Genesis of wollastonite- and grandite-rich skarns in a suite of marble-calc-silicate rocks from Sittampundi, Tamil Nadu: constraints on the P–T–fluid regime in parts of the Pan-African mobile belt of South India

The Pan-African tectonothermal activities in areas near Sittampundi, south India, are characterized by metamorphic changes in an interlayered sequence of migmatitic metapelites, marble and calc-silicate rocks. This rock sequence underwent multiple episodes of folding, and was intruded by granite bat...

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Veröffentlicht in:Mineralogy and petrology 2009-03, Vol.95 (3-4), p.179-200
Hauptverfasser: Sengupta, P., Dutta, U., Bhui, Uttam K., Mukhopadhyay, D.
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Sprache:eng
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Zusammenfassung:The Pan-African tectonothermal activities in areas near Sittampundi, south India, are characterized by metamorphic changes in an interlayered sequence of migmatitic metapelites, marble and calc-silicate rocks. This rock sequence underwent multiple episodes of folding, and was intruded by granite batholiths during and subsequent to these folding events. The marble and the calc-silicate rocks develop a variety of skarns, which on the basis of mineralogy; can be divided into the following types: Type I: wollastonite + clinopyroxene (mg# = 71–73) + grandite (16–21 mol% Adr) + quartz ± calcite, Type II: grandite (25–29 mol% Adr ) + clinopyroxene (mg# = 70) + calcite  +  quartz, and Type III: grandite (36–38 mol% Adr) + clinopyroxene (mg# = 55–65) + epidote + scapolite + calcite + quartz. Type I skarn is 2–10 cm thick, and is dominated by wollastonite ( > 70 vol%) and commonly occurs as boudinaged layers parallel to the regional foliation Sn 1 related to the Fn 1 folds. Locally, thin discontinuous lenses and stringers of this skarn develop along the axial planes of Fn 2 folds. The Type II skarn, on the other hand, is devoid of wollastonite, rich in grandite garnet (40–70 vol%) and developed preferentially at the interface of clinopyroxene-rich calc-silicates layers and host marble during the later folding event. Reaction textures and the phase compositional data suggest the following reactions in the skarns: 1. calcite + SiO 2  → wollastonite + V, 2. calcite + clinopyroxene + O 2  → grandite + SiO 2  + V, 3. scapolite + calcite + quartz + clinopyroxene + O 2  → grandite + V and 4. epidote + calcite + quartz + clinopyroxene + O 2  → grandite + V Textural relations and composition of phases demonstrate that (a) silica metasomatism of the host marble by infiltration of aqueous fluids (X CO2  
ISSN:0930-0708
1438-1168
DOI:10.1007/s00710-008-0037-y