Igneous Processes and Products

Pregunta	Respuesta
Igneous Rocks	those that have cooled from magma
Magma	molten rock
Lava	molten rock that cools at the surface
Silicic igneous rocks	have a composition rich in silica, of more than 66% and are light coloured (leucocratic)
Intermediate igneous rocks	Have a silica content of 66 to 52% and are grey (mesocratic)
Mafic igneous rocks	have a silic contnent of less than 45%
Felsic minerals	light coloured and silica rich
Mafic minerals	dark coloured, silica poor and rich in magnesium and iron
Cooling	igneous rocks may be at the surface or the depth
Extrusive	general term for all igneous rocks that cool at the surface - both lava and pyroclasts
Intrusive	term for igneous rocks that cool below the surface
Hypabyssal	igneous rocks form at relatively shallow depths below the surface
Plutonic	when igneous rocks form deep below the surface
Divergent plate margin	where two plates are moving apart and magma is rising up between them
Convergent plate margin	where two plates are colliding and magma is formed above a subduction zone or deep in the crust
Hot spot	formed by a fixed mantle plume bringing magma to the surface
Partial melting	occurs where some of the minerals in a rock melt to form a magma
Country rock	any rock, whether sedimentary, igneous or metamorphic into which an igneous rock is intruded
Minor intrusions	cool at hypabyssal depth below the surface and include sills and dykes
Major intrusions	plutonic and cool deep below the surface and include batholiths
Contact	where igneous rock meets country rock
Chilled margin	where the igneous rock has cooled rapidly so it has fine crystals
Baked margin	country rock that was heated and altered by the intrusion
Metamorphic aureole	large area around a batholith where the rocks have been metamorphosed
Pyroclast	an individual fragment ejected during an eruption
Pyroclastic	fragmental materials formed by explosive eruptions, including bombs, blocks, lapilli and ash
Volcano	a vent at the surface of the Earth through which magma and other volcanic materials are ejected
Pyroclastic rocks	are formed when the pyroclastic material is compacted into rocks
Pyroclastic flow	a hot mixture of pyroclastic material and gas. A nuee ardente is a type of pyroclastic flow
Isopachyte	a line joining points of equal thickness of a deposit such as ash. The maps may be called isopach maps
Lahars	mudflows of wet ash and volcanic debris that can flow rapidly down a mountainside
Viscosity	measure of a fluid's resistance to flow and controls the stickiness of a magma, which in turn depends on the silica content
Shield volcanoes	gentle slopes of less than 10 degrees and a roughly circular shape around a central vent
Fissure eruptions	where magma reaches the surface along long, linear cracks or fissures
Submarine eruptions	where magma comes from a vent or fissure on the sea floor
Low viscosity	where magma is fluid and flows freely
Effusive	term used to describe the fluid, non-explosive, basalt lava
Hawaiian eruption	large amounts of very fluid basaltic magma from which gases escape, but few pyroclasts
Strombolian eruption	more explosive with less fluid basalt and andesite lava. Regular explosions of gas and pyroclastic material
Vulcanian eruption	violent with viscous andesitic lava and large quantities of pyroclastic material from large explosions
Plinian eruptions	extremely explosive with viscous as-filled andesitic and rhyolite lava and tremendous volumes of pyroclastic material blasted out
active	volcano has eruptive activity within recorded history. Currently there are about 600 active volcanoes and each year 50 to 60 actually erupt
extinct	volcano has not shown any historic activity and is usually deeply eroded
dormant	volcano is one that has not shown eruptive activity within recorded history, but shows geological evidence of activity within the geologically recent past

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	Creado por siobhan.quirk hace más de 11 años