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Article Dans Une Revue Journal of Metamorphic Geology Année : 2002

Melt-producing and melt-consuming reactions in the Achankovil cordierite gneisses, South India

Résumé

Migmatitic cordierite gneisses within the Achankovil Zone (AZ) of southern Pan-African India record melt-producing and subsequent melt-consuming mineral reactions. Early mineral assemblages Bt-Sil-Qtz and Bt-Sil-Spl, deduced from inclusion textures in garnet prophyroblasts, break down via successive dehydration melting reactions to high-T phase assemblages (e.g. Grt-Crd-Liq, Opx-Liq, Spl-Crd-Liq). Later back reactions between the restite and the in situ crystallizing melt resulted in thin cordierite coronas separating garnet from the leucosome, and partial resorption of garnet to Opx-Crd or Crd-Bt-Qtz symplectites. Leucosomes generally display a moderate (low-strain gneisses) to strong (highstrain gneisses) depletion of alkali feldspar attributed to mineral-melt back reactions partly controlled by the degree of melt segregation. Using a KFMASH partial petrogenetic grid that includes a melt phase, and qualitative pseudosections for microdomains of high and low Al ⁄ Si ratios, the successive phase assemblages and reaction textures are interpreted in terms of a clockwise P-T path culminating at about 6-7 kbar and 900-950 °C. This P-T path is consistent with, but more detailed than published results, which suggests that taking a melt phase into account is not only a valid, but also a useful approach. Comparing P-T data and lithological and isotopic data for the AZ with adjacent East Gondwana fragments, suggests the presence of a coherent metasedimentary unit exposed from southern Madagascar via South India (AZ) and Sri Lanka (Wanni Complex) to the Lu¨tzow-Holm Bay in Eastern Antarctica.

Dates et versions

hal-04404304 , version 1 (24-01-2024)

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Citer

B. Cenki, L. Kriegsman, I. Braun. Melt-producing and melt-consuming reactions in the Achankovil cordierite gneisses, South India. Journal of Metamorphic Geology, 2002, 20 (6), pp.543-561. ⟨10.1046/J.1525-1314.2002.00388.X⟩. ⟨hal-04404304⟩
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