week 1 - 4 igneous rocks Flashcards
what is younging direction
the direction in which beds get younger
cross bedding are how big
> 1m
cross ripple lamination are how big
<1m
what are syn depositonal minor structures and examples
used to determine the strata
graded bedding: sorted material with coarse to fine up top
Pillow lava: in the form of distored globular masses
what are post depositional primary structures and examples
used to determine the strata
load clasts: sand can load mud below - bulbous
flame structures: mud pushed up by load clasts
convolute bedding: laminae are contorted by high velocity currents
mud cracks and burrows
what is strike, dip and dip direction
strike: direction of a horizontal line in the plane (3 numbers)
dip: inclination of plane, measured down from horizontal (2 numbers)
dip direction: compass sector toward which the plane dips (3 numbers)
what is apparent dip
dip angle in a section not normal to the strike
what are outliers
younger rocks surrounded by younger rocks, common with erosional, fold, fault and depositional outliers
what are inliers
older rocks surrounded by younger, common with erosional, fold and fault outliers
a paraconformity is what
an unconformity with no obvious erosional surface (flat, clear boundary)
a disconformity is
an erosional surface between sequences
a non conformity consists of what
sedimentary layer ontop of igneous/metamorphic layer (blob like, intrusive)
how to recognise unconformities
sedimentary: conglomerates, weathered surfaces, truncation of bedding planes, surfaces altered by burrowing, boring or cementation in hard grounds and surfaces that show relief due to erosional episode
paleontological: one or more faunal zones missing
structural: trucated dykes or faults, gently discondant dups above and below unconformity
what are concordant intrusions
lavas, tuffs, sills and lacoliths
what are disconcordant intrusions
dykes, radial dyk, cone sheets, and plugs
what are the 5 steps in identifying faults
- trends that share orientation
- displacement type (apparent or true)
- relative ages
- sets
- systems
what are the different types of ore deposition
placer, orogenic, epithermal, porphyry, VMS synsedimentary and hydrothermal
what are the fluid sources of hydrothermal deposits
magmatic, metamorphic, meteroic, connate and seawater
what is stratabound
bound within stratigraphic layer, often limestone or organic rich sediments (chemically reactive)
what is stratiform
having the form of stratigraphic layering such as an evaporative deposits
examples of epigeneitc deposits
same age as intrusion such as a vein of gold or porphyry
what range is gentle fold
180 - 120
what range is open fold
120 - 70
what range is closed fold
70 - 30
what range is tight fold
30 - 5
what range is isoclinal fold
< 5
what is the range of gently inclined
10 - 30
what range is recumbent incline
< 10
what range is moderately inclined
30 - 60
what range is steeply inclined
60 - 80
what range is upright incline
80 +
hinge line at 90 means
vertical
hinge line at 80
steeply plunging
hinge line at 20
gently plunging
what is the order of describing a fold
plunge and trending direction
inclination
tightness of fold
