Regional metamorphism Metamorphic rock

mississippian marble in big cottonwood canyon, wasatch mountains, utah.



dynamic metamorphism

regional metamorphism, known dynamic metamorphism, name given changes in great masses of rock on wide area. rocks can metamorphosed being @ great depths below earth s surface, subjected high temperatures , great pressure caused immense weight of rock layers above. of lower continental crust metamorphic, except recent igneous intrusions. horizontal tectonic movements such collision of continents create orogenic belts, , cause high temperatures, pressures , deformation in rocks along these belts. if metamorphosed rocks later uplifted , exposed erosion, may occur in long belts or other large areas @ surface. process of metamorphism may have destroyed original features have revealed rock s previous history. recrystallization of rock destroy textures , fossils present in sedimentary rocks. metasomatism change original composition.

regional metamorphism tends make rock more indurated , @ same time give foliated, shistose or gneissic texture, consisting of planar arrangement of minerals, platy or prismatic minerals mica , hornblende have longest axes arranged parallel 1 another. reason many of these rocks split readily in 1 direction along mica-bearing zones (schists). in gneisses, minerals tend segregated bands; there seams of quartz , of mica in mica schist, thin, consisting of 1 mineral. along mineral layers composed of soft or fissile minerals rocks split readily, , freshly split specimens appear faced or coated mineral; example, piece of mica schist looked @ facewise might supposed consist entirely of shining scales of mica. on edge of specimens, however, white folia of granular quartz visible. in gneisses these alternating folia thicker , less regular in schists, importantly less micaceous; may lenticular, dying out rapidly. gneisses also, rule, contain more feldspar schists do, , tougher , less fissile. contortion or crumbling of foliation no means uncommon; splitting faces undulose or puckered. schistosity , gneissic banding (the 2 main types of foliation) formed directed pressure @ elevated temperature, , interstitial movement, or internal flow arranging mineral particles while crystallizing in directed pressure field.

rocks sedimentary , rocks undoubtedly igneous may metamorphosed schists , gneisses. if of similar composition may difficult distinguish 1 if metamorphism has been great. quartz-porphyry, example, , fine feldspathic sandstone, may both metamorphosed grey or pink mica-schist.