科研之友
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摘要
We report the occurrence of sapphirine, spinel, quartz and Mg-staurolite as inclusions in garnet from quartzo-feldspathic gneiss and garnet-biotite gneisses in the northernmost sector of the Madurai Granulite Block along the Palghat-Cauvery Shear Zone System in southern India, suggesting metamorphism under ultrahigh-temperature conditions. Poikiloblastic garnet grains contain numerous inclusions of quartz, rutile, apatite, biotite and zircon with rare associations of sapphirine spinel and sapphirine staurolite. We characterize the inclusion population based on detailed petrologic, mineral chemical and laser Raman spectroscopic studies. A direct contact of sapphirine and/or spinel with the quartz inclusions within garnet is not seen, which we attribute to the low modal abundances of sapphirine and spinel, and/or the progress of reactions during retrograde metamorphism. Staurolite occurs as inclusions in garnet and is partially mantled by sapphirine, suggesting the progress of the reaction: St -> Grt Spr Sil or Ky H(2)O. Such relict occurrences of staurolite with Mg/(Fe Mg) of 0.42-0.44 are regarded as evidence of prograde high-pressure metamorphism in the northern Madurai Block. Lack of sillimanite or kyanite within garnet implies that all aluminosilicates have been completely consumed by reactions: Grt Sil -> Spr Qtz and/or Grt Sil -> Spl Qtz to form possible sapphirine quartz and/or spinel quartz assemblages. Our results confirm that the northern Madurai Block along the Palghat-Cauvery Shear Zone System underwent high-pressure and ultrahigh-temperature metamorphism along a decompressional clockwise P-T-time path associated with the collisional amalgamation of southern India with the Gondwana supercontinent assembly.
- 出版日期2009-3
