GLG 111 Study Guide - Midterm Guide: Migmatite, Phyllite, Amphibole
26 Jun 2018
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DEFORMATION
Deformation: folding, faulting, shearing, compression and extension of rock by plate tectonic
forces
Compressional stress: squeeze and shorten rock formations; dominate at convergent bounds
Tensional stress: stretch and pull rock formations apart; dominate at divergent boundaries
Shearing forces: shear two parts of a rock formation in opposite directions; dominate at
transform boundaries
Anticlines: folds in which layered rocks are bent upward into an arch
Synclines: folds in which layered rocks are bent downward into a trough
Symmetrical folds: limbs that dip symmetrically from the axial plane
Asymmetrical folds: one limb dips more steeply than the other
Overturned folds: limbs that dip in the same direction, but one limb has been tilted beyond the
vertical
Fault: fracture that displaces the rock on either side of it
Hanging wall: block of rock above a dipping fault
Foot wall: block of rock below a dipping fault
Normal fault: dip-slip fault where the hanging wall moves downward relative to the foot wall,
extending the structure horizontally
Reverse fault: dip-slip fault where the hanging wall moves upward relative to the foot wall,
causing a shortening of the structure
Thrust fault: low-angled, reverse fault; dip is less than 45 degrees, so movement is more
horizontal than vertical
Left-lateral strike-slip fault: observer on one side of the fault sees that the block on the opposite
side has moved to the left
Right-lateral strike-slip fault: observer on one side of the fault sees that the block on the
opposite side has moved to the right
Oblique-slip fault: faults that show both strike-slip and dip-slip motions
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1. Be able to classify fault types based on block diagrams or cross sections of displaced
geological units.
2. Know what types of faults most commonly develop along convergent, divergent and
transform plate tectonic boundaries.
METAMORPHISM
Re-crystallization: preexisting minerals recrystallize to form new crystals that are different sizes
and shapes; if under tectonic stress, the crystals will be aligned with the long-axis orientation
perpendicular to the stress direction
Remobilization: elements in pre-existing minerals can diffuse, dissolve or partially melt and be
recombined to form new mineral crystals elsewhere; if under tectonic stress, the crystals will be
aligned with the long-axis orientation perpendicular to the stress direction
Grain flattening/elongation: tectonic stresses accompanying metamorphism will flatten or
elongate preexisting mineral crystals
Rotation: platy minerals can be rotated by tectonic stresses accompanying metamorphism to
form metamorphic cleavage, foliation and lineation
Shearing: shear (created by tectonic stress) between grains or along discrete planes will stretch
pre-existing mineral crystals
Protolith: parent rock
Contact metamorphism: heat from an igneous rock metamorphoses the rock immediately
surrounding it; normally only affects a thin zone of country rock along the zone of contact
Non-foliated metamorphic rocks: form from contact metamorphism
Regional metamorphism: takes place where both high temperatures and high pressures are
imposed over large parts of crust; forms foliated rocks
Foliation: sheets of metamorphic minerals aligned perpendicular to the direction of maximum
force; occurs from regional metamorphism
Slate: lowest grade of foliated rocks; so fine-grained that their individual crystals cannot be
seen easily without a microscope; commonly produced by the metamorphism of shales
Phyllite: slightly higher grade than slate; similar in character and origin; more or less glossy
sheen resulting from crystals of mica and chlorite
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Deformation: folding, faulting, shearing, compression and extension of rock by plate tectonic forces. Compressional stress: squeeze and shorten rock formations; dominate at convergent bounds. Tensional stress: stretch and pull rock formations apart; dominate at divergent boundaries. Shearing forces: shear two parts of a rock formation in opposite directions; dominate at transform boundaries. Anticlines: folds in which layered rocks are bent upward into an arch. Synclines: folds in which layered rocks are bent downward into a trough. Symmetrical folds: limbs that dip symmetrically from the axial plane. Asymmetrical folds: one limb dips more steeply than the other. Overturned folds: limbs that dip in the same direction, but one limb has been tilted beyond the vertical. Fault: fracture that displaces the rock on either side of it. Hanging wall: block of rock above a dipping fault. Foot wall: block of rock below a dipping fault.
