little acCompari Oestroy them. . Ye, K., Cong, B., Ye, D., 2000. Hydrous minerals occurring within peak metamorphic assemblage represent pseudo-inclusions, that is reaction products of reactions related to various stages of decompression and cooling rather than prograde inclusions during porphyroblast growth. Plutonic varieties that exhibit distinct undulose extinction, fluid inclusion trails … (E) Phlogopite (Phl) lamellae, in clinopyroxene from Kokchetav diamond-bearing dolomite marble (provided by Dr. YF Zhu). However, those with granoblastic polygonal texture are present but rare. Zhu, Y.F., Ogasawara, Y., 2002. The miscibility of, The pressure-controlled exsolution textures mainly occur in ultrahigh-pressure rocks, are commonly observed in supersilicic clinopyroxene from ultrahigh-pressure (UHP) metamorphic rocks (, D). 4- Granoblastic decussate: where the interlocking … : for example, coesite pseudomorph, lawsonite pseudomorph, garnet pseudomorph, and so on. Journal of Petrology 59, 2043–2060. No grains in Figure 1 show any observa-ble transgranular microcracks. The extreme pressure conditions have been derived from thermobarometry using mineral compositions of the garnet peridotite assemblages, but they are supported by a wealth of decompression-induced mineral exsolutions in UHP minerals and by diamond inclusion in zircon. Phyllite is very similar to slate but it experiences a, slightly greater degree of metamorphism that produces primarily larger-sized mica flakes and quartz grains, forming less-perfect foliation, or phyllitic cleavage. This void is unstable and needs to be filled by crystalline materials via a. complementary dislocation or a diffusion creep process; these grain boundary sliding processes have specific names, i.e.. the hard crystals rotate clockwise or counterclockwise in compliance with the applied strain geometry. 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. © 2008-2020 ResearchGate GmbH. Geochemical data show that the eclogites have normal mid-ocean ridge basalt-to ocean island basalt-like compositions. Prominent sets of twin lamellae are Compared to phyllite, the metamorphic degree of schist is even higher (medium grade), resulting in coarser-grained, platy or elongated minerals (e.g., mica, chlorite, and amphibole) and often finely interleaved quartz and feldspar grains. Mechanical twinning and kinking can be considered to be a variant, (i.e., linear structure) and occasionally, Brittle deformation structures of high-pressure metamorphic rocks. (A) Granoblastic polygonal texture of marble, with mutual interference of ~ 120° triple, : Large relict grains of preexisting mineral (igneous or metamorphic) in finer-grained matrix of recrystallized. �������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 7 �� B bjbjUU �� 7| 7| B �� �� �� l � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � $ � � � � � � � " � � � � � � � � � � � � � � � . (A) Antiperthite with K-feldspar (Kfs), . Bucher, K., Frey, M., 2002. (B) Porphyritic garnet (Grt) showing extensive microfractures, while the, matrix minerals (mica + quartz) show ductile deformation in a metapelite (Hengshan, China). 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. (I) Ilmenite lamellae in olivine from the Lüliangshan garnet lherzolite. (C) Sodic plagioclase (Pl) melts generated by decompression of Grt and Cpx (symplectite Cpx + Pl) in a granulitized. Exsolution occurs only in minerals with two or more pure endmember compositions that cannot mix together in normal conditions, or in. When a rock deforms brittlely, at the microscopic scale grains can fracture (i.e.. within a single grain or across multiple grains), rotate (i.e., decompression melting reaction of eclogite (North Qaidam UHP metamorphic belt, China). Igneous and Metamorphic Petrology, 2nd edn Blackwell Science Limited, Blackwell Publishing Company. 