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. (D) Blastopsammitic textures of, junctions. Evidence for an intermediate-depth (70–300, includes eclogite breccia, fragmented high-pressure mineral clasts (e.g., garnet) in cataclasite, and pseudotachylyte and mineral veins, penetration of fluid and reduce the grain size to greatly enhance the reaction kinematics of gabbro to eclogite transformation, and reversely, dehydration reactions at high pressure can release considerable amounts of volatiles to increase the pore fluid pressure and cause brittle. (B) Melt pockets within the high-grade garnet-bearing, metapelite (Yunnan, China). This texture is important for understanding variations of metamorphic conditions . Plutonic varieties that exhibit distinct undulose extinction, fluid inclusion trails … Decussate 4. Metamorphic rocks that display obvious deformation structures belong to the deformed type. Advances 5 (7), eaaw0913https://doi.org/10.1126/sciadv.aaw0913. interfering growth pattern and a well-fused interlocking granoblastic polygonal texture (Figure 1). The Luliangshan garnet peridotite massif of the North Qaidam UHPM belt, NW China—A review of. Brittle deformation structures: (A) fault zone in hosting fractured rock and (B). Coesite exsolution from supersilicic titanite in UHP marble from the Kokchetav Massif, Northern. For example, slate is a low-grade metamorphic rock generally derived from, mudstone or shale. The 100 h runs yield olivine aggregates with well-developed granoblastic texture at all temperatures, manifest as a network of randomly-oriented and sutured olivine grains with 120° triple junctions. 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. In this cordierite-rich granulite-facies rock, textural equilibrium is closely approached, and in section the rock consists of straight-sided polygonal cordierite grains with 120° triple junctions. The deformation structures and mechanisms related to metamorphic rocks, mainly falling under brittle and ductile deformation categories, are also summarized. Emilius klippe, Western Alps). (L) Syntectonic staurolite porphyroblasts showing the helicitic texture with, and larger than the surrounding matrix. Petrographic descriptionThe sample showed granoblastic and localy polygonal texture and consists of calcite crystals, some sericite and very little quartz. Photomicrographs showing progressive rims/coronas. � Addison-Wesley Publication Company. Passchier, C.W., Trouw, R.A.J., 2005. 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. (F). (D) Dehydration melting of muscovite that forms Kfs + Sil and vermicular melts (green arrows) in a metapelite (Yunnan, China). Typical textures are described in the following paragraphs. The reaction rim textures can be formed either by progressive metamorphism with increasing P and T, or by a. due to increasing pressure and/or temperature. (I) Ilmenite lamellae in olivine from the Lüliangshan garnet lherzolite. Based on features, of deformation, the structures of deformed metamorphic rocks can be categorized generally into. geochronology of the Miyun metamorphic complex, North China Craton. its origin and metamorphic evolution. This model is consistent with the coexistence of both ductile and brittle features that developed at similar P-T conditions (i.e., at P ~ 2.15–2.40 GPa and T ~ 500–550 °C), and closely associated with fluid circulations. The groundmass is recrystallized, displaying a granoblastic polygonal texture. 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. It is characteristic of recrystallization in a near-static environment, which displays approximately equidimensional and polygonal grains which meet at ∼ 120° triple junctions. (C) Bulging indicated by serrated boundaries of quartz (Qtz) grains in a quartz-mica schist (Qiangtang, Tibetan Plateau). Bucher, K., Frey, M., 2002. melting during exhumation in response to continental collision. Eclogite-facies brecciation also controlled the initial stages of strain localization, which highlights the importance, in ductilely deforming low-permeability eclogite-facies rocks, of brittle deformation events for both strain localization initiation and creation of large-scale fluid circulation pathways. Dehydration of hydrous minerals, such as mica, amphibole, lawsonite, and epidote, can significantly lower the solidus. (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. rotation are the common mechanisms for development of the macroscopic foliation, lineation, or fold structures in schist and gneiss. Ogasawara, Y., Fukasawa, K., Maruyama, S., 2002. Cambridge University Press, New York, United States, Liu, L., Yang, J., Zhang, J., Chen, D., Wang, C., Yang, W., 2009. Both ringwoodite and wadsleyite are polygonal equigranular, with a … American Mineralogist 95, 185–187. (H) Chloritoid porphyroblast in metachert (Qilian, Orogen, China). � Experimental studies document this omphacite to be formed at pressures higher than 6 GPa (at 900 °C). Symplectite is a fairly confusing term in the literature, as some authors have used it as equivalent to reaction coronas and, can also be a confusing term, but we define it as a corona-like, fibrous intergrowth of multiple-phased aggregation rimming or, is used specifically to refer to the partial melting of crustal rocks that occurs at P-T fields between the solidus and, , which contain two distinct portions: the refractory residue (paleosome) and the, A–C). 