GEO Test 2

Basaltic Lava

Pahoehoe Aa

pyroclastic flow

The expulsion of ash, cinders, bombs, and gases during an explosive volcanic eruption

Intermediate composition (Andesitic)

Contain atleast 25% dark silicate materials, associated with volcanic activity

volcanic neck

A deposit of hardened magma in a volcano's pipe

Viscosity

A liquid's resistance to flowing

cinder cone volcano

A small, steeply sloped volcano that forms from moderately explosive eruptions of pyroclastic material.

Rhyolite

Aphanitic Extrusive version of Granite May contain glass fragments Less Common and less voluminous than

Basaltic Rocks

Basalt Gabbro Diabase

Why does buoyant material segregate into regular spaced domes when it begins

Because granitic magma flows so slowly through thin sheets, it is believed that this highly viscous magma finds it easier to rise through the lower crust in the form of large domes. It cannot rise everywhere at the same time, so instead it develops a series of evenly spaced domes on its upper surface in which the buoyant material rises and between which the denser material sinks.

Shield volcano

Broad, slightly domed-shaped Composed primarily of basaltic lava Generally cover large areas Produced by mild eruptions of large volumes of lava Mauna Loa on Hawaii is a good example

Pegmatitic Texture

Exceptionally coarse grained Form in late stages of crystallization of granitic magmas

Highly viscous lava (Andesite)

Explosive Lava

contrast the eruptive styles of hawaiin strombolian vulcanian Plinian and plean volcanoes

Hawaiin: Slow viscous/fluid like flow, quiet Strom: Mild with more explosive activity with cinders, lapilli and bombs vulcan: short viiolent with viscous lava pilian: Intensely violent, lots of ash pelean: Similar to vulcan, viscous, explosive outburst.

How do intrusive igneous bodies make room for themselves

Igneous bodies make room for themselves by going into empty spaces usually horizontally. Sills will make room by lifting overlying rock. Uplifting and spreading laterally, this can form lacoliths.

Slow Growth Rate

Less Crystals but Larger

Fast Growth Rate

Many small crystals Can form glass

Porphyritic Texture

Minerals form at different temperatures and rates larger crystals called phenocrysts are embedded in a matrix of smaller crystals called groundmass

Basaltic Magma

Much lower silica content, fluid like behavior, crystalizes at higher temperatures, some of the hottest magmas on earth!

Granitic Rocks

Obsidian Pumice

dark silicates (ferromagnesian)

Olivine, Pyroxene, Amphibole, Biotite Mica

General Characteristics of magma

Parent material of igneous rocks Forms from partial melting of rocks inside the earth Magma that reaches the surface is called Lava

Granite

Phaneritic 25% quartz 65% or more feldspar May be porphyritic Very abundent

Light Silicates (nonferromagnesian)

Quartz, Muscovite Mica, Feldspars

Fluid basaltic lavas

Quiet Eruptions

What determines the grain size of igneous rock

Rate of cooling

Laccolith

Relatively small, mushroom-shaped pluton that forms when magma intrudes into parallel rock layers close to Earth's surface.

Classification of Plutons

Shape (tabular, cylindrical, and massive). Orientation with respect to host rock (discordant, concordant).

Why are the viscosities of basaltic and rhyolitic magma so different

Temperature Composition Basalts are mafic less silica Rhyolitic is felsic high silica Dissolved gases

From the crosscutting relations in fig 10.2 deduce the chronolgy of intrusive events seen in

The discordant vertical intrusions are dikes and the concordant horizontal intrusions are sills.

How does magma viscosity affect the shape of volcanoes

The more viscous the lava the steeper it is. Whearas less vsiscous lava such as basaltic lava is more fluid and creates shield shaped lavas

Pyroclastic Rocks

Tuff Volcanic Breccia

Pyroclastic Texture

Various fragments ejected during a violent volcanic eruption. Look similar to sedimentary rocks

Glassy Texture

Very rapid cooling of molten rock Obsidian

Pluton

a body of intrusive igneous rock.

Caldera

a summit depression typically greater than 1 km in diameter, produced by collapse following a massive eruption

sill

a tabular igneous body formed when magma is injected long sedimentary bedding surfaces

Dike

a tabular, discordant pluton

Batholith

a very large igneous intrusion extending deep in the earth's crust. 100 km

composite cone volcano

a volcano formed by a mixture of lava eruptions and more explosive ash eruptions Large

Intermediate Rocks

andesite diorite

Types of igneous textures

aphanitic, phaneritic, glassy and vesicular, and porphyritic

Lava domes

bulbous mass of congealed lava; associated with explosive eruptions

Phaneritic Texture

coarse grained, slow cooling, crystals have a long time to grow

basaltic composition

composed of dark colored silicates and calcium rich feldspars, more dense than granitic rock, Comprise the ocean floor and volcanic islands.

Granitic Composition (Felsic)

composed of light colored silicates, high amounts of silica, main constituents of continental crust

Nueé ardentes

fiery pyroclastic flow

Aphanitic Texture

fine grained, rapid cooling of lava or magma, microscopic crystals, may contain vesicles

fissure eruption

fluid basaltic lava extruded from crustal fractures

Granitic Magma

high in silica, extremely viscous, liquid exists a temperatures as low as 700º C

How are sulfide ore deposites formed near mid ocean ridges

hydrothermal circulation and exhalation of sulfides which are independent of sedimentary processes.

Phenocrysts

large crystals in porphyritic rocks

Vent

opening connected to the magma chamber via a pipe

Ultramafic composition

rare composition that is high in magnesium and iron composed entirely of ferromagnesium silicates

Factors that affect crystal size

rate of cooling, amount of silica, amount of dissolved gases

intrusive igneous rock

rock formed from the cooling and solidification of magma beneath Earth's surface

extrusive igneous rock

rock that forms from the cooling and solidification of lava at Earth's surface

igneous rock

rock that forms when magma cools and solidifies

Volcanic Pipes

short conduits that connect a magma chamber to the surface

crater

steep-walled depression at the summit, generally less than 1 km in diameter

Factors affecting viscosity

temperature, composition, dissolved gases

Groundmass

the matrix of smaller crystals within an igneous rock that is porphyritic

What are the main rocks in an ophiolite suite, and how are they formed

uncolsolidated sediments, pillow basalts, sheeted dikes, gabbro, dunite, and peridotite.

Lahar

volcanic mudflow

Why are igneous rocks at mid-ocean ridges so altered to hydrous material

when water is present there is an increase in pressure along with a decrease in melting point. Therefor these rocks are more likely to be affected and changed