Geology 1200 Lecture Quiz 4 (Appold)
High Gas Content of Magma
more likely to erupt explosively
Gneiss
most coarse-grained and highest graded foliated rock. alternating bands of dark and light minerals
glassy texture
no crystals. very rapid cooling. forms when magma spewed into air, or as skin on surface of lava. typically associated with silica-rich magmas
Diagenesis may include...
o Compaction o Cementation o Mineral alteration by chemical reactions
Formation of sedimentary rocks
o Weathering and erosion o Transportation o Deposition o Burial o Diagenesis Process whereby sediment is converted to rock
Our most IMPORTANT energy resource are sedimentary:
oil, natural gas, coal
phaneritic texture
• coarse-grained (large) crystals• implies slow cooling• formed at deeper levels within the Earth
Sedimentary rocks provide info about what?
Climate Topography and landscape Geographic environment: e.g. lake, river, desert, ocean, swamp Plants and animals
Factors affecting magma viscosity
- silica content (high silica content increases viscosity) - temperature (high temp. lowers viscosity) - water content (high water content lowers viscosity)
3 factors controlling magma formation
1. Increasing temperature or heat 2. Decreasing pressure 3. High water content promotes melting
Magma
A molten mixture of rock-forming substances, gases, and water from the mantle
Is clastic or chemical sedimentary rocks more abundant?
Clastic
Classifications of sedimentary rocks
Clastic (detrital) or Chemical
aphanitic texture
Fine-grained (small) crystals. Implies rapid cooling. Formed at surface of Earth or at shallow depths.
Mafic/Ultramafic magmas
Less likely to have high gas contents
Felsic magmas
More likely to have high gas contents
Chemical sedimentary rocks
Result from lithification of inorganic and organic precipitates from water
Foliation
The metamorphic rock texture in which mineral grains are arranged in planes or bands.
Most common gases in magmas
Water vapor and carbon dioxide
Schist
a coarse-grained metamorphic rock that consists of layers of different minerals and can be split into thin irregular plates.
Viscosity
a measure of a fluid's resistance to flow
Phylitte
a metamorphic rock made from slate that has been subjected to heat and pressure. Very fine-grained but has pearly sheen
Sedimentary rocks
a rock formed by: o The accumulation and cementation of mineral grains transported by wing, water, or ice to site of deposition OR... o By chemical precipitation at the depositional site
vesicular texture
a texture characterized by numerous pores or vesicles, where gas escaped as the magma cooled rapidly
Slate
a very fine-grained rock that can be parted along distinct planes
pyroclastic texture
characterized by angular fragments, formed by violent volcanic eruptions
Evaporites
chemical sediments produced from the evaporation of water Examples: Halite and Gypsum
porphyritic texture
coarse-grained crystals contained within a matric of fine-grained crystals. Hybrid origin : magma began cooling slowly at depth, then transported ti shallow levels where it finished cooling more quickly
Dolostone
composed of dolomite.
Sorting
degree of similarity in grain size. increases w/ transport distance
pegmatitic texture
extremely coarse-grained crystals, very slow rate of color coupled w/ high water or volatile content for efficient ion transport, crystal size from centimeters to meters
Mylonite
form in deep portions of fault zones. fine-grained recrystallized material.
chemical sedimentary rock
formed from chemical precipitation from a solution
clastic sedimentary rock
formed from rock fragments
Felsic Magmas
have high viscosity (analogous to toothpaste)
Mafic Magmas
have low viscosity (analogous to water or honey)
Lava
magma that reaches the surface of the Earth and is expelled onto it
metamorphism
process by which mineralogy or textures of rocks is altered by pressure, temperature, or reaction w/ fluids.
Sedimentation
process of deposition of mineral grains or precipitates in beds or other accumulations
Limestone
rock composed primarily of calcite. most abundant chemical sedimentary rock
igneous rock
rock that forms when magma cools and solidifies
Metamorphic rock
rock whose original mineralogy or texture has been altered due to effects of pressure, temperature, or reaction w/ fluids.
Extrusive Rocks
rocks that form as result of cooling and crystallization of lavas
Intrusive Rocks
rocks that form from magmas that didn't reach the Earth's surface
Low Gas Content of Magma
typically quiescent