Introduction to Igneous and Metamorphic Rocks

Igneous rocks

Rocks that formed from a melt that cooled (other melted rocks)

Magma

Intrusive/plutonic rocks

Lava

Extrusive/volcanic rocks

Difference between Magma and Lava

Magma is underground, lava is above ground

Felsic magma

Feldspar & Quartz, high silica content >65%

Intermediate magma

53-65% silica

Ultramafic magma

<45% silica, rare

Mafic magma

Poor silica content 45-52%, oceanic crust & volcanic islands

Geotherm

A line or surface on the earth that connects two points of equal temperature (hot springs, geysers, fumaroles, and volcanic activity)

Bowen's reaction series

Describes the point at which heat certain minerals crystalize/melt at

Bowen's continuous reaction series

Describes the evolution of the plagioclase feldspars as they evolve from being calcium-rich to more sodium rich.

Bowen's discontinuous reaction series

Describes the formation of the mafic minerals olivine, pyroxene, amphibole, and biotite mica.

Silica content and viscosity

Magma with high silica content has a much higher viscosity than magma with low silica content.

Decompression

Rock from a higher pressure area (lower) rises to a lower pressure area (higher) and melts without a significant change in temp occurs mainly at divergent plate boundaries.

Addition of volatiles

Volatile substances (water vapor) enter a rock, lowering its melting point, allowing it to melt at lower temperatures.

Transfer of heat

AKA Conductive melting, Heat from a hot rock moves into a cooler rock, melting it if the cooler rock reaches its melting point.

Pluton

Deep seated intrusion of igneous rock.

Batholith

>100+ km^2, biggest pluton.

Laccolith

Mushroom or lens shaped pluton.

Dike

Tabular, discordant pluton.

Sill

Tabular, concordant pluton.

Supervolcano

A volcanic center that has had an eruption of magnitude 8 on the Volcano Explosivity Index (VEI), meaning that at one point in time it erupted more than 1,000 cubic kilometers (240 cubic miles) of material.

Hot-spot volcanoes

An area of the Earth's mantle from which hot plumes rise upward, forming volcanoes on the overlying crust.

Hot-spot track

A chain of volcanoes forms as a tectonic plate moves over a plume of hot mantle material.

Stratovolcanos

Have steep sides formed by alternating layers of thick, nonflowing lava and ash.

Cinder Cones

A small, steep-sided volcanic cone formed by the accumulation of small, solidified lava fragments.

Shield Volcanos

Gently sloping, wide volcano formed by very runny lava.

Pahoehoe

Lava flow that is characterized by ropey, smooth, or billowy surface.

A'a'

Lava flow with a rough surface and a thick interior.

Ash

<2mm pyroclastic debris.

Lapilli

2 to 64mm pyroclastic debris.

Bomb

>64mm pyroclastic debris.

Pillow lavas

A formation that occurs from lava erupting underwater and cooling quickly, causing a pillowy appearance.

Basaltic lavas

Mafic=low silica content.

Rhyolitic lavas

High silica content.

Weathering

Breaking down of rocks where they are in place.

Erosion

The action of surface processes that removes soil, rock, or dissolved material from one location on the Earth's crust and then transports it to another location.

Transportation

The processes by which the sediment is moved along.

Lithification

The process by which sediments are compacted or cemented together to form sedimentary rock.

Diagenesis

The chemical, biological, or physical process by which sedimentary rocks change after sediments are deposited.

Transgression

When the sea level rises relative to land causing the sea to flood previously dry land.

Regression

When sea level falls relative to land.

Metamorphism

Rocks are transformed into a much denser, more compact rock with different mineral compositions and textures.

Protolith

The original rock, before undergoing metamorphosis.

Blueschist formation conditions

High pressure, low temp, 200-500 C.

Aureole

The zone surrounding an intrusion, which is a mass of igneous rock that solidified between other rocks located within the Earth.

Non-foliated metamorphic rock characteristics

Do not have a plated texture, typically grow crystals in no particular direction.