IGNEOUS ROCKS & VOLCANISM

a rock is an aggregate of mineral(s) or mineral matter which occurs inmassive deposits

bedrock is a massive unbroken solid rock directly overlain by soil in many locations

an outcrop is a massive unbroken solid rock exposed at the Earth’ssurface

IGNEOUS ROCK FAMILY• Definition of igneous rock

• Origin of magma

• convergent plate boundaries (subduction zones)

• divergent plate boundaries (ridges or rifts)

• isolated magma plumes (hot spots)

IGNEOUS ROCK FAMILY• Assimilation

• melting of other rock material incorporated into a magma causing original composition magma to change

• an example is the mixing of magma originating in mantle with a different composition of continental crust as magma rises

IGNEOUS ROCK FAMILY• Intrusive and extrusive as applied to

magmas and igneous rocks

• intrusive refers to any igneous activity below Earth’s surface

• extrusive refers to any igneous activity at the Earth’s surface

IGNEOUS ROCK FAMILY• Texture, mineral composition , and igneous

rock names

• texture

• grain size of mineral fragments in rock and depends on the cooling rate of magma

• smaller in rock if magma cools fast

• larger in rock if magma cools slower

IGNEOUS ROCK FAMILY• kinds of textures

• phaneritic (coarse grained)--intrusive

• aphanitic (fine grained)--extrusive

• glassy--extrusive

• vesicular (comprised of many holes called vesicles --extrusive

• porphyritic--more than 1 size mineral fragment present--phenocrysts and matrixphenocrysts and matrix

IGNEOUS ROCK FAMILY• pegmatitic--intrusive

• pyroclastic--extrusive

Phaneritic

Aphanitic

Igneous Rock Textures

Glassy

Vesicular

Igneous Rock Textures

Porphyritic

Pegmatitic

IGNEOUS ROCK FAMILY• mineral composition

• igneous rocks are comprised of a combination of silicate minerals

• Bowen’s mineral series

• describes an orderly sequence of mineral formation from a cooling magma and explains specific mineral combinations in the rock

• discontinuous and continuous series

• hydrothermal solutions

IGNEOUS ROCK FAMILY• magma composition

• can change (1) as cooling progresses and minerals separate; (2) magma assimilation

• igneous rock names

• essential minerals

• minerals in rock used to classify rock by name

• accessory minerals

• minerals not used to classify rock

IGNEOUS ROCK FAMILY• felsic

• rocks light in color and contain a lot of feldspar and quartz

• mafic

• rocks dark in color because they contain a lot of biotite, hornblende, or other dark minerals

• ultramafic

• rocks that contain augite and olivine

• igneous rock chart

Igneous Rock Classification Table

Granites

Phaneritic Textured Igneous Rocks

Diorite

Gabbro Dunite

Aphanitic Textured Igneous Rocks

Rhyolite

Basalt

Porphyritic Textured Igneous Rocks

Granite Porphyry

Rhyolite Porphyry

Andesite Porphyry

Glassy and Vesicular Textured Igneous Rocks

Obsidian

Pumice (2)

Scoria

IGNEOUS ROCK FAMILY• Igneous rock bodies

• intrusive (plutons)

• discordant-- bodies which cut across sedimentary rock contacts or boundaries

• batholith--largest pluton body and irregular in shape--ore deposits like gold, silver, copper etc. are often associated with these

Batholiths in Western USA

IGNEOUS ROCK FAMILY• stock--smaller irregular shaped body with possible associated ore bodies

• dike--very small tabular shaped body

• concordant--do not cut across sedimentary rock boundaries

• laccolith--large lens shaped body

• sill-- a small tabular shaped body

Igneous Rock Bodies (Plutons)

IGNEOUS ROCK FAMILY• Important uses of igneous rocks

• used as building materials and tombstones--this use is the same for all 3 families of rocks

• pumice is used an an abrasive material

VOLCANISM

VOLCANISM• Some common terms

• volcanism

• the processes by which magma and/or gases or volatiles are transferred to the Earth’s surface

• volcano

• an elevated area or mountain formed from accumulations of lava and/or pyroclastic materials

VOLCANISM• active, dormant, and extinct volcanoes

and volcanic areas

• activeactive--eruption can occur in the near future--Mt. St. Helens and other Cascade mountains are examples

• dormantdormant--presently inactive but believed capable of future eruptions

• extinctextinct--expected not to erupt again

• Origin and global distribution of volcanism

• origin of volcanic materials

VOLCANISM• global distribution

• “Ring of Fire” or circum-Pacific region is the greatest concentration of volcanic activity on Earth

• Mediterranean Region---2nd largest region of volcanoes on Earth

Concentration of Volcanic areas on Earth

VOLCANISM• Volcanic rocks, volatiles (gases and

vapors), and manner of eruption

• volcanic rocks

• include all extrusive textured rocks and include basalt, andesite, rhyolite, pumice, scoria, tuff, obsidian and volcanic breccia

• volatile emissions

• steam (water vapor)--most abundant

VOLCANISM• carbon dioxide is next abundant while sulfur dioxide, nitrogen, and sulfur trioxide are others

• carbon dioxide additions into the atmosphere can add to the “Greenhouse Effect” and the others can contribute to acid rain formation

• burning or decomposition of fossil fuels are synthetic contributions to the“Greenhouse Effect and acid rain

VOLCANISM• manner of eruption (passive or explosive)

• depends largely on viscosity of magma

• viscosity depends on composition and temperature of the magma associated with the eruption--the higher the silica content or the cooler the magma, the more explosive the eruption, and vice versa

• most ocean basin eruptions are passive while most continental are explosive--why???

