Very Low-grade Metamorphic Evolution of Pelitic Rocks under High-pressure/Low-temperature Conditions, NW New Caledonia (SW Pacific) |
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| Authors: | POTEL S; MAHLMANN R FERREIRO; STERN W B; MULLIS J; FREY M |
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| Institution: | MINERALOGISCH–PETROGRAPHISCHES INSTITUT DER UNIVERSITÄT BASEL, BERNOULLISTRASSE 30, CH-4056 BASEL, SWITZERLAND |
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| Abstract: | The P–T gradient in a Late Eocene low-T high-P metamorphicbelt in northern New Caledonia increases from SW to NE. Metapelitesin the pumpellyite–prehnite and blueschist zones containlawsonite, Mg-carpholite, Fe-stilpnomelane and Fe-glaucophane.Thermodynamic calculations indicate a progression of metamorphicconditions from less than 0·3 GPa and 250°C in akaolinite-bearing rock in the SW, up to 1·5 GPa and 410°Cin a lawsonite–glaucophane-bearing sample in the NE ofthe Diahot terrane. Through a multi-method investigation ofphyllosilicates, organic matter and fluid inclusions, we demonstratethat the evolution of organic matter and illite crystallinitydepends strongly on the evolution of the P–T path withtime. In addition, we show that the illite–muscovite bcell dimension provides a robust estimate of maximum pressurereached in low-temperature domains with polyphase metamorphichistories, despite subsequent high-temperature–low-pressureevents. Fluid inclusion study reveals an isothermal decompressionin the Diahot terrane. KEY WORDS: low-temperature/high-pressure metapelites; illite crystallinity; coal rank; illite–muscovite b cell dimension; New Caledonia |
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| Keywords: | : low-temperature/high-pressure metapelites illite crystallinity coal rank illite– muscovite b cell dimension New Caledonia |
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