Igneous Structures: Intrusive

Viscosity

• Units: pascal-seconds (kg/m-sec)• How many pascals pressure x how many

seconds to squash fluid flat?• Viscous: Material flows as long as pressure is

applied, however small• Pseudoviscous: Material flows after some

threshold stress

Viscosity of Common Materials

Material Viscosity Pa-Sec

Hydrogen gas, 15 degrees K 0.0000006 (6 x 10-7)

Air, 0 degrees C 0.000017 (1.7 x 10-5)

Liquid Hydrogen 0.00001 (10-5)

Water 0 degrees C 0.0018 (1.8 x 10-3)

Water 100 degrees C 0.0003 (3 x 10-4)

Heavy Machine Oil 15 C 0.66

Glycerin, 20 degrees C 1.5

Honey 20 degrees C 1.6

Geologic Viscosities

Material Viscosity Pa-Sec

Basalt Lava 1000

Rhyolite Lava 1,000,000

Rock Salt 1014 (Pseudoviscous)

Marble 1016

Granite, Quartzite 1018 - 1020

Asthenosphere 1019 - 1020

Deep Mantle 1021 - 1022

Shallow Mantle 1023 - 1024

What Drives Magma?

• Magma is typically 10% lighter than equivalent solid rock– Why pressure inhibits melting

• Buoyancy drives magma upward– Weight of rock around volcanic conduit > weight

of magma• Gas pressure powers volcanic eruptions• Mafic (dense) rocks can sink in crust by

viscous flow

Plate Tectonics and Volcanoes

Cullain Layered Complex, Scotland

Cullain Layered Complex, Scotland

Cullain Layered Complex, Scotland

Cullain Layered Complex, Scotland

Cullain Layered Complex, Scotland

Filter Pressing, Scotland

Filter Pressing? Scotland

Lava Flows and Dike, Scotland

Magma Mixing, Scotland

Pseudotachylite, Scotland

Sill, Scotland

Extrusion Striae, Scotland

Keeweenawan Sills, Ontario

Keeweenawan Sills, Ontario

Columnar Jointing, Ontario

Batholith, California

Sierra Nevada Batholith

Roof Pendants, Sierra Nevada

Columnar Jointing, Devil’s Postpile, California

Columnar Jointing, Devil’s Postpile, California

Columnar Jointing, Idaho

Columnar Jointing, Scotland

Devil’s Tower, Wyoming

Phonolite, Devils Tower, Wyoming

Jointing, Devils Tower, Wyoming

Laccolith, Bear Mountain SD

Laccolith, Wyoming

How Laccoliths Form

How Devil’s Tower Formed

Intrusions, Mount Rushmore

A Rarely Seen Perspective

Granite Intrusion, Black Hills

Dike and Shear Zone, Washington

Dikes, Lead, South Dakota

Dike, Redgranite, Wisconsin

Dike, Redgranite, Wisconsin

Dike, Black Hills, SD

Palisades, New Jersey

The Palisades

Base of Palisades Sill, NJ

Intrusion Breccia