southern Bemarivo Belt, Anaboriana Belt and Imorona-Itsindro Suite likely formed together in the same long-lived volcanic arc. In contrast, the northern Bemarivo Belt contains juvenile εHf(t) and mantle-like δ18O values, with no probable link to the rest of Madagascar. We propose that the northern Bemarivo Belt formed in a juvenile arc system that included the Seychelles, Malani Igneous Suite of northwest India, Oman, and the Yangtze Belt of south China, outboard from continental India and south China. The final assembly of northern Madagascar and amalgamation of the northern and southern Bemarivo terranes occurred along the Antsaba subduction zone, with final assembly constrained by the c. 520 Ma post-tectonic Maevarano Suite.

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