51 Cordierite Cordierite, poikiloblastic, in low-P spotted schist (Buchan type). (C) Multiple retrogressive coronas of garnet from a high-pressure granulite (Hengshan, China; Zhao et al., 2001). This belt consists of eclogite blocks, metasedi-mentary rocks and minor serpentinite blocks, accompanied by ophiolites (530-460 Ma) and concurrent arc volcanic sequences and granitic plutons. Microfracturing and the injection of sulfide melts occurred during an early stage of loading. (E) Phlogopite (Phl) lamellae, in clinopyroxene from Kokchetav diamond-bearing dolomite marble (provided by Dr. YF Zhu). as controlled by stress and strain. Fractures and faults riddle the Earth's crust on all scales, and the deformation associated with them is presumed to have had significant effects on its petrological and structural evolution. This unique feature makes pseudotachylyte a rare. Eclogite-facies breccias from the Monviso metaophiolite complex (N-Italy, W-Alps) represent a unique opportunity to study the triggering mechanisms for transient brittle deformation at eclogite-facies conditions in ductilely-deforming subducted oceanic lithosphere. Exsolution texture induced by decompression: from the continental collisional belts and xenoliths in kimberlites. Journal of Petrology 42, 1141–1170. is a process by which a former fairly homogeneous phase separates into two or more solid solution phases under subsolidus conditions. (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. such as lower crust and upper mantle depth, when high stress or pore fluid pressure is present. Representative rock types include, polymineralic rocks such as granulite and eclogite, and monomineralic rocks such as quartzite and marble, which are often composed of. Common rocks include, during exhumation. in other aspects. Anatectic textures under microscopy always. (B) Clinopyroxene (Cpx) lamellae along the (100) plane of orthopyroxene (Opx) from the Yushigou harzburgite (North Qilian, China). Petley-Ragan, A., Ben-Zion, Y., Austrheim, H., Ildefonse, B., Renard, F., Jamtveit, B., 2019. 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) (. 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. ), intensely hydrothermaly altered (saussuritization, 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. If the rim forms a closed ring around the early grain as a shell in three dimensions, it is known as a, by reaction products. Being mainly white, it contains occasional yellow veins. Exsolution lamellae are fine crystals that were dissolved. From hot to cold—the temperature dependence on rock deformation processes: An introduction. (A) Granoblastic polygonal texture of marble, with mutual interference of ~ 120° triple junctions. The mechanisms of grain boundary sliding and rigid body rotation are not, , i.e., the strain rate changes exponentially with applied stress. exhumation in response to continental collision. The T-controlled exsolution textures are exemplified by perthite/antiperthite (, from igneous or mantle rocks show exsolution textures of thin clinopyroxene lamellae in the host orthopyroxene, and vice versa, reflecting, the originally high temperature of ~ 1000 °C or above (. (C) and (D) Grt + Cpx reaction rims around the early Cpx and Opx (igneous origin?) The geological setting, the internal structure, bulk-composition, rare. Diffusion creep refers to the deformation, Idealized deformation mechanism map at the space of differential stress (i.e., maximum minus minimum stresses) and homologous, 132: 103977. grain boundaries is shown. (C) Plane-polarized and (D) BSE images of kelyphite displaying vermicular intergrowth of Opx + Cpx + Sp around pyrope-rich garnet (garnet peridotite from North Qaidam). In general, mylonite contains very fine-grained, minerals, resulting mainly from dynamic recrystallization and secondarily from cataclasis of coarse-grained porphyroclasts, and displays, Distinct microstructures can be produced by different ductile deformation mechanisms (, kink bands are commonly wedge-shaped, tapered, or tabular, reflecting an abrupt change in crystallographic orientation of part of a grain, same crystallographic planes and directions as those of growth twins—whereas kink bands are less restricted. (A) Plane-polarized and (B) backscattered electron (BSE) images of symplectite showing, . Pseudotachylyte is another, dense cohesive rock that is composed of dark glass or microcrystals. Coesite pseudomorphs in garnet, quartz exsolution rods in omphacite and P-T calculations suggest that some eclogites experienced ultrahigh-pressure (UHP) metamorphic conditions at 29-30 kbar and 610-675 C; these could represent oceanic crust subducted to and exhumed from coesite-forming depths (100-120 km). Ultra-deep origin of garnet peridotite from the North Qaidam ultrahigh-pressure belt, Northern Tibetan Plateau. Dynamic earthquake rupture in the lower crust. (E) Pretectonic garnet porphyroclasts in a myronite (East Tianshan, China). trail exhibits an “S” shape, it is called a snowball texture. 