Ch. 07 Flashcards
The transformation of rocks into new types by the recrystallization of their constituents, originating from the Greek “meta” (change) and “morphe” (shape).
Metamorphism
Primary agents responsible for metamorphism, acting on igneous, sedimentary, or previously metamorphosed rocks.
Heat and pressure
Heat and pressure mobilize mineral constituents, leading to their reassembly as new minerals in equilibrium with existing conditions, transforming rocks.
Mobilization and reassembly
Significance of textures in defining the history of metamorphic rocks, where composition and orientation of new minerals reflect metamorphic conditions.
Textural history
Process where metamorphic minerals develop within solid rock, aided by solvents like water expelled from pores and dehydration of clay minerals.
Solvent-assisted growth
3 Metamorphic Classes
Thermal or Contact Metamorphism
Dynamic or Dislocation Metamorphism
Regional Metamorphism
Dominated by stress, particularly in belts of shearing, where the primary control is exerted by pressure.
Dynamic or Dislocation Metamorphism
Dominated by temperature rise, often occurring in contact zones adjacent to igneous intrusions or when sediments are down-folded into hotter regions in the crust.
Thermal or Contact Metamorphism
Influenced by both temperature and pressure acting over a large regional area, resulting in significant alterations to the rocks.
Regional Metamorphism
What metamorphic process occurs due to the intrusion of a hot igneous mass, resulting in the recrystallization of surrounding rocks and the formation of new minerals?
Contact Metamorphism.
In which metamorphic process do rocks undergo mechanical breakdown under stress, such as shearing or brecciation?
Dislocation Metamorphism.
What is the term for metamorphism that results from both stresses and temperature rise, typically occurring in orogenic belts of the crust?
Regional Metamorphism.
What determines the ease of growth for metamorphic minerals during metamorphism?
Crystal Shape.
What are conspicuous crystals in metamorphic rocks, such as garnet and andalusite, called?
Porphyroblasts.
What term refers to the arrangement of mineral constituents and textural elements in a rock, particularly in metamorphic rocks?
Fabric.
What term describes a series of parallel surfaces in metamorphic rocks?
Banding.
What term refers to a series of parallel surfaces in metamorphic rocks
Foliation.
What term describes a series of parallel lines produced by the trace of foliation on a rock surface, such as the wall of a tunnel?
Lineation.
What term refers to the ability to distinguish individual crystals in a rock?
Visible Crystallinity.
What term describes a texture where individual crystals can be distinguished?
Phaneritic.
What term describes a texture where granularity is visible due to the presence of crystals, but individual crystals cannot be distinguished?
Aphanitic.
What term describes the size of crystals in a rock?
Crystal Size.
What term describes crystals that are larger than 2.0 mm in size?
Coarse.
What term describes crystals that are smaller than 0.06 mm in size?
Fine.
What term describes crystals that range in size from 2.0 mm to 0.06 mm?
Medium.
What term describes the uniformity of crystal size in a rock?
Relative Crystal Size.
What term describes a texture where all crystals in a rock are approximately the same size?
Granoblastic.
What term describes a texture where larger crystals are surrounded by much smaller crystals
Porphyroblastic.
What visible character is most useful for the classification of metamorphic rocks?
Classification.
What term is used for metamorphosed sandstone?
Metasandstone.
What term describes metamorphosed arenaceous sediments, such as sands?
Psammitic.
What term describes metamorphosed argillaceous sediments, such as silts and clays?
Pelitic.
What metamorphic rock is formed from clays and silts?
Slate.
What metamorphic rock is formed from volcanic ash?
Phyllite.
What metamorphic rock, with no noticeable foliation, is formed from all rock types of all grain sizes?
Mylonite.
What metamorphic rock is formed from mixed detrital terrigenous materials and is moderately foliated?
Migmatite.
What metamorphic rock is formed from mixed detrital terrigenous materials and is well-foliated?
Gneiss.
What metamorphic rock, well-foliated, is formed from basic igneous rocks?
Schist.
What metamorphic rock, with no noticeable foliation, is formed from sand?
Quartzite.
What metamorphic rock, with no noticeable foliation, is formed from limestone?
Marble.
What metamorphic rock, with no noticeable foliation, is formed from basic igneous rocks?
Amphibolite.
What metamorphic rock, with no noticeable foliation, is formed from basic igneous rocks?
Serpentine.
What term refers to the metamorphic changes occurring in rocks due to the intrusion of a hot igneous mass?
Contact Metamorphism.
What term describes the zone of metamorphism surrounding an igneous intrusion?
Aureole.
What term describes a hard, fine-grained metamorphic rock resulting from the recrystallization of shale or clay due to contact metamorphism?
Hornfels.
What mineral, formed during contact metamorphism of shale, is characterized by distinct spots and is a variety of andalusite?
Chiastolite.