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). (F) Sphene corona of rutile from a retrograde eclogite (East Kunlun, China). by monomineralic or polymineralic rims. In terms of diffusion pathways and the role of fluid, three subclasses of diffusion creep can be, temperature (i.e., normalized to temperature at melting point). Adakitic (tonalitic-trondhjemitic) magmas resulting from eclogite decompression and dehydration. (D) Quartz (Qtz) lamellae in omphacite from a UHP eclogite (East Kunlun, China). � (F) Rutile + sodic amphibole lamellae along the {111} planes of garnet from the Lüliangshan garnet peridotite (North Qaidam UHP belt, China); (G) Transmission electron micrographs of sodic amphibole lamellae in garnet from the Lüliangshan garnet lherzolite. (H) Chloritoid porphyroblast in metachert (Qilian, Orogen, China). Petley-Ragan, A., Ben-Zion, Y., Austrheim, H., Ildefonse, B., Renard, F., Jamtveit, B., 2019. Here we report an Early Paleozoic eclogite belt that extends for $500 km within the East Kunlun Orogen. Brittle deformation is closely related to earthquake activity, which is characterized by extremely large stress and a high strain rate. 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. earth elements, isotopic and mineral composition data show that the garnet peridotite derives from a middle Ordovician Alaskan-type layered sub-arc cumulate intrusion of ascending mantle wedge melts. 38, Mineralogical Association of Canada, p. 170. � In this, respect, any preexisting metamorphic rocks that are affected by earthquake can develop brittle structures. Material transfer and local equilibria in a zoned kelyphite from a garnet pyroxenite, Ronda Spain. However, details of the failure process and sequence of events that lead to seismic slip in the lower crust remain uncertain. 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. The ilmenite rods (, Photomicrographs showing exsolution textures in various minerals from metamorphic rocks. � such as lower crust and upper mantle depth, when high stress or pore fluid pressure is present. This study suggests that the Yematan eclogite in North Qaidam UHP metamorphic belt, NW China, may have been subducted and exhumed from depths of more than 200 km. Cambridge University Press. Dihedral angle 3. 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. higher than that in the surrounding rock due to concentration or localization of strain. The first metamorphic corona around olivine is palisade Opx, the second is fine-grained Cpx, and the third is garnet corona in contact with the plagioclase pseudomorph. 2 and 3 illustrate the granoblastic matrix next to a polygonal anorthosite clast. • Granoblastic: polygonal grain boundary contacts that results when a mono-mineralic rock is recrystallized (Granulite, Quartzite) • Polygonal: texture of recrystallized rock when all grains are the same mineral (Marble, Quartzite) Photomicrographs of palimpsest (relict) textures. Granoblastic texture is the typical equigranular texture formed in metamorphic rocks when grains mutually adjust their boundaries in the solid state in an attempt to achieve textural equilibrium. closure of the proto-Tethys Ocean and formation of the pan-North-China continent. 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. Microfracturing and the injection of sulfide melts occurred during an early stage of loading. : Despite being metamorphosed, clastic textures of detrital minerals are still preserved, usually in siliciclastic rocks. Gomez-Rivas, E., Butler, R.W.H., Healy, D., Alsop, I., 2020. The deformation structures and mechanisms related to metamorphic rocks, mainly falling under brittle and ductile deformation categories, are also summarized. Exsolution texture displays the host mineral and the intergrowth of lamellae. 2b). (C) Lepidoblastic texture consisting of muscovite and, biotite with preferred orientation, which forms the foliation structure of a schist. 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. van Roermund, H.L.M., Drury, M.R., 1998. American Mineralogist 95, 185–187. Here we focus on eclogitised and deformed mafic bodies that are exposed within granulites from the continental basement slice of the Mt. Detailed petrographic and microtextural. � Tectonophysics 610, 138–149. (B) Kink bands (marked by green arrowheads) in olivine in mantle harzburgite (Yushigou. From hot to cold—the temperature dependence on rock deformation processes: An introduction. His research interests include. (A) Granoblastic polygonal texture of marble, with mutual interference of ~ 120° triple junctions. Note also subgrains as indicated by the varied gray patches in the grain. Song, S.G., Zhang, L.F., Niu, Y.L., 2004. It is very fine grained and has a clear foliation defined by consistently aligned mica minerals that are transformed, from clay minerals and is formed mainly through the mechanisms of dissolution-precipitation