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