most plates have oceanic and continental lithosphere  both have two compositional layers?
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your question is a little confused , but here goes...\n\nthe lithospere is the name for the outer/upper layer of the earths surface. It has 2 compositional layers, the CRUST, the upper solid layer, and the MANTLE, the lower molten layer. They are separated by the MOHO DISCONTINUITY. the moho discontinuity diffracts earthquake waves, which is why it is believed that the mantle is composed of molten rocks (other waves, such as sound and light waves are diffracted when crossing the boundary between a solid/liquid or liquid /gas, so it is believed there is a change of state at the moho). The Moho occurs at a depth of about 200-300 km beneath the earths surface.\n\nMost plates do have oceanic and continental lithosphere, the difference is only that oceanic is under the sea, and continental is on land, if you consider that the deepest ocean, and the highest mountain are both roughly 3 miles deep/high, and the lithosphere is about 300 miles deep , you will see that defining  a plate as oceanic or continental has little impact on its overall composition or behaviour.\n\nIn short the crust is the upper, the mantle is the lower , the moho is the boundary\n\n\n**\n\nin answer to bertrum ( see below) the North Sea is hardly an ocean, continents usually have a 'continental shelf' around them, which is considered geologically to be part of the continent, and beyond which the true ocean starts, the North Sea covers  part of the continental shelf of the European Plate
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because there is a subduction zone. One plate goes under the other and melts into the earth's mantle.
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Here is a chart of various estimates of the mantle's composition that have been made:\nhttp://www.mpch-mainz.mpg.de/~jesnow/Ozeanboden/2004/Lecture4/Composition.html\n\nThe answer in terms of minerals is (I quote) "The uppermost mantle is comprised of a peridotite with about 60% olivine 30% enstatite 6% clinopyroxene, 2% plagioclase and 2% spinel. At slightly greater depth, the plagioclase disappears and is replaced by spinel and clinopyroxene. Deeper still, garnet appears." from the above site. \n\nThe other thing you should realize is that while the earth's mantle may be 'plastic' it is not molten. From Wikipedia: "Although these temperatures far exceed the melting points of the mantle rocks at the surface, particularly in deeper ranges, they are almost exclusively solid. The enormous lithostatic pressure exerted on the mantle prevents them from melting."  From: http://en.wikipedia.org/wiki/Mantle_%28geology%29\n\nMagma coming from volcanoes actually originates in the asthenosphere, which is above the mantle.
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There are volcanoes because of the interaction between multiple plate boundaries which causes the magma in the upper mantle (from beneath the crustal lithosphere) to rise, erupt and form lava at the surface.  \n\nVolcanoes tend to occur at either subduction zones, rifts or at hot spots.  Subduction zones are located at convergent oceanic/oceanic or oceanic/continental plate boundaries, where the denser oceanic crust sinks into the mantle beneath the other plate.  The minerals in the subducted slab dehydrates through metamorphic processes, which releases fluids to the mantle wedge to produce the melt (magma), which erupts to form volcanoes.  \n\nFor rifts, during the early stages of continental rifting (where continents are pulled apart because of extensional forces), volcanic activity can occur because crustal extension can allow magma to rise and intrude further up the crust.  Therefore, volcanic activity can occur in such situations.  eg: East African Rift. \n\nIn mid oceanic ridges, the divergent motion of oceanic plates allows mantle material to rise from below.  This tends to form a submarine ridge rather than a volcano.\n\nHowever, volcanoes can occur within the plate.  These are usually called hotspots, where a plume (a plume of anomalously hot magma) rise from deep within the mantle (probably as deep as the core-mantle boundary) to the surface.  These are stationary and therefore, it can leave a trail of volcanoes as the lithospheric plates move over the mantle.  Eg: Hawaii-Emperor seamount chain.
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Nope; the oceanic plates are spreading apart, as new material (magma) is pushed up from below.  They are not crashing together at all.
