Quiz 5- Ch. 3/5/13 Flashcards
Divergent boundaries
plates move apart, narrow rifts created, divergent boundaries within continents are more complicated and distributed over a wider area
mid ocean ridge
An undersea mountain chain at a divergent boundary, characterized by earthquakes, volcanism, and rifting, all caused by the tensional forces of mantle convection that are pulling the two plates apart.
spreading center
A divergent boundary, marked by a rift at the crest of a mid-ocean ridge, where new oceanic crust is formed by seafloor spreading
magnetic anomaly
One in a pattern of long, narrow bands of high or low magnetic intensity on the seafloor that are parallel to and almost perfectly symmetrical with respect to the crest of a mid-ocean ridge.
relative plate velocity
The velocity at which one lithospheric plate moves relative to another.
2 geometric principles that govern the behavior of plate movement
transform-fault boundaries indicate the directions of relative plate movement
Seafloor isochrons reveal the positions of divergent plates at earlier times
porphyry
An igneous rock of mixed texture in which large crystals (phenocrysts) “float” in a predominantly fine-grained matrix.
Extrusive Igneous rocks
Lavas: volcanic rock that ranges in appearance from smooth and ropy to sharp and spiky depending on the conditions
Pyroclasts: fragments of lava are violently erupted and thrown into the air
Felsic rocks
are poor in iron and magnesium and rich in minerals that are high in silica. i.e. granite
mafic rocks
contain large proportions of pyroxenes and olivines. These minerals are relatively poor in silica but rich in magnesium and iron i.e. gabbro
partial melting
Incomplete melting of a rock that occurs because the minerals that compose it melt at different temperatures.
decompression melting
The spontaneous melting of rising mantle material as it reaches a level where pressure decreases below a critical point, without the introduction of any additional heat
magma chambers
magma-filled cavities in the lithosphere that form as rising pools of melted rock push aside surrounding solid rock
Earthquake
The violent motion of the ground that occurs when brittle rock under stress suddenly breaks along a fault.
elastic rebound theory
stressed rocks are strained elastically, so that when a fault breaks, the rocks on either side of the fault return to their undeformed, stress-free shape.