Metamorphic Rocks (Part 2 - Metamorphic Rocks w/ Textures and Metamorphic Zones) Flashcards
Rocks that formed as a result of metamorphism.
Metamorphic Rocks
A sub-branch of Petrology that focuses on the composition, characteristics and origins of metamorphic rocks.
Metamorphic Petrology
A fine grained (<1.0 mm diameter), non foliated fabric that develops by contact metamorphism, with predominantly equant grains.
Hornfelsic Texture
Non-foliated metamorphic rocks that are derived from fine-grained protolith rocks that develop in metamorphic aureoles, adjacent to igneous intrusions.
Hornfels
Characterized by large (>1.0 mm diameter) equant grains or large equant grains that lack foliation, occur in high grade rocks that form at elevated temperature and pressure conditions, and develop during metamorphism of a wide range of protoliths under uniform stress conditions.
Granoblastic Texture
Also called quartzite
Metaquartzite
A non-foliated, metamorphic rock with a granoblastic texture that contains >90% quartz and derived
from quartz-rich protoliths, such as sandstone or chert.
Metaquartzite
Granoblastic, metamorphic rock rich in calcite and/or dolomite, derived from recrystallization of limestone or dolostone protoliths from dynamothermal, burial or contact metamorphism.
Marble
Other term for Skarn
Tactite
A granoblastic calc-silicate rock formed by contact metamorphism of carbonate metamorphic rocks through metasomatism from the release of silica and volatiles from the magma which also generates calc-silicate mineral assemblages and/or metallic ore deposits.
Skarn
Metamorphic rocks that show fractured, angular particles that form in response to the brittle crushing of grains during deformation in the upper crustal fault zones.
Cataclastic Texture
Metamorphic rock with cataclastic texture derived from metamorphism of sedimentary or igneous breccias that develop during dynamic or dynamothermal metamorphism.
Metabreccia
Cohesive metamorphic rock with cataclastic texture produced by brittle deformation in zones under low temperature, high strain, dynamic metamorphic conditions.
Cataclasite
Glassy metamorphic rocks produced by high strains generating localized melting in fault zones, and commonly occur as vein material in cataclastic rocks such as fault breccias and cataclasites.
Pseudotachylite
High strain rate cataclastic rocks created by the tremendous short-term stresses that are typically associated with extraterrestrial rock bodies impacting Earth.
Impactites
Non-crystalline, highgrade coals that are vitreous, light weight and jet black in color that commonly display conchoidal fractures, forms from bituminous coal experiencing metamorphism through burial or dynamothermal metamorphism.
Anthracite
Metamorphic rocks derived from conglomerate protoliths and contain sub-rounded to rounded relict clasts with >2 mm diameter, and can form from a wide range of protolith clast compositions from burial, dynamothermal or contact metamorphism.
Metaconglomerate
Serpentine-rich metamorphic rocks that can occur either foliated or non-foliated forms that form through hydrothermal alteration of ultrabasic rocks at temperatures below 50d °C, hydrating olivines and pyroxenes into serpentine minerals.
Serpentinite
Fine-grained alteration rocks produced from the alteration of ultrabasic rocks or Mg-rich sedimentary rocks through low temperature and pressure hydrothermal fluids, where Talc contributes to its soapy feel and low hardness.
Soapstone
Green-colored metamorphic rocks rich in silicate minerals that commonly include chlorite, epidote, prehnite, pumpellyite, talc, serpentine, actinolite, albite, forms by low to moderate (200-500 °C) temperature alteration of basic to ultrabasic igneous rocks, and commonly develop from hydrothermal metamorphism in oceanic crust near divergent plate boundaries.
Greenstone
Sodium-rich basalt that can occur in greenstones.
Spilite
Sodium-rich andesite that can occur in greenstones.
Keratophyre
A greenstone characterized by the abundance of chlorite, epidote, prehnite, pumpellyite, talc, serpentine, actinolite and albite, with a foliated texture.
Greenschist
Dark—colored metamorphic rocks composed largely of amphiboles, and form by medium to high temperature °C) regional metamorphism of basic igneous rocks or sedimentary rocks.
Amphibolite
Amphibolites derived from basic igneous rocks.
