2Metamorphic Rocks Metamorphism: The transition of one rock into another in the solid state under conditions unlike those under which it formedMetamorphic rocks are produced from:Igneous rocksSedimentary rocksOther metamorphic rocks
3Agents of Metamorphism Heat- The most important agentRecrystallization results in new, stable mineralsTwo sources of heatContact metamorphism – heat from magmaRegional Metamorphism - increase in temperature with depth due to the geothermal gradient
4Agents of Metamorphism PressureIncreases with depthConfining pressure applies forces equally in all directionsRocks may also be subjected to differential stress which is unequal in different directions and causes deformation
6Types of Metamorphism Contact metamorphism From Understanding Earth, Press and Siever. Freeman.Contact metamorphism
7Regional metamorphism Types of MetamorphismRegional metamorphism
8Regional metamorphism Types of MetamorphismRegional metamorphismMore Uplift
9Regional metamorphism Types of MetamorphismRegional metamorphismFrom Understanding Earth, Press and Siever. Freeman.
10Metamorphic TexturesFoliation - any planar arrangement of features within a rockFoliation can form in various ways:Rotation of platy and/or elongated mineralsRecrystallization of minerals in the direction of preferred orientationChanging the shape of equidimensional grains into elongated shapes that are aligned
11Metamorphic TexturesFoliation can form in various ways:
12Metamorphic Textures Foliated textures Slaty cleavage Closely spaced planar surfaces along which rocks split
13Metamorphic Textures Foliated textures Schistosity Platy minerals are discernible with the unaided eye and exhibit a planar or layered structureRocks having this texture are referred to as schist
14Metamorphic Textures Foliated textures Gneissosity During higher grades of metamorphism, ion migration results in the segregation of minerals into layersGneissic rocks exhibit a distinctive banded appearance
15Metamorphic TexturesMetamorphic rocks that lack foliation are referred to as non-foliatedDevelop in environments where deformation is minimalAnd/or composed of minerals that exhibit equidimensional crystalsGeneral name is granofels
16Metamorphic Rocks Foliated Metamorphic Rocks a b Slate: compact, very fine-grained, metamorphic rock with a well-developed cleavage. Freshly cleaved surfaces are dullPhyllite: a rock with a schistosity in which very fine phyllosilicates (sericite/phengite and/or chlorite), although rarely coarse enough to see unaided, impart a silky sheen to the foliation surface. Phyllites with both a foliation and lineation are very common.
17Metamorphic Rocks Foliated Metamorphic Rocks Schist: a metamorphic rock exhibiting a schistosity. By this definition schist is a broad term, and slates and phyllites are also types of schists. In common usage, schists are restricted to those metamorphic rocks in which the foliated minerals are coarse enough to see easily in hand specimen.
18Metamorphic Rocks Foliated Metamorphic Rocks Gneiss: a metamorphic rock displaying gneissose structure. Gneisses are typically layered (also called banded), generally with alternating felsic and darker mineral layers. Gneisses may also be lineated, but must also show segregations of felsic-mineral-rich and dark-mineral-rich concentrations.
19Metamorphic Rocks Specific Metamorphic Rock Types Marble: a metamorphic rock composed predominantly of calcite or dolomite. The protolith is typically limestone or dolostone.
20Metamorphic Rocks Specific Metamorphic Rock Types Quartzite: a metamorphic rock composed predominantly of quartz. The protolith is typically sandstone.
21Metamorphic RocksGreenschist/Greenstone: a low-grade metamorphic rock that typically contains chlorite, actinolite, epidote, and plagioclase. Such a rock is called greenschist if foliated, and greenstone if not. The parent is either a mafic igneous rock or graywacke.
22Metamorphic Rocks Specific Metamorphic Rock Types Amphibolite: a metamorphic rock dominated by hornblende + plagioclase. Amphibolites may be foliated or non-foliated. The parent is either a mafic igneous rock or graywacke.