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Continental/Continental plate convergence.\n\nThis happens during mountain building episodes called orogenies.
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Definitely continental to continental convergence. When continental crust meets continental crust neither will be subducted so they press together under extreme pressure over large amounts of time which leads to deformation of the crust (folding & faulting). This is one of several ways that mountains can be produced. AKA orogenesis.
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This is the Wilson Cycle, and it is driven by plate tectonics. \n\nContinents are composed of relatively light weight felsic igneous rocks such as granites and granodiorites. Ocean basins are composed of mafic igneous rocks like basalt and gabbro that are heavier than continental crust. Since the earth's mantle is plastic, these different masses of rock tend to 'float' at different levels. This is called isostacy.\n\nOceanic plate motion originates at the mid-ocean ridges, pushing oceanic plates outward towards the continents. This motion and force is far from being uniform from one ocean basin to another, and is not even consistent along the length of the mid-ocean spreading centers. \n\nWhere oceanic plates meet continental plates there is a convergent plate boundary and generally this leads to subduction of the oceanic plate. There is considerable force however, and the style of subduction does vary. Since the forces that are being applied, as well as the resistance of the continental plates all are varied, there are inequities that cause the continents to move in one direction. Eventually this motion results in a collision of continents called a supercontinent because continents will not subduct under one another. India and Asia, and the Himalayas are a great example of a continental convergent plate boundary. Eventually the convection forces that cause the supercontinent to form will begin rifting it apart again creating new smaller continents. \n\nHere is a model of the Wilson Cycle:\nhttp://csmres.jmu.edu/geollab/vageol/vahist/wilsonsimp.html
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The crust and mantle are generally solid.  The inner and outer core are molten rock and metal...very dense, but still liquid.
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Divergent Boundaries...\n\nContinental/Continental: rift valleys i.e. East African Rift Valley\n\nOceanic/Oceanic: new crust is being formed on the ocean floor at oceanic ridges. The Mid-Atlantic Ridge is an example. The U.S. moves about 5cm away from Europe each year b/c of this.\n\nConvergent Boundaries...\n\nContinental/Continental: Both are of the same density & both are less dense than the molten material beneath so neither will be subducted. They form folded mountain chains such as the Appalachians of the U.S. & the Alps of Europe.\n\nContinental/Oceanic: Ocean crust is much denser & will be subducted under the continental. Friction from plate movement underneath the crust will cause melt & the crust will thin causing some volcanic mountains to appear.\n\nOceanic/Oceanic: One of the oceanic crusts will be subducted & a trench will be created. Volcanic island arcs are associated w/ this type of boundary.
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Are you serious? ;) Well, I'll try to be:\n\n1. Continents are made up mostly of intrusive or plutonic granitic rocks, oceanic crust of extrusive or volcanic basaltic rocks. Example: compare some Himalayan rock with a hardened lava fragment from Mauna Loa in Hawaii.\n\n2. Continental rocks are lighter and of greater volume - they therefore protrude above the oceanic crust, if you dig very deep down they also have deeper roots. The oceanic crust is denser but thinner.\n\n3. Continental rocks are in general much older. This doesn't mean that oceanic rocks didn't exist before, but they get swallowed up (well, buried real deep and remelted, etc.) in trenches, the deepest parts of the oceans.
