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-Alluvial fans:cone shaped wedges of sediments that pile up where a rapid drop in stream velocity occurs at a mountain front. -River delta:sediment accumulates where the river velocity drops upon entering the sea. Deltasgrow over time, building out into the basin. Sedimentary deposits of deltas are typically composed of 3 components: -Nearly horizontal topset beds of gravel -Sloping foreset beds of gravel and sand deposited on the slope -Nearly horizontal silty bottom beds formed at depth on the seafloor Marine transgression:rise in sea level Marine regression:fall in sea level -Results in subaerial exposure and an increased tendency for erosion Sea level changes result from: -Changes in the volume of water in the oceans(growth and collapse of continental ice sheets – climate) -Changes in the volume of the ocean basins (tectonic activity and the rate of seafloor spreading
Protoliths: the preexisting rocks that are altered during metamorphism. Metamorphism can alter any protolith (igneous, sedimentary, or metamorphic) Metamorphism occurs when the protolith is subjected to: -Heat: causes atoms to vibrate faster, stretching and bending chemical bonds. If bonds are stretched too far and break, they detach from their original neighbors, move slightly, and form new bonds with other atoms (recrystallization) -Pressure: mineral grains will deform. As confining pressure increases, so does density. -Differential stress (push, pull, shear): pressure is not applied equally in all directions - Bathing in hydrothermal fluidsRecrystallization: rearrangement of atoms within grains or the migration of atoms into and out of grains. -Modification of the shape and size of grains without a change in mineralogy. -One mineral changes into another mineral of the same composition (polymorph) How can you tell it’s a metamorphic rock? -Mineral grains typically large + interlock with each other rather than being cemented -Foliation:parallel alignment of platy minerals and/or the presence of alternating light and dark coloured layers. Striped or streaky appearance, and/or the ability to split into thin sheets. Metaconglomerate:metamorphosed conglomerate Slate:finest-grained foliated metamorphic rock, formed by metamorphism of shale Cleavage:develops perpendicular to the direction of compression/stress, irrespective of the original bedding Neocrystallization:formation of new minerals from old ones -Protoliths become unstable and undergo chemical reactions that recycle elements to form a new mineral assemblage Phyllite:metamorphic transformation of clay minerals (slate) to white mica (muscovite) Schist:shistosity is defined by the preferred orientation of large mica flakes Gneiss:highest metamorphic grade -Light layers contain felsic minerals -Dark layers contain mafic minerals Anatexis of partial melting:at very high temperatures or if water enters the rock, lowering its melting point -Light-coloured (felsic) minerals melt at a lower T -Dark-coloured (mafic) minerals melt at a higher T -The felsic bands melt and recrystallize in the gneiss