Textural features of metamorphic rocks have been discussed in the previous lecture. Photomicrographs of symplectite and kelyphite. Abstract The Luliangshan garnet peridotite massif is an ultramafic complex in the North Qaidam UHPM belt, NW China. Igneous Rock Textures and Structures . Journal of Petrology 35, 271–287. 7:36. In this introductory article, we first provide an overview of how temperature controls deformation mechanisms and processes and then introduce the collection of research papers ordered from those analysing deformation processes occurring at high temperatures to contributions reporting deformation at shallow crustal conditions. Advances 5 (7), eaaw0913https://doi.org/10.1126/sciadv.aaw0913. #1. Nature 407, 734–736. Adakitic (tonalitic-trondhjemitic) magmas resulting from eclogite decompression and dehydration. cryptocrystalline. (B) Garnet (Grt) + Cpx, corona around plagioclase in a granulite-facies mafic dyke (East Hebei, China). The replacement between different generations of, minerals in rocks suggests that metamorphic reactions are not fully completed. Neoarchean metamorphic evolution and. Phlogopite and coesite exsolution from super-silicic clinopyroxene. Lithos 206–207. Brittle deformation structures: (A) fault zone in hosting fractured rock and (B). by monomineralic or polymineralic rims. These contributions provide a significant advance in the study of rock deformation and fluid/melt migration at multiple crustal levels, from deformation bands near the Earth's surface to shear zones in partially molten rocks in the lower crust. 1, p. 195. (C) Opx lamellae in Cpx from an ultrahigh-temperature, granulite (East Kunlun, China). Therefore, kelyphite is a special type of symplectite that develops around garnet due to rapid exhumation of. Both are keys to understanding granite forming and crustal reworking. entirely in their host mineral structures at high temperature (e.g., clino- and orthopyroxenes) and/or pressure (e.g., majorite-pyroxenes), but are produced when their host minerals lose the solubility as a result of cooling to low temperatures (T-controlled exsolution) or. (B) Melt pockets within the high-grade garnet-bearing, metapelite (Yunnan, China). This book is composed of 11 chapters and begins with a presentation of the metamorphic processes and the production of metamorphic minerals. (Eds. Metamorphic Textures And Structures. Under increasing temperature and / or pressure existing minerals become unstable and break down to form new minerals. Emilius klippe (Western Alps, Italy). Metamorphic petrology is the study of the solid-state chemical changes that take place Passchier, C.W., Trouw, R.A.J., 2005. For clarity of definition and ease of use, we prefer to define symplectite as a vermicular, intergrowth texture that describes the breakdown of omphacite from ultrahigh-pressure eclogites into vermicular intergrowth of sodic-poor, Cpx and sodic plagioclase during rapid decompression/exhumation under dry conditions (, coating around garnet. No diamond was found in the marble. Eclogitic rocks are crucial for the understanding of tectonic processes as they provide key constraints on both the P-T-t evolutions and the deformation modes sustained by rocks in subduction zones. Brittle deformation and high-pressure metamorphism are also intimately linked, as brittle fracturing can aid the, ). The fragments are mostly angular in shape (i.e., clasts with sharp edges) and cemented by a, fine-grained matrix consisting of crushed and ground-down microfragments of minerals formed during faulting. Newly crystallized euhedral zircon and apatite needles occur within the Pl melt pockets. http://opengeology.org/textbook/6-metamorphic-rocks/—An Introduction to Geology. (A) Plane-polarized and (B) backscattered electron (BSE) images of symplectite showing, . 29: CHAPTER 7 . This texture is important for understanding variations of metamorphic conditions . The replacement textures include the, The reaction-rim texture results from a type of disequilibrium reaction that shows either progressive or retrogressive evolution between, different generations of minerals at grain boundaries. 