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Introduction

Metamorphic rocks room "changed rocks". A mineral assemblage secure at low temperatures and pressures may not be secure at elevated temperatures and pressures. Together temperature and/or pressure boosts "old minerals" may readjust (typically they boost in size) or new minerals might form. In this photo a basalt circulation has small the underlying limestone. The realm of metamorphism deserve to be depicted on a plot of temperature versus pressure.

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Types the Metamorphism

Different species of metamorphism are presented in the plot above:Contact Metamorphism - reaction driven mainly by temperature at relatively low pressure - connected with the injection or extrusion that a magma or a lavaDynamic Metamorphism - reaction driven mainly by press at relatively low temperaturesRegional Metamorphism - no discernible resource of warmth (no adjacent magma chamber, because that example) - with boosting depth the temperature and also pressure increaseHigh pressure - short Temperature Metamorphism - pressures are higher than would certainly be predicted native the supposed geothermal gradient (field lies above the straight line in the figure given above)At i beg your pardon of the following plate boundaries might you intend to find evidence of dynamic metamorphism?divergent margintransform marginconvergent marginWhat kind of metamorphism might you mean to uncover taking location deep in the sediments that have accumulated in the Gulf the Mexico?regional metamorphismcontact metamorphismdynamic metamorphism

Metamorphic Processes

Prograde metamorphism
describes metamorphic reactions that take place with raising temperature (and pressure). Retrograde metamorphism refers to metamorphic reactions that accompany diminish temperature (and pressure).During metamorphism the texture of the parent product (the protolith) may readjust or its mineralogy may readjust -- brand-new minerals may grow at the cost of the initial minerals. Metasomatism occurs IF the mass composition of the protolith changes.Metamorphic procedures tend to cause small grains to "grow" (recrystallization) into larger grains. Recall that this is the contrary of the propensity in sedimentary processes. Brand-new minerals may kind during metamorphism:Calcite + Quartz = Wollastonite + Carbon Dioxide:CaCO3 + SiO2 = CaSiO3+CO2If the CO2 "escapes" Wollastonite will certainly be preserved in the metamorphic rock. That is, without CO2 the reaction will not it is in reversed. Various other metamorphic minerals include:garnetkyanitetourmalineCertain mineral are thought about to be extremely "reactive" during metamorphism. Minerals prefer mica and also amphibole save on computer (OH-) which may be released as water throughout metamorphism. Minerals favor calcite and dolomite may release carbon dioxide.

Metamorphism and also Plate Boundaries

We have looked in ~ several setups in i m sorry temperatures and pressures change as geologic processes operate:At a divergent margin basaltic lava flows out on the relatively cold sea floor. Warm flows from the magma right into the cold sea floor sediments/rocks and also bakes castle : contact metamorphismAt a convergent margin cold sea floor is subducted beneath an additional plate. As the oceanic crust is pushed (pulled?) to greater depths it slowly heats up yet remains cooler than the various other plate until good depths are got to : high press - short temperature metamorphismWhen two plates containing continent crust converge a suture region is formed and the continent crust thickens. Temperatures and also pressures in ~ the base of the thickening crust slowly increase : local metamorphismWhen two plates "slide" past one one more the pressure (directed) have the right to be quite high whereas the increase in temperature because of friction often tend to be relatively low : dynamic metamorphism.At some mix of temperature and pressure the product may start to partly melt and an Igneous process is initiated.

Classification of Metamorphic Rocks

Banded (mineralogically layered) : GneissNot Banded (no discernible mineralogical layers) - not foliated (no discernible airplane of weakness) : granofels if coarse grainedhornfels if fine grainedNot Banded (no discernible mineralogical layers) - foliated (discernible plane of weak - generally produced by the alignment the the cleavages of clay minerals) : slate - well grainedphyllite - "surface "sparkles"schist - rough circuit grained We have actually talked around a variety of common Igneous and Sedimentary rocks. Every of these rocks may be subjected to metamorphic conditions. The goal of the geologist is come "see through" the effects of metamorphism and also determine the parental rock type. Quartzite : Quartz-rich sandstonesMarble : Limestone or DolomiteGranite Gneiss : a Granite Granofels: Graniteslate / phyllite / schist : shales and also mudstonesConsider the following scenario. A granite magma invades a limestone unit which includes quartz and clay minerals. In ~ the contact in between the magma and also the nation rock warmth flows native the magma chamber into the country rock in an effort to being the 2 bodies into thermal equilibrium. In general, together the street from the magma room increases, the temperature decreases. Therefore, one can observe mineralogical zones approximately the granite v the greatest temperature minerals uncovered closest to the granite. At some distance native the call the nation rock will present no impacts of call metamorphism. One would expect a temperature gradient in thickened continental crust in a convergent zone. The better the pressure and also temperature the higher the degree of metamorphism.

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Mineral that form during metamorphism may permit estimation that the temperature attained. Together minerals space termed index minerals by some geologists.Sillmanite - high grade conditionsGarnet - intermediate grade conditionsChlorite - low grade conditionsWhich that the complying with "protoliths" is least likely to exhibit a response to short to moderate grade metamorphism?shalesmudstonesquartz arenitescarbonatesWhich that the complying with "protoliths" is most likely the parental of an alkaii feldspar - quartz - biotite gneiss?shalemudstonequartz arenitegranite_________________________________________________________________________________________________| ?SUBJECT=OnlinePhysical" > jbutler