class7

Geology 101Class 7

Spring 2014

Volcanoes of the World

Source:After R. Decker and B. Decker, Volcanoes, 1981, W.H. Freeman and Company, New York, NY.

Igneous Processes and Mineralization

Most copper, silver, gold, iron, chrome, etc. found in ores in deposits created near the edges of intrusive plutonic interaction

Fractional crystallization leaves behind concentrated minerals in hot (steam)water solution

Pegmatite contains large crystals formed in mineral rich hot/steamy remains of fractional crystallization

Example of Hydrothermal Formation

Hot fluids are mineral-rich and are forced into cracks, fissures and pores. Gold and silver are commonly associated with hydrothermal formation.

480km to east-west and 240km to north-south,

Bushveld Igneous ComplexLarge layered igneous intrusion - tilted and eroded in South Africa. This basin contains some of the richest ore deposits on Earth

Vast quantities of platinum, iron, tin, chromium, titanium and vanadium

Bingham Canyon Copper mine south west of Salt Lake City is ¾ mile deep, several miles across and produces copper, gold, and silver. The ore is low grade, yielding 13 lb of copper for every ton of ore. http://academic.emporia.edu/aberjame/histgeol/penrose/penrose.htm

Igneous rock groups

Granite-Rhyolite (Orthoclase and quartz) Diorite-Andesite (Sodic plagioclase, Pyroxene,

Amphibole) Gabbro-Basalt (Calcic plagioclase, olivine, pyroxene) Peridote – Ultra-mafic (Olivine&pyroxene) Obsidian – glassy Scoria – Surface frothy basalt- low silica Pumice – gassy, light basalt - high silica Tuff – pyroclastic rock formed from ash and dust Breccia – volcanic rock formed from larger

fragments, glass, pumice and scoria

http://csmres.jmu.edu/geollab/fichter/IgnRx/disthtml.html

ENVIRONMENT OF FORMATION

Later we will see how this relate to

how rocks erode?

Class Objectives - Chapter 4 Explain the conditions under which rocks melt into magma

and the relationship of those conditions to plate tectonics Describe the processes that produce the three major types

of magma and the resulting differences in the nature of the eruptions and intrusions that take place

Relate the magma types to the range of minerals produced.

Recognize the various types of the igneous structures and the resulting landforms and mineral/rock textures

Recognize the connection between igneous processes and the creation of valuable mineral ores like gold, silver, copper, iron, platinum, etc.

Objectives – Chapter 5 Describe the two types of rock weathering and the

resulting sediment types Describe the processes that lithify sediments

into sedimentary rocks Classify the major clastic and chemical/biogenic

rock types by composition and texture Describe the connection between depositional

environment and the type of sedimentary rock that can develop there.

Define the connections between sedimentary formations and fossil fuels

Sedimentary rocks Almost 90% of earth crust - igneous rocks Sediments and Sedimentary rock- 5% of

outer 16km of Earth but 75% of surface Fluid deposited minerals that lithified 99% shale, limestone, or sandstone 46% 22% 32% Clay CaCO3 SiO2

Sedimentary rocks form from weathered, transported and deposited sediments

Weathering Weathering is simply:

Chemical and/or Physical

breakdown of a rock material

Physical or Mechanical Weathering

Rock is split or broken into smaller pieces of the same material - No change composition.

Example: Breaking of a rock cliff into boulders and pebbles

Types of Mechanical Weathering

Frost action or Ice Wedging: Water expands 10% when it freezes. Tremendous pressure on container. Water in the cracks of rocks wedges the

rock apart when it freezes.

Environments where temperatures range around 0 degrees Celsius

Effective on rock and northern highways

Mt. Whitney, CA

Bare mountaintops are especially subject to ice wedging.

Types of Mechanical Weathering Repeated wetted and drying

Especially good at destroying rocks that contain clay.

Clays swell up when wet and shrink when dry.

Mudstones and shales most suspectible.

Types of Mechanical Weathering Action of plants and animals:

Larger trees and shrubs may grow in the cracks of boulders.

Ants, earthworms, rabbits, woodchucks, and other animals dig holes in the soil. These holes allow air and water to reach

the bedrock and weather it.

Types of Mechanical Weathering Loss of Overlying Rock and Soil

Sheet jointing on a granite outcrop produces cracks - exposing more of the rock surface to weathering.

EXFOLIATION

Central Texas Uplift

Enchanted Rock

Types of Mechanical Weathering Action of plants and animals:

Lichens and mosses grow on rocks They wedge their tiny roots into spores and crevices. Larger trees and shrubs may grow in the cracks of

boulders. When the roots grow, the rock splits.

Roots use chemical warfare more than force!

Ants, earthworms, rabbits, woodchucks, and other animals dig holes in the soil and weathered material.

Lichens and grass attacking andesite outcrop in Bogota, Colombia - Summer 2012

Bio-Mechanical Weathering

Types of Mechanical WeatheringGranite exfoliation

Summary Physical Weathering

Frost action

Wetting and drying

Action of plants and animals

Loss of overlying rock and soil EXFOLIATION

Chemical Weathering Rocks’ minerals are changed into different

substances.

Water and water vapor are important agents of chemical weathering.

WATER and its bi-polar covalent bond will eventually wear everything down

Example: Formation of clay minerals from feldspar

Types of Chemical Weathering

Results mainly from the action of rainwater, oxygen, carbon dioxide, and acids of plant decay on rocks.

Dissolves

Oxidizes

Hydrolysis reactions

Agents - Chemical Weathering

Rainwater dissolving oxygen, carbon dioxide, and acids of plant decay.

Carbon dioxide dissolves easily in water.

Carried through the ground to the bedrock.

Dissolves the ionic bonded minerals like rock salt, calcite, (limestone, dolomite), and gypsum

Agents of Chemical Weathering

Has the greatest effect on calcite than any other mineral.

It dissolves it completely, with no clay left over.

Agents of Chemical Weathering

Hollows out great caverns in limestone bedrock.

And Sinkholes like the Wink Sink

This photo of Lime Sink was taken on 20 July 1932, over a week after the drawdown, which occurred over the night of 9-10 July.

‘Karst’ landforms develop in areas underlain with limestone

Hydrolysis of Igneous Rocks Chemical Weathering

The chemical reaction of water with other substances is called hydrolysis.

This attacks minerals in our igneous rocks like :Feldspar

Common Clay Type

Oxidation of Igneous Rocks Chemical Weathering

The chemical reaction of oxygen with other substances is called oxidation. Iron-bearing minerals are the ones most

easily attacked by oxygen These include

Magnetite Pyrite Dark-colored ferromagnesian silicates

OLIVINE AMPHIBOLE PYROXINE