Topic
Granulite
About: Granulite is a research topic. Over the lifetime, 6763 publications have been published within this topic receiving 268925 citations.
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TL;DR: Most of the inferences about fluid action in the deep crust are drawn from field, petrographic, and geochemical studies in the granulite facies terrains as mentioned in this paper, which are made from major and minor element distributions and isotopic patterns in metamorphic rocks, calculations of fluid-mineral equilibria based on observed assemblages, fluid inclusions, and field evidence of fluid pathways.
Abstract: Most of the inferences about fluid action in the deep crust are drawn from field, petrographic, and geochemical studies in the granulite facies terrains. Deductions on the nature of fluids are made from major and minor element distributions and isotopic patterns in metamorphic rocks, calculations of fluid-mineral equilibria based on observed assemblages, fluid inclusions, and field evidence of fluid pathways. Discussion of these features has focused attention on several major problems concerning the timing, flow mechanisms, and origin of the fluids. A key issue concerns episodicity versus secular activity of fluids. There are strong arguments that most fluid action in the deep crust is linked to thermal/deformational events, including magmatism and regional meta morphism. Discrete radiometric ages of high-grade terrains often define relatively short periods of crystallization or recrystallization. The late Archean granulite facies metamorphism of southern India is an example, where U-Pb systems of zircons (Buhl et al 1983), whole-rock U-Pb data (Peucat et al 1 987), and Sm-Nd systems of whole-rocks and minerals (Bernard-Griffiths et al 1 987) all show a major high-temperature recrys tallization event, inferred by several workers to have involved pervasive fluid action, centered closely around 2.5 Ga. Another geochemical indi cation of episodic fluids comes from stable isotope studies of progressive metamorphic sequences, as in the Damara orogen, Namibia, where whole rock b 180 increases slightly at isograds representing arrested dehydration events but is monotonous between isograds (Hoernes & Hoffer 1 985).
79 citations
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TL;DR: In this article, a combined study of mineral inclusions, cathoduluminescence (CL) images, U-Pb LA-ICP-MS dates, and in-situ trace element compositions of zircon provide clear evidence on the nature and timing of partial melting in these UHP rocks.
Abstract: Thin layers and lenses of granitic leucosome are widely distributed within amphibolites, paragneisses and orthogneisses of the Sulu UHP terrane. They are parallel to, or cross-cut, foliations in the host rocks at different scales and show evidence of coalescence and migration to form centimetre- to decimetre-scale segregations. Variously migmatized rocks extend at least 350 km from SW Sulu (Maobei) to NE Sulu (Weihai), in a band at least 50 km wide. A combined study of mineral inclusions, cathoduluminescence (CL) images, U–Pb LA-ICP-MS dates, and in-situ trace element compositions of zircon provide clear evidence on the nature and timing of partial melting in these UHP rocks. Most zircon from the granitic leucosomes occurs as distinct overgrowths around inherited (igneous or metamorphic) cores or as new, euhedral crystals. The overgrowths and new crystals commonly show perfectly euhedral shapes, have pronounced oscillatory zoning and contain felsic mineral inclusions, such as Kfs + Pl + Qtz ± Ilm ± monazite (Mon). In contrast, the inherited igneous or metamorphic cores are rounded or irregular, contain low-P or UHP mineral inclusions and show clear dissolution textures. These data suggest that the new zircon is anatectic in origin and that it grew during partial melting of the UHP rocks. The REE patterns of the anatectic zircon show steep slopes from the HREE to LREE with strongly to moderately negative Eu anomalies (Eu/Eu* = 0.31–0.72) and pronounced positive Ce anomalies (Ce/Ce* = 6.8–26.5). Abundant U–Pb spot analyses of the anatectic zircon reveal two discrete and meaningful ages of partial melting within the Sulu UHP terrane. Anatectic zircon from 12 granitic leucosomes within amphibolites, paragneisses, and orthogneisses from Sulu UHP slices II and III yields consistent mean U–Pb ages of 219.0 ± 1.2 to 218.3 ± 1.6 Ma, 218.8 ± 2.0 to 217.3 ± 1.7 Ma and 218.2 ± 1.4 to 215.0 ± 1.5 Ma, respectively. In contrast, anatectic zircon from six granitic leucosomes within paragneisses and orthogneisses from Sulu UHP slice III records younger mean U–Pb ages of 151.9 ± 1.3 to 151.1 ± 1.8 Ma and 155.9 ± 1.8 to 153.7 ± 1.7 Ma, respectively. These data imply that the Sulu UHP terrane experienced two Mesozoic partial melting events. The first partial melting event (219–215 Ma) was probably associated with a Late Triassic granulite facies stage of ‘hot’ exhumation, whereas the second (156–151 Ma) is interpreted as the result of Middle-Late Jurassic extension and thinning of the previously thickened crust of the Sulu UHP terrane. Both partial melting events induced extensive retrograde metamorphism of the eclogites and their country rocks.
79 citations
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TL;DR: In this article, the suture zone between the Bhandara craton and the granulite-facies rocks of the Eastern Ghats Province in SE India contains a number of deformed alkaline and tholeiitic intrusives.
Abstract: The suture zone between the Bhandara craton and the granulite-facies rocks of the Eastern Ghats Province in SE India contains a number of deformed alkaline and tholeiitic intrusives. The Khariar alkaline complex is one of the several occurrences which intruded in the Mesoproterozoic (1,480±17 Ma, 2σ) and was deformed during the Pan-African tectonothermal event. The geochemical signatures indicate a rift-related setting for the magmatic activity. The nepheline syenite parent magma may have been produced by in-mantle fractionation of clinopyroxene and Ti-rich amphibole from a basanitic primary magma derived from an enriched spinel lherzolite mantle source in the sub-continental lithosphere. Geochemical variations in the Khariar alkaline suite can be modeled by the fractionation of clinopyroxene, amphibole, titanite, zircon, apatite and allanite. The Mesoproterozoic alkaline magmatism at Khariar marks the initiation of a NE-SW rift which formed several craton margin basins and opened an ocean towards the south. The sediments of the cratogenic basins and the Eastern Ghats Province were deposited in these rift-related basins. A K-Ar age of 1,330±53 Ma from glauconites in sandstone suggests that the NW-SE trending Godavari–Pranhita graben formed at approximately the same time as the rift at the craton margin. If the two are related, the Godavari–Pranhita graben may represent the failed arm of a rift system in which the NE-SW arm was the active segment. The granulite-facies deformation and metamorphism of the Eastern Ghats Province sediments may be related to an episode of Grenvillian basin inversion. The Mesoproterozoic rifting and Grenvillian basin closure may thus represent two well-defined parts of a Wilson cycle i.e. the opening and closure of an ocean. The Khariar and other alkaline bodies were, however, deformed during a Pan-African collisional event associated with the westward thrusting of the Eastern Ghats Province granulites over the cratonic foreland.
79 citations
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TL;DR: In this paper, the authors used the finite differences method for a Newtonian incompressible fluid to model the P-temperature (T) path of metamorphic rocks within the Earth's crust and found that the average rate of exhumation of granulites during the gravitational redistribution process is about 2.5 mm per year.
79 citations
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TL;DR: In situ anatectic features have been identified on the basis of the existence of new generations of cordierite and/or garnet produced as the solid products of incongruent anatexis within or adjacent to leucosomes.
79 citations