ISSN:
1525-1314
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Geosciences
Notes:
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 (high-strain 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 Lützow–Holm Bay in Eastern Antarctica.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1046/j.1525-1314.2002.00388.x
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