What mineral, frequently formed during contact metamorphism of shale, grows as porphyroblasts and is associated with andalusite?
Cordierite.
What metamorphic rock is formed from the recrystallization of a siliceous rock like sandstone due to contact metamorphism?
Quartzite.
What metamorphic rock is formed from the recrystallization of limestone due to contact metamorphism?
Marble.
What mineral is formed during contact metamorphism of limestone containing silica and forms tabular, translucent crystals?
Wollastonite.
What mineral, formed during contact metamorphism of dolomitic limestone, hydrates readily to form hexagonal crystals?
Brucite.
What metamorphic rock is formed from limestone containing silica and clay minerals during contact metamorphism?
Calc-silicate-hornfels
What metamorphic rock, formed from basic rocks like gabbro, is characterized by equigranular texture and results from prolonged high-grade metamorphism?
Granulite.
What term describes the reaction between volatile substances from an igneous mass and the surrounding rocks, resulting in the formation of characteristic minerals near a contact zone?
Pneumatolysis.
What mineral is formed by the pneumatolytic action of boron and fluorine on mafic minerals near an igneous contact, and is often found in radiating clusters embedded in quartz?
Tourmaline.
What calcium-boron-silicate mineral occurs in contact metamorphic aureoles where boron has been introduced into limestone or altered rocks containing calcite, and typically has flat and acute-edged crystals?
Axinite.
What mineral occurs in cavities in acid igneous rocks, often associated with beryl, tourmaline, and fluorite, and is commonly found in greisen?
Topaz.
What term describes the alteration of feldspars of granites resulting in the formation of kaolinite, often observed in granites where hydrothermal action has decomposed the rock into quartz, kaolin, and mica?
Kaolinization.
What rock, composed essentially of quartz, white mica, and accessory minerals like tourmaline and fluorite, is formed from granite under certain pneumatolytic conditions, inhibiting the formation of potassium carbonate?
Greisen.
What represents an arrested stage in the kaolinization of granite, containing quartz, decomposed feldspar, and frequently topaz and fluorspar?
China-stone.
What type of metamorphism occurs over large surface areas and is associated with colliding plates, resulting in the formation of mountains?
Regional metamorphism.
What are the three main grades of metamorphism based on temperature and stress conditions, named after the main rock types produced?
Slate, schist, and gneiss grades.
How are zones of increasing metamorphism revealed in clayey sediments, and what minerals define these zones?
Zones are defined by the appearance of index-minerals at successively higher temperatures. Index-minerals include chlorite, biotite, garnet, staurolite, kyanite, and sillimanite.
What is the first zone of metamorphism where chlorite is formed from sericite and other minute mineral particles in the original sediment?
Chlorite-zone.
What zone follows the chlorite-zone and is characterized by the formation of red-brown biotite, marking moderate temperatures during metamorphism?
Biotite-zone.
What zone follows the biotite-zone and is defined by the appearance of abundant pink garnet, resulting in garnetiferous mica-schists?
Garnet-zone.
What zone is characterized by the presence of kyanite, indicating moderate to high-grade metamorphism?
Kyanite-zone.
What is the last zone of metamorphism where sillimanite is formed at higher temperatures, resulting in the formation of schists and gneisses?
Sillimanite-zone.
What type of rock is formed from argillaceous sediments under high stress combined with low to moderate temperature, characterized by a preferential direction of splitting known as slaty cleavage?
Slate.
What is the distinctive feature of slate, characterized by smooth-sided thin plates of rock due to the orientation of minerals such as chlorite, sericite, and quartz?
Slaty cleavage.
What determines the commercial value of slate, and what are some British localities known for their slate production?
The commercial value of slate depends on the perfection of its cleavage and absence of accessory minerals like calcite and pyrite.
How is slaty cleavage developed in slate, and what minerals are involved in its formation?
Slaty cleavage is developed when argillaceous sediments are compressed under stress, causing minute crystals of flaky minerals like chlorite and sericite to grow with their cleavage surfaces at right angles to the direction of maximum compression. Quartz grains may also recrystallize with their length parallel to this direction.
Besides argillaceous sediments, what other type of rock can give rise to slate, and what is an example of such slate?
Some slates are derived from fine-grained volcanic tuffs. An example is the green Cumbrian slates of andesitic composition.
How are fossils affected by the metamorphism process that forms slate?
Fossils may be deformed by the metamorphism process that forms slate, as the rock undergoes compression and mineral reorientation.
How does slaty cleavage relate to folds in the rock, and what forces are involved in their formation?
Slaty cleavage is often parallel to the axial surfaces of folds, and the angle between cleavage and bedding varies. Deforming forces cause cleavage to develop in the direction of easiest relief, often parallel to the axial surfaces of folds.
What type of rock results from the continued growth of minerals like muscovite and chlorite under increasing stress and some rise in temperature?
Phyllite.
