PLATE TECTONICS Plate boundaries

WORK IN GROUP AND AGREE ON A DEFINITION FOR THE WORD BOUNDARY Before studying WORK IN GROUP AND AGREE ON A DEFINITION FOR THE WORD BOUNDARY

WILE READING Mid-plate tectonic activity                  ▶ READ THE TEXT CAREFULLY. UNDERLINE ANY WORDS YOU DON’T UNDERSTAND AND WRITE THEM ON A SHEET OF PAPER. CHEK WITH YOUR GROUP LOOKING THEM UP IN A DICTIONARY

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THE DIFFERENT TYPES OF PLATE BOUNDARIES PLATES CAN MOVE APART FORMING DIVERGENT BOUNDARIES PLATES CAN MOVE PUSH AGAINST EACH OTHER FORMING CONVERGENT BOUNDARIES PLATES CAN MOVE SLIP PAST EACH OTHER FORMING TRANSFORM BOUNDARIES

DIVERGENT BOUNDARY WATH? WHERE MANTLE CONVECTIVE CELLS DIVERGE, THE OVERLYING CRUST AND MANTLE ROCKS CAN PARTIALLY MELT DUE TO THE DECOMPRESSION. Magma produced is almost free of gas and vapor. It can solidify into the crust as gabbro or erupt at the surface as basalt in huge fluid and quite lava flows. The majority of magmatic roks on the Earth and the formation of new oceanic crust is produced by this process.

DIVERGENT BOUNDARY Where? The most prominent feature of divergent margins is in the mid – ocean ridge that form a continuos submarine chain crossing all the ocean. If the ridge itself emerges, a very active volcanic iseland, like Iceland, is formed. Iceland is a place in the word where is possible to step on the mid-ocean ridge as it not coverd by the sea. The ridge is visible as an aligment of faults, fractures and cliffs from where basaltic lava is eupted frequently.

The evolution of a divergent boundary WHEN DIVERGENCE BEGINS WITHIN A CONTINENT THE BOUNDARY EVOLVES THROUGH SEVERAL STAGES The evolution of a divergent boundary After a initial volcanism (a) a rift valley is formed (b) and as it deepens, it is covered by seawater (c) until, at a mature stage an ocean with mid-ocean ridge is borned (d)

CONVERGENT BOUNDARIES OCEAN-CONTINENT CONVERGENT BOUNDARY They are associated with plate collision and with different possible plates configurations. At convergent plate boundaries, the oceanic plate subductsnthe continental plate and partial melting of the underlying plate produces volcanism as volcanic arc

OCEANIC-OCEANIC CONVERGENT PLATE BOUNDARY When subduction occurs between two oceanic crust plates, the volcanic arc grows on the oceanic crust and form a chain of volcanic islands knowna as an island-arc.

CONTINENT-CONTINENT CONVERGENT PLATE BOUNDARY When two continental crust plates collide, neither can sink and rocks are deformed and uplifted giving rise to high mountain ranges. This process of mountain building at collision zone, takes the name of orogenesis.

TRANSFORM BOUNDARY When the direction of movement of the two plates is parallel to the plate boundary, we have a transform boundary. The plate slide side-by-side so this boundary does not show the huge deformation and active volcanism but friction between plates often generates strong and shallow eartquakes that are hihly destructive.

AERIAL VIEW OF SAN ANDREAS FAULT The San Andreas Fault in California is the best known and most studied transform boundary. It is still very active.