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Rivanna Master Naturalists
Geology
Marilyn Smith, Annuitant of ExxonMobil and VMN
Matt Heller, Virginia Department of Mines,Minerals,
and Energy and VMN
What is Geology?
“The study of the planet Earth, the materials of which it
is made, the processes that act on these materials, the products formed and the history of the planet and its life forms since it origin.”*
Why should a Master Naturalist study Geology?
•Geology can help explain
• the types soils in our region (hence different plants)
• distribution and flow of rivers, lakes, and groundwater
• distribution of mineral and hydrocarbon resources.
• Better understand our landscape, topography and history of the area
*AGI Glossary of Geology, 5th Edduction Reivsed Ver 1.8
1. Understand magnitude of geologic time
2. Introduce Plate Tectonic Theory
3. Examine some rock forming minerals and three basic rock types and processes that form them
4. Discuss the physiographic provinces of Virginia and
5. Learn about the geology in different parts of Virginia.
Objectives of Geology Session.
Uniformitarianism assumes that the same natural laws and processes that operate in the universe now, have always operated in the universe in the past and apply everywhere in the universe. Said another way, “ the present is the key to past”. Formulated in 18th century by James Hutton, popularized by Charles Lyell in 1830
4James Hutton Charles Lyell
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Both laws and theories are products of the scientific process Based on empirical data Help to unify a scientific
discipline
Scientific Law Predicts results Frequently represented by a
formula
Scientific Theory provides an explanation of
why or how Explain most of the data Predict previously observed
phenomena
Charles Darwin’s theory of evolution, 1859
1. Evolution occurs --- organisms change through time and life on earth has changed
2. Natural Selection – living things with beneficial traits for survival produce more offspring
Simply stated: the gene distribution changes over time
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1. Fossil Record
2. Homologus Structures ---Comparative Anatomy
3. Molecular Biology – RNA/DNA sequencing
4. Biogeography – Spatial distribution
5. Direct Observation
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1. Fossils represents the remains of once living organisms
2. Most fossils are the remains of extinct organisms; that is, they belong to species that are no longer living anywhere on Earth
3. The kinds of fossils found in rocks of different ages differ because life on Earth has changed through time
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.
.
.
1. .
http://pubs.usgs.gov/gip/fossils/succession.html
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A theory of global tectonics in which the lithosphere is divided into a number of plates that interact with one another causing seismic and tectonic activity along these boundaries
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In 1912 ,Alfred Lothar Wegener, German meteorologist proposed one supercontinent 200 million years ago
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1. Ruggedness and youth of the ocean floor;
2. Confirmation of repeated reversals of the Earth’s magnetic field in the geologic past and the continents have “wandered” around the globe
3. Emergence of the seafloor-spreading hypothesis and associated recycling of oceanic crust
4. Precise documentation that the world's earthquake and volcanic activity is concentrated along oceanic trenches and submarine mountain ranges.
15http://pubs.usgs.gov/gip/dynamic/stripes.html
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1. Divergent - where earth’s crust is created2. Convergent - where crust is returned to mantle or obducted to
create mountains.3. Transform – plates move past one another
Artist's cross section illustrating the main types of plate boundaries (see text); East African Rift Zone is a good example of a
continental rift zone. (Cross section by José F. Vigil from This Dynamic Planet -- a wall map produced jointly by the U.S. Geological
Survey, the Smithsonian Institution, and the U.S. Naval Research Laboratory.)
Plates move apart from one another
New crust is created between
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http://blogs.ei.columbia.edu/2010/02/05/continental-breakup-in-east-africa/
http://pubs.usgs.gov/gip/dynamic/ridge.html
TerrestrialMarine
19http://pubs.usgs.gov/gip/dynamic/understanding.html#anchor5567033
20http://pubs.usgs.gov/gip/dynamic/understanding.html#anchor5567033
• Commonly offset the active spreading ridges, producing zig-zag plate margins.
• Few occur on land, e.g. the San Andreas whichconnects the East Pacific Rise, a divergent boundary to the south, with the South Gorda --Juan de Fuca -- Explorer Ridge, another divergent boundary to the north.
21http://oceanservice.noaa.gov/facts/tectonics.jpg
Start here
Old Rag granite
intruded
Catoctin
Basalts
Appalachian
Mountains
Mesozoic
Basins
http://twentytwowords.com/a-map-of-pangea-overlaid-with-current-countrys-borders/
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Naturally occurring
Inorganic solid
Ordered internal molecular structure
Definite chemical composition
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These elements combine to make more than 4000 minerals
Should not be surprising that many of the minerals contain silicon, oxygen
and aluminum
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Most common
mineral in
oceanic crust
As a group,
feldspar - most
common mineral in
continental crust
Second most
common
Working in groups describe the minerals at your station using your own words
Consider:
Shape
Luster
Density (heft)
Transparency
Using the Rocks and Minerals Quick Study Guide can you identify any minerals?
We will review these minerals in the class
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“An aggregate of one or more minerals, e.g. granite, shale, marble; or a body of undifferentiated mineral matter, e.g.
obsidian; or lithified organic material, e.g. coal”*
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*AGI Glossary of Geology, 5th Ed.
