Igneous Petrology

Question 1

The Earth’s Interior

Answer 1

Crust, Mantle, Core

Question 2

Tell me something about the CRUST

Answer 2

Oceanic crust
Thin: 10 km
Relatively uniform stratigraphy while Continental Crust
Thicker: 20-90 km average ~35 km
Highly variable composition
Average ~ granodiorite

Question 3

The Ophiolite Suite

Answer 3

Sediments, pillow basalt, sheeted dikes, more massive gabbro, ultramafic (mantle)

Question 4

Tell me something about the MANTLE

Answer 4

Mantle:
Peridotite (ultramafic)
1. Upper to 410 km (olivine ® spinel)
Low Velocity Layer 60-220 km
2. Transition Zone as velocity increases ~ rapidly
660 spinel ® perovskite-type 3. Lower Mantle has more gradual velocity increase

Question 5

Tell me something about the CORE

Answer 5

composed of Fe-Ni metallic alloy, OC is L, and IC is S

Question 6

Nomenclature and Classification

Answer 6

Textural, Chemical, Mineralogical, Genetic

Question 7

Genetic

Answer 7

GENETICbasic system which classifies rocks on the basis of where they form. Classified into 1. plutonic - at depth 2. hypabyssal - intermediate depth 3. volcanic - on the Earth’s surface. This system is not very practical, but it serves as a first approximation, it tells nothing about mineralogy, chemistry of the rocks and can not distinguish basalt from rhyolite.

Question 8

Textural

Answer 8

relies on the grain size of indovidual minerals in a rock

Question 9

Chemical

Answer 9

requires a complete chemical analysis of a rock

Question 10

Mineralogical

Answer 10

The one gaining application is the result of several years work by the IUGS Subcommission on the Classification of Igneous Rocks or Streckeissen Classification.

Question 11

What is an Ophitic Texture?

Answer 11

Ophitic Texture - having or being a rock fabric in which lath-shaped plagioclase crystals are enclosed in later formed augite.

Question 12

Classification Sysyems

Answer 12

1. Gradation in Silica Content 2. Colour Gradation 3. Chemistry of the Rocks 4. Saturation