Phys Geology Test Review (Ch. 1-4)

German meteorologist Alfred Wegener proposed what in 1915?

Continental Drift Hypothesis

Evidence of Pangaea (200 mya)

1) the shape of the continents

2) continental fossil organisms that matched across oceans

3) matching rock types and modern mountain belts on separate continents

4) sedimentary rocks that recorded ancient climates (including glaciers on the Southern portion)

2 flaws of Continental Drift Hypothesis

1) Tidal forces as the mechanism for continental movement

2) Implied that continents plowed through weaker oceanic crust

Lithosphere

Earth’s outermost rocky layer

Asthenosphere

A relatively weak layer of solid rock that deforms by flowing. Under the lithosphere, part of upper mantle

Lithospheric plates

Numerous segments of irregular size and shape contained by the lithosphere; boundaries can interact via convergent, divergent, or transform

How many large lithospheric plates?

7

Seafloor spreading leads to formation of new oceanic lithosphere at…

Oceanic Ridge Systems

Seafloor spreading forms new oceanic lithosphere at a rate of…

2 to 5 centimeters (or 1-6 inches)/year

What happens to oceanic lithosphere as it ages?

It becomes denser and subsides from the oceanic ridge, and the cooling asthenosphere adds new material to the underside of the plate (new lithosphere is formed from asthenosphere after the old is recycled)

On continents, divergent plate boundaries create…

a continental rift (creating a rift valley) (can lead to ocean basin)

What happens during convergent plate boundary interactions (subduction zones)?

Plates move toward one another.

Oceanic lithosphere subducts into the mantle and is recycled.

Subduction manifests a deep ocean trench.

Deep-ocean trench

The result of oceanic lithosphere subducting into the mantle (in convergent plate boundaries)

Subducted oceanic lithosphere activates…

Partial melting in the mantle, producing magma

What happens to magma produced by partial melting?

It can 1) thicken the crust OR 2) make it to earth’s surface, erupting as a volcano

Continental volcanic arc

A line of volcanoes emerging through continental crust

Volcanic island arc

A line of volcanoes arising in an overriding plate of oceanic lithosphere

Continental crust _______ subduction due to its relatively low density; instead, it generates a mountain range as intervening ocean basins are destroyed + continents on either sides collide

resists

What happens at a transform plate boundary (transform fault)?

Lithospheric plates slide horizontally past each other. No new lithosphere is generated, and no old lithosphere is consumed.

Fracture zones

Prominent linear breaks in the seafloor

Mantle plume

A roughly cylindrical upwelling of hot rock that originates deep within the mantle

Hot spot

The surface manifestation of mantle plume activity; maintains a relatively fixed position within the mantle

Hot-spot track

A chain of volcanic structures resulting from plate movements over hotspots

Curie point

A threshold temperature for magnetism (~1085°F), exceeded by eruptions of basaltic lava

Paleomagnetism/preserved magnetism

A property of rocks formed thousands to millions of years ago and contain a “record” of the direction of the magnetic poles at the time of their formation

Magnetic reversal

Earth’s magnetic north and south poles switch places

Normal polarity

Rocks exhibit the same magnetism as the present magnetic field

Reverse polarity

Rocks exhibit the opposite magnetism of the present magnetic field

Magnetic time scale

a geological timescale that records the reversals of Earth's magnetic field by analyzing magnetic anomalies in seafloor rocks and dated land basalts

Magnetometer

Passive instrument that measures changes in Earth’s magnetic field

Convection

Upward movement of less dense material and downward movement of more dense material. Drives the motion of plates.

Slab pull

The subduction of cold, dense slabs of oceanic lithosphere

Ridge push

Occurs along the ocean ridges, where newly formed oceanic lithosphere is being pushed away from the ridge axis

Mineral

A naturally occurring, inorganic solid that possesses an orderly crystalline structure and a characteristic chemical composition

Chemical bonds

Form when atoms are attached to other atoms, leading to the transfer or sharing of valence electrons

Ionic bonds

Form when atoms of one element give up one or more valence electrons to atoms of another element, forming positively and negatively charged ions

Covalent bonds

Form when adjacent atoms share valence electrons

Octet Rule

The most stable arrangement for most atoms is to have eight electrons in the outermost principal shell

Luster

Mineral’s ability to reflect light (transparent, translucent, opaque)

Streak

The color of the powder generated by scraping the mineral against a porcelain streak plate

Crystal shape is also called crystal _____, and is useful for mineral identification.

habit

Hardness 

Resistance to being scratched

Tenacity

Resistance to deforming stress

Cleavage

The preferential breakage of a mineral along planes of weakly-bonded atoms

Density

The amount of matter packed into a given volume

Specific gravity definition

The ratio between a mineral’s density and the density of water

Specific is used to…

compare the densities of minerals

Diagnostic properties

Characteristics used for identifying minerals

Crystals

Naturally occurring solids with orderly, repeating internal structures

Unit cell

The building blocks of the crystal lattice, and therefore the crystal’s structure

Steno’s Law

Regardless of how big a crystal of a given mineral may be, the angles between its faces will always be the same.

Steno’s Law is also known as…

The Law of Constancy of Interfacial Angles

Polymorphs

Different minerals with the same chemical composition

Rock-forming minerals

Minerals that make up the Earth’s crust

Economic minerals

Minerals used extensively in the manufacturing of products

Silicate

A mineral containing the silica tetrahedron (SiO4). Most abundant kind of rock-forming mineral (90% of Earth’s crust)

Nonsilicate

Minerals that lack silicon as a major part in their structure. Less abundant

Silicon-Oxygen Tetrahedron

Four-sided, pyramid-like structure found in silicates.