Volcanic Eruptions on Continents

VOLCANISM• Major categories of volcanic deposits

(Classification of volcanoes)

• deposits are comprised of lava flows and/or pyroclastics

• shield type---broad with gentle slopes

• thick deposit of basaltic lava flows with little or no pyroclastic materials

• associated with ocean basin eruptions

• Hawaiian shield is about 28,000 feet thick with pimple-like islands

Shield Type of Volcanic Deposit

Shield Type of Volcanic Deposit-- Hawaiian Islands Kilauea–

Earth’s most active and Mauna Loa—Earth’s largest volcano

Shield Type of Volcanic Deposit--Hawaiian Islands

VOLCANISM• cinder cone or scoria cone

• small deposit of pyroclastic or ejected materials

• steep slopes and less than 1000 feet tall

• represents last stage (cooler) of basaltic or less commonly andesite eruptions

• example is Paricutin, Mexico which erupted in 1943 and grew 120 feet tall the first day

Cinder Cone Type of Volcanic Deposit

Cinder Cones in Arizona

VOLCANISM• composite or stratovolcano

• very tall deposit of alternating lava flow and pyroclastic deposits

• comprised of andesite or rhyolite, occur on the continents and are explosive

• examples include: Mt. Vesuvius, Mt. Fujiyama, Mt. Kilamanjaro and mountains in the Cascades including Mt. St. Helens

Stratovolcano Type of Volcanic Deposit

Mt. FujiMt. Kilimanjaro

Mt. Shasta

VOLCANISMFamous Composite Volcanoes

volcanic dome

solidified lava, hundreds of meters high volcanic ash mixed with rock fragments

viscous felsic or intermediate magma piled up around a vent found in composite volcanoes

VOLCANISM

• Eruptions with special volatile emissions

• strombolian type

• incandescent cloud is stable over vent and reflects light from magma

• Mt.Stromboli is best example and called “Lighthouse of the Mediterranean”

Mount Stromboli

VOLCANISM

VOLCANISM• Nuee Ardentes (fiery or glowing cloud)

type---pyroclastic flow

• a very hot cloud of volatiles and ash

• Mt. Pelee on Martinique emitted a 700 degree (C) cloud and killed 30,000 people in a few minutes in St. Pierre

VOLCANISM

pyroclastic flow

VOLCANISM

St. Pierre after Mount Pelee’s eruption

Art 06.08a1

Artist’s conception of Vesuvius’ eruption in A.D. 79 over Pompeii and Herculaneum

VOLCANISM

Lake Nios type

volcanic carbon dioxide trapped in the subsurface was emitted and killed 1746 villagers in Cameroon, Africa in 1986

VOLCANISM

Special features and benefits associated with volcanism

special featurescontinental flows

Continental Lava Flows in Western USA

VOLCANISM• ocean basin flows--associated with the shield type deposit

• pahoehoe--ropy surface lava

• aa--blocky surface lava

• lava tubes or tunnels

• volcanic neck and radiating dikes

Volcanic neck and Radiating Dikes at Shiprock, New Mexico

VOLCANISM• caldera

• a crater caused by the collapse of a volcanic cone

• Crater Lake, Oregon is the best terrestrial example

• Crater Lake is 5 miles in diameter

Formation of a Caldera

Crater Lake, Oregon

Could the Yellowstone Caldera Cause a Future Disaster?

Yellowstone is one of the world’s largest active volcanic areas. Abundant geysers, hot springs, and other hydrothermal activity are

leftovers from its recent volcanic past. It erupted about 600,000 years ago and is about time again.

Olympus Mons, Mars---Shield Type with Caldera

formally known as Nix Olympica, it rises about 13 miles high, or 3 times higher than Mtn. Everest and covers an area equal to Arizona. It is the largest volcano in the solar system— it has 6 calderas—

VOLCANISM• Benefits related to volcanism and igneous

activity

• fertile soils formed from weathering of igneous rocks

• magma in contact with or in the vicinity of groundwater produces steam which is a source of geothermal energy

CLICK HERE

Geothermal Energy From Hydrothermal Ocean Vents

VOLCANISM

subsurface volcanic water mined on extra-terrestrial bodies may affect colonization of those bodies

VOLCANISM• Mass wasting associated with volcanism

• severe damage can result from mudflows on the sides of volcanoes---these flows are called lahars which can form when highly unstable layers of volcanic ash and debris are saturated with water

A house moved by a lahar

VOLCANISM

VOLCANISMLahar mudflow

VOLCANISM

• Prediction of volcanic eruptions

• the increase in the number and magnitude of earthquakes associated with volcanic activity favors volcanic activity sooner

• the magnitude of bulging of Earth’s surface can be used an eruption predictor

• tilt meters and laser mirrors can be used to measure the magnitude of bulge

VOLCANISM

• Volcanism in the solar system

• on the moon

• presence of light colored and basaltic lava flows

• Mars

• Olympus Mons and other caldera, and is 13 miles high and its base covers an area the size of Arizona—good extra- terrestrial example of a shield volcano

VOLCANISM• Io, a moon of Jupiter

• only other place where volcanic activity was actually observed happening