Plate Tectonics Key Terms Flashcards
Accretionary Wedge (prism)
A zone of deformed sediment made up of thrust slices scraped off a subducting oceanic plate and added onto the over-riding plate. Occur at oceanic-oceanic and oceanic-continental destructive plate boundaries
Andesite
A fine grained volcanic rock formed by a complex series of processes at destructive plate margins. in mantle - richer in silica and more viscous than basalt. Typically produces explosive volcanic eruptions e.g.Andes mountain chain
Asthenosphere
Layer of the earth immediately below the lithosphere. Hotter and weaker than lithosphere
Basalt
A fine grained volcanic rock formed by the partial melting of the mantle, typically at constructive plate margins. submarine eruptions of basalt lava produce pillow lavas - form upper part of oceanic crust
Benioff Zone
An inclined zone of earthquake foci in the upper part of a subducting oceanic plate at a destructive plate margin. AKA Benioff Wadati Zone
Continental Crust
The crust that forms the continents. average thickness of 35km, can be upto 70km in mountain ranges. Granite rock, density of 2.7 - doesnt subduct
Continental Drift
Theory proposed by Alfred Wegener in 1915 to support the notion that the continents had changed position through geological time. Unable to propose a mechanism to explain how drift occurred - theory ignored
Convection Currents
Heat generated by the breakdown of radioactive materials in the mantle is redistributed by currents that rise at the mid ocean ridges and descend at the ocean trenches
Conservative Margin
A plate margin where two plates slide past each other along a transform fault. Shallow focus earthquakes but no volcanoes. e.g. San Andreas Fault - North American and Pacific plates
Convergent (destructive) Oceanic-Oceanic Margin
A plate margin where two oceanic plates collide and one is subducted to produce a volcanic island arc oceanic trench system. Andesitic volcanoes and shallow, intermediate and deep focus earthquakes. e.g. Caribbean Islands - South American plate subducted down the Puerto Rican Trench
Convergent (destructive) Oceanic-Continental Margin
A plate margin where an oceanic plate is subducted beneath a continental plate - produces an ocean trench mountain belt system. Andesitic and rhyolitic volcanoes and shallow, intermediate and deep focus earthquakes. as oceanic plate subducts, accretionary wedge forme. e.g Andes fold mountain
Convergent (destructive) Continental-Continental Margin
A plate margin wherean ocean closesand two continental plates collide.They are to bouyant to subduct so they form a mountain belt with thick continental crust. shallow focus earthquakes, folding, faulting and regional metamorphism. e.g. Himalayas
Divergent (constructive) Margin
A plate margin where two oceanic plates are moving away from each other. responsible for the formation of ocean basins - start out as rift valleys e.g. African Rift
Plates move apart - mantle melts and forms basalt magma. New oceanic crust formed at ridge. shalow focus earthquakes and basaltic volcanoes. e.g. Mid Atlantic Ridge
Hess
Harry Hess proposed the idea of Sea Floor Spreading, following echo sounding work to reveal the topography of the ocean basins
Hotspot
An area of abnormally intense active volcanism thought to be underlain by a mantle plume. e.g. Hawaii, ocated in the middle of lithospheric plate
e.g. Iceland - located on constructive plate margins
Intrusion
Igneous rocks that crystallise beneath the earths surface. smaller scale intrusions - dykes/sills, larger - plutons/batholiths