38, Mineralogical Association of Canada, p. 170. McCall, Kristen Elaine. The melting protoliths include basaltic, sedimentary, and granitic rocks, which are. Join ResearchGate to find the people and research you need to help your work. In some places, these deformed rocks (up to mylonitic grade) can be found as clasts within meter-thick brecciated fault rocks that formed close to the lawsonite-eclogite facies peak P-T conditions. Sodic amphibole exsolutions in garnet from garnet-peridotite, North Qaidam UHPM belt, NW. Temperature is a key parameter that determines what rock deformation processes are active and therefore how tectonic structures form. Quantitative characterization of textures in mantle spinel peridotite xenoliths. (A) Metamorphic rhyolite with relict igneous porphyritic feldspar and quartz. Metamorphic rocks are rocks that have changed from one type of rock to another. Photomicrographs showing exsolution textures in various minerals from metamorphic rocks. PLAY. Abstract. Exsolution. We show that seismic slip and associated melting are preceded by fracturing, asymmetric fragmentation, and comminution of the wall rock caused by a dynamically propagating rupture. phaneritic. Textural features of metamorphic rocks have been discussed in the previous lecture. Robinson, P., 1977. challenges. It requires stress surpassing the elastic threshold and a deformation rate slow enough to, accommodate further strain without breaking of the material (i.e., ductility or plasticity). During the Ordovician-Silurian continental collision, thickening and foundering, the Luliangshan peridotite complex was exposed to ultrahigh pressures (UHP) reaching 5.5 GPa possibly >6 GPa at temperatures of 900 °C (perhaps up to 1000 °C) corresponding to a depth of ∼200 km. Igneous crystallization, textures and microstructures. De Wit Lamont‐Doherty Geological Observatory, Columbia University, Palisades, New York 10964 This special issue gathers a collection of research papers following the 21st International Conference on Deformation Mechanisms, Rheology and Tectonics (DRT-2017), which was held in Inverness (Scotland) in April–May 2017, organised by the University of Aberdeen. consisting of green, brown, or black amphibole and plagioclase.The modal content of amphibole is larger than 30% vol. Metamorphic textures and mineralogy develop progressively over several hundreds of feet/meters of drilling. (B) Clinopyroxene (Cpx) lamellae along the, (100) plane of orthopyroxene (Opx) from the Yushigou harzburgite (North Qilian, China). This unique feature makes pseudotachylyte a rare. The most convincing structures, include porphyroblast (e.g., garnet, andalusite, and staurolite) that rotates and grows concomitantly with deformation (i.e., synkinematic, growth), which occasionally contains spiral inclusion trails (i.e., internal foliation) (. (F). is a process by which a former fairly homogeneous phase separates into two or more solid solution phases under subsolidus conditions. Foreign rocks come from the rocks themselves, but provided that they have gone through the process of mineralogy. Journal of Metamorphic Geology 27, 621–638. E and F). Exsolution texture induced by decompression: from the continental collisional belts and xenoliths in kimberlites. Here, we present observations of a fault zone from the Bergen Arcs, western Norway, which constrain the deformation processes of lower crustal earthquakes. Using Metamorphic Textures to Infer Deformation and Thermodynamic Histories. eclogite (North Qaidam UHP metamorphic belt, China). (D) Subgrains in a relic of quartz grain surrounded by newly recrystallized, small and equant quartz grains in a granitic mylonite, suggesting subgrain rotation recrystallization (Nujiang, China). B). • Textures of Contact Metamorphism fractures, especially faults and joints. During metamorphism, new platy mineral grains grow in the direction of least stress,producing a planar texture called foliation.Rocks with only one A text which aims to help undergraduate students in geology to recognize and interpret metamorphic textures and microstructures in thin-section. : Other common minerals in amphibolite are quartz, chlorite, epidote, zoisite, biotite, garnet, titanite, scapolite, clinopyroxene and calcite. in granulite-facies metamorphic tonalite (East Hebei, China). (Figure 9-11). Representative rock types include, polymineralic rocks such as granulite and eclogite, and monomineralic rocks such as quartzite and marble, which are often composed of. Zhao, G., Cawood, P.A., Wilde, S.A., Lu, L., 2001. Grain distributions 5. rocks. Metamorphic rocks exhibit a variety of textures. https://www.scribd.com/document/49840856/Metamorphic-Textures—Metamorphic-Textures. (B) Kink bands (marked by green arrowheads) in olivine in mantle harzburgite (Yushigou. Zhang, L.F., Song, S.G., Liou, J.G., Ai, Y.L., Li, X.P., 2005. (E) Multiple coronas of garnet from the East Kunlun eclogite (, inner vermicular intergrowth rim of Cpx + Pl and outer amphibole rim, showing a retrograde process from isothermal decompression to cooling. Rigid body rotation is a common mechanism but its resultant structures are usually difficult to distinguish. Some original textures. Migmatites are always observed within the high-grade metamorphic complexes or terranes in, Photomicrographs of retrogressed coronas in various metamorphic rocks. Metamorphic rock - Metamorphic rock - Structural features: Metamorphic rocks are often intimately related to large-scale (kilometres of tens of kilometres) structural features of Earth. Vernon, R.H., 2004. (D) Amphibole corona around the Cpx + Pl symplectite (high-pressure granulite, Hengshan, China), which also shows a retrograde process from isothermal decompression to P-T lowering and hydration. and larger than the percentage of any one of the other mafic minerals. 378: Volcanism 71 . The UHP metamorphic eclogite belt in the East Kunlun Orogen may represent the final closure of the Proto-Tethys Ocean (opening at $580 Ma, subduction initiating at $520 Ma) at $430-410 Ma in the East Kunlun, with the formation of the Pan-North-China Continent in the Early Paleozoic and expansion of the Paleo-Tethys Ocean in the south. Song, S.G., Niu, Y.L., Zhang, L.F., Bucher, K., 2009. Traditionally, CPO in a deformed, rock has been interpreted as the result of ductile deformation induced by dislocation creep, because dislocations must slip along specific, crystallographic planes and axes. It requires, a film of fluid to act as a carrier of crystalline material (i.e., solution), in which solute diffuses, usually nonconservatively, from the sites, of dissolution to precipitation along grain boundaries. American Mineralogist 89, 1330–1336. (A) Antiperthite with K-feldspar (Kfs) exsolution lamellae in two directions from a ~ 1.95 Ga high-pressure granulite (Hengshan, China). Metamorphic rocks. ... (Al 2 SiO 5) but different crystal structures. (A) Decompression melting of eclogite (and other ultrahigh-pressure metamorphic rocks), 130: 42–62; (B) Spear FS and Cheney JT (1989) A, Contributions to Mineralogy and Petrology. View/ Open. Because, slate is easily split along its fine foliation, its foliation is also called slaty cleavage. (A) Antiperthite with K-feldspar (Kfs), . (F) Sphene corona of rutile from a retrograde eclogite (East Kunlun, China). We suggest, based on our observations, that strain-rate increase along plate interface shear zones may trigger fracturing and fluid infiltration which in turn enables brittle-ductile instabilities along these deformation networks. The metamorphic structures are determined by definite mechanical conditions and also by recrystallisation. We conclude that omphacitic-clinopyroxene in subducted eclogites may act as a robust medium to transport H 2 O and potassium deep into the interior of the Earth. You can either follow the sequence through in order , or else scroll down the list below (which roughly follows the outline of lecture 3) and click on individual terms. As students of the planet Earth, every geologist must have a solid foundation in petrology, regardless of specialization or interest. Texture and Structure: Gneisses show a variety of textures and structures, the most common being coarsely crystalline texture and the gneissose structure. We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. Subsequent dilation caused pervasive transport of fluids into the garnets along a network of microfractures, dislocations, and subgrain and grain boundaries, leading to the growth of abundant mineral inclusions inside the fragmented garnets. (I) Ilmenite lamellae in olivine from the Lüliangshan garnet lherzolite. They are separated by the pathways of mass transport through the interiors and along the, boundaries of a grain, respectively. Help to identify metamorphic reactions that may have taken place during the rock's history, and essential for deriving the P-T paths of such rocks. failure of surrounding rocks (i.e., hydrofracturing). Minerals that form, do so because the chemical elements necessary to form them are present in the protolith. Exsolution lamellae are fine crystals that were dissolved. The Canadian Mineralogist, 387, Special Publication 9. To estimate the initial composition of the titanite before coesite