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How old are the rocks at the Juan De Fuka ridge when they come to subduction?
Age of oceanic crustal rocksOceanic crust spreads away from the ridge axis. New crust is closer to the ridge; older crust farther away.Oldest oceanic crust is found at the far end of the basin. Oceanic Lithosphere The hot asthenosphere is at the base of the MOR (Mid-Ocean Ridge). Aging ocean crust moves away from this heat source oCooling, increasing in density and sinkingoOlder, thicker lithosphere sinks deeper into mantle. Use the velocity equation if given distance, time, or velocity East pacific rise: oFastest spreading ridgeo14cm/year The mid Atlantic ridge: oSpreading at 2.5 cm per year at the top and 3.5 near the bottom juan de fuka ridge: o2 cm/year towards NA oNA towards juan de fuka from the Mid Atlantic ridge at 1.5cm/year o4 cm/year collision rate with the NA plate Metamorphism from a mudstoneMetamorphism is the transformation of a parent (pre-existing) rock into a texturally and mineralogically new rock due to changing temperature and pressure conditions. The parent rock may be igneous, sedimentary, or another metamorphic rock. The changes take place in the solid-state (without melting) in Earth’s middle to lower crust. Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. With increased pressure over time, the platey clay minerals may become aligned, with the appearance of fissility or parallel layering. This finely bedded material that splits readily into thin layers iscalled shale, as distinct from mudstone.Mud, when lithified, becomes mudstone or shale.Metamorphism of a mudstone will produce slate, schist, gneiss, and hornfels.MarbleThe metamorphism of limestone yields marble.During the formation of marble, calcite composing the protolith recrystallizes, so fossil shells, pore space, and the distinction between grains and cement disappear. Marble typically consists of a fairly uniform mass of interlocking calcite crystals.Sculptors love to work with marble because it is relatively sof and has uniform texture that givesit the cohesiveness and homogeneity needed to fashion large, smooth, highly detailed sculptures. Colors of marble = white, pink, green, and black (depending on impurity it contains)
Not all marble is nonfoliated. If the original protolith contained layers with different impurities, resulting marble has color banding that makes it a prized decorative stone. Causes of mass extinctionsCauses:voluminous volcanic eruptions impact of a comet or an asteroid with the Earth. Either of these events could eject enough debris into the atmosphere to block sunlight.Without the warmth of the Sun, winter-like or night-like conditions would last for weeks to years, long enough to disrupt the food chain.