Pressure, Temperature, and Relative Time Indicators in Mafic Schist

Tsung-Siang Chiu

Abstract

The investigation shows that mafic schist can be used as a sensitive indicator of pressure, temperature, and relative time. From the coexisting mineral compositions in common mafic schist, we can now subdivide the P, T fields diagnostic of greenschist and low-grade amphibolite facies. According to electron microprobe analysis recoded of chemical component of hornblende, plagioclase, and micas. With increasing pressure, the glaucophane component of amphibole increase. For medium pressure metamorphism the albite-plagioclase gap is in the garnet zone, but amphibole is below.

Mineral growth periods observed are characterized by metamorphic grade and facies series and are assigned to four events. We could recognize two periods of low-pressure Devonian metamorphism from northeastern Vermont and two periods of medium-pressure and low-pressure Ordovician metamorphism from west to south Vermont. The high-pressure metamorphism only observed along GreenMountain anticlinoria axis in north-central Vermont. It is proposed that the metamorphism occurred during the Ordovician.

Reference

Jo Laird and Arden L. Albee (1981) High pressure metamorphism in mafic schist from northern VermontAmerican journal of science, vol. 281, February, 1981, p. 97-126

(Abstract) (Full text)

Jo Laird and Arden L. Albee (1981) Pressure, temperature, and time indicators in mafic schist: their application to reconstructing the polymetamorphic history of Vermont American journal of science, vol. 281, February, 1981, p. 127-175

(Abstract) (Full text)