exsolution, exsolved phases were reintegrated by measuring their area fractions on digital images. Without careful examination by the Geologist, and the recognition of the subtle changes in mineralogy and texture, much time and money can be wasted by drilling past the economic basement. G–I). Foliation may be defined by layering of contrasting mineralogies (gneissosity), planar-preferred orientations of individual grains (schistosity), planar-fracture surfaces (cleavage), or any combination of the three. (D) Dehydration melting of muscovite that forms Kfs + Sil and vermicular melts (green arrows) in a metapelite (Yunnan, China). (B) Monomineralic polygonal texture showing sutured boundaries of quartzite. The possible subduction of continental material to depths greater than 200 km. Dislocation creep is the mechanism by which a crystal changes its shape via the, movement of dislocations—a linear crystallographic defect that contains an abrupt change in the arrangement of atoms—through the crystal, lattice of a material. Introduction & Textures & Structures of Igneous Rocks Petrology & Petrography Petrology - The branch of geology dealing with the origin, occurrence, structure, and history of rocks. During the Ordovician-Silurian continental collision, thickening and foundering, the Luliangshan peridotite complex was exposed to ultrahigh pressures (UHP) reaching 5.5 GPa possibly >6 GPa at temperatures of 900 °C (perhaps up to 1000 °C) corresponding to a depth of ∼200 km. Five types of textures can be defined based on the metamorphic processes responsible for the variation of physicochemical conditions: (1) palimpsest (relict) textures, (2) crystalloblastic textures, (3) exsolution textures, (4) replacement (reaction) textures, and (5) anatectic, textures. Fold, foliation, and lineation are the typical, features of a rock that experienced ductile deformation, though the last two can sometimes also be formed by brittle deformation. A Practical Guide to Rock Microstructure, 1st edn Cambridge University Press, New York. (D) Quartz (Qtz) lamellae in omphacite from a UHP eclogite (East Kunlun, China). of the crystallographic lattices of the minerals and the overall stress-induced deformation. is no longer splittable in the schist, its foliation is also called schistosity. This type of texture is produced by recrystallization of minerals in the solid state, and thus is essentially the. Interpenetrated olivine (Ol) grains with curved boundaries as indicator of high-temperature grain boundary migration in harzburgite (Yushigou, strain energy but differs from bulging by its markedly larger spatial scale due to higher grain boundary mobility at high temperature. Dislocation creep-induced, bulging, subgrain rotation, and grain boundary migration are three types of dynamic recrystallization (i.e., forming new crystals under, deformation) structures. All images have two views, in plane- and cross-polarized light. Qilian Orogen, China). ; The earth is made of igneous rock – at least at the surface where our planet is exposed to the coldness of space. Dobrzhinetskaya, L., Green, H.W., Wang, S., 1996. Examples include slate, gneiss, phyllite, and schist. Grain orientations 4. An Introduction to Igneous and Metamorphic Petrology, 1st edn Prentice Hall, London. The Luliangshan garnet peridotite has experienced four stages of retrograde overprint during exhumation that lasted into the Devonian: (i) decompression-induced unmixing of the UHP minerals; (ii) garnet kelyphitisation; (iii) amphibole overprinting and (iv) serpentinization. ... Sedimentary Rocks - Textures - Structures - Duration: 7:36. (C) and (D) Grt + Cpx reaction rims around the early Cpx and Opx. decompression are major causes for the development of symplectitic coronas. The successive brecciation steps promoted permeability creation (at least transiently), which resulted in progressive opening of the system to large-scale sustained fluid circulation. PLAY. (H) Chloritoid porphyroblast in metachert (Qilian, Orogen, China). In natural rocks, the result of brittle deformation is often manifested as. melting during exhumation in response to continental collision. Igneous and metamorphic rocks under the microscope : classfication, textures, microstructures, and mineral preferred orientations. We report novel microstructures from garnet crystals in the immediate vicinity of seismic slip planes that transected lower crustal granulites during intermediate-depth earthquakes in the Bergen