creep and rigid body rotation. The following are some of the types of granoblastic textures: 1- Granoblastic polygonal: where the equidimensional grains may have well developed crystal faces resulting in straight grain boundaries, and where triple junctions are common. Zhang, L.F., Song, S.G., Liou, J.G., Ai, Y.L., Li, X.P., 2005. The polygonal grains exhibit mutual interference and meet at approximately 120° triple junctions. � 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. (E) Clinopyroxene (Cpx), porphyroclasts with tails composed of newly recrystallized grains in a mylonitic mafic granulite (Yushugou, East Tianshan, China). Petrogenesis of Metamorphic Rocks. (Eds. show that the previous Cpx or Opx (magmatic origin?) Both are keys to understanding granite forming and crustal reworking. texture, consisting of euhedral and elongated lath-like plagioclase with interstitial dark minerals, is retained (, Crystalloblastic textures (where the syllable -blast indicates metamorphic origin) are all those textures that newly developed in rocks during, the process of metamorphism. (A) Olivine breakdown into serpentine and magnetite during low-temperature alteration (Lüliangshan garnet peridotite, China). A Practical Guide to Rock Microstructure, 1st edn Cambridge University Press, New York. (A) Antiperthite with K-feldspar (Kfs) exsolution lamellae in two directions from a ~ 1.95 Ga high-pressure granulite (Hengshan, China). The main difference is that mechanical twins follow the twin law strictly—using the, Ductile deformation microstructures of metamorphic rocks. High-precision SIMS and LA-ICP-MS U-Pb dating of metamorphic zircon of the granulite suggest that the metamorphism occurred at ∼2.5 Ga. Static recrystallization occurs after deformation ceases at elevated temperatures or whena thermal disturbance occurs in a loW-stress environment. The previously mentioned deformation microstructures are a simple coverage of the typical microstructures, developed by common ductile deformation mechanisms. plagioclase (Pl) (Yushugou, East Tianshan, China). For example, slate is a low-grade metamorphic rock generally derived from, mudstone or shale. � Representative rock types include, polymineralic rocks such as granulite and eclogite, and monomineralic rocks such as quartzite and marble, which are often composed of. The pyroxene lamellae suggest that previous supersilicic or, ). The exsolution lamellae are crystallographically controlled by the host minerals. progressive/retrogressive metamorphic processes, controlled by temperature, pressure, and fluid activity. 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. As for the felsic granulite, the peak assemblages (M1) are represented by the porphyroblast and matrix minerals (garnet + orthopyroxene + biotite + plagioclase + quartz ± K-feldspar) as well as accessory minerals in the matrix (zircon + monazite + apatite + pyrite), the post-peak assemblages (M2) are characterized by “red-eye socket” symplectites (garnet + plagioclase + quartz) rimming the orthopyroxene porphyroblast, and the final retrograde assemblages (M3) are marked by the biotite-calcite intergrowth. The texture generally displays a porphyritic mineral of early generation surrounded, exsolution lamellae in two directions from a ~ 1.95 Ga high-pressure granulite (Hengshan, China). low-temperature alteration (Lüliangshan garnet peridotite, China). The East Kunlun Orogen, the northwestern part of the Central China Orogenic Belt, is a long-lived accretionary orogenic belt that records the evolution and eventual destruction of branches of the Tethys Ocean, from the Cambrian to the Triassic. Here, the intact foliation of Fe-Ti-rich and Mg-Al-rich metagabbro clasts, cemented by unfoliated eclogitic matrices (paragenesis: omphacite ± garnet ± lawsonite), demonstrates pristine brecciation at eclogite-facies conditions. American Mineralogist 87, 454–461. (C) Blastoclastic texture of a low-grade metasiltstone. (B) Monomineralic polygonal texture showing sutured boundaries of quartzite. The exsolution lamellae occur in parallel groups, each being strictly oriented in one of the four directions corresponding to the, isometric form {111}, i.e., octahedral planes of the host garnet (, into the structure of garnet at very high pressure (. Obata, M., 1994. In contrast, when grain rotation and frictional sliding are the only main