METAMORPHIC TEXTURES & MINERALS GROUP 20: MEGHAN CLARK, MICHAEL FORNEA, MARK FRITCHIE, SAVINA NGUYEN, BRYCE

PENNY

Textures Introduction •  Textural changes take place as rocks

undergo prograde metamorphism. •  Deformation fabrics •  Coarsening of grain size

•  Metamorphic minerals may grow and modify rock texture.

Arrangements: •  Porphyroblasts – large crystals are

formed and surrounded by smaller crystals

•  May form by recrystallization of minerals already in a rock

•  Ex: augen gneisses •  In some deformed rocks, mineral

grains assume distinctive arrangements called deformation fabrics.

•  Lineation •  Foliation

•  Rocks lacking lineation or foliation are termed hornfels.

Metamorphic Grades from Foliated Rocks: •  Low metamorphic grades - shale •  Medium metamorphic grades - schists •  High metamorphic grades - gneisses

Elevated Temperatures •  >700°C mineral in pelitic rocks

(metamorphosed clay-rich sediments) may melt.

•  Partial melting often produces a migmatite, a rock containing veins and patches composed of quartz and feldspar that crystallized from the partial melt.

http://lh4.ggpht.com/-K6F3xegQmIw/UCp5HOwZeSI/AAAAAAAABjE/uLMCbc2NxSg/s720/00149%2525204625%2525208%252520cm.jpg Mineralogy

•  Metamorphic rocks may contain all minerals common in sedimentary and igneous rock.

•  Two factors controlling mineralogy •  Parent rock composition •  Grade of metamorphism

•  Facies – range of T & P at which a rock is metamorphosed

http://legacy.belmont.sd62.bc.ca/teacher/geology12/photos/rocks/class_metamorphic_rocks%5b1%5d.gif

Earth Materials – GEOL 3200 – Louisiana State University. Pearson Learning Solutions. 2013.

http://www.earth.lsa.umich.edu/earth118/05-metamorphic%20rock%20names%20in%20P-T%20space.jpg

http://lh4.ggpht.com/-K6F3xegQmIw/UCp5HOwZeSI/AAAAAAAABjE/uLMCbc2NxSg/s720/00149%2525204625%2525208%252520cm.jpg

http://legacy.belmont.sd62.bc.ca/teacher/geology12/photos/rocks/class_metamorphic_rocks%5b1%5d.gif

http://www.nps.gov/shen/naturescience/basement-rocks.htm

http://www.cprm.gov.br/33IGC/1202819.html

http://www.cnpc.com.cn/en/aboutcnpc/technologyinnovation/RandDProgress/RDProgressin2010/1Reservoir-forming.shtml?COLLCC=93433351&

http://www.earth.lsa.umich.edu/earth118/05-metamorphic%20rock%20names%20in%20P-T%20space.jpg

Relationship to the Petroleum Industry

https://www.fas.org/irp/imint/docs/rst/Sect5/Sect5_5.html

•  Petroleum hydrocarbons are rarely found in metamorphic rocks.

•  Metamorphic rocks often make traps for petroleum hydrocarbons as well as make up basement formations.

•  Traps – occur after tectonic processes bury and carry rocks to the surface.

•  Basement rock formation – complex set of metamorphic & igneous rocks found below sedimentary rocks/basins.

•  Recent discoveries show metamorphic basement rocks have the capability of holding petroleum hydrocarbons.

http://geology.isu.edu/Digital_Geology_Idaho/Module1/mod1.htm

References