Physical geology lecture outline

Physical geology lecture outline - Igneous Rocks

rock -> naturally occurring aggregate of mineral matter.

Major divisions of rock types:

igneous
sedimentary
metamorphic
hydrothermal
Is this a classification based on description or on genesis?

Igneous rocks in general:

Igneous rocks and the process of crystallization:
- disassociated ionic groups --> lattice structure.
- liquid (solution) --> crystalline solid.
- salty water --> ice and salts.
- magma/lava --> plutonic rock/volcanic rock.
- granitic melt --> granite.
In what different ways can the crystallization process be studied and observed?
Bowen's reaction series - a schema.
Phaneritic = coarse grained, identifiable by eye; aphanitic = fine grained.
What controls the grain size of an igneous rock?
Volcanic vs. plutonic rocks.
The initial enigma of phenocrysts - why are only some of the grains coarse?

Volcanic rocks

how does one identify a rock as volcanic?
volcanic rock types: komatiite (rare) --> basalt --> andesite/dacite --> rhyolite.
3 tectonic settings for volcanism:
- volcanic arcs associated with subduction.
- rift zones (continental and oceanic).
- hot spots.
how do you melt source rocks to create magma?
Figure of phase space for silicate melt. The space makes intuitive space. The hotter the more likely it will be molten. The higher the pressure the more likely it will be solid. Note that material can move from the solid to the melt field in at least three different manners: reducing pressure while keeping temperature constant, increasing temperature, and by shifting the boundary .
shield volcanoes versus strato- or composite volcanoes.
- shield volcanoes:
  - predominantly basalt flows.
  - low angle slopes.
  - small collapse calderas.
  - Mauna Loa.
- composite volcanoes:
  - interlayered flows and pyroclastics, usually intermediate to sialic in composition.
  - higher angle slopes (cone shape).
  - larger calderas.
  - Mt. Fuji and Mt. St Helens.
- Why the difference?
flood basalts and volcanic plateaus and large igneous provinces (LIPs):
- relationship of large igneous provinces to mantle convection.
- Columbia River Flood basalts:
  - circa 15 Ma.
  - Roza basalt member: 100-200'thick, 20,0000 square miles.
  - large fissure eruptions.
  - USGS site describing these basalts.
- Deccan Traps in India: some 65 Ma old. Same time as mass extinction? Role?
- Siberian Traps: 270 Ma. Same time as largest mass extinction.
types of eruptions.
- flows vs. pyroclastic.
- types of pyroclastic:
  - ash fall
  - glowing avalanches (debris flows)
  - lahars
textures in volcanic rocks.

Plutonic rocks

map and/or cross section relationships of plutonic rocks and inferred genesis.
intrusion geometries:
- planar intrusions: dikes and sills (discordant and concordant).
- irregular intrusions (proverbial blobs): stocks, batholiths.
- in what tectonic setting do batholiths form?
- La Paz batholith, Baja California.
plutonic rock types: peridotite, pyroxenite, dunite (all ultramafic) -> gabbro -> diorite -> granite.
plutonic rock textures and the information they carry.
how and why do magmas ascend?

Image of a sheet like (tabular) intrusion cutting the Madison limestone in Spearfish canyon in the Black Hills. This body is part of a suite of intrusions of Tertiary age found concentrated in the N part of the Black Hills uplift. Devil's Tower is a part of the suite.

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