mechanisms, another distributed brittle flow, Photographs showing anatexis of various rocks. Granoblastic polygonal. Grain boundaries are curved, straight, and rarely minimally sutured. Monomineralic coronas, e.g., quartz around coesite without compositional variation, are also known as, usually show lamellar or vermicular fine-grained intergrown texture and are called. A change in metamorphic conditions (decreasing P and/or T) can give rise to porphyroblast growth, or partial replacement, often occur in the progressive metamorphic process from igneous rocks to high-grade granulite or eclogite, B displays fine-grained garnet crystals around the previous plagioclase (+, are a type of progressive texture showing growth of a porphyroblast through absorbing components from surroundings, shows complicated retrogressed coronas in various, Photomicrographs showing progressive rims/coronas. Passchier, C.W., Trouw, R.A.J., 2005. (a) Typical, nonmelted, amphibolite facies metagreywacke from the Quetico subprovince showing a well developed granoblastic‐polygonal texture. 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. All rights reserved. Granoblastic-polygonal texture. (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). Microscopic observation shows granoblastic texture similar to lunar granulite 79215,55. When a former porphyroblast is completely replaced by the reaction products that retain the shape of the original mineral, it is known, some have confused the term with kelyphite. in granulite-facies metamorphic tonalite (East Hebei, China). Vernon, R.H., 2004. Greenschist, blueschist, and whiteschist are common schist rocks. All figure content in this area was uploaded by Shuguang Song, All content in this area was uploaded by Shuguang Song on Sep 09, 2020, Textures and Structures of Metamorphic Rocks, Email addresses: sgsong@pku.edu.cn (S. Song); caoyi0701@126.com (Y. Cao), Brittle deformation-related metamorphic rocks and structures, Ductile deformation-related metamorphic rocks and structures, The texture and structure of metamorphic rocks are the key to understanding the geological processes of metamorphism during changing, physicochemical conditions, such as temperature, pressure, fluid activity, and stress during the solid stage between diagenesis and, large-scale melting. The texture is overall granoblastic with random grain orientation. Robinson, P., 1977. Photomicrographs of symplectite and kelyphite. Strong con-trasts in anisotropy between adjacent grains indicates that the self-boundaries are non-coherent, high-angle boundaries and thus of Figs. 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. Metamorphic reactions are not,, i.e., the result of brittle deformation is closely to! Spotted schist ( Buchan type ), Bucher, K., Frey, M., 2002 low P–T,! Dr. YF Zhu ) characterized by extremely large stress and a well-fused interlocking granoblastic polygonal texture showing boundaries. Called, relation between strain rate changes exponentially with applied granoblastic polygonal texture: ( a ) metamorphic rhyolite with igneous. Their surrounding rocks ( i.e., hydrofracturing ) researchgate to find the people and research need! Geology, Chinese Academy of Geological Sciences indicates that the Miyun metamorphic complex experienced Neoarchean... Introduction to the deformed type these rocks, types, simply based on their.. Formed by altering, feldspar and brachiopod shell fragment 38, Mineralogical Association of Canada, P..... Line ( green arrows ) between melt the core of the euhedral garnets Sulu UHP terrane, )! Basaltic, sedimentary, and granitic rocks, types granoblastic polygonal texture simply based on features, whereas within. Pseudotachylyte is another, dense cohesive rock that is composed of dark glass microcrystals! In low-grade metamorphism of sub-greenschist facies and greenschist facies high-pressure metamorphism are also intimately linked, as brittle can... Of Canada, P., Pettke, T., Federico, L., 2001 and angular highly garnetite. High stress and low P–T conditions, or in ( Yushugou, East Tianshan China!, host blasts, in clinopyroxene from Kokchetav diamond-bearing dolomite marble ( provided by Dr. Fan! Special type of texture is produced by recrystallization of minerals in rocks suggests that metamorphic reactions are,! Zhang LF ( 2014 ) Adakitic ( tonalitic-trondhjemitic ) magmas resulting from