1. Igneous – (“ignis” Latin for fire) rocks that solidify from molten material (magma beneath the earth, lava at the surface)
2. Metamorphic – rock derived from preexisting rock by chemical, mineralogical or structural change IN THE SOLID STATE as a result of changes in temperature, pressure or stress.
3. Sedimentary – rock formed by the consolidation of loose sediment (transported by water, air, ice) that has accumulated in layers – or– chemically precipitated from solution, e.g. rock salt --- or–organic rock made from remains of plants and animal shells, e.g. limestone
Result of plate
tectonic processes
Formed by weathering, erosion and
deposition or chemical
precipitation
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1. Rifting
2. Subduction
3. Hot Spots
Created during both plate tectonic processes
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Rifting/Sea floor spreading where earth’s crust is created
Subduction, where crust is returned to mantle or obducted to create mountains.
Extrusive – magma reaches the surface of the earth and cools quickly
Intrusive – magma cools slowly beneath the surface of the earth
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www.geology.ohio-state.edu
ExtrusiveIntrusive
http://news.nationalgeographic.com/news/2010/04/photogalleries/100402-iceland
IGNEOUS ROCK – EXTRUSVE - ICELAND
Which plate tectonic process?
IGNEOUS ROCKS - EXTRUSIVE
For more than 9 hours a vigorous plume of ash erupted from Mt. St.
Helens, eventually reaching 12 to 15 miles above sea level. The
plume moved eastward at an average speed of 60 miles per hour,
with ash reaching Idaho by noon. By early May 19, 1980, the
devastating eruption was over. Shown here is a close-up view of the
May 19 ash plume.
Mt. St. Helens soon after the May 18, 1980 eruption, as
viewed from Johnston's Ridge. Photo taken September
10, 1980.
Copyright © USGS Cascade Volcano Observatory; Image courtesy Earth Science World ImageBank
http://www.earthscienceworld.org/imagebank
Which tectonic process?
Extrusive – magma reaches the surface of the earth and cools quickly
Intrusive – magma cools slowly beneath the surface of the earth
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www.geology.ohio-state.edu
ExtrusiveIntrusive
IGNEOUS ROCKS - INTRUSIVE
Image of Yosemite Valley and Half Dome in
Yosemite National Park - plutonic granite
exposed by erosion and subjected to
glaciation Image courtesy Earth Science World ImageBank
http://www.earthscienceworld.org/imagebank
Mt. Rushmore National Monument
located in Black Hills of South Dakota.
Granite sculpture by Gutzon Borglum.
The busts of these presidents are 60 feet
high. Mount Rushmore National Memorial (NPS Photo)
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Extrusive rocks cool very rapidly and produce fine-grained minerals or glassy appearance
Intrusive rocks cool very slowly and produce coarse-grained rocks
Classification of Igneous Rock based on
1. Texture - Appearance or character of rock including size, shape and arrangements of the individual components
2. Mineral Composition
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Basalt
(mafic)
Rhyolite
(felsic)
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Gabbro
(mafic)Granite
(felsic)
Dark silicate minerals Rich in iron and magnesium: Olivine, Pyroxene,
Amphibole, Biotite mica
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Basalt Gabbro
Light silicate minerals
Light silicates: Feldspars, Quartz, muscovite mica
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Rhyolite Granite
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Water
Wind
Ice
Gravity
From Key Conepts in Geomorphology by P. Bierman and D.
Montgomery 2014
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Sedimentary Rocks
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Composition
What minerals make up the rock?
Are there fossils?
Texture
the shape, size and orientation of the mineral grains (layers?)
Composed of clastic grains?
Can you see grains?
Fig. 3-14, p. 54
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1. Rifting/Sea floor spreading where earth’s crust is created
2. Subduction, where crust is returned to mantle or obducted to create mountains.
The transition of one rock into another by temperatures and/or pressures unlike those in which it formed. Chemical, mineralogical and structural changes occur in the solid state.
Metamorphic rocks are produced from Igneous rocksSedimentary rocksOther metamorphic rocks
The process of metamorphism occurs near plate boundaries
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Slate
Gneiss
Eclogite
How would you
describe the texture
of these rocks?
Texture refers to the size, shape, and arrangement of grains within a rock
Foliation – any planar arrangement (or banding)of mineral grains or structural features within a rock
Composed of interlocking crystals
Common metamorphic minerals: kyanite, staurolite, chlorite, garnet, serpentine
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Schist with garnet Gneiss
Slate
Transforms hard rock into material that can be moved by surface processes and used by living organisms
Physical
Biological
Chemical
biological
chemical
physical
From Key Conepts in Geomorphology by P. Bierman and D. Montgomery 2014
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The Rock CycleWeathering
Transportation
Deposition
Lithification
Crystallization
Consolidation
Uplift and Exposure
Melting
Metamorphism
Sediments
Sedimentary
Rocks
Metamorphic
Rocks
Igneous Rocks
(Intrusive)
Igneous Rocks
(Extrusive)
Magma
