Chapter 3 - Rock Processes And Identification

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Igneous Rock

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derived from magma

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Magma

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originated in the asthenosphere at about 100 km.

Principal component is silicate anion, magma commonly called " silicate Melt"

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Magma vs Lava

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Magma is below the earth, when magma is exposed, called Lava

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Factors that determine type of Igneous Rock

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-Cooling rate of magma (determines crystal size)

-Chemical Composition of magma

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Why does magma move to the surface of the earth?

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Magma is less dense than the crust, so it rises due to buoyancy.

-gas propulsion and hydrostatic pressure help

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Aphanitic

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Igneous rock with mineral crystals, but they are not visible to the naked eye/hand lens.

Example: Basalt, Andesite, Rhyolite

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Phaneritic

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Igneous rock with mineral crystals clearly visible

Example: Granite, Gabbro

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Pegmatitic

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Igneous rock with extra large mineral crystals, more than 4 mm

Example: Pegmatitic Granite

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Porphyritic

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Igneous rocks that have two distinctly different sizes of crystals present.

Example: Porphyritic Granite

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Vesicular

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Igneous rock with porous texture due to entrapped gas bubbles

Example: Pumice, vesicular basalt.

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Pyroclastic

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Igneous rock with rough, cinder-like texture. May be porous. Frothy.

Example: Scoria, Volcanic breccia

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Dike

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Intrusive Igneous rock.

Formed when magma cuts across existing rock beds. Vertical, tubular

Discordant

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Sill

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Intrusive igneous rock.

sheet-like horizontal intrusions.

Follow the lineation of host rock - concordant.

Formed by lifting the overburden, so tend to occur at shallow depth

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Batholith

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Intrusive Igneous rock

huge mass of igneous rock that invades a sequence of existing rocks.

Usually granite.

Discordant, since it cuts across existing rock.

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Laccoliths

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intrusive body of magma that causes overlying sedimentary beds to bulge upwards

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Extrusive igneous rock

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-flows (Aa lava [rough] or panahoe lava [smooth]

-Volcanoes/Calderas (a large crate-like depression that form around a volcanic vent)

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Clastic Rock

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formed from rock fragments.

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Non-Clastic Rock

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Rocks formed by chemical precipitation, evaporation, Flocculation

Example: Limestone (from chemically precipitated calcium carbonate)

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Diagenesis

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low temperature rock formation. Occurs for both clastic and non clastic sedimentary rocks.

-Burial (1000-2000m)

-Compaction

-Cementing Agents

-Pressure Solution

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Diagenesis turns the follow into what sedimentary rocks:

1. Cobbles

2 Gravel

3 Sand

4 Silt

5 Silt/mud/Clay
6 Carbonate-rich ooze

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1 Fanglomerate

2 Conglomerate (round)/Breccia (angular)

3 Sandstone

4 Siltstone

5 Mudstone (silt/clay)/Shale (mostly clay size, fissile)

6 Limestone

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Where does Chert usually occur

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a non clastic sedimentary rock that occurs as impurities within beds of limestone and dolomite.

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How is Gypsum formed?

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forms from seawater/lake basins by evaporation and concentration of minerals

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What events cause sedimentary rocks to exhibit cross-bedding?

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deposited by moving water or wind currents.

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Metamorphic rock

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adding elevated pressure, temperature, or chemical fluid to existing rock.

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Regional Metamorphism

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Two tectonic plates are colliding causing high pressure or high temperature. Causes folliation

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Contact Metamorphism

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Occurs when an intrusion of igneous magma heats up the surrounding rocks.

Examples: hornfels, shale, marble.

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Metamorphic series of sandstone from in increasing metamorphism

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sandstone -> Quartzite

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Metamorphic series of Limestone from in increasing metamorphism

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Limestone-> Marble

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Metamorphic series of Shale from in increasing metamorphism

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shale -> slate (argillite) -> Phylite -> mica schist -> Gneiss -> Migmatite -> Granite

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Metamorphic series of Basalt-Gabbrofrom in increasing metamorphism

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Basalt-Gabbro -> Greenschist -> Amphibolite -> Anorthosite/Granite

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Metamorphic series of sedimentary rock from in increasing metamorphism

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sedimentary rock -> hornfels

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Usual rock of veins

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quartz or calcite

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Pegmatite

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sheet-like intrusion into existing rock. Looks like vein, but is filled with granite