Geology - Metamorphic Rocks Flashcards
What does metamorphism derive from?
Constant changing geologic systems such as rock, magma and fluid movement constantly occuring disrupting thermodynamic equilibirum.
What are equilibra factors governed by?
Kinetic factors, depending on compositon/fabric of the parent rock, fluid composition and temperatures and pressures
Diagenesis
This is the physical and chemical processes affecting sedimentary materials after depoisiton and before metamorphism and between deposiiton and weathering.
What is onset of partial melting based on?
Rock composition, metamorphic regimes and heterogenous rock bodies overlapping in hundreds of degrees.
What are the lower limit changes of metamorphic rock?
The distinction between metamorphism and diagenetic changes in sedimentary/volcanistic deposits.
Metastable
This is a phase in which an energy barrier must be surmounted before that phase can be transformed to one of lower energy.
Example of a metamorphic rock?
Migmatites formed by anatexis are generally heterogenous and preserves evidence of partial melting at micro/mcaroscopic scales.
Vitroclasts may undergo diagenesis to zeolites
Antexis
This refers to partial melting of crustal rocks at the P-T fields between the solidus and liquidus
What is metamorphism the product of?
Chemical equilibria of sedimentary and igneous rocks
Example of the process of metamorphism?
Mudrock is a sedimentary product by mixture of quartz and clay being an accidental assemblage of mineral grains deposited in a basin.
Widest thermal stability of any material?
Quaerz
In mudrock deformation, how does change occur?
Clay minerals affected whilst quartz are not, where clays decompose forming one or more new minerals like mica or chlorite, or react with quartz or another material in the mudrock to generate a new metamorphic material.
Example of temperature and pressure fluctuations produce different materials?
Mid-ocean ridge eruption forming basalt.
What happens when basalt reacts with water?
Water acts as a catalyse, enhancing basalt to seek a new more thermodynamically facourable configuration.
Metamorphic Facies
Describe mineral assemblages in metamorphic rocks formed under similar pressures and temperatures.
What does metamorphic facies observe?
Mineral assemblages abundant in metamorphic rocks are limited, both within individual rocks and across spectrums of rock composition.
What are pressure-temperature time models used for?
Understanding relationship of the P-T paths taken by rocks in metamorphism
What are the four types of metamorphism?
Burial
Regional
Contact
Burial Metamorphism
This is where sediments are buried deeply enough such that heat and pressure cause recrystallisation of the minerals allowing new minerals to grow
Regional Metamorphism
This is a large-scale action of heat and pressure across and extensive area.
QContact Metamorphism
This is either due to heating, with our without burial or by lying close to magma intrusions.
What minerals are shared with metamorphic and igneous rocks?
Quartz, feldspars, micas and apatite.
Orthosilicates
Lack sharing of tetrahedral units, like olvine and garnet
Pyroxenes
This is a group of silicates of calcium, magnesium, iron and amphiboles.
Amphiboles
These are complex hydrated silicates of Ca, Mg, Fe and Al
Ferromagnetism
This is the containing of electrons in unfilled shells with permanent magnetic moements in absence of external fluids.
What metamorphic rocks are othosilicates commonly found in?
They coexist with quartz and feldspars in recrystallised quartz like mudstones
Examples of metamorphic chain silicates?
Single chain like pyroxenes and double chain like amphiboles
Example of chain silicates?
Hornblende and pyroxenes
Porphyroblasts
These are large mineral crystal in a metamorphic rock that has grown within the finer grained matrix
Foliated
These are planar and linear fabric elements in a rock.
What are the most commmon metamorphic rocks?
Mudrocks
Calcareous
Mafic/Ultramafic
What do mudrocks develop from?
Recrystallization and modificaiton of clay minerals with microscopic graind sizes that form new crystal structures.