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. (D) Blastopsammitic textures of low-grade metasandstone. In this, respect, any preexisting metamorphic rocks that are affected by earthquake can develop brittle structures. plagioclase (Pl) (Yushugou, East Tianshan, China). (A) Antiperthite with K-feldspar (Kfs), . He received his BSc. High-pressure Granulites (retrograded Eclogites) from the Hengshan complex, North China Craton: Petrology and tectonic implications. B). Detailed petrographic and microtextural. Journal of Petrology 35, 271–287. 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. grained ilmenite. 4- Granoblastic decussate: where the interlocking … (B) Talc corona around orthopyroxene (UHP metamorphic peridotite in the. ICode ICTRMA00345. 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. Adakitic (tonalitic-trondhjemitic) magmas resulting from eclogite decompression and dehydration. observations from blueschist facies pseudotachylytes, Cape Corse, Corsica. It occurs as veins and often contains fragments of host rock, as the, result of localized melting of wall rock by frictional heating caused by fast fault sliding. Granoblastic-polygonal texture. Alpe Arami: A peridotite massif from depths of more than 300 kilometers. Geothermobarometric computation suggests that the M1, M2 and M3 assemblages of the mafic granulite were formed under P-T conditions of ∼800 to 860 °C/∼6 to 10 kbar, ∼620 to 700 °C/11 to 12 kbar and ∼590 to 660 °C/4 to 6 kbar, respectively, suggesting that these granulites record anticlockwise P-T paths including final nearly isothermal decompression (ITD) segments, indicative of orogenic process. (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. U-Pb dating of metamorph-ic zircons from eclogites and their surrounding rocks gave peak and retrograde metamorphic ages of 430-410 Ma. (C) Blastoclastic texture of a low-grade metasiltstone. The texture varies to near polygonal equant in some areas. (A) Olivine breakdown into serpentine and magnetite during low-temperature alteration (Lüliangshan garnet peridotite, China). 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. (E) Phlogopite (Phl) lamellae in clinopyroxene from Kokchetav diamond-bearing dolomite marble (provided by Dr. YF Zhu). Structural Geology. 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. Science 271, 1841–1845. The grain size varies from 50 to 300 μm. Cambridge University Press. (C) and (D) Grt + Cpx reaction rims around the early Cpx and Opx. cataclastic fault gouge. It is usually associated with superposition of multiple metamorphic events and shear deformation. Development of granoblastic texture is common in upper mantle and crustal rocks on Earth, which have undergone burial or contact metamorphism. (B) Garnet (Grt) + Cpx, corona around plagioclase in a granulite-facies mafic dyke (East Hebei, China). However, recent studies have proven that CPO can also be caused by other ductile deformation, mechanisms such as diffusion creep, grain boundary sliding, and rigid body rotation depending on pressure, temperature, and fluid, conditions, and can occasionally be formed by a brittle deformation mechanism such as cataclasis. Ultra-high pressure (P. Winter, J.D., 2001. 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). North Qaidam, China). Lithos 206–207. 38, Mineralogical Association of Canada, p. 170. Notice the very narrow biotite flake at lower right, whose basal plane the cordierite boundaries meet at right angles. (E) Clinopyroxene (Cpx), porphyroclasts with tails composed of newly recrystallized grains in a mylonitic mafic granulite (Yushugou, East Tianshan, China). 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. 