Metamorphic Rocks

Metamorphic Rocks Metamorphism: The transition of one rock into another in the solid state under conditions unlike those under which it formed Metamorphic rocks are produced from: Igneous rocks Sedimentary rocks Other metamorphic rocks

Agents of Metamorphism Heat- The most important agent Recrystallization results in new, stable minerals Two sources of heat Contact metamorphism – heat from magma Regional Metamorphism - increase in temperature with depth due to the geothermal gradient

Agents of Metamorphism Pressure Increases with depth Confining pressure applies forces equally in all directions Rocks may also be subjected to differential stress which is unequal in different directions and causes deformation

Agents of Metamorphism Pressure

Types of Metamorphism Contact metamorphism From Understanding Earth, Press and Siever. Freeman. Contact metamorphism

Regional metamorphism Types of Metamorphism Regional metamorphism

Regional metamorphism Types of Metamorphism Regional metamorphism More Uplift

Regional metamorphism Types of Metamorphism Regional metamorphism From Understanding Earth, Press and Siever. Freeman.

Metamorphic Textures Foliation - any planar arrangement of features within a rock Foliation can form in various ways: Rotation of platy and/or elongated minerals Recrystallization of minerals in the direction of preferred orientation Changing the shape of equidimensional grains into elongated shapes that are aligned

Metamorphic Textures Foliation can form in various ways:

Metamorphic Textures Foliated textures Slaty cleavage Closely spaced planar surfaces along which rocks split

Metamorphic Textures Foliated textures Schistosity Platy minerals are discernible with the unaided eye and exhibit a planar or layered structure Rocks having this texture are referred to as schist

Metamorphic Textures Foliated textures Gneissosity During higher grades of metamorphism, ion migration results in the segregation of minerals into layers Gneissic rocks exhibit a distinctive banded appearance

Metamorphic Textures Metamorphic rocks that lack foliation are referred to as non-foliated Develop in environments where deformation is minimal And/or composed of minerals that exhibit equidimensional crystals General name is granofels

Metamorphic Rocks Foliated Metamorphic Rocks a b Slate: compact, very fine-grained, metamorphic rock with a well-developed cleavage. Freshly cleaved surfaces are dull Phyllite: 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.

Metamorphic 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.

Metamorphic 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.

Metamorphic Rocks Specific Metamorphic Rock Types Marble: a metamorphic rock composed predominantly of calcite or dolomite. The protolith is typically limestone or dolostone.

Metamorphic Rocks Specific Metamorphic Rock Types Quartzite: a metamorphic rock composed predominantly of quartz. The protolith is typically sandstone.

Metamorphic Rocks Greenschist/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.

Metamorphic 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.