Yellow Stone Plateau (NW Wyoming) VOLCANISM AND PLATE TECTONICS: ORIGIN OF MAGMA Partial melting of rocks - partial melting is the incomplete melting of a rock to produce magma - composition of the magma is different from that of the parent rock - generates rocks with higher silica content than parent rock Heat source for melting rocks 1) heat from radioactive decay in the upper mantle/crust 2) geothermal heat (gradient of 20-30 0 C/km) 3) heat transfer - from mantle plumes/convection cells 4) frictional heat (friction in subducting plates) Factors that influence melting of rocks 1) temperature of melting - usually between 800-1200 0 C 2) composition of the rock - granite melts ~ 800 0 C and basalt ~1200 0 C (reflects silica content - BRS) 3) pressure at melting - a drop in pressure will cause hot rock to melt resulting in "pressure relief melting" without need for increased temperature - most important at spreading centers 4) water content of rock - water lowers the melting point of magmas - dry granite melts at 700 0 C while wet granite (10-15% water) melts at 600 0 C ****important only for low temperature melting So when do rocks melt?
(ORIGIN OF MAGMA Partial; melting; of rocks - partial melting) (4) frictional heat (friction in subducting plates) Factors that influence melting of rocks 1) temperature of melting - usually between 800-1200 0 C 2) composition of the rock - granite melts; ~; 0 C (reflects silica content - BRS) 3) pressure at melting - a drop in pressure will cause hot rock to melt resulting in "pressure relief melting" without need for increased temperature - most important at spreading centers 4) water content of rock - water lowers the melting point of magmas - dry granite melts at 700 0 C while wet granite (10-15% water) melts at 600 0 C ****important only for low temperature melting) Context(4 ) frictional heat ( friction in subducting plates ) Factors that influence melting of rocks 1 ) temperature of melting - usually between 800-1200 0 C 2 ) composition of the rock - granite melts ~,List([496, 688))):(4) frictional heat (friction in subducting plates) Factors; influence; melting of rocks 1) temperature of melting - usually between 800-1200 0 C 2) composition of the rock - granite melts) Context(4 ) frictional heat ( friction in subducting plates ) Factors that influence melting of rocks 1 ) temperature of melting - usually between 800-1200 0 C 2 ) composition of the rock - granite melts ~,List([496, 688))):(0 C; reflects; silica content - BRS) (melting - a drop in pressure; will cause; hot rock to melt resulting in "pressure relief melting" without need for increased temperature - most important at spreading centers 4) water content of rock - water lowers the melting point of magmas - dry granite melts at 700 0 C) (pressure relief; melting; ) (hot rock; resulting; in "pressure relief melting" without need for increased temperature - most important at spreading centers 4) water content of rock - water lowers the melting point of magmas - dry granite melts at 700 0 C)
4 ) frictional heat ( friction in subducting plates ) Factors that influence melting of rocks 1 ) temperature of melting - usually between 800-1200 0 C 2 ) composition of the rock - granite melts ~,List([496, 688)) 4 ) frictional heat ( friction in subducting plates ) Factors that influence melting of rocks 1 ) temperature of melting - usually between 800-1200 0 C 2 ) composition of the rock - granite melts ~,List([496, 688))
ORIGIN OF MAGMA Partial 4) frictional heat (friction in subducting plates) Factors that influence melting of rocks 1) temperature of melting - usually between 800-1200 0 C 2) composition of the rock - granite melts 4) frictional heat (friction in subducting plates) Factors 0 C melting - a drop in pressure pressure relief hot rock
melting ~ influence reflects will cause melting resulting
of rocks - partial melting
0 C (reflects silica content - BRS) 3) pressure at melting - a drop in pressure will cause hot rock to melt resulting in "pressure relief melting" without need for increased temperature - most important at spreading centers 4) water content of rock - water lowers the melting point of magmas - dry granite melts at 700 0 C while wet granite (10-15% water) melts at 600 0 C ****important only for low temperature melting
melting of rocks 1) temperature of melting - usually between 800-1200 0 C 2) composition of the rock - granite melts
silica content - BRS
hot rock to melt resulting in "pressure relief melting" without need for increased temperature - most important at spreading centers 4) water content of rock - water lowers the melting point of magmas - dry granite melts at 700 0 C
in "pressure relief melting" without need for increased temperature - most important at spreading centers 4) water content of rock - water lowers the melting point of magmas - dry granite melts at 700 0 C