The Setters Formation, identified on the southeast side of Pleasant Hill valley in well Cb13-16, contains the prograde mineral assemblages (1) microcline, biotite, and sillimanite +/- garnet, and (2) microcline, biotite, sillimanite, and muscovite +/- garnet. These pelitic assemblages allow us to infer peak metamorphic conditions between 620° and 680°C and 4 to 6 kilobars pressure, if PH20/Pfluid is > 0.5. There is some evidence in the drill cuttings to indicate that partial melting accompanied the formation of sillimanite, thus constraining peak temperature to > 640°C.
Please give proper credit to the Delaware Geological Survey.
Plank, M.O. and Schenck, W.S. , 1997, The Setters Formation in the Pleasant Hill Valley, Delaware: Metamorphism and Structure: Delaware Geological Survey Report of Investigation 56,
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