GEOLOGY EXAM 3

metamorphic rocks

those that have undergone solid-state alteration of preexisting rocks

protoliths

parent, preexisting rocks that are altered during metamorphism

protolith: limestone

marble

diagenesis

the process that describes physical and chemical changes in sediments first caused by water-rock interactions, microbial activity, and compaction after their deposition. excludes weathering and deep metamorphism

recrystallization

with heat only, minerals can recrystallize, destroying the original texture by growing larger and becoming interlocking. does not change mineral composition

foliation

with heat and pressure minerals recrystallize and are squeezed so that they grow in alignment with the new direction of stress and re-form into minerals stable at higher T and P

Agents of metamorphism

main: temperature and pressure

other: tectonic stress and fluids

contact metamorphism

due to contact with or proximity to an igneous intrusion, small area

regional metamorphism

affects rocks over an extensive area as a result of the large-scale action of heat and pressure

neocrystallization

formation of new(metamorphic) minerals from old(those from the protolith). old minerals become unstable and undergo chemical reactions that recycle elements to form a new mineral assemblage

pressure solutions

mineral grains partially dissolve where their surfaces press together. dissolved ions migrate in a thin water film and reprecipitate in areas where pressure is low

plastic deformation

mineral grains soften and deform when rock is squeezed or sheared at elevated temperature and pressure

overprinting

when a combination of metamorphic processes occur on a single rock

increasing metamorphic grade

shale, slate, phyllite, schist, gneiss

normal stree

operates perpendicular to a surface

compression

push-together normal stress

tension

pull-apart normal stress

shear stress

acts parallel to a surface

hydrothermal fluid

hot water with dissolved ions and volatiles, accelerates metamorphism

metasomatism

hydrothermal alteration, speeds up chemical reactions and add/subtract elements

slate

foliated, fine-grained, low-grade metamorphic shale

phyllite

foliated. fine-grained, mica-rich formed from slate

schist

fine to coarsely crystalline rock indicating medium-high grade metamorphism

gneiss

distinct compositional bands, light and dark

metaconglomerate

metamorphosed conglomerate. gravel clasts are flattened by pressure solution and plastic deformation. foliation is defined by the flattened gravel clasts

compositional banding

during solid-state differentiation, chemical reactions segregate light and dark layers to create compositional banding

migmatite

partially melted gneiss

nonfoliated

have no plaanar fabric evident because they lack inequant minerals and/or they recrystallized without differential stress

quartzite

metamorphic quartz sandstone, nonfoliated

tennessee marble

crystalline limestone, not marble

metamorphic grade

measure of the intensity of T and P conditions that lead to alteration

metamorphic indicator minerals, low → high grade

chlorite, biotite, garnet, staurolite, kyanite, sillimanite

thermal

heating by plutonic intrusion

burial

deep burial in a basin

dynamic

shearing in a fault zone

regional

P and T change due to orogenesis

hydrothermal

alteration by hot water leaching

subduction

high P and low T alteration

shock

extreme high P from a bolide impact

orogenesis

mountain building process

undeformed rocks

display horizontal beds, spherical sand grains, and no folds or faults

deformed rocks

show tilted beds, metamorphic alteration, folding, and faulting

displacement

change in location

deformation

changes in the shape of a rock (strain) caused by impact of forces (stress)

strain

result of deformation, a change of shape of a rock, which is caused by force acting on a rock

stress

force applied across a unit area

brittle deformation

occurs in shallow crust, rocks break by fracturing

joints

cracks or fractures

ductile deformation

greater depth, some bonds in rock break but new ones quickly form. occurs at higher T and P conditions, which caused deformation by flowing and folding

joints

planar rock fractures without any offset that develop from tensile stress in brittle rock.

compression

object is squeezed and deformation shortens and thickens the material. differential stress

tension

occurs when the ends of an object are pulled apart, which stretches and thins the material

shear

when surfaces slide past one another, neither thickens nor thins the crust

pressure

when an object feels the same stress on all sides

slip lineations

slickenslides and linear grooves

fault scarps

visible when faults intersect the surface

dip-slip faults

show vertical offset of primary structures, indicated at surface by scarp, slip up or down slope of fault plane

reverse fault

hanging wall moves up relative to the footwall

normal fault

hanging wall moves down relative to the footwall

strike slip faults

caused by shear stress, opposing forces pushing past one another along a plane of weakness

oblique slip faults

combinations of lateral shear and compression or tension, results in diagonal movement along the fault plane

hinge

line along which curvature is greatest

limbs

less curved sides of a folda

axial plane

connects hinges of successive layers

anticlines

up folds

synclines

down folds

hypocenter

focus, location where the fault slip occurs. usually on the fault surface (underground)

epicenter

is the land surface directly above the hypocenter. maps often portray this

common non-fault causes of seismicity:

magma movement

nuclear detonations

eruptions, landslides, tsunamis

body waves

travel inside the surface

surface waves

travel along the surface

compressional force

crust moves back and forth in the direction of travel

shear force

crust moves perpendicular to the direction of travel

p-waves

slinky like motion that causes compression and extension, body waves

s-waves

rope like vertical movements that cause shear, body waves

love waves

rope like side to side movements that cause shear, surface

rayleigh wave

rolling movements that cause vertical and horizontal shear and result in an elliptical motion of particles, surface