Geology Exam #2
the volcanic rock type that transports diamonds and mantle xenoliths to the surface, but diamonds are not made from this rock
kimberlite
volcanic precipitation
occurs when melts solidify or freeze
what crystal habit do diamonds have
octahedral
describe the role that pressure can play in determining whether a rock will melt
pressure increases with depth, but increased pressure raises the melting temperature, so melting is less likely to occur at higher pressures
how deep do diamonds originate
150 km or lower
Different types of sedimentary rocks
All formed by some kind of weathering Clastic- loose fragments (clasts) cemented together Non-clastic- Biochemical- cemented sea shells of organisms Organic- carbon-rich remains of once-living organisms Chemical- minerals that crystallize directly from water
igneous intrusions- discordant
Dike- vertical to angular cross-cutting intrusions that follow fractures Stocks- form as small intrusions, much larger, intrude through fractures Batholith- composed of stocks
common clastic sedimentary rocks
Conglomerate- distal- gravel Breccia- proximal- gravel Sandstone- distal- sandstone Shale- distal-clay
cross bedding
Created by ripple and dune migration Thin= made from water Thick= made from wind
Goldich Stability Series
Felsic rocks are the most stable mineral when it comes to weathering Mafic rocks are the least stable when it comes to weathering
Classifying sedimentary rocks
Grain size Angularity of fragments Composition
Geological settings of volcanoes
Island arcs Hot spots Continental arcs Mid-ocean ridges Continental rifts
common non-clastic sedimentary rocks
Made of biotic particles or chemical precipitates Limestone- shells made of calcite/ions in solution Peat/coal- decayed compacted vegetation Salt- ions in solution Chert- ions in solution
differentiation of mafic magma chambers
Melting Fractional crystallization Assimilation
sorting
Poorly sorted- different coarser grain size, some angular Well sorted- finer grained, rounded
aphanitic
Rapid cooling at earth's surface results in tiny mineral crystals that can only be seen under a microscope.
Silica composition and volcano shape
Shield- basalt, low viscosity, less silica, not steep Strato- andesitic flow, steep but not too steep Cinder cones- rhyolitic lava builds a dome, steep
porphoritic
Texture that indicates two different stages of cooling (large crystals embedded within matrix of smaller crystals)
graded bedding
The result of sorting from settling, turbidity currents Larger grains settle at the bottom, finer grains at the top
what is a joint
a break or fracture in a body of rock
rock
a coherent, naturally occurring solid of aggregate minerals
what is magmatic differentiation
any process that causes magma composition to change
A'ã
basalt that solidifies with a jagged, sharp, angular texture
Pahoehoe
basalt with a glassy, ropy texture
pillows
blobs of basalt cooled rapidly by quenching in water
fragmental (pyroclastic)
broken, abraded, or irregular particles on the surface, made by explosive eruptions
volcanic flow bands
caused by friction of viscous magma in contact with solid rock, swirly
Angular fragments
close to the source, proximal
different igneous textures and their cooling rates
coarse grained- slow cooling porphyritic- slow and fast cooling fine grained- fast cooling glassy- very fast cooling
phaneritic
coarse-grained, crystals are large enough to be seen w/out a microscope, formed by slow cooling (intrusive)
What are two major factors that determine the composition of igneous rocks?
color and grain size
For the sedimentary rocks, besides grain size, what are three other characteristics we take note of?
composition, sedimentary type, and texture
mafic melts
contain relatively high proportion of magnesium oxide and iron oxide relative to silica
high viscosity
cooler, high silica (felsic), more volatiles rhyolites
what is the source of energy to cause melting for magma
decay of radioactive elements
are diamonds stable or metastable
diamonds are metastable at the surface of the earth
chemical weathering mechanisms
dissolution- when water dissolves the mineral that make up the rock, on the surface hydrolysis- the breakdown of rock by acidic water, deep within the rock
fragmental textures are most commonly associated with
explosions from the volcano
rounded fragments
far from the source, distal
What are the four major groups of igneous magma/rocks as classified by composition?
felsic- light, high silica intermediate- grey mafic- dark, black ultramafic- greenish, dark, low solica
Basic mapping unit of sedimentary rocks
formation
what temperature and pressure are diamonds made at
high temperature and high pressure
What is the term used to describe how different minerals crystallize at different temperatures?
fractional crystallization
physical weathering mechanisms
freeze thawing thermal expansion abrasion by organisms
trace fossils
from an animal burrowing into a crack in a rock or a plant starts growing in a crack
felsic melts
have a relatively high proportion of silica
ultra mafic melts
have an even higher proportion of magnesium oxide and iron oxide relative to silica
low viscosity
hot, less silica (mafic), less volatiles basalt
what is a caldera
huge hole left by the collapse of a volcanic mountain
the process of loose grains becoming hard rock
lithification 2 main steps in the process are compaction and cementation
where do diamonds originate from
lithospheric cratonic roots
plume hot-spots
mantle plumes that cut through continental crust create large volumes of felsic magma
What is the term used to describe how rocks melt over a range of temperatures?
metamorphism
magma
molten rock beneath the earth's surface
3 common mineral cements that hold sedimentary rocks together
quartz, calcite, and hematite
a texture of glass indicated the lava was
quenched by water
cross bedding
ripple and dune migration (current flowing in one direction across sediment)
parallel bedding
settling from suspension
igneous intrusions- concordant
sill- igneous rock between pre-existing layered rock, roughly horizontal, injected parallel to preexisting layers Laccolith- dome-like intrusion at shallow depth Lopolith- magma intrusions
vesicles
small holes left behind as lava cools
What does the combination of the three characteristics tell us about the sediments' history?
the formation, transport, and maturity of the rocks
deposition
the process of moved particles being deposited
weathering
the process of natural forces breaking down rocks in place
erosion
the process which the broken pieces are transported, or moved
Bowen's Reaction Series
the simplified pattern that illustrates the order in which minerals crystallize from cooling magma according to their chemical composition and melting point Rocks formed from minerals at the top of the series are mafic (low temperature) Rocks formed from the bottom of the series are felsic (high temperature)
transportation
the transport of particles
graded bedding
turbidity currents (sorting during settling)
polymorphs
two minerals with the same composition, but with different chemical structures diamond and graphite
current (asymmetric) ripples
water flowing in one direction over loose sediment
wave (symmetric) ripples
water/current moving in both directions over loose sediment
what is decompression melting
when a portion of the earth's mantle is pushed up into the crust, this causes the mantle to move to a location with lower pressure which makes it a lower melting point through the process of convection, so it will melt pressure changes, temperature doesn't
what is assimilation
when solid or fluid material is incorporated into the magma
mud cracks and rain drop impressions
when there are cracks/rain drop marks and sediment is dragged across and fills into the marks and makes casts
what is flux melting
when water and other volatile materials are introduced to hot solid rock and break chemical bonds lowering the melting temperature, causing the rock to melt