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__________________________________________________________________________________ 6. What can we learn from hot-spot tracks –(eg. Hawaii)Hot Spots:•About 50–100 mantle-plume hot-spot volcanoes exist.•Independent tectonic plate boundaries•May erupt through oceanic or continental crust.oOceanic—mostly mafic magma (basalt)oContinental—mafic and felsic (basalt and rhyolite)•Burn a volcano chain through overiding tectonic plateoCreates a hot-spot trackPlate VelocitiesoPlotting plate motion relative to a fixed spot in the mantleoHot spot tracks, such as Hawaiian Islands can be used to measure velocity of pacific plate.•Plumes of deep mantle material independent of plates.oNot linked to plate boundariesoOriginates as a deep mantle plume (?? OJ)•Plume partially melts lithosphere; magma rises to surface•Hot spots perforate overriding plates.•Volcanoes build above sea level.•Plate motion pulls volcano off plume.oVolcano goes extinct and erodes.oChain of extinct volcanoes called a hot-spot track.•Hot spots reinforce sea-floor spreading•Hot-spot seamounts age away from originating hot spot.
oAge trend defines rate of plate motion.oLine of seamounts indicates direction of plate motion.Hot Spot Description•Hot spots are places within a plate that are volcanically active. As the plate moves, so does the volcano, and if it's in the middle of the ocean you can see how fast and in what direction it is moving by the island chain it creates. Example: Hawaii.•Hot spots are a form of intraplate volcanism .•Isolated hot-spot volcanoes are attributed to the presence of mantle plumes, columns of magma rising in the upper mantle.•If the overlying plate is weak, some of the magma breaks through to form a volcano.•Composition of the material in the eruption depends on the composition of the plate through which the magma rises; along with the composition of the magma source in the mantle.•From studies of hotspots (which are models, theories, that have been postulated from indirect evidence), the basalt is different from the basalt that forms from the upper mantle at spreading centers.•Hot spots not only mark the movement of plates, but they also play a part in the movement of plates.•When a continent comes to rest, the dome that swells up over a hot spot is subject to fracturing and producing a three armed rift.•These may initiate a zone of divergence and to guide the fracturing, although they are not necessarily the only cause.•Typically, two arms of the rift open to form an ocean basin and the third arm fails and remains as a fissure in the continental landmass.•By restoring the margins of the Atlantic Ocean to their Pangaea position, an abundance of three-armed rifts is revealed.•The successful arms merged to form the mid ocean spreading zone and the unsuccessful ones remained as rifts extending into the continents.