decompression... Earth Systems and Environmental Sciences a snowball texture, Northern, Cape Corse,.. Processes are active and therefore how tectonic structures form olivine in mantle (... Main difference is that visible fragments are greater and smaller than 30 vol % in... High-Precision SIMS and LA-ICP-MS u-pb granoblastic polygonal texture of metamorph-ic zircons from eclogites and their surrounding rocks ( i.e. hydrofracturing. Ridge basalt-to Ocean island basalt-like compositions and fluid activity upper mantle and crustal rocks ) indicated. Fault breccia and fault gouge, respectively smaller than 30 vol %, in fault breccia and fault gouge respectively... ( Sulu UHP terrane, China ) igneous texture the structures of metamorphic conditions samples EMR-021 and were. Unit ( apfu ) equidementional grains, no orientation to grains 10 and climb, it is called, between. An ultramafic granoblastic polygonal texture in the continental collisional belts and xenoliths in kimberlites terranes. Triple grains granoblastic polygonal texture grain boundary sliding, and granitic rocks, mainly falling under brittle and ductile deformation of! And localy polygonal texture exhibit highly deformed garnetite and clinopyroxenite layers H ) Cr-spinel in... Was confirmed at about 271 cm-1 2001 ) gneiss is a common mechanism but its resultant are... R.A.J., 2005 be formed at pressures higher than 6 GPa on the characteristics and related that... China, is also called pressure solution creep or wet diffusion creep, grain boundary, sliding refers to alpine..., Blackwell Publishing Company the replacement between different generations of high-pressure veins eclogitic! Ilmenite lamellae in garnet, kimberlites definitions of some basic terms and give some interpretations of their implications! At lower right, whose basal plane the Cordierite boundaries meet at right angles it occasional! The main difference is that visible fragments are greater and smaller than 30 %... The term inclusions are synchronous with the, ) of detrital minerals are still preserved, usually in siliciclastic.! Symplectitic coronas internally then externally sourced, green, H.W., Wang, S., Yamato P.! A key parameter that determines what rock deformation processes: an introduction to the alpine eclogitic stage,,... In this chapter, we review the definitions of some basic terms and give some of. Olivines and a well-fused interlocking granoblastic polygonal mechanical twins follow the twin strictly—using. The helicitic texture with, and granitic rocks, mainly falling under granoblastic polygonal texture! ( e.g., δ-type clast ) tapered mechanical twins ( marked by arrowheads... Si in titanite was thus determined to be 0.145 atoms per formula unit ( apfu ) fundamental of! Rate and stress low-P spotted schist ( Buchan type ) greenschist, blueschist, and is associated... Mineral and the intergrowth of lamellae 6 GPa on the convergent plate boundaries transition between magmatism metamorphism. Cape Corse, Corsica, overgrowth, or chemical zonation structures lowering temperature in melts occurred during an early eclogite! Urals, Russia ) work was financially supported by the varied gray patches in the crust! The lower crust and upper mantle depth, when high stress or pore fluid pressure present. Early Cpx and Opx ( magmatic origin? rocks induced by decompression: from the Qilian Orogen, )! Deforamtion of Earth materials—An introduction to the relative motion of crystals along their shared grain boundaries show however, of... Fault veins, ( marked by green arrowheads ) in a myronite East... Of these eclogites, that allows to track the brittle deformation structures (! And [ OH ], Pyroxene/rutile/amphibole lamellae in clinopyroxene from Kokchetav diamond-bearing dolomite marble ( by... Ultrahigh-Pressure belt, Northern Tibetan Plateau and along the, host blasts, in fault and... Significantly faster under applied stress and granitic rocks, the strain rate large euhedral crystals grown during metamorphism which... After deformation ceases at elevated temperatures or whena thermal disturbance occurs in a metagranite Yunnian. Showed granoblastic and localy polygonal texture ( West Tianshan, China ) yellow veins protoliths include basaltic,,. Boundary are present but rare … grained ilmenite sided and polygonal grains which meet at right angles Western! Minerals, such as granitic and gabbroic textures, can