Describe the gradation of rocks from shale to mica-schist based on increasing metamorphism.
Shale transforms into slate, then phyllite, and eventually into mica-schist under conditions of increasing metamorphism.
How is mica-schist formed, and what are its primary mineral constituents?
Mica-schist is formed from argillaceous or pelitic sediments and composed of muscovite and biotite, along with variable amounts of quartz.
What type of sedimentary rock gives rise to quartz-schist, and what distinguishes it from mica-schist?
Quartz-schist is derived from sandy sediment with a smaller clay content than sediment forming mica-schist. It has coarser foliation and forms at a higher grade of metamorphism.
What are the main minerals found in chlorite-schist, and what type of rocks does it originate from?
Chlorite-schist consists predominantly of chlorite crystals and may contain quartz and porphyroblasts of magnetite or garnet. It is derived from basalt or dolerite under moderate stress and temperature.
What minerals characterize hornblende-schist, and from which rocks does it originate?
Hornblende-schist contains hornblende and quartz, forming from basic rocks like dolerite at a higher grade of metamorphism.
Describe the banding or foliation in gneiss, and what distinguishes orthogneiss from paragneiss?
Gneiss exhibits banding or foliation with alternating bands of quartz and feldspar parallel to streaks of mafic minerals. Orthogneiss is derived from igneous rocks like granite, while paragneiss originates from sediments.
What is biotite-gneiss composed of, and what sedimentary rocks does it derive from?
Biotite-gneiss contains bands of quartz and feldspar with interposed mica-rich bands, representing a higher grade of metamorphism from argillaceous rocks such as shales.
What distinguishes augen-gneiss, and what is an example of its formation?
Augen-gneiss exhibits eye-shaped clusters of feldspar within quartz-feldspar bands. An example is the metamorphosed granite of Inchbae, N. Scotland.
How are injection-gneisses formed, and what is their characteristic appearance?
Injection-gneisses result from the injection of thin sheets of quartz-feldspar material along parallel surfaces, presenting a veined, striped appearance.
What type of metamorphism occurs on faults and thrusts due to earth movement?
Dislocation metamorphism
Which minerals are commonly found in greater quantities in zones of dislocation metamorphism?
Mica and amphibole
Where are ancient shear zones containing rocks metamorphosed by dislocation commonly found?
In the roots of the Caledonian mountains in Scotland and ancient mountain belts elsewhere
What risk is associated with excavation into rocks with complex metamorphic structures?
he risk of slabs of rock becoming detached and falling into the excavation
Which metamorphic minerals are of great value to the refractory industry?
Sillimanite, kyanite, and andalusite
Where are commercial concentrations of sillimanite, kyanite, and andalusite found?
Kenya, the Appalachians, California, India, South Africa, and Western Australia
Which metamorphic mineral is important as an abrasive and is mined from gneiss in New York, New Hampshire, and North Carolina?
Garnet
What type of rocks are produced when earth movements cause brittle fracture, shearing, grinding, and crushing of rocks near the surface?
Brecciated rocks or cataclastic rocks
In dislocation metamorphism, what term describes the breaking down of rock caused by shearing, grinding, and crushing?
Brecciation or cataclasis
What are fine-grained rocks produced by plastic deformation at depths greater than 10 km during dislocation metamorphism called?
Mylonites
Where are modern examples of dislocation metamorphism found?
In the Alpine-Himalayan chain and circum-Pacific orogenic belts
Apart from metamorphic rocks, which minerals are associated with metamorphism but not restricted to its formation?
Asbestos, graphite, and talc
What is the industrial value of the metamorphic minerals sillimanite, kyanite, and andalusite?
They are valuable to the refractory industry.
Which metamorphic mineral is used as an abrasive and is mined from gneiss in certain regions of the United States?
Garnet
What type of metamorphism occurs on faults and thrusts due to earth movement?
Dislocation metamorphism
What type of rock results from the introduction of igneous material into country-rocks, producing mixed rocks?
Migmatite
How is the mixing in migmatites achieved, as described in the text?
Mechanical injection of veins or stripes, or chemical permeation or soaking of country-rocks
Where are migmatites commonly found in terms of geological settings?
In Precambrian rocks of Scandinavia, Finland, the Baltic Shield, and areas of high-grade metamorphism in orogenic belts
What is the typical texture of granulite, and under what conditions is it believed to form?
Granoblastic texture with equidimensional grains; it forms under conditions of high temperature and pressure.
What is the term used to describe gneiss with bands of quartz-feldspar composition parallel to oriented biotite or hornblende streaks?
Augen-gneiss
In which conditions are granulites believed to form?
High temperature and pressure
From which type of sedimentary material are mica-schists primarily formed?
Argillaceous or pelitic sediments such as shale or clay
What is the metamorphic equivalent of basalt or dolerite, consisting predominantly of chlorite crystals in parallel orientation?
Chlorite-schist
