Rock Melting

Factors

5.1 Lecture Notes

Mineral Composition:

Different minerals melt at different temperatures.

Pressure:Rocks that can withstand higher pressures required higher temperatures in order to melt.

Explain:

Explain:

Water and carbon dioxide:

H2O & CO2 help lower the pressure within a rock; thus lowering the rock’s melting temperature.

Where it (rock) melts

Location: Upper asthenosphere: 50-200 km below Earth’s surface.

Subduction Zones

Rocks subducted along plate boundaries are subjected to increased temperatures & begin to melt.

At underwater subduction areas: rocks melt faster because pressure is reduced.

situations

Mantle plumes:Areas with hot, rising magma (mantle plumes) melt rocks as they rise.

Mantle plumes (hot spots) on Earth’s surface result in volcanoes.

situations

Divergent Boundaries:

As plates pull away from one another, a decrease in pressure occurs, and thus triggers melting.

situations

Intrusive Igneous RockDescribe:

Magma that crystallizes before it reaches earths surface.

Cooling rate: Slow.

Crystal size and texture: Large; phaneritic

Porphyritic Texture

Describe: Magma that cools slowly & then rapidly will have large crystals “floating” in smaller crystals.

Extrusive Igneous Rock

Describe: Magma that crystallizes on Earth’s surface.

Cooling rate: Rapid

Crystal Size and Texture: Small; Aphanitic

Stop here, do rest of notes another day!

Three Methods of Formation of Intrusive Igneous RocksStoping:

Pieces of older rock break from the magma chamber’s wall, drop into the magma, & melt.

Magma Chamber:

Magma Injection:Magma is forced out of magma chamber & into pre-existing fractures.

Sometimes magma crystalizes within a magma chamber.

Intrusive Igneous BodiesBatholith:

Large intrusive masses that cut across older rocks & cover areas greater than 100 sq km.

Stocks:

Laccoliths:

Large, dome-shaped intrusions injected into shallow, sedimentary rock beds.

Smaller intrusive masses less than 100 sq km.

Dikes: Small, shallow intrusions that cut across pre-existing rock.

Sills: Small, shallow intrusions that get injected parallel to the rock layers.

Pyroclasts

Describe: Fragments ejected from a volcano; includes small ashes to large rocks!

Ex: Mt. St. Helens!

Pyroclastic flow

Lava Flow

Describe: Molten rock from an erupting lava vent. Lava flow speed depends on its composition & the slope’s steepness.

Lahar

Describe: A mix of hot or cold water & rock fragments flowing down a volcano slope or a river valley.