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Metamorphic Material
Metamorphic flash cards
| Question | Answer |
|---|---|
| Metamorphism | set of processes that produce textural changes, mineralogical changes, or both, in rocks under conditions in the Earth between those of diagenesis and weathering (at the lower limit) and melting (at the upper limit.) |
| Cataclasis | crushing and breaking of grains in rocks |
| Recrystallization | process of reorganization of crystal lattices and intergrain relationships through ion migration and lattice deformation, without accompanying breaking of grains |
| Neocrystalliaztion | process that results in the formation of new minerals that did not previously exist in the metamorphic rock |
| 4 agents of metamorphism | Pressure, temperature, deviatoric stress, chemically active fluids |
| Isochemical metamorphism | no change in the bulk chemistry of the rock volume (domain) |
| Allochemical metamorphism | there is change in the bulk chemistry of the domain (metasomatism) |
| Contact metamorphism | temperature dominant, local |
| Dynamic metamorphism | induced primarily by deviatoric stress |
| Static metamorphism | pressure is principal agent at regional scale |
| Metasomatism | produced by chemically active fluids (hydrothermal) |
| Dynamothermal metamorphism | induced primarily by a combination of pressure and temperature. |
| Local metamorphism | - affects relatively small volumes of rock (less than 100 km3) |
| Regional metamorphism | typically affects thousands of cubic kilometers of rock |
| Prograde metamorphism | progressed from lower to higher temperatures. |
| Retrograde metamorphism | re-metamorphism that progressed from higher to lower temperatures. |
| Tectonites | containing a fabric that reflects a history of deformation |
| Preferred Orientation | where cleavage reflects the textural alignment of mineral grains |
| Gneissic Structure | foliation and banding in which alternate layers are composed of different minerals. |
| Folds | bends in planar structures of the rock |
| Kink Bands | small, abrupt, folds developed in rocks that already have a fabric. -most common in fine-grained rocks, such as Phyllite |
| Boudin- | cylindrical masses of rock, originally part of a single bed or layer that has been stretched and pulled apart |
| Mullions | similar to boudins, columns 2cm to 2 or more meters in diameter, composed of the country rock of the metamorphic terrains in which they occur. |
| Rods | similar to mullions, but composed of segregated or introduced material (dike or vein material) such as quartz. |
| Joints | fractures along which there has been significant movement parallel to the plane of the structure. |
| Mylonites | recrystallized and/or neocrystallized under the influence of a shearing stress. |
| Metamorphic Differentiation | Process or processes that lead to the development of banded or lenticular segregation of minerals from an initially homogenous rock |
| Continuous Cleavage | Describes fine grained rocks consisting of platy minerals evenly distributed in a preferred orientation. e.g. Slaty cleavage |
| Spaced Cleavage | Occurs in rocks with minerals that are not evenly distributed and as a result the rock forms discontinuous layers or lenses of different types of minerals. |
| Crenulation Cleavage | Contains microlithons that were folded by a previous foliation |
| Disjunctive Cleavage | Type of spaced cleavage where the microlithons are not deformed into microfolds, and formation is independent from any previous foliation present in the rock |
| Foliated Textures | Textures characterized by an alignment of mineral grains in such a way as to give the rock the appearance of or the tendency for splitting into layers or flat pieces (minerals commonly acicular or tabular). |
| Strongly Foliated Rocks | rocks dominated mineralogically by platy, bladed, or acicular minerals |
| Weakly Foliated Rocks | linear, but not planar, arrangements of bladed to acicular grains dominate the texture, minerals are weakly aligned |
| Granoblastic Textures | Characterized by more or less equidimensional mineral grains. |
| Diablastic Textures | Tabular or acicular minerals are intergrown in a nonfoliated, interlocking, locally radiating manner. |
| Cataclastic Textures | Nonfoliated textures characterized by fractured rock materials and mineral grains. |
| Relict Textures | Same as when describing structures: refers to textures retained from a protolith |
| 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 |
| Schist | schists are restricted to those metamorphic rocks in which the foliated minerals are coarse enough to see easily in hand specimen. |