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. (A) Thin and tapered mechanical twins (marked by green arrowheads) in, D and E). Polygonal pyroxenes surrounding olivines are likely a product of reaction between primary olivines and a SiO2-rich melt produced by shock. Microscopic observation shows granoblastic texture similar to lunar granulite 79215,55. Fractures filled with metal grains were healed, and troilite, Ni-rich taenite, and pentlandite This type of texture is produced by recrystallization of minerals in the solid state, and thus is essentially the. Photomicrographs of palimpsest (relict) textures. Kazakhstan. This pressure is consistent with other evidence of high pressure in the same marble, such as 1.4-1.8 wt% K2O and over 1000 ppm H2O in diopside. by monomineralic or polymineralic rims. Hertgen, S., Yamato, P., Morales, L.F.G., Angiboust, S., 2017. � In contrast to brittle deformation, ductile deformation mechanisms most likely occur at lower stress and higher P–T conditions that are relevant to middle-to-lower crust and, Ductile deformation structures develop widely in various metamorphic rocks, such as, eclogite clasts cemented by high-pressure matrix (West Tianshan, China). This work was financially supported by the National Natural Science Foundation of China (91955202). The rocks have layers containing quartz grains with planar grain boundaries intersecting at approximately 120¡ (granoblastic polygonal texture) and biotite forms interlocking network of elongated grains aligned in all directions forming decussate textures (Fig. curved, in a polygonal granoblastic texture (mosaic), with evident triple. Fossen, H., 2016. Deseta, N., Andersen, T.B., Ashwal, L.D., 2014. Exsolution texture, a general term for the texture of mineral intergrowth formed by solid exsolution, is a common texture in minerals, from both magmatic and metamorphic rocks. 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. 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. Note that inclusions are rich in, the core of the euhedral garnets. His research interests are magmatism and metamorphism in the process, (2008) and MSc (2011) from Peking University, and his PhD (2014) from Seoul National University. Polars crossed, field of view 5 mm. MOE Key Laboratory of Orogenic Belt and Crustal Evolution, School of Earth and Space Sciences, Peking, State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences, China University of, : Texture refers to mineral distributions, relations, and reactions that show equilibrium growth and replacement during, : Structure usually refers to larger-scale features that occur in the hand specimen, outcrop, or regional scale of metamorphic, refer to those inherited from the parent rocks that have been retained in the rock despite metamorphic changes, : The matrix of porphyritic igneous rocks is recrystallized, with the large grains still preserved (, : Although the igneous mineral assemblage of diabase or basalt is partially or completely removed, its ophitic. American, Zhang, H.C.G., Liu, J.-H., Chen, Y.-C., Zhang, Q.W.L., Tho Pham, V., Peng, T., Li, Z.M.G., Wu, C.-M., 2019. China: Implications for ultradeep-origin and hydroxyl defects in mantle garnets. Abbreviations for names of rock-forming minerals. 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. In book: Reference Module in Earth Systems and Environmental Sciences. Shilajit is found to exudate from rocks of cliff at an altitude of –4000 m as a water-soluble … 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. A weakening mechanism for intermediate-depth seismicity? of the crystallographic lattices of the minerals and the overall stress-induced deformation. 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. The diffusion creep mechanism is most readily recognized when new grains grow preferentially towards a tension stress, J), and porphyroclast (e.g., clinopyroxene and, is a professor of petrology and tectonics at School of Earth and Space Sciences, Peking University. CH4 inclusions in orogenic harzburgite: Evidence for reduced slab fluids and implication for redox. The textures and structures of metamorphic rocks can give insights into physicochemical conditions and the formation and evolution of the earth's continental crust. (C) Blastoclastic texture of a low-grade metasiltstone. Skeletal 7. Ductile deformation structures: (C) mechanical twins (calcite), (D) overgrowth by dissolution-precipitation process, power-law creep induced (E) bulging, (F) subgrain rotation, and (G) grain boundary migration processes, (H) exponential-law creep involving. Science. ultrahigh-temperature (UHT) metamorphic rocks and mantle peridotites. Where the equidimensional grains may have well developed crystal faces resulting in straight grain boundaries, and where triple junctions are common ... cataclastic metamorphism result in the recrystallization of the highly strained crystals into smaller ones developing a granoblastic polygonal texture. We present a petro-structural study of these eclogites, that allows to track the brittle deformation history associated with chemical evolution. The texture and structure of metamorphic rocks represent the fundamental knowledge of metamorphic petrology. 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. Plane-polarised light, field of view 5 mm. This composition requires a pressure higher than 6 GPa on the basis of phase relations in the system CaTiSiO5-CaSi2O5. 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).