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"Metamorphic"
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What are metamorphic rocks?
Heat, pressure and stress can also change some igneous or sedimentary rocks into other kinds of rocks. This fact-filled book describes the process that turns limestone into marble, shale into slate, and granite into gneiss. Metamorphic rocks are often used as materials for floors, roofs, and counter tops because of their beauty.
Book
In situ Rb-Sr and .sup.40Ar-.sup.39Ar dating of distinct mica generations in the exhumed subduction complex of the Western Alps
Dating specific pressure-temperature-time-deformation-fluid (P-T-t-d-f) events is a major petrological issue, particularly for polymetamorphic assemblages. In order to better assess such events using mica populations, this study uses a combined in situ Rb-Sr and Ar-Ar dating approach coupled with chemical mapping, with application to an exhumed subduction complex (Schistes Lustrés, Western Alps). Geochronological investigation of the most Si-rich (Tschermak substitution) mica population allows us to investigate the (near-)peak burial ages of the various tectonometamorphic units of this high-pressure/low-temperature subduction complex. In the blueschist-facies units, a wide range of ages between ~36 (younger than previously obtained peak ages) and ~ 52 Ma suggests a diachronous slicing of units with different initial paleogeography and/or a long residence time at near-peak conditions. The combined use of Ar-Ar and Rb-Sr isochron ages reveals the existence of some excess argon in the studied metamorphic rocks, interpreted as the result of (i) heterogeneous contamination from an argon-rich fluid in the higher grade eclogite-facies units and (ii) partial removal, during pseudomorphic recrystallization, of argon inherited from earlier stages of metamorphism in the lower grade blueschist-facies units.
Journal Article
Metamorphic rocks
Explores Earth science's natural processes, how geologists study metamorphic rocks, and how metamorphic rocks relate to our daily life.
Book
3‐D Modeling of Differential Exhumation of Ultrahigh‐Pressure Metamorphic Rocks Driven by Increasing Plate Divergence
Petrological and seismic constraints suggest differential sampling depth for ultrahigh pressure (UHP) metamorphic rocks exposed in different segments of the fossil subduction zone of the Western Alps. However, the mechanisms for the observed differential exhumation remain to be understood. Here, we account for the continental margin subduction within double subduction systems coupled with three‐dimensional (3‐D) geodynamic models to investigate the potential for this phenomenon. We tested two end‐member scenarios of upper‐plate motion, including Adria counterclockwise rotation and divergent motion away from the trench. Results show that both scenarios can produce a unidirectional increase in the metamorphic peak of exhumed UHP rocks along the orogen strike. Only in the simulations where the counterclockwise rotation of the upper plate acts as the primary driver of exhumation did the resulting characteristics of the deep structure fit with those observed in the Western Alps. They include the presence of an exhumed mantle wedge beneath the southern UHP domes and its absence beneath the northern UHP domes. Our results can be exported to other subduction zones where kinematic constraints suggest a component of upper‐plate rotation, such as eastern Papua New Guinea, and to older subduction zones where the kinematics is poorly assessed.
Journal Article
Correction to: The effect of CO.sub.2 and N.sub.2 on phase relations, fluid composition, and quartz solubility in amphibolite facies metamorphic rocks
The cell containing the values of H 0.015, 0.020, 0.025 in Table 1 of the original paper is published incorrectly. The correct values are shown below.
Journal Article
What are metamorphic rocks?
\"This fact-filled resource explains metamorphic rocks, the different ways in which they are formed and how they can change into different metamorphic rocks through contact, metamorphism and shock metamorphism, for example. Plate tectonics is described, as is the formation of mountains. Gneiss, slate, fulgurite, quartzite, marble, schist, and hornfels are investigated as well as their practical uses. Readers learn about foliated and nonfoliated metamorphic rocks and how to identify them through crystal structure, color, hardness, and streak tests.\"--Provided by publisher.
BOOK
Garnet major-element composition as an indicator of host-rock type: a machine learning approach using the random forest classifier
The major-element chemical composition of garnet provides valuable petrogenetic information, particularly in metamorphic rocks. When facing detrital garnet, information about the bulk-rock composition and mineral paragenesis of the initial garnet-bearing host-rock is absent. This prevents the application of chemical thermo-barometric techniques and calls for quantitative empirical approaches. Here we present a garnet host-rock discrimination scheme that is based on a random forest machine-learning algorithm trained on a large dataset of 13,615 chemical analyses of garnet that covers a wide variety of garnet-bearing lithologies. Considering the out-of-bag error, the scheme correctly predicts the original garnet host-rock in (i) > 95% concerning the setting, that is either mantle, metamorphic, igneous, or metasomatic; (ii) > 84% concerning the metamorphic facies, that is either blueschist/greenschist, amphibolite, granulite, or eclogite/ultrahigh-pressure; and (iii) > 93% concerning the host-rock bulk composition, that is either intermediate–felsic/metasedimentary, mafic, ultramafic, alkaline, or calc–silicate. The wide coverage of potential host rocks, the detailed prediction classes, the high discrimination rates, and the successfully tested real-case applications demonstrate that the introduced scheme overcomes many issues related to previous schemes. This highlights the potential of transferring the applied discrimination strategy to the broad range of detrital minerals beyond garnet. For easy and quick usage, a freely accessible web app is provided that guides the user in five steps from garnet composition to prediction results including data visualization.
Journal Article
A look at metamorphic rocks
\"Describes metamorphic rocks, how they are formed, how they are used, and their role in the rock cycle\"-- Provided by publisher.
Book
Petrology on Mars
Petrologic investigations of martian rocks have been accomplished by mineralogical, geochemical, and textural analyses from Mars rovers (with geologic context provided by orbiters), and by laboratory analyses of martian meteorites. Igneous rocks are primarily lavas and volcaniclastic rocks of basaltic composition, and ultramafic cumulates; alkaline rocks are common in ancient terranes and tholeiitic rocks occur in younger terranes, suggesting global magmatic evolution. Relatively uncommon feldspathic rocks represent the ultimate fractionation products, and granitic rocks are unknown. Sedimentary rocks are of both clastic (mudstone, sandstone, conglomerate, all containing significant igneous detritus) and chemical (evaporitic sulfate and less common carbonate) origin. High-silica sediments formed by hydrothermal activity. Sediments on Mars formed from different protoliths and were weathered under different environmental conditions from terrestrial sediments. Metamorphic rocks have only been inferred from orbital remote-sensing measurements. Metabasalt and serpentinite have mineral assemblages consistent with those predicted from low-pressure phase equilibria and likely formed in geothermal systems. Shock effects are common in martian meteorites, and impact breccias are probably widespread in the planet's crustal rocks. The martian rock cycle during early periods was similar in many respects to that of Earth. However, without plate tectonics Mars did not experience the thermal metamorphism and flux melting associated with subduction, nor deposition in subsided basins and rapid erosion resulting from tectonic uplift. The rock cycle during more recent time has been truncated by desiccation of the planet's surface and a lower geothermal gradient in its interior. The petrology of Mars is intriguingly different from Earth, but the tried-and-true methods of petrography and geochemistry are clearly translatable to another world.
Journal Article