| Gneiss | a metamorphic rock displaying gneissose structure. Gneisses are typically layered (also called banded), generally with alternating felsic and darker mineral layers |
| Metamorphic chemistry groups: | Ultrabasic (<45 silica), basic (45-52%), carbonate, non-silicate, aluminous, siliceous-alkali-calcic (SAC), silicic/siliceous (>90%) |
| 2 main categories of metamorphic rocks | Crystalline and clastic |
| Metamorphic Facies | Defined as a set of rocks representing the full range of possible rock chemistries, with each rock characterized by an equilibrium assemblage of minerals that reflects a specific, but limited, range of metamorphic conditions. |
| Low-P, high-T, characterized by LP contact metamorphism | Sanidinite Facies Albite-Epidote Hornfels Facies Hornblende Hornfels Facies Pyroxene Hornfels Facies |
| Characteristic of dynamothermal (regional) metamorphism | Greenschist Facies: Med P, Med T Amphibolite Facies: Med P, Med-High T Granulite Facies: Med P, High T |
| Characterized by static metamorphism | Low P, Low T Zeolite Facies Prehnite/Pumpellyite Facies Med-High-P, Low T Blueschist Facies High P, High T Eclogite Facies |
| Index Mineral | Minerals for which the stability fields are generally known and which may be used to distinguish between a facies or zone. |
| Andalusite- Low P, Low to High T Kyanite- High P, low to High T Sillimanite- Low to Med P, Med to High T | |
| Isograd | A line of “constant grade”, is a line on a map (a surface in three dimensions) that separates rocks that appear to be at different grades |
| Facies Series | progression of facies across a metamorphic belt |
| Metamorphic Facies Series: 5 Types (in order of increasing pressure) | Contact, Buchan, Barrovian, Sanbagawa, Franciscan |
| Two common products of contact metamorphism | Skarns and hornfels |
| Aureoles | Zones of metamorphic rock surrounding and associated with plutons |
| Pressure Shadows | Associated with shear stress, fringes or halos differing from the groundmass that often accompany porphyroblasts in schistose rocks. |
| Buchan | P in middle grades of metamorphism, but form under pressures lower than the aluminum silicate triple point, andalusite present |
| Barrovian | P in middle grades of metamorphism, but form where P are higher that the aluminum silicate triple point, kyanite present |
| Buchan Phase Assemblages | Characteristic minerals include: Andalusite, biotite, cordierite GreenschistAmphiboliteGranulite |
| Greenschist Facies | Perhaps the most widely distributed (recognized) metamorphic assemblages on Earth. |
| Barrovian Facies Series | 6 distinct mineral assemblages Chlorite zone Biotite Zone Garnet Zone Staurolite zone Kyanite zone Sillimanite zone |
| Migmatite | masses of crystalline, mixed rocks, consisting of various proportions of dark, ferromagnesian mineral-rich rock and light quartz- or feldspar-rich rock, that occur in medium to high grade metamorphic terrains |
| Leucosome | light part of migmatite |
| Melanosome | dark part of migmatite |
| Neosome | the rock formed collectively from leucosome and melanosome |
| Mesosome | typically of intermediate shade that has the appearance of ordinary metamorphic rock. |
| Restite | term applied to the residual rock after leucosome has been removed from a protolith. |
| Sanbagawa Series (Japan - higher T) | ZeolitePrehnite-PumpellyiteBlueschistGreenschistAmphibolite |
| Franciscan Series (western CA - Lower T) | ZeolitePrehnite-PumpellyiteBlueschistEclogite |
| Blueschist Facies | Abundance of glaucophane (blue amphibole) in glaucophane schists -metabasites, metawackes, metapelites, carbonate rocks |
| Eclogite | Chemically, a basic rock composed predominantly of pyroxene and red to red-brown garnets, but lack plagioclase (67 % pyroxene and garnet, 30% garnet) |
| Fibroblastic | Diablastic texture consisting of acicular minerals, all of which are about the same size |
| Porphyroblastic | Equaivalent to porphyritic texture in which two distinct size populations exist. Typically consist of minerals different from those comprising the majority of the matrix in which they occur. |
| Slaty | Aphanitic, foliated with smooth, flat surfaces |
| Phyllitic | Aphanitic to fine-grained, foliated with micaceous sheen , microfolds or kink bands |
| Schistose | Phaneritic foliated, without banding Lepidoblastic-dominated by phyllosilicates Nematoblastic- dominated by inosilicates or other needle-like minerals |
| Gneissose | Phaneritic foliated with bands of alternating darker and ligher minerals |
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