How Does The Grain Size Of Sandstone Change During Metamorphism
Metamorphic Rocks
When rocks are subjected to elevated temperatures and pressures, for example due to deep burial in orogenic (mountain building) zones when ii continents collide, they may go metamorphosed (metamorphism is from the Greek, to change in grade). They slowly recrystallize while remaining in the solid state. This may takes thousands or millions of years. Metamorphism is essentially an isochemical procedure, i.due east. the bulk chemical composition of a rock torso is more than or less unchanged from the protolith, or original rock. But the minerals may be largely recrystallized into a new mineral assemblage. In addition, new structural features are frequently imparted to the rocks, such every bit slaty cleavage or schistosity.
Metamorphic recrystallization is acquired past one or both of one) elevated temperatures and ii) loftier pressures
one) Regional Metamorphism is the result of loftier pressures and elevated temperatures associated with deep burying in an orogenic chugalug. Platy minerals (micas) and elongate minerals (hornblende) recrystallize and/or rotate into a new orientation perpendicular to the applied stress, while other minerals recrystallize into new crystals which are stable at the higher pressures and temperatures.
Foliation is the effect of the parallel arrangement of (micas, etc.) in a airplane perpendicular to the maximum principal applied stress. A lineation is caused by a similar growth of elongate minerals (eg. hornblende) in this airplane. Slate, schist, and gneiss are three common foliated metamorphic rocks. Slate is a hard, fine-grained rock with a well-developed rock cleavage or slaty cleavage caused by the incipient growth of platy (micaceous) minerals, due to metamorphism of fine-grained clastic sediments such every bit shale and siltstone and also volcanic tuffs. Schist is a still higher degree of metamorphism, characterized past coarse grained foliation and/or lineation, with mica crystals large plenty to be easily identified with the unaided heart. Gneiss is a medium to coarse-grained, irregularly banded rock with simply poorly adult cleavage. The light and dark bands (gneissic banding) are alternations of felsic vs. mafic layers.
Slate is a product of low grade metamorphism (not terribly great burial temperatures and pressures are required). Schist and gneiss are produced by medium to loftier grade metamorphism . In some cases gneisses are produced by higher form metamorphism than schists. Low-course metamorphic rocks tend to be fine-grained (the newly formed metamorphic mineral grains that is). High-course metamorphic rocks tend to exist fibroid-grained. Simply grain size is also dependent on the grain size of the protolith.
Not-foliated metamorphic rocks include quartzite, which is metamorphosed sandstone in which the quartz grains take recrystallized into a very solid interlocking network, and marble, which is metamorphosed limestone composed of recrystallized and interlocking calcite or dolomite crystals.
Foliation in metamorphic rocks is related to the orientation of the applied stresses and not the original sedimentary or before metamorphic structures. The original shale bedding (relict bedding) is sometimes preserved as color contrasts in a slate. In virtually cases the slate's fracture cleavage lies at some angle to the original bedding plane.
Three other types of metamorphism are important in certain tectonic environments.
2) Contact Metamorphism is the result of baking the surrounding state rocks past an igneous intrusion. The metamorphic aureole surrounding an igneous body may be only 2 centimeters wide adjacent to a modest dike or it may be ii kilometers wide at the contact with a large, slow-cooling granite pluton. Contact metamorphosed rocks may be bleached out looking and non-descript fine-grained. A common contact metamorphic rock is hornfels (German for "hard rock").
three) Hydrothermal alteration, sometimes considered a grade of metamorphism, is related to the circulation of hot, mineral-laden fluids through stone bodies. This is especially of import in alteration of bounding main crust in the high heat flow regime almost the mid-ocean ridges. Serpentinites form from the hydration of peridotites, olivine rich rocks at the base of the oceanic crust. Hydrothermal alteration also occurs as a issue of hot fluids escaping from a cooling pluton, in add-on to the loftier-temperature contact metamorphism occurring there.
4) Cataclastic metamorphic rocks grade where rocks are beingness faulted and sheared. Cataclasite or fault breccias form in breakable fault zones and consist of larger athwart rock fragments dispersed in a fine-grained matrix. Mylonites are foliated, actually sheared, stretched, and streaked rocks, formed in plastic shear zones, at depths and pressures too peachy for rock to intermission. The stone becomes drawn out like modeling dirt or bubble glue.
Source: http://www.columbia.edu/~vjd1/meta_rx.htm
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