Prograde amphibole dehydration reactions during highgrade regional metamorphism, central massachusetts u. Prograde muscoviterich pseudomorphs as indicators of. Pdf twostage prograde and retrograde variscan metamorphism. Other articles where prograde metamorphism is discussed. Retrograde metamorphism is often observed in hpuhp eclogites during the exhumation of deeply subducted continental crust. Being a metamorphic change resulting from a higher pressure or temperature. In contrast, as soon as crystalline rocks begin to cool free water is consumed by retrograde hydration reactions yardley, 2009. Retrograde metamorphism an overview sciencedirect topics. Acadian prograde metamorphism in schists reached staurolite or sillimanitemuscovite grade, producing the assemblage.
Prograde and retrograde fluid flow during contact metamorphism of siliceous carbonate rocks from the ballachulish aureole, scotland john m. Mukasa department of geological sciences, university of michigan, 2534 c. New growth of metamorphic zircon on the rims of detrital grains. Inspire your inbox sign up for daily fun facts about this day in history, updates, and special offers. In contrast, the ophiolite above was subjected to eclogite grade metamorphism t approx.
Retrograde retrogressive metamorphism is a metamorphism giving rise to the formation of. Prograde metamorphism and decompression of the gfohl gneiss, czech republic article pdf available in lithos 383. Prograde metamorphism begins with cold, fluid water rich rocks and proceeds to hot and dry rocks. However, relics of them may survive trapped inside other minerals, like garnet, muscovite, and quartz. Definition of retrograde metamorphism the mineralogical adjustment of relatively highgrade metamorphic rocks to temperatures lower than those of their initial metamorphism, characteristically inducing hydration and hydrous minerals.
Metamorphic rocks and rock cycle all the rocks are interconvertable to metamorphic rocks. Gy 111 lab manual chapter 4 a prograde metamorphism today will be a nice and easy day as we only have to deal with one more metamorphismrelated. Retrograde metamorphism of the lower devonian littleton. Prograde metamorphism an overview sciencedirect topics. However, the process should not be considered as reversible with respect to prograde metamorphism. Concentration of gold during retrograde metamorphism of. As a result, the basic schists were dehydrated to form eclogitic basic schists, i. Changes occur in the solid state because melting doesn t occur. Prograde destruction and formation of monazite and allanite. Here, sillimanite was completely lost from the assemblage, but a few grains remain inside these quartz crystals where they were protected from reaction. In metamorphism they are retrograde metamorphism, the response of mineral assemblages to decreasing temperature and pressure. If retrograde metamorphism were a common process then upon uplift and unroofing metamorphic rocks would progressively return to mineral assemblages stable at lower pressures and temperatures.
Retrograde metamorphism involves the reconstitution of a rock via revolatisation under decreasing temperatures and usually pressures, allowing the mineral assemblages formed in prograde metamorphism to revert to those more stable at less extreme conditions. Geologic setting renge metamorphic belt as an older sangun metamorphic belt the term sangun metamorphic rocks proposed by kobayashi 1941 had been used for the highpressure schists that were widely scattered in the. Similar values were computed assuming that part of the isotopic exchange was retrograde. Prograde and retrograde pt paths of the late paleozoic.
Within aif, banded pyrrhotite is in textural equilibrium with prograde metamorphic minerals. Prograde and retrograde metamorphic processes in high. During metamorphism, new minerals grow at the expense of old minerals, andor the shape, size, and arrangement of grains in the rock may change. Pdf prograde metamorphism and decompression of the gfohl. If thermodynamic equilibrium were always maintained, one might expect all the. Prograde and retrograde history of eclogites from the eastern blue ridge, north carolina, usa f. Metamorphism and metamorphic rocks tulane university. During metamorphism, evidence of the prograde path is commonly obliterated by continued. C retrograde metamorphism the diagram on the next page shows the type of retrograde pathway that might occur. These garnet features, monazite traceelement signatures, and monazite ages suggest that prograde metamorphism was still underway at 29 ma, but that decompression or cooling was occurring by 25 ma, consistent with the interpretation that peak metamorphism and midcrustal ductile extension began at 35 ma, was ongoing at 23 ma, and had ceased by 16 ma lee and whitehouse, 2007. The absence of metamorphic olivine suggests that these serpentinites were most likely formed at slightly higher temperature and pressure conditions compared to the first serpentinite group, corresponding to medium or high temperature blueschist facies metamorphism.
The starting assemblage for prograde metamorphism of diopsidefree peridotite is the low temperature form of serpentine chrysotile, brucite, andor talc, depending on the amount of enstatite. If thermodynamic equilibrium were always maintained, one might expect all the reactions. Japan, and documents prograde and retrograde pt paths, with discussion of their significance. Prograde and retrograde eclogites in the sambagawa.
In effect, the underlying sioncourmayeur tarentaise nappe was not subjected to a pressure of more than 10 kb. Common pt paths, including a clockwise versus counterclockwise paths, b paths with similar vs different prograde and retrograde segments, and c paths with coincident maximum p and t conditions vs paths with very different maximum p and t conditions. Prograde and retrograde history of eclogites from the eastern. Request pdf prograde and retrograde processes in migmatites revisited. Pelites from the chlorite zone of each area contain monazite that has an inclusionfree core surrounded by a highly irregular, inclusionrich rim. Retrograde metamorphism university of south alabama. However, prograde pseudomorphs that are common in many terrains may provide insight into this portion of the metamorphic path if their mineralogy can be accurately interpreted. Prograde amphibole dehydration reactions during highgrade.
