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 |
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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
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ISSN: | 0930-0708 1438-1168 |
DOI: | 10.1007/s00710-008-0037-y |