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The lithosphere (from the Greek for "rocky" sphere) is the solid outermost shell of a rocky planet. On the Earth, the lithosphere includes the crust and the uppermost layer of the mantle (the upper mantle or lower lithosphere) which is joined to the crust.\n\nAs the cooling surface layer of the Earth's convection system, the lithosphere thickens over time. It is fragmented into relatively strong pieces, called tectonic plates (shown in the picture), which move independently relative to one another. This movement of lithospheric plates is described as plate tectonics.\n\nThe distinguishing characteristic of the lithosphere is not composition, but its flow properties. Under the influence of the low-intensity, long-term stresses that drive plate tectonic motions, the lithosphere responds essentially as a rigid shell and thus deforms primarily through brittle failure, whereas the asthenosphere (the layer of the mantle below the lithosphere) is heat-softened and accommodates strain through plastic deformation. Both the crust and upper mantle float on the more plastic asthenosphere. The crust is distinguished from the upper mantle by the change in chemical composition that takes place at the Moho discontinuity.\n\nThere are two types of lithosphere:\n\noceanic lithosphere \ncontinental lithosphere \nOceanic lithosphere is about 70 km thick (but can be as thin as 1.6 km at the mid-ocean ridges), while continental lithosphere is about 150 km thick (and can be considerably thicker at continental collision zones). Oceanic lithosphere consists mainly of mafic and ultramafic rocks and is denser than continental lithosphere, which consists predominantly of felsic rocks. This higher density has the effect that at subduction zones the oceanic plate will invariably sink underneath the continental plate. New oceanic lithosphere is constantly being produced at mid-ocean ridges from mantle material and is recycled back to the mantle at subduction zones. As a result, oceanic lithosphere is much younger than continental lithosphere: the oldest oceanic lithosphere is about 200 million years old, while parts of the continental lithosphere are billions of years old. As oceanic lithosphere grows older, it gets cooler and denser, with the result that if two oceanic plates converge, the older one will subduct below the younger one.\n\nhttp://en.wikipedia.org/wiki/Lithosphere\n\nBoys mature slower than girls so they seem stupid. \n\nGood Luck!
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Those would be the Eurasian and Australian plates:\n\nhttp://www.cotf.edu/ete/modules/msese/earthsysflr/plates1.html\n\nTambora was affected by the subduction of the Australian plate under the Eurasian in the same way subduction affects most plate-boundary volcanoes; by the partial melting of the the descending plate, which created magma that ultimately fed the volcano.
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mantle\nThe Mantle. It is divided into two parts. The upper portion, which is called the Asthenosphere, is a plastic like fluid. This is where the mantle convection currents occur. The rest of the mantle is made up of dense rock. The mantle is the thickest layer. Approximately 2900 km thick
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The process as a whole is known as 'continental drift,' or 'plate tectonics'. This process is further divided into several processes: divergence, or where plates are moving away from one another as a result of lava welling up and cooling in a mid-ocean ridge; convergence, where two plates collide and either form mountains or subduct depending on their types; and transformance, where tow plates move at opposite directions parallel to one another. \n\nKnowing this, your question can be answered. You are describing convergance between either two oceanic plates or one oceanic plate + one continental plate. The process is also known as subduction, and can form large mountains and volcanic/seismic activity.
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try this:\nhttp://www.seismo.unr.edu/ftp/pub/louie/class/100/plate-tectonics.html
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Key principles\n\nThe key principle of word formation is that the wordsphere exists as separate and distinct letter plates, which float on the fluid-like (visco-elastic liquid) phrasesphere. The relative fluidity of the phrasesphere allows the letter plates to undergo motion in different directions. One plate meets another along a plate boundary.\n\nTypes of plate boundaries\n\nThere are three types of plate boundaries, characterized by the way the plates move relative to each other.\n\n   1. Transform boundaries occur where plates slide, or perhaps more accurately grind, past each other along transform faults. The relative motion of the two plates is either sinistral (left side toward the observer) or dextral (right side toward the observer).\n\n   2. Divergent boundaries occur where two plates slide apart from each other (examples of which can be seen at mid-ocean ridges and active zones of rifting (such as with the East Africa rift)).\n\n   3. Convergent boundaries (or active margins) occur where two plates slide towards each other commonly forming either a subduction zone (if one plate moves underneath the other) or a continental collision (if the two plates contain continental crust). Deep marine trenches are typically associated with subduction zones. Due to friction and heating of the subducting slab volcanism is almost always closely linked. Examples of this are the Andes mountain range in South America and the Japanese island arc.