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

4

A Basic Principle of Geology

James Hutton Charles Lyell

Scientific Laws and Theories

5

● 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

6

1. Theory of Evolution

7

Geologic Time Exercise

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

8

The Fossil Rock Record

http://pubs.usgs.gov/gip/fossils/succession.html

540

Ma*

*Million years ago

252

66

9

Structure of the Earth

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

10

2. Plate Tectonic Theory

● In 1912 ,Alfred Lothar Wegener, German meteorologist proposed one supercontinent 200 million years ago

11

Continental Drift

12

What’s missing?

13

Four major scientific developments 1950s-1970s spurring Plate Tectonic Theory Development

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.

14

Map created by Marie Tharp and Bruce Heezen (Lamont-Doherty Earth Observatory and the estate of Marie Tharp)

http://www.smithsonianmag.com/hi)

15

Whole-mantle convection

https://www.youtube.com/watch?v=kwfNGatxUJI

16

Linchpin for Plate Tecontonic Theory - Magnetic Stripes on the Seafloor

http://pubs.usgs.gov/gip/dynamic/stripes.html

17

Three types of plate boundaries

1. Divergent - where earth’s crust is created 2. 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.)

Divergent Boundaries

● Plates move apart from one another

● New crust is created between18

http://blogs.ei.columbia.edu/2010/02/05/continental-breakup-in-east-africa/

http://pubs.usgs.gov/gip/dynamic/ridge.html

TerrestrialMarine

Convergent Boundaries

19http://pubs.usgs.gov/gip/dynamic/understanding.html#anchor5567033

20

Transform Boundaries

http://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 which connects 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.

21

Plate Tectonic Boundaries

http://oceanservice.noaa.gov/facts/tectonics.jpg

Highlights of Virginia Geologic History

Old Rag granite intruded

Catoctin Basalts

Appalachian Mountains

Mesozoic Basins

Current Geopolitical BoundariesPangaea Supercontinent 250 MYBP

http://twentytwowords.com/a-map-of-pangea-overlaid-with-current-countrys-borders/

24

Earth Viewer APP

●Naturally occurring ● Inorganic solid ●Ordered internal molecular

structure ●Definite chemical composition

25

What is a mineral?

Elemental abundances in continental crust

26

These elements combine to make more than 4000 minerals Should not be surprising that many of the minerals contain silicon, oxygen and aluminum

27

Common Rock Forming minerals

Most common mineral in oceanic

crust

As a group, feldspar - most common

mineral in continental crust

Second most common

“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”*

What is a rock?

28

*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

THREE BASIC GROUPS OF ROCKS

Result of plate

tectonic processes

Formed by weathering, erosion and

deposition or chemical

precipitation

30

1. Rifting

2. Subduction 3. Hot Spots

Igneous Rocks Created during plate tectonic processes

31

PLATE TECTONICS

● 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 32

Igneous Rock Formation

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 35

Igneous Rock Formation

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)

37

Recognize this feature?

● 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

38

Classification of Igneous Rocks

39

Fine-grained texture

Basalt (mafic)

Rhyolite (felsic)

40

Coarse-grained texture

Gabbro (mafic)

Granite (felsic)

●Dark silicate minerals ● Rich in iron and magnesium: Olivine, Pyroxene,

Amphibole, Biotite mica

41

Igneous Compositions

Basalt - Extrusive Gabbro - Intrusive

● Light silicate minerals ●Light silicates: Feldspars, Quartz, muscovite

mica

42

Igneous Compositions

Rhyolite - Extrusive Granite - Instrusive

43

Sedimentary Rocks

Transforms hard rock into material that can be moved by surface processes and used by living organisms ● Physical ● Biological ● Chemical

Weathering biological

chemical

physicalFrom Key Conepts in Geomorphology by P. Bierman and D. Montgomery 2014

45

Agents of erosion and transport

Water Wind Ice

Gravity

From Key Conepts in Geomorphology by P. Bierman and D. Montgomery 2014

Sedimentary Rocks

47

Sedimentary Rock Identification is based on:

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

Metamorphic Rocks

49

50

PLATE TECTONICS

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 rocks ●Sedimentary rocks ●Other metamorphic rocks

● The process of metamorphism occurs near plate boundaries

51

Metamorphism

52

Metamorphic rocks

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

53

Metamorphic textures and minerals

54

Foliated Metamorphic RocksSchist with garnet Gneiss

Slate

55

Metamorphic changes in rock structure

56

ROCK IDENTIFICATION

Rock Type Characteristics

Igneous Interlocking grainsGenerally not layeredMay contain holes or vesiclesTends to be heavy

Sedimentary Grains are cemented togetherFrequently layeredMay contain fossilsMay feel sandy

Metamorphic Interlocking grainsFoliated – tendency to split along parallel planes or mineral grains alignedMay look folded or faulted

● Many thanks to Amy Gilmer and David Spear who provided several slides as input to this presentation

57

Acknowledgements