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21.
P. SENGUPTA S. SANYAL S. DASGUPTA M. FUKUOKA J. EHL & S. PAL 《Journal of Metamorphic Geology》1997,15(5):551-564
ABSTRACT A suite of garnet-wollastonite-scapolite-bearing calcsilicate granulites from the Eastern Ghats has been investigated to document the controls of mineral reactions during the metamorphic evolution of the deep continental crust. The rocks studied show heterogeneity in modal mineralogy and phase compositions in millimetre-sized domains. Textural relations, and the compositional plots of the phases, established that the clinopyroxene exerts a strong influence on the formation and composition of garnet in the complex natural system. P-T estimates using the vapour-independent equilibria involving garnet define a near isobaric cooling path from c. 850C at c. 5.5–5.2 kbar. The deduced trajectory tallies well with the terminal segment of the overall retrograde P-T path construed from the associated rocks using well-calibrated thermobarometers. The ubiquitous occurrence of wollastonite and scapolite in the main calcsilicate body suggests low aCO2 during peak metamorphic condition. Fluid compositions constrained from mineral-fluid equilibria of the garnet-bearing assemblages show domainal variations as a function of the compositions of the solid phases, e.g. garnet and clinopyroxene. A quantitative log/CO2-log/O2 diagram has been constructed to depict the stability of the different calcsilicate assemblages as functions of the compositions and the behaviour of these fugitive species. The results of the mineral-fluid equilibria and the quantitative fluid/rock ratio calculations, in conjunction with the topological constraints, imply vapour-deficient meta-morphism in the rocks studied. It is argued that fO2 during peak metamorphism was monitored by the ambient fO2. Subsequently, during retrogression, different domains evolved independently, whereas the fluid composition was controlled by the mineral-fluid equilibria. 相似文献
22.
For curves over a horizontally stratified earth where any of the layers has a conductivity variation proportional to (1 +β·z)N, where β and N are arbitrary constants and z is the depth to the layer, expressions for apparent resistivity for Wenner and Schlumberger sounding are derived. No assumption has been made about the continuity of conductivity at the interface. It is shown that most of the previous investigations in this connection can be regarded as particular cases of the present study. 相似文献
23.
Petro-tectonic Imprints in the Sapphirine Granulites from Anantagiri, Eastern Ghats Mobile Belt, India 总被引:5,自引:0,他引:5
SENGUPTA PULAK; DASGUPTA SOMNATH; BHATTACHARYA P. K.; FUKUOKA M.; CHAKRABORTI SUBRATA; BHOWMICK SANTANU 《Journal of Petrology》1990,31(5):971-996
Sapphirine granulite occurring as lenses in charnockite at Anantagiri,Eastern Ghat, India, displays an array of minerals which developedunder different P-T-X conditions. Reaction textures in conjunctionwith mineral chemical data attest to several Fe-Mg continuousreactions, such as
- spinel+rutile+quartz+MgFe1=sapphirine+ilmenite
- cordierite=sapphirine+quartz+MgFe1
- sapphirine+quartz=orthopyroxene+sillimanite+MgFe1
- orthopyroxene+sapphirine+quartz=garnet+MgFe1
- orthopyroxene+sillimanite=garnet+quartz+MgFe1
- orthopyroxene+sillimanite+quartz+MgFe1=cordierite.