Question

Part 1: Melting rocks and Plate Tectonics
Part 1: Melting rocks and Plate Tectonics (18 pts) Below is a cross-section showing subduction of an ocean plate beneath a continental plate. Active volcanism is represented by the black triangle. Oceanic cryst= Lithosphere mantle Continental crust Lithosphere mantle Asthenosphere Asthenosphere Figure 2 a) Explain where the magma feeding these volcanoes is generated (and draw a star on Figure 2 to show this location) and the process through which this material melts. (4 pts) b) What type of magma is generated at the source? (2 pt) c) What type of magma may erupt at the surface? If it is different, explain why. (4 pts)

Answer 1

@ The Beleduction ofane is generally Characlerised by trencă system. The highly dense beaches loceanic plates) Beledelsto beneath the less dence Plate. (conténereal folate). • of the depla lecteween 100 - 200 kms; meeting of descending plate takes place due do frictional heat and high geothermal gradient • The arc-french gap depends upon the angle of subidrotton Higher the angle 0 of subduction. gap lower the angle Oceanic creest Vaivolcano continenteel - corest Lithosphere de plate lithospherica plate magma magma As the nosphere As then osphere

predominales b) In the beginning theolitec lava come out from the occanic crustal meets Later on andese fic lava predome due do magmatic diſporenci cetrös .etlog with the down leent peale, opart of the trench asediments and some wa is also carried down to the hotter enecer onment. Leeêfl the reise in temperatu and pressure in depth this water gets released and reise into the overlying plate Causing partial meeting of rock o O ley lowering ielo melting point. Even if the magma is non- andisêtic, a part of it may diff erentiate into anduritib. © When Guleduction of voceanic lithosphere receches a depth in excess of so km and magmas are created & reaches the sleeface cohé'ch cis charactis ed - dey three type of magmas series : -

© ☺ Theolitic Series calc- alkaline series Alkaline series rees - O The theolitic series is fixed in young areas and older areas are characterised lley Call- alkaline series.