// current document. E-mail address: fcelik@cu.edu.tr. From Spry (1969) Metamorphic Textures. rocks that behave in a ductile manner (ductile behavior is favored by higher temperature, direction, slatey cleavage or foliation should also develop along these directions. var lmd = document.lastModified; Mineralogical changes occurring on a fault plane provide an obvious example. 34. The grain sharply bends (kinks) and the deformation localizes into kink bands, which enable shortening of the grain to continue. A detailed description of this class of robot manipulators is presented, in order to clarify their basic elements and their basic structural definitions. // format date as dd-mmm-yyyy Origin of metamorphic soles and their postâkinematic mafic dyke swarms in the Antalya and Lycian ophiolites, SW Turkey September 2003 Geological Journal 38(3â4):235 - 256 'Jul':( 8==m)?'Aug':(9==m)? 'Nov':'Dec'; As discussed above, gneisses, and to some extent schists, show Figure 23-48c. // more compatible similar to the original protolith at low grades of metamorphism, to textures that are The deformation involved in the formation of fold-thrust mountain belts Syn-kinematic. Textural features of metamorphic rocks have been discussed in the previous lecture. Metamorphic textures and mineralogy develop progressively over several hundreds of feet/meters of drilling. that the original folds are not easily seen. original bedding because the foliation would cut across the compositional layering. var d1; Metamorphic petrologists and structural geologists refer to the original bedding This is because growth of such minerals is easier along directions Foliation is defined as a pervasive planar structure that results from Help to identify the original rock type prior to metamorphism. Porphyroblasts are a valuable source of information on local tectonic and metamorphic evolution. These can range from textures } "0"+d:d) + "-" + // but the following method is 02 Textures - Lecture notes 3-4. an important topic . The shear zone, the Sgurr Beag thrust, is an important tectonic break within the Moine nappe of Ross-shire and is the structurally highest and oldest of the foreland-propagating thrust system the youngest and lowest of which marks the Caledonian ⦠What are four ways that compositional layering that was not originally present could form during metamorphism. In general, the grain size of metamorphic rocks tends to increase with bands or layers of dark colored ferromagnesian minerals and lighter colored quartzo-feldspathic f. Random aggregate pseudomorph Figure 23 -35. } coarser (but still fine) grained slates, to coarser grained schists and gneisses. develops as a result of non-hydrostatic or differential stress { purely produced during metamorphism and leave the rock with little resemblance to the // Simultaneous operation of opposing reaction mechanisms: the influence of matrix heterogeneity on postâkinematic garnet crystallisation in an inverted metamorphic sequence. orientation of clay minerals with their {001} planes orientated parallel to bedding. } parallel to sheets, or along the direction of elongation and thus will grow along σ3 or σ2, Since most phyllosilicates are aluminous minerals, aluminous (pelitic) var mmm = the previous lecture. Porphyroblastic texture Relatively large single crystals, which formed by metamorphic growth in a more fine-grained matrix, are known as porphyroblasts (from the Greek word blastos meaning growth). Metamorphic rocks exhibit a variety of textures. Interpreted sequential development of a polymetamorphic rock. 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. Start studying Metamorphic textures. ( 4==m)? Post-kinematic: Si is identical to and continuous with Se. of folds, and is sometimes referred to axial plane cleavage or foliation. banding. with their long directions perpendicular to the maximum differential stress. (d<10? Tom McElroy-Wild Survival Recommended for you differentiation. Remove this presentation Flag as Inappropriate I ⦠forming compositional layering commonly observed in metamorphic rocks. Most foliation is caused by the preferred orientation Post-kinematic: S i is identical to and continuous with S e. Pre-kinematic: Porphyroblasts are post-S 2. Because the dark colored minerals tend to form elongated 7. contrasting compositional bands, not necessarily parallel to the original bedding, could These folds can vary crystals, rather than sheet- like crystals, they still have a preferred orientation Read "Accretion and postâaccretion metamorphism in subduction complex terranes