CEE 437 Lecture 4 Igneous and Metamorphic Rocks, Rock Lab October 10, 2002 Thomas Doe

Outline Igneous Rocks Metamorphic Rocks Rock Identification Lab

Northwest Igneous and Metamorphic Rocks Columbia River Basalts (miocene) Snake River Basalts (pliocene ) Yellowstone Region Acidic Volcanics (Pleistocene to recent) Cascade Volcanoes (recent) Recent Basaltic Volcanism (Newberry Crater) Cascade Batholiths (Felsic, Cret- Miocene)

Geologic Settings for Igneous Rocks Oceanic –Hi Fe, Mg, Ca, low Si –basalt, gabbro Continental –Hi Si, Na, K –granite, rhyolite, andesite

Igneous Origins Intrusive –Batholithic or plutonic: phaneritic –Dikes or sills that chill rapidly: aphanitic Extrusive –deposition as melt (lava) –pyroclastic tuff tephra pyroclastic flows

Identifying Igneous Rocks Chemistry –Acidic: Basic (more Si, less Si) Texture –Aphanitic: crystals not visible –Phaneritic: made of visible crystal components –Porphyritic: Larger crustals in aphanitic or phaneritic ground mass

Igneous Rock Identification

Igneous Rock Classification SERPENTINITE Acidic, FelsicBasic, MaficUltramafic Common Types in RED outline

Igneous Structural Features

Magma Generation on Continental Margins

Magma Generation in Convergent Continental Plate Margins

Igneous Structures

Extrusives Viscosity varies with Si and water content –Basalt — low viscosity –Rhyolite — high viscosity Rhyolite flows relatively unusual as rhyolite does not flow well –Explosive –Tuffs, pyroclastics

Volcano Types Basaltic: low viscosity — Hawaii, Columbia Plateau Andesitic/Rhyolitic

Structures of Basalt Flows Lava Tubes Flow Stratigraphy –collonade –entablature –flow top breccia/scoria

Hawaii Basalt Flows

Basalt Flow Structures

Eruptions of Acid-Rock Volcanoes

Rhyolite Dome

Caldera

Mt. St. Helen’s Blast Zone

Mt. Mazama Ash Distribution

Subduction-Zone Metamorphism

Metamorphism Recrystallization of Rock Under Temperature and Pressure

Metamorphic Rock Classification

Metamorphic Classification Original Material –sandstone, limestone, shale, basalt) Metamorphic Grade (Temperature, Pressure) Source of Metamorphism (Regional, Contact)

Basic Metamorphic Types Quartz Sandstone  Quartzite Limestone, Dolomite  Marble Shale  –Slate — cleavage, no visible xl’s –Phyllite — foliation, mica sheen but xl’s not visible –Schist — clear foliation, visible mica –Gneiss — like granite but with foliation/gneissosity Basalt  greenschist, amphibolite

Origin of Foliation (gneissosity, schistosity)

Metamorphism at Continental Collisions

Contact Metamorphism

Metmorphic Grade

Northwest Igneous and Metamorphic Rocks Columbia River Basalts (miocene) Snake River Basalts (pliocene ) Yellowstone Region Acidic Volcanics (Pleistocene to recent) Cascade Volcanoes (recent) Recent Basaltic Volcanism (Newberry Crater) Cascade Batholiths (Felsic, Cret- Miocene)

Sauk River Quadrangle

Malpasset Dam