• Consists of one silicon atom surrounded by four oxygen atoms

Polymerization

A process that forms long chains between structures by sharing oxygen atoms.

• Can form single chains, double chains, sheets, or even complicated three-dimensional framework of tetrahedral that share all the oxygen atoms in the mineral.

Light (nonferromagnesian) silicates

• light in color

• relatively low specific gravity (2.7)

• Al, K, Ca, Na

• examples: feldspar, quartz, muscovite, clays

Dark (ferromagnesian) silicates

• dark in color

• relatively dense

• Fe, Mg

• examples: olivine, pyroxene, amphibole, biotite, garnet

Feldpsar

Type of light silicate that contains primarily potassium, sodium, and calcium.

Potassium feldspar

One of the feldspar structures that contains potassium ions

• Examples: Orthoclase and microcline

Plagioclase feldspar

One of the feldspar structures that contains both sodium and calcium ions that substitute for one another

Quartz

• 2nd most abundant mineral in the continental crust

• Only common silicate mineral that consists entirely of silicon and oxygen

• Neutral (consistent ratio of O- and Si+)

• Hard due to composition

• Resists weathering

• No cleavage

• Pure form is clear, but impurities can cause changes in color.

Muscovite

• Common member of the mica family

• Light in color + pearly luster

• Good cleavage in one direction

• Clear in thin sheets

• Can be found in sand grains

Clay

A category of complex minerals that have a sheet structure.

• Most originate as the products of weathering of other silicate minerals

• Makes up a large percentage of the soil

• Account for nearly half the volume of sedimentary rocks

• Generally very fine-grained

• Layered structure, weak bonding = slippery feel when wet

• Common in shales, mudstones, and other sedimentary rocks

Olivine

A family of high-temperature silicate minerals

• Black to olive-green in color

• Glassy luster

• Conchoidal fracture

• Transparent olivine = peridot gemstone

• Commonly forms small, rounded crystals that give a granular appearance

• Typically found in basalt

Augite

• Most common member of the Pyroxene group

• Black, opaque

• Dominant mineral in basalt

Hornblende

• Most common member of the amphiboles

• Dark green to black in color

• Forms elongated crystals

• Often makes up the dark portion in an otherwise light-colored rock

• Cleavage: 2 planes meet at 60 and 120 degree angles

Biotite

Dark, iron-rich member of the mica family.

• Sheet structure that gives excellent cleavage in one direction

• Very shiny

• Common constituent in granite

Garnet

• Structure composed of individual tetrahedral linked by metallic ions.

• Glassy luster

• Lacks cleavage

• Conchoidal fracture

• Colors vary, but most often brown to deep red

• Well-developed crystals have 12 diamond-shaped faces + most commonly found in metamorphic rock

• Semiprecious gemstones when transparent

Calcite

A mineral of the carbonate group

• When dominant mineral, rock is called limestone

Dolomite

A mineral of the carbonate group

• When dominant mineral, rock is called dolostone

Halite

A mineral of the halide group

• Frequently found in sedimentary rocks

• “Common table salt”

Gypsum

A mineral of the sulfate group

• Calcium sulfate with water bound into the structure

• Mineral from which plaster and other similar building materials are composed

Magma

Completely or partly molten rock; below Earth’s surface

Igneous rocks

Rocks composed primarily of silicate minerals and are the result of molten rock (magma) cooling

Lava

Molten rock that has reached earth’s surface

Melt

The liquid portion of magma

Volatiles

The gaseous components of magma

Crystallization

The process in which cooling reverses the events of magma; temperature of the liquid drops and ions pack more densely together, movement slows, and chemical bonds take over again to form an orderly crystalline arrangement

Intrusive/plutonic igneous rocks 

Rocks that crystallize from magma at depth 

Extrusive/volcanic igneous rocks

Rocks that crystallize from molten rock at the surface (from lava)

Felsic composition

Almost entirely light-colored silicates: quartz and potassium feldspar

Felsic rocks most commonly solidify to form ______

granite

Mafic composition

At least 45% dark silicates: olivine, pyroxene, anything high in iron or magnesium, poorer in silica

Intermediate/andesitic composition

Between felsic and mafic; typical of continental volcanic arcs

Peridotite

An important, ultramafic igneous rock that contains mostly olivine and pyroxene

Ultramafic composition

Almost entire ferromagnesian minerals; rare at the surface while dominating in the upper mantle

Texture

Overall appearance of a rock based on the size, shape, and arrangement of its mineral grains

Aphanitic texture

A fine-grained texture resulting from rocks forming at the surface or as small intrusive masses within the upper crust (where cooling is rapid)

Phaneritic texture

A coarse-grained texture resulting from rocks forming at great depth. Consists of a mass of intergrown crystals that are roughly equal in size and large enough to distinguish

Porphyritic texture

A rock texture in which there are large crystals (phenocrysts) embedded in a mix of smaller matrix crystals (groundmass)

Vesicular texture

A rock texture with vesicles that results from extrusive formation in the upper lava flow

Vesicles in rocks are formed by…

Gas bubbles escaping as the lava solidifies, leaving the voids (vesicles)

Glassy texture

A rock texture that occurs when the ions are frozen into place. This can happen when molten rock ejected into the atmosphere is rapidly cooled before they are able to develop an orderly crystalline structure

Pyroclastic/fragmental texture

A rock texture characterized by different rock fragments that were ejected by a volcanic explosion and consolidated into a larger mass

Pegmatite

A rock texture that only forms under special, fluid-rich conditions in which melts such as carbon dioxide and fluorine constitute the magma. (Ions can move freely and as a result the rocks are huge)

Granite

A coarse-grained rock composed of about 10-20% quartz and ~50% feldspar, and small amounts of dark silicates. Tends to appear grey in color at a distance.