Ortho-amphibolite
Amphibolites derived from sedimentary protoliths.
Para-amphibolite
Medium to coarse-grained rocks that contain granoblastic to foliated textures that form by high temperature (>800°C ) and high pressure (>10 kbar, or 33 km depth) metamorphism.
Granulite
Schistose metamorphic rocks produced in subduction zone settings, characterized by significant amount of glaucophane, lawsonite, aegirine and kyanite.
Blueschist
Very high pressure, high temperature rocks that develop principally from basic protoliths, and may be the major rock type in Earth’s lower crust due to its high temperature (>400°C) and high pressure (1.2 GPa at >40 km depth) conditions. It commonly appears as red and green due to its major minerals being jadeite, pyroxene, omphacite, and red garnets.
Eclogite
Closely spaced layers along which metamorphic rocks break or cleaves readily to produce flat surfaces with a dull luster.
Slaty Cleavage
Fine-grained, aluminum-rich, pelitic metamorphic rocks that possess flat, planar cleavage that develops during metamorphism under non-uniform stress at relatively low temperatures (150-200 °C) and low pressures.
Slate
Rock cleavage characterized by larger crystals and more wavy surfaces compared to slaty cleavage.
Phyllitic Cleavage
A very common foliation defined by the sub-parallel arrangement of macroscopic platy minerals in closely spaced metamorphic layers.
Schistosity
Metamorphic rock characterized by its phyllitic cleavage and glossy sheen, and commonly develop by the recrystallization of slate, possessing the same protolith as slates, at temperatures 250-300 °C and pressure conditions exceeding slates.
Phyllite
Metamorphic rock characterized with schistosity, enriched in aluminosilicate minerals, derived from various protoliths, and produced by dynamothermal metamorphism at convergent plate boundaries with temperatures 300-400 °C
Schist
A foliation characterized by the arrangement of minerals into distinct color bands, which are commonly alternating light-colored quartz and dark colored biotites and amphiboles.
Gneissosity
Metamorphic rock with a gneissose structure that develop from lower grade metamorphic rocks from a wide variety of protoliths, and form from dynamothermal settings at temperatures exceeding 600 °C.
Gneiss
Gneisses that develop from igneous protolithts
Orthogneiss
Gneisses that develop from sedimentary protoliths
Paragneiss
“Mixed” rocks that possess textural and structural characteristics of both igneous and metamorphic rocks, displaying an irregular, swirling mix of colors, and develop under high temperature (>800°C) conditions in the lower crust.
Migmatite
Commonly banded metaquartzite that contains 20-30% iron.
Taconite
Pervasively deformed metamorphic rocks that have their original composition and texture largely obliterated.
Tectonite
A by-product glassy rock produced by the explosion during the Trinity Test.
Trinitite
Zones where Index Minerals can be notably
found, bounded by isograds
Barrovian Zones
Imaginary lines on geologic maps marking the first appearance of an index mineral.
Isograd
A British geologist who discovered a key to interpreting progressive metamorphism whereby progressively higher grades of metamorphic minerals and rocks are produced with increasing temperature in an evolving orogenic belt.
George Barrow (1912)
Common rocks include chlorite-bearing
slate, chlorite-sericite phyllite and chlorite-sericite schist.
Chlorite Zone
Chlorite becomes unstable and begins to be replaced by what mineral at the upper temperature limit of the chlorite zone?
Biotite
What zone does common rocks include garnet schist or garnet-mica schist. Garnets commonly occur as porphyroblasts.
Almandine Zones
How does almandine form?
Chemical transformation of chlorite and magnetite
What zone does common rocks include staurolite-mica schist and staurolite-garnet-mica schist.
Staurolite Zone
What zone does common rocks include kyanite-schist and kyanite-mica schist.
Kyanite Zone
How does kyanite form?
Transformation of aluminosilicate minerals such as andalusite (a low pressure polymorph) or through
dehydration of staurolite or pyrophyllite.
Common rocks include sillimanite schist, sillimanite gneiss and cordierite gneiss.
Sillimanite Zone
How does sillimanite form?
Developed by dehydration of muscovite
in the presence of quartz.
Inherited textures from a metamorphic rock’s protolith
Relic Texture
