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Zeolite facies describes the mineral assemblage resulting from the pressure and temperature conditions of low-grade metamorphism.. The zeolite facies is generally considered to be transitional between diagenetic processes which turn sediments into sedimentary rocks, and prehnite-pumpellyite facies, which is a hallmark of subseafloor alteration of the oceanic crust around mid-ocean ridge ...
The albite-epidote-hornfels facies is a facies at low pressure and relatively low temperatures. It is named for the two minerals albite and epidote, though they are also stable in other facies. Hornfels is a rock formed by contact metamorphism, a process that characteristically involves high temperatures but low pressures/depths. This facies is ...
Low temperature, high pressure conditions are characterized by blueschist facies and eclogite facies. Common minerals include: lawsonite, garnet, glaucophane, coesite, pumpellyite, hematite. Such mineral assemblages indicate temperatures of 500-800 degree Celsius at pressure of 2.5-3.5 GPa.
The transformation converts the minerals in the protolith into forms that are more stable (closer to chemical equilibrium) under the conditions of pressure and temperature at which metamorphism takes place. [5] [6] Metamorphism is generally regarded to begin at temperatures of 100 to 200 °C (212 to 392 °F).
[5] [6] Clockwise P-T-t path normally consists of three parts: [2] Initial heating and compression until arriving a peak, a high pressure-low temperature peak is often observed. (Prograde metamorphism until peak) [2] Near-isothermal decompression after the peak (Stage 1 retrograde metamorphism) [2]
The greenstone belts are surrounded by high-grade gneiss terrains showing highly deformed low-pressure, high-temperature (over 500 °C (932 °F)) metamorphism to the amphibolite or granulite facies. These form most of the exposed rock in Archean cratons. [38]
Low U concentrations in the SMZ are not a consequence of high grade metamorphism. The NMZ, with high Th, U concentrations (10.8 and 2.5 ppm) and radiogenic Pb, resembles the adjoining Zimbabwe craton more. The differences in late Archean tectonic styles between NMZ and SMZ+KC is a possible consequence of the differences in Th and U content of ...
The foliations are symmetrically arranged with respect to the axial plane, depending on the composition and competency of a rock. For example, when mixed sandstone and mudstone sequences are folded during very-low to low grade metamorphism, cleavage forms parallel to the fold axial plane, particularly in the clay-rich parts of the sequence. In ...