Prograde and retrograde metamorphism of hematitebearing. Growth of new metamorphic minerals as a result of progressive increase in temperature and or pressure. Prograde, peak, and retrograde pt paths from aluminium in. Prograde progressive metamorphism is a metamorphism giving rise to the formation of minerals which are typical of a higher grade i. The starting assemblage for prograde metamorphism of diopsidefree peridotite is the low temperature form of serpentine chrysotile, brucite, and or talc, depending on the amount of enstatite. The distribution pattern of about 40 elements in zoned prograde metamorphic complexes of andalusitesillimanite and kyanites sillimanite. But, if the temperature and pressure decline then the rock undergoes retrograde metamorphism as the rocks and minerals adjust to the reduced temperature and pressure.
Prograde and retrograde metamorphism of hematitebearing basic. Prograde and retrograde growth of monazite in migmatites. Read prograde and retrograde metamorphism of hematitebearing basic schists in the sanbagawa belt in central shikoku, journal of metamorphic geology on deepdyve, the largest online rental service for scholarly research with thousands of academic publications available at your fingertips. Retrograde reactions may completely destroy prograde minerals like sillimanite. Growth of new metamorphic minerals as a result of progressive increase in temperature andor pressure. The rate of this process may obviously be controlled by the rate. Note that the t maximum is known as the peak of metamorphism. Muscovite prograde metamorphism metamorphism that occurs while temp and pressure progressively increase retrograde metamorphism metamorphism that occurs when temp and pressure decreases. In general, the changes in mineral assemblage and mineral composition that occur during burial and heating are referred to as prograde metamorphism, whereas. Prograde, peak, and retrograde pt paths from aluminium in orthopyroxene. Geochemistry of prograde and retrograde metamorphism, baikal.
The mechanisms of metamorphism james madison university. Retrograde hornblende, garnet, zoisite, apatite, carbonate, ferroactinolite, and goldbearing sulphide minerals replace the prograde mineral assemblages on the margins of quartz veins that intensify at aif fold hinges. The temperature of metamorphism ranged from 400 to 750c for both complexes, and pressure was 36 kb for khamardaban and 48 kb for patom. Geochemistry of prograde and retrograde metamorphism, baikal region, ussr. In general, the changes in mineral assemblage and mineral composition that occur during burial and heating are referred to as prograde metamorphism, whereas those that occur during uplift and cooling of a rock represent retrograde metamorphism. Prograde and retrograde processes in migmatites revisited. A process of change 1 metamorphic rock forms from a preexisting rock or protolith. Ferry 1 contributions to mineralogy and petrology volume 124, pages 235 254 1996 cite this article. The retrograde metamorphic trend was studied for the protoophiolite baikalmuya complex, north baikal region t 850360c, high pressure. Thus, two types of ecologite, retrograde and prograde, converged into the same metamorphic condition, 610650 c, 717 kb, in a part of the ecologite facies during the sambagawa metamorphism. The emphasis here is on how quickly this happens and the resulting implications for deformation of cooled crystalline crust. Yet, high grade metamorphic rocks are common at the surface of the earth and usually show only minor retrograde minerals.
This is called retrograde metamorphism and it is our last topic for today. Pdf prograde and retrograde growth of monazite in migmatites. A prograde metamorphism b retrograde metamorphism reference. If thermodynamic equilibrium were always maintained, one might expect all the reactions that occur during prograde metamorphism to be reversed during. Prograde metamorphism article about prograde metamorphism. In order to enable prograde metamorphism, these anhydrous assemblages must first be hydrated to serpentinites in the course of ocean floor metamorphism. Retrograde rehydration of uhp rocks may replace the mobile elements lost during prograde metamorphism. Metamorphic rock retrograde metamorphism britannica.
Well it stands to reason that if you can get an increase in metamorphism over time that you must also be able to go backwards go from high grade metamorphism to low grade metamorphism. Metamorphic rocks of the silgara formation show evidence of a complex metamorphic history characterized by crustal thickening during heating and a regional retrograde metamorphism after the peak metamorphic temperature rios et al. Shikoku retrograde metamorphism of hematite schists in the sanbagawa belt in central. The isotopic ratios suggest average timeintegrated fluid fluxes of 3. This is a relatively uncommon process, because volatiles must be present. Rates of retrograde metamorphism and their implications for.
Gy 111 lecture notes 34 retrograde metamorphism 2008. The conditions at which monazite and allanite were produced and destroyed during prograde metamorphism of pelitic rocks were determined in a buchan and a barrovian regional terrain and in a contact aureole, all from northern new england, usa. The starting assemblage for prograde metamorphism of diopsidefree peridotite is the low temperature form of serpentine chrysotile, brucite, andor talc, depending on the amount of enstatite and forsterite in the protolith. Retrograde metamorphism diaphthoresis, retrogressive metamorphism is the mineralogical adjustment of relatively highgrade metamorphic rocks to temperatures lower than those of. Metamorphic rock metamorphic rock retrograde metamorphism. Retrograde metamorphism diaphthoresis, retrogressive metamorphism is the mineralogical adjustment of relatively highgrade metamorphic rocks to temperatures lower than those of their initial metamorphism. Retrograde metamorphism heating are referred to as prograde metamorphism, whereas those that occur during uplift and cooling of a rock represent retrograde metamorphism. In contrast to prograde metamorphism that produces fluids at a rate controlled by heat transport, retrograde metamorphism is normally associated with consumption of fluids when a metamorphic rock formed at elevated temperatures is exposed to fluids at lower temperature. Porosity, permeability, and basalt metamorphism lowgrade.