Chapter 11 Flashcards
Rock Cycle
Igneous —> Sedimentary —> Metamorphic
Igneous Rock
Rock that has solidified from magma.
Ex: Basalt
Contact
A surface seperating different rock types.
Country Rock
An accepted term for any older rock into which an igneous body intruded.
Chill Zones
Finer-grained rocks that indicate magma solidified more quickly here because of the rapid loss of heat to cooler rock.
Plutonic Rocks
Igneous rocks that are formed at considerable depth(more than several km).
Coarse-grained(grains>5cm), reflecting the slow cooling and solidification of magma.
Porphrytic Rocks
Large crystals are enclosed in a groundmass of finer crystals or glass.
Ex: appearance of milk chocolate bar containing whole almonds.
Gabbro
Formed of course-grained ferromagnesian minerals and gray, plagioclase feldspar.
Basalt
Gabbro’s fine-grained counterpart, also composed of ferromagnesian minerals and plagioclase.
Xenoliths
Fragments of rock that are distinct from the body of igneous rocks in which they are enclosed.
Rhyolite
Fine-grained Composed predominantly of feldspars (pink and white) and quartz.
Granite (course-grained counterpart).
Diorite and Andesite
Composed of feldspars and significant amounts of ferromagnesian minerals (30-50%).
Diorite is course grained
Andesite is fine grained(grey-green)
Mafic Rocks
Igneous Rocks with silica content close to 50% by weight are considered silica-poor, despite being the most abundant component. But have relatively high content of Mg, Fe, and Ca.
Ex: basalt, gabbro
Tend to be darker in color due to high presence of Fe, Mg minerals.
Felsic Rocks
Rocks that are (Silicic) silica-rich (65% or more SiO2) and very small amounts of oxides, Ca, Fe, Mg…
Ex: Rhyolite, granite.
Tend to be lighter in color due to lack of Fe, Mg minerals.
Intermediate Rocks
Rocks with chemical content between that of felsic and mafic.
Ex: andesite
Color is also mid range such as grey, green..
Ultramafic Rocks
Composed entirely of ferromagnesian minerals. No feldspars present, or quartz.
Ex: Peridotite (course, pyroxene and olivine), contains less than 45% SiO2
Intrusive bodies
Intrusive rock whose names are based on size and shape and relation to surrounding rocks.
Volcanic Neck
A shallow intrusive structure formed from magma that solidified within the throat of a volcano.
Dikes and Sills
Shallow intrusive structures.
Dike: tabular, discordant(body not parallel to any layering in country rock).
Sill: tabular, concordant(are parallel to any planes or layering in the country rock).
Intrusives that Crystallize at Depth
Pluton: Body of magma or igneous rock that crystallized at considerable depth within the crust.
Stock: small, discordant pluton (less than 100km square).
Batholith: large pluton (greater than 100 sq km)- predominantly granite.
Diapirs: large blobs of magma worked upward through the lower crust and collected, and solidified 5-30kms below surface.
Geothermal Gradient
The rate at which temperature increases with increasing depth beneath the surface.
On average: 3 deg Celcius for each 100m of depth in the upper crust decreasing in the mantle.
Decompression Melting
Takes place when a body of hot mantle rock moves upward and the pressure is reduced.
Bowen’s Reaction Series
Series of experiments that determined the sequence in which minerals crystallize in a cooling magma.
Can be used to show differentiation and partial melting- two processes that create/modify magma.
(1) A mafic magma will crystallize into pyroxene and calcium rich plagioclase(basalt or gabbro) if the early formed crystals are not removed from the remaining magma.
(2) if minerals are separated from the magma, the remaining magma is more slilicic than the original magma.
(3) if you heat a rock, the minerals will melt in reverse order.
Differentiation
The process by which different ingredients separate from an originally homogenous mixture.
Ex: separating whole milk into cream and nonfat milk.
Takes place mainly through Crystal settling.
