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37 Cards in this Set
- Front
- Back
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significance of metamorphic rocks |
they provide a window into past temperatures, |
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metamorphical rocks are changed mineralogically and/or texturally through |
heat and/or pressure, fluids are commonly involved |
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metamorphism |
- occurs at pressures and temperatures much higher than those on the Earth's surface - occurs below P and T conditions that cause melting |
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where do metamorphic rocks form |
middle and lower crust |
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metamorphic rocks remain in the |
solid state |
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metamorphic change depends on |
protolith (starting rock) |
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metamorphic processes are |
slow |
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2 categories of metamorphic rock |
foliated, non-foliated |
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Slate |
- foliated metamorphic rock - shale is protolith elongated and platy minerals aligned and compressed - breaks smoothly along foliation planes - very fine grained |
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phyllite |
- foliated metamorphic rock - shale - micas start growing perpendicular to stress - shiny surface due to micas - fine grained |
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schist |
- foliated metamorphic rock - micas growing parallel - coarser than phyllite, will break along cleavage planes - often folded - more heat and pressure |
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gneiss |
- foliated metamorphic rocks - can be tightly folded - coarser than schist, won't break along foliation planes - minerals segregated into light (quarts and feldspar) and dark (biotite and amphibole) bands |
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migmatite |
- foliated metamorphic rocks - partial melting in the core of mountain belt - extremely high grade metamorphic rock - border of melting |
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progression of foliated - shale |
shale - slate - phyllite - schist - gneiss - migmatite |
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equigranular texture |
if rocks composed of granular minerals such as calcite or quartz are subjected to stress |
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non foliated metamorphic rocks |
- equigranular texture - no preferred orientation/alignment - there are no elongated or platy minerals such as amphiboles or micas to define a foliation in these rocks |
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what are the metamorphic rocks of these non foliated parent rocks a) limestone (CaCO3) b) Sandstone (SiO2) |
Marble (CaCO3) Quartzite (primarily SiO2) |
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NF - Quartzite |
- non foliated - composed almost purely of quartz - some sedimentary structures may survive recrystallization - contact or regional metamorphism |
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NF - Marble |
- composed of calcite - impurities result in secondary minerals, streaks and bands - these impurities are valuable in commercial marble quarries - contact or regional metamorphism |
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sources of heat in metamorphism |
- magma (700 - 1200 degrees C) - burial (15 - 30 degrees C/km) |
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effects of heat in metamorphism |
- speeds up chemical reactions (input energy) |
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confining pressure |
uniform pressure applied to all areas |
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source of confining pressure |
- pressure of surrounding rocks |
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effect of confining pressure |
- reduces space |
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differential stress |
directed pressure, pressure coming from different directions causing squashing or shear, resulting in foliation |
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source of differential stress |
- plate collisions - faults |
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contact metamorphism |
in contact with high heat, localized scale, hornfels, caused by heat from igneous intrusion |
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2 kinds of pressure |
confining and differential |
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effects of differential stress |
- causes alignment of elongated or platy minerals and growth of new minerals in same direction - foliation - minerals align themselves perpendicular to directed pressure |
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helpers for metamorphism |
fluids, usually water |
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sources of fluids in metamorphism |
- ground/sea water - magma - release of water from minerals |
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effect of fluids in metamorphism |
- changes chemical environment the way heat and pressure change the physical environment |
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metasomatism |
chemical change in a rock as a result of interaction with fluids, not pure metamorphism because you change the chemistry, water released in subduction zone alters rocks it passes through |
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types of metamorphism |
contact, shock, regional |
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shock |
results from impact of meteorites - melting (not M) - fractures - glass beads (not M) - recrystallization |
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regional metamorphism |
- usually associated with plate collisions (subduction zones) |
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metamorphic grade |
reflects the intensity of metamorphism experienced by a rock - low, intermediate, high |