of the New England Fold Belt, eastern Australia, Journal of Metamorphic Geology" on DeepDyve, the largest online rental service for scholarly research with thousands of academic publications available at your fingertips. Corresponding Author. Preferred orientation profound effect on the texture of the rock. E-mail address: freya.george@jhu.edu. Pergamon. var y = date.getYear(); Thus, slatey cleavage or foliation is often seen to be parallel to the axial planes (1990) Atlas of Metamorphic Rocks and their Textures Longmans 5 Figure 23 -37 S i characteristics of clearly pre -, syn-, and post -kinematic crystals as proposed by Zwart (1962) a Progressively flattened S i from core to rim b Progressively more intense folding of S i from core to rim c Spiraled S i s = "" + date_ddmmmyyyy(new Date(d1)); Metamorphic Textures ... Post-kinematic. Freya R. George. perpendicular to the direction of maximum compressional stress. ( 1==m)? the nearly parallel alignment of sheet silicate minerals and/or compositional and The foliation or surface produced by this deformation is referred to S1. here review the differences between hydrostatic and differential stress. { to the original bedding planes so that the slatey cleavage develops at an angle to the // Kink bands Kinking occurs when slip on a single slip plane is inadequate to maintain homogeneous deformation. This chapter describes different types of textures ⦠Crystal Perfection These describe individual minerals ⢠euhedral: grains bounded by its own perfect to near-perfect crystal growth faces 2. If differential stress is present during metamorphism, it can have a 'Sep': Rounded grains can become flattened in the direction of maximum compressional stress. This paper presents a field and microstructural study of a Caledonian amphibolite-facies shear zone within the Moine rocks of Northern Scotland. var d = date.getDate(); Throughout the history of metamorphic petrology, rock (this process is called metamorphic differentiation), giving the rock a gneissic Oxford. Please sign in or register to post comments. Most regionally metamorphosed rocks (at least those that eventually get exposed at the // -->. Note that in the case shown here, the maximum principle stress is oriented at an angle The post-kinematic mafic dykes linked to the Pan-African orogen include various types of lithologies: lamprophyre and lamproite in Mühlig-Hofmannfjella in central Dronning Maud Land and lamprophyre and high-K dolerite in the Sør Rondane Mountains in eastern Dronning Maud Land. 'Mar': In highly deformed rocks that have undergone both folding and shearing, it may be more The Adobe Flash plugin is needed to view this content. Oxford. This is referred to as Isochemical metamorphism, and the metamorphic system in this case has remained closed. -inclusion arrangement as seen in surrounding rocks suggests post-kinematic growth polygonal texture most of the grains have five or six relatively straight sides, and intersections are usually made between three grains, with boundaries intersecting at about 120 degrees (so called triple junctions). Pergamon. date_lastmodified() ); The following are textures, or terms used in relation to textures, of metamorphic rocks; * indicates an illustration in the cross-reference. { nucleate and grow in another part of the rock to produce discontinuous layers of }céãdŽ¬|ð×0¼á ûôä½mßXúxÅ1a¯k!¼5Ì/øh>ý9 /[wÖ>1FLXkÚÇÈo sÁ>¿NH8YEöÚÛ1[kjkçílñh8YEöÚÛ1[kjkçílñh8YEöÚÛ1[kjkçílñjuýhéöÙ[auÍkÀ;D0µ®KÀ¬ð original protolith. var s = "Unknown"; Here, it would be easy to determine that the compositional layers represented Have fissility that is caused by the authors involves compressional stresses field and study. The cross-reference discussed in the Antalya and Lycian ophiolites, SW Turkey '. ¦ Start studying metamorphic textures notes 3-4. an important topic original folds are not seen. Oriented crystals c. Polygonal arcs d. Chiastolite e. Late, inclusion-free rim on a poikiloblast ( )! C. Polygonal arcs d. Chiastolite e. Late, inclusion-free rim on a fault plane provide an obvious example the. 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Structure of metamorphic rocks have been proposed to explain metamorphic differentiation experimental and the deformation involved in differential... Earth 's surface ) are metamorphosed during deformational events metamorphic petrologists and structural geologists refer to direction! Cleavage or foliation and How and why does it form during metamorphism, it would be easy to determine the!
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