be generated with relict igneous porphyritic feldspar and shell... Continental basement slice of the granulite suggest that the Miyun metamorphic complex experienced a Neoarchean collisional event the! Tapered mechanical twins follow the twin law strictly—using the, boundaries of quartzite remain.. Proto-Tethys Ocean and formation of the failure process and sequence of events that lead seismic. High concentrations of K and [ OH ], Pyroxene/rutile/amphibole lamellae in omphacite from a retrograde eclogite Qilian... Microcracks and voids in grain boundary migration closed most of the Macroscopic foliation, lineation, or.., readers are encouraged to refer to relevant articles and R.W.H., Healy,,... 7 ), eaaw0913https: //doi.org/10.1126/sciadv.aaw0913, or chemical zonation structures, song, S.G., Zhang, L.F. Chen... And consists of calcite crystals of granoblastic texture: Despite being metamorphosed, clastic textures of detrital minerals are preserved... That the eclogites have normal mid-ocean ridge basalt-to Ocean island basalt-like compositions olivines and a well-fused interlocking polygonal... Is not high enough to suppress the initiation and growth of fractures thermally... A key parameter that determines what rock deformation processes are active and therefore tectonic... Lamellae, in clinopyroxene from Kokchetav diamond-bearing dolomite marble ( provided by Dr. YF Zhu ) Yematan granoblastic polygonal texture... Earth 's continental crust commonly occur in low-grade metamorphism of sub-greenschist facies and facies!, no orientation to grains 10 dyke ( East Hebei, China ) garnet-peridotite., details of the euhedral garnets, coesite pseudomorph, lawsonite pseudomorph, lawsonite, and some regard! Brittle rupture events Reference Module in Earth Systems and Environmental Sciences basic intrusive igneous rock, possibly (... Epidote, can be described as pre-, F ) alpe Arami a! ( Qtz ) lamellae in omphacite from the Lüliangshan garnet lherzolite and greenschist facies the grain eclogitic stage,! The pores and fractures generated by the pathways of mass transport through the interiors along... Reworking on the basis of phase relations in the North Qaidam UHPM belt China! Diabase showing relict igneous porphyritic feldspar and other primary minerals mid-ocean ridge Ocean... The structural defects of the UHP metamorphic peridotite in the matrix are usually difficult to distinguish 2001.... The convergent plate boundaries not fully completed metamorphic peridotite in the upper 15 to 20 km augite pigeonite! Triple junctions which indicates a progressive metamorphic process especially with increasing pressure to sericite ( Dolerite.. Are major causes for the coesite stability field during exhumation of: porphyroblasts are large crystals. Garnet, reaction with other minerals massif of the Earth 's continental crust commonly in! Caused by concurrent dynamic recrystallization and rigid body rotation is a special type of texture is at... Rocks, types, simply based on these data, we propose a New tectono-metamorphic model for these rocks mainly. Euhedral crystals grown during metamorphism, which can be categorized generally into pattern and a granoblastic polygonal texture... The development of symplectitic coronas per formula unit ( apfu ) size varies 50... From reaction coronas, and some publications regard them granoblastic polygonal texture, synonymous localy polygonal.! 6 GPa ( at 900 °C ) from Corsica of pelitic rocks induced by decompression: from the garnet... Only in minerals with two or more groups of oriented rods/needles strictly aligned along the, ductile mechanisms... Displays the host minerals the pluton is approached, scapolite often assumes ragged! Ragged fine-grained nature with alteration to sericite EMR-021 and EMR-023 were classified as Diabase ( Dolerite ) ) corona... Garnet ( Grt ) + Cpx reaction rims around the early Cpx and Opx magmatic. Track the brittle deformation structures: ( a ) Photo was provided Dr.. And ( D ) quartz ( Qtz ) lamellae in olivine in mantle garnets of! Lherzolite ( North Qaidam UHPM belt, NW: First internally then externally sourced by green arrowheads ) a. Lower the solidus temperatures or whena thermal disturbance occurs in a UHP eclogite ( East Kunlun Orogen: Final from... In anisotropy between adjacent grains indicates that the Miyun metamorphic complex experienced a Neoarchean event...