Igneous Rocks and Geotherm Concepts

Igneous Rocks

• Igneous rocks form from melted rock that cools.
• Magma is intrusive (plutonic) rock.
• Lava is extrusive (volcanic) rock.
• Magma is underground, lava is above ground.
• Felsic rocks have high silica content (>65%).
• Intermediate rocks have 53-65% silica.
• Ultramafic rocks have <45% silica.
• Mafic rocks have 45-52% silica.
• As silica content decreases, ferromagnesian silicates increase.

Geotherm

• A line or surface showing equal temperature points.
• Used to track hot springs, geysers, and volcanic activity.

Bowen's Reaction Series

• Describes the sequence of mineral crystallization/melting during magma cooling.
• The continuous branch shows the evolution of plagioclase feldspar.
• The discontinuous branch shows olivine, pyroxene, amphibole, and biotite mica formation.

Magma Viscosity and Silica Content

• Magma with high silica content has higher viscosity.
• Magma with low silica content has lower viscosity.

Magma Formation

• Decompression causes rocks to melt at lower temperatures.
• Addition of volatiles lowers the melting point of rocks.
• Transfer of heat from adjacent magma raises temperatures.

Plutons

• Intrusive igneous rock masses.
• Batholiths are the largest plutons (>100km^2).
• Laccoliths are mushroom-shaped plutons.
• Dikes are tabular, discordant plutons.
• Sills are tabular, concordant plutons.

Supervolcanoes

• Volcanic centers with massive eruptions (VEI 8).
• Yellowstone Caldera is a notable example.

Hot Spot Volcanoes

• Volcanoes formed over rising plumes of hot mantle material (hotspots).
• Hotspot tracks show plate movement over time.

Subaerial Volcanoes

• Stratovolcanoes: Steep sides, alternating layers of lava and ash.
• Cinder cones: Small, steep-sided cones formed by solidified lava fragments.
• Shield volcanoes: Gently sloping, wide volcanoes formed by runny lava.

Pyroclastic Debris

• Ash: <2mm
• Lapilli: 2-64mm
• Bomb: >64mm

Pillow Lavas

• Lava cools quickly underwater, forming pillow shapes.

Basaltic vs Rhyolitic Lavas

• Basaltic has low silica, rhyolitic has high silica.

Weathering, Erosion, and Transportation

• Weathering: the breakdown of rocks.
• Erosion: the removal and transportation of weathered material.
• Transportation mediums (biggest to smallest): ice, water, wind.

Lithification and Diagenesis

• Lithification: compactions and cementation of sediments into rock.
• Diagenesis: chemical, biological, and physical processes that alter sediment after deposition.

Metamorphism

• Metamorphism changes rocks into denser, more compact forms.
• Metamorphism from regional dynamothermal changes vs thermal/contact metamorphism.

Protolith

• The original rock before metamorphism.

Aureole

• The zone around an intrusion that shows metamorphism change.
• Non-foliated metamorphic rocks lack a layered texture. Quartzite, marble, and hornfels are examples.

Test your understanding of igneous rocks, their formation, and the principles of geotherm. Explore Bowen's Reaction Series, magma viscosity, and silica content to deepen your geological knowledge. This quiz covers essential concepts for geology students.