Igneous Petrology Exam Review

What are 2 types of physical processes of crystal-liquid separation? Describe Each. Which process occurs at the fastest rate?

crystal settling, compaction

What are 2 types of rock that might remain after melting the mantle?

Harzburgite and dunite

What is anorthosite?

A mafic rock consisting of almost all plagioclase

What is peridotite?

A mantle rock with pyroxene and a high percentage of olivine

What is the asthenosphere?

A plastic layer of the mantle

What is trachyte?

A quartz poor , K-feldspar rich volcanic rock

What is rhyolite?

A quartz rich volcanic rock

What is a sedimentary rock?

A rock type that makes up 66% of exposed rock on land

What is phonolite?

A rock with 15wt% total alkalies and 60wt% SiO2

What is dacite?

A rock with 3wt% total alkalies and 60wt% SiO2

What is hornblendite?

An ultramafic rock consisting of almost all hornblende

What is pyroxenite?

An ultramafic rock consisting of almost all pyroxene

What type of meteorite represents the undifferentiated Earth?

Carbonaceous Chrondites (contains pyroxene and olivine globules)

Explain how we can locate an ancient volcanic vent by using the size of lithic clasts

Bigger clasts are near the vent because they can't travel very far, smaller clasts are farther away

What is a lithic?

Debris that has been caught in a volcanic rock

Where does a magma begin to fragment and produce pumice and ash?

During explosion, glass transition into pyroclastic flow/hot ash

What mechanical process of crystal-liquid separation would you expect to be occurring in the mantle?

Gravity settling, compaction, and flow segregation

Name 5 types of textures that are most closely associated with a high degree of undercooling in felsic magmas?

Glassy, flow banding, graphic, granophyritic, dendritic

What key observation led B. Marsh to suggest that the rheological locking point for mist magma was when they reached ~50% crystals?

He didnt find volcanic rock that had >50% crystals. When magma reaches 50% crystals, it reaches the rheological locking point at which it is uneruptable

High pressure mantle melting favors the production of quartz-saturated or under-saturated melts?

High pressure favors under-saturated melts because high pressure means greater depth where quartz does not exist as a crystal

Name 3 ways by which the mantle melts and give an example of the tectonic settings

Increase temperature, lower pressure, add volatiles (H2O). Subduction zones(add volatiles), mid ocean ridges(lower pressure), hot spots (temp increase)

What is a Moho?

The separation between crust and mantle

Name 3 ways we can generate compositional diversity in magmas

Melt of the crust combining with magma, liquid crystal separation (crystal fractionization), and magma mixing

What is a metamorphic rock?

Mantle rock type

Describe 3 ways by which we have determined the composition of the mantle

Meteorites, volcanic xenoliths, komatiites, opheolites (oceanic thrust)

What are the requirements for melting in the mantle system as seen in the diagram below?

Must cross (be on the right side) the purple lines to dehydrate the mineral and create melt

Will mantle melting occur in a phlogopite-bearing peridotite along the ocean geotherm at ~1000C and 130km depth? Explain.

No because it is not past (on the right side) the Phlogopite line

Explain why heating of amphibole or phlogopite bearing peridotite is not an effective way of producing mantle melts. See diagram.

Not enough water, they will never be heated enough to overcome the pressure due to depth in order to melt

What ultramafic rock best represents the upper mantle in composition/mineralogy?

Peridotite

By what proposed mechanism do magmas ascend through the brittle crust? Ductile crust?

Plume vs. stoping

If magma undergoes a slow rate of cooling followed by a very fast rate, what rock texture is likely to develop?

Porphyritic

What key features in an igneous rock will allow one to differentiate between pyroclastic debris and lava flow

Pyroclastic debris would accumulate lithics and be very large and blocky as it has a high viscosity. Lava flows have low viscosity so they are more consistent and have smaller crystals

What is a Transform Fault?

Shear boundaries

Explain how the geothermal gradient changes from oceanic to continental lithosphere

Steep geothermal gradient when the crust is thin (oceanic) shallow geothermal gradient for a thicker crust because conduction is harder through a thick crust

Describe 3 different volcano morphologies and the composition of magma associated with each

Strato = rhyolitic, alternating layers of lava and tephra Cinder come = basalt, conical piles of tephra Shield = basalt, runny lava flows

What is differentiation?

The process of enriching elements in Si, K, and Al

What is the lithosphere?

The rigid layer of the mantle

Describe how the dihedral angle influences melt migration

This influences the ability to form an interconnected film. The lower the angle, the higher the permeability

Which 2 magma types are subalkaline?

Tholeiitic and calc-alkaline

What tectonic setting are tholeiitic, calc-alkaline, and alkaline basalts typically associated with?

Tholeiitic is associated with any environment, calc-alkaline is associated with subduction zones, alkaline is associated with plume magma, convergent margins, oceanic, and continental environments

What types of igneous rocks formed the early continental crust?

Tronjamite, Tonalite, Granodiorite, (NOT GREENSTONE)

What factors play the most important role in determining the explosive potential in magma?

Viscosity(Building pressure), water(bubble coalescence)

Explain what a vitrophere and vapor phase alteration is

Vitrophere = a glassy rock with phenocrysts on the bottom VPA = When hot gas alters the vitrophere by baking it on top. Causes welding of the rock, gas streamed out and froze in place

Name 3 factors that affect the movement of magma

Volatiles(H2O), Temp, Silica content