Prehnite-pumpellyite facies

The prehnite-pumpellyite facies is a metamorphic facies typical of subseafloor alteration of the oceanic crust around mid-ocean ridge spreading centres. It is a metamorphic grade transitional between zeolite facies and greenschist facies representing a temperature range of 250 to 350 °C and a pressure range of approximately two to seven kilobars. The mineral assemblage is dependent on host composition.

• In mafic rocks the assemblage is chlorite, prehnite, albite, pumpellyite and epidote.
• In ultramafic rocks the assemblage is serpentine, talc, forsterite, tremolite and chlorite.
• In argillaceous sedimentary rocks the assemblage is quartz, illite, albite, and stilpnomelane chlorite.
• In carbonate sediments the assemblage is calcite, dolomite, quartz, clays, talc, and muscovite.

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References

• Blatt, Harvey and Robert Tracy, 1995, Petrology: igneous, sedimentary, and metamorphic, Freeman, ISBN 0-7167-2438-3