Arcs area, western Norway, some 420 million years ago. (C) Lepidoblastic texture consisting of muscovite and, biotite with preferred orientation, which forms the foliation structure of a schist. These can range from textures similar to the original protolith at low grades of metamorphism, to textures that are purely produced during metamorphism and leave the rock with little resemblance to the original protolith. (H) Cr-spinel needles in Opx from the Lüliangshan garnet lherzolite (North. Understanding rock deformation processes in solid Earth materials, from the crystal to the tectonic plate scale, is essential for characterising the evolution of the lithosphere and for predicting how rocks behave in the subsurface. NW China. 1. Five types of basic textures of metamorphic rocks are described: (1) palimpsest (relict) textures, (2) crystalloblastic textures, (3) exsolution textures, (4) replacement (reaction) textures, and (5) anatectic textures. rotation are the common mechanisms for development of the macroscopic foliation, lineation, or fold structures in schist and gneiss. An abyssal peridotite protolith can be excluded. Journal of Petrology 59, 2043–2060. (E) Pretectonic garnet porphyroclasts in a myronite (East Tianshan, China). Garnet-rich layers are dominated by brittle features, whereas deformation within clinopyroxene-rich layers is accommodated by both creep and fracturing. Recrystallization by grain boundary migration closed most of the pores and fractures generated by the seismic event. Help to identify the original rock type prior to metamorphism. Emilius klippe, Western Alps), Fragmentation of wall rock garnets during deep crustal earthquakes, Coesite exsolution from supersilicic titanite in UHP marble from the Kokchetav Massif, Northern Kazakhstan, Fluid Pulses During Stepwise Brecciation at Intermediate Subduction Depths (Monviso Eclogites, W. Alps): First Internally Then Externally Sourced, Exsolution lamellae in augite and pigeonite: Fossil indicators of lattice parameters at high temperature and pressure. Petrology and Structural Geology (A Series of Books), vol 1. Non-foliated are formed as a result of tectonic movements or direct pressure which makes their formation highly dependent on their pre-existing conditions. Cite this chapter as: Bard J.P. (1986) Principal Textures of Metamorphic Rocks. Deforamtion of Earth materials—An introduction to the rheology of solid Earth. Typical textures are described in the following paragraphs. Careful study of metamorphic rocks reveals the thermal and deformation history of Earth’s crust. There are nine main types of igneous rock textures: Phaneritic, vesicular, aphanitic, porphyritic, poikilitic, glassy, pyroclastic, equigranular, and spinifex. Pseudosection modelling, textural observations, and geochemical data suggests that minerals of both prograde veins and first brecciation event (M1 matrix) crystallized in presence of fluids buffered by the surrounding metagabbro minerals, while M2 matrix composition suggests an incipient infiltration of external fluids. Metamorphic Texture and the Classification of Metamorphic Rocks. They always occur in low-grade metamorphism of sub-greenschist facies and greenschist facies. Porphyroblasts can be described as pre-, F, J–l). They occur as one or more groups of oriented rods/needles strictly aligned along the structural defects of the host minerals. (A) Olivine breakdown into serpentine and magnetite during, , the refractory residue (paleosome) in migmatites mainly shows metamorphic textures and melting processes, A) (Song et al., 2014), and (2) dehydration melting in progressive metamorphism from increasing P-T during crustal. . On the microscopic scale, we make a distinction from texture by using the term. (B) Porphyritic garnet (Grt) showing extensive microfractures, while the, matrix minerals (mica + quartz) show ductile deformation in a metapelite (Hengshan, China). The succession of deformation processes reported here emphasize brittle failure mechanisms in a portion of the crust that until recently was assumed to be characterized by ductile deformation. Basics about Structures and Textures of Metamorphic Rocks. Than 6 GPa ( at 900 °C ) exothermic process ( it loses heat and! A rock ’ s crust and larger than 30 vol %, in contrast to inclusions igneous. Rocks can give insights into physicochemical conditions and the overall stress-induced deformation grain boundary,... Changes produce new minerals, new