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6874139 
Journal Article 
Composition of pumpellyite, epidote and chlorite from New Caledonia - How important are metamorphic grade and whole-rock composition? 
Potel, S; Schmidt, ST; de Capitani, C; , 
2002 
STAUBLI VERLAG AG 
ZURICH 
82 
2 
229-252 
English 
WOS:000177970600008 
In New Caledonia, pumpellyite occurs in association with epidote. chlorite and amphibole in metabasites, metapelites and metatuffs. The metamorphism in New Caledonia is related to two subduction events, one during Cretaceous time and a second one during Oligocene time. Metamorphism in the different metamorphic zones displays an increase in metamorphic grade from pumpellyite-actinolite (Pmp-Act) facies at high pressure to prehnite-pumpellyite (Prh-Pmp) facies at intermediate to low pressure.Detailed chemical analysis of pumpellyite, epidote, chlorite and actinolite from various lithologies shows different compositions in the metamorphic zones. Bulk-rock compositions, metamorphic grade and mineral associations were determined to define the factors that control these mineral compositions.Equilibrium phase diagrams were calculated using the DOMINO-THERIAK software and an updated thermodynamic database. To test the effect of bulk-rock composition, the calculations were done in systems of varying Mg/(Mg+Fe) and Al/(Fe+Al) ratios at 3 kbar and using the hematite-magnetite buffer as a control for aO(2). Equilibrium assemblages corresponding to observed mineral associations occur in the predicted phase diagrams. Pumpellyite is stable over a wide compositional range in these different systems at temperatures below 235 degreesC, whereas epidote becomes stable at temperatures above 235 degreesC. In systems of low Mg/(Mg+Fe) and high Al/(Fe+Al), epidote and pumpellyite are predicted to be stable between 235 and 290 degreesC. The association pumpellyite-prehnite appears to be characteristic of low Mg/(Mg+Fe) and high Al/(Fe+Al), whereas the association pumpellyite-actinolite seems to be characteristic of high Mg/(Mg+Fe) systems. Variations of oxygen fugacity play an important role on the observed mineral associations and the compositions of pumpellyite and epidote. 
Epidote; Equilibrium phase diagram; Oxygen fugacity; Pumpellyite-actinolite facies; Pumpellyite-prehnite facies; chemical composition; chlorite; fugacity; low grade metamorphism; phase equilibrium; pumpellyite; New Caledonia 
Symposium on Diagenesis and Low-Grade Metamorphism 
STRASBOURG, FRANCE