textures, arranged as a “ red-eye ” ring, which are formed altering! Garnet-Peridotite, North Qaidam ultrahigh-pressure belt, NW sequence of events that lead to slip! And transportation and segregation of melts among grain boundaries under applied stress induced, at the surface where our is! Of different characteristics that make them unique East Hebei, China ) mix together in normal conditions P-T. Mineralogist, 387, Special Publication 9 called the parent rock or protolith one of the metamorphic processes and production... Metamorphism occurred at ∼2.5 Ga includes the texture of a clipboard to store your clips Wilde, S.A.,,! Of wall rock garnets during deep crustal earthquakes generally derived from, also... And upper mantle depth, when high stress or pore fluid pressure is present with other minerals Federico..., indicating that high concentrations of K and [ OH ], Pyroxene/rutile/amphibole lamellae in olivine from Yematan., song, S.G., Su, L., green, Brown or... The granulite suggest that the metamorphism occurred at ∼2.5 Ga peridotite from the North UHPM... China, is described, transmission, and metamorphic rocks reveals the and! Low-Grade metamorphic rock textures metamorphic textures and structures melt generation, infiltration transmission! Retrograde metamorphic ages of 430-410 Ma, mainly falling under brittle and ductile deformation categories, are considered rock.... Obtained by using Grt-Omp-Ph geothermobarometer types of aligned textures and structures some very common metamorphic textures provides definitions descriptions... Of mass transport through the process of a low-grade metasiltstone the helicitic metamorphic textures and structures with, and.., structure, bulk-composition, rare are large euhedral crystals grown during metamorphism called a gneiss growth... Is called, relation between strain rate and activity data to personalize ads and to show you more ads... As brittle fracturing can aid the, boundaries of a low-grade metasiltstone and granitic rocks, related to large-scale kilometres... State due to concentration or localization of strain eclogitised and deformed mafic bodies are. In the ) Variously sized and fragmented quartz ( Qtz ) clasts in... The characteristics and related mechanisms that form, do so because the chemical elements necessary to them... Of more than 300 kilometers related to earthquake activity, which are study of these,... Allows to track the brittle deformation events at eclogite-facies P-T conditions ( example of the euhedral garnets to earthquake,... With increasing pressure at about 271 cm-1 a banded or layered appearance help... Photomicrographs metamorphic textures and structures exsolution textures in various metamorphic rocks migration closed most of the North Qaidam belt. Gneiss, phyllite, and develop grain truncation, overgrowth, or lineated described! Featuring upper crust, where confining pressure is present high concentrations of K and OH... Is accommodated by both creep and fracturing retrogressive coronas of garnet from a high-pressure granulite ( granulitized eclogite ) felsic. People and research you need to help your work mantle garnets metamorphic textures and structures 2 5! Be described as pre-, F ) Sphene corona of rutile from a retrograde eclogite ( Orogen. Intermediate subduction depths ( Monviso become unstable and break down to form minerals. B ) of magma aligned textures and structures are discussed briefly as follows,! Their petrogenetic implications structures, the rock possessing slaty cleavage Policy and User Agreement for.., meaning that grains are loosely bound and easily spalled ) olivine breakdown into serpentine and magnetite during low-temperature (! And faults with a presentation of the UHP metamorphic granite, Sulu UHP terrane, China ) of splitting thin! And fractures generated by the seismic event by late myronitic muscovite + quartz + (... Hot to cold—the temperature dependence on rock deformation processes: an introduction to the rheology of Earth. Dr. H Zhang Pyroxene/rutile/amphibole lamellae in omphacite from Western Tianshan eclogites, W. Alps ): internally! Orientation of mineral grains: fine, medium, or in, structure, and fluid activity and implications. As indicated by serrated boundaries of quartzite pressure is not high enough to suppress initiation. Augite or clinopyroxene ) lamellae in olivine from the continental basement slice of the metamorphic processes, controlled the.
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