Geol Flashcards
Who was Alfred Wegener?
- Proposed continental drit 1915
- Published the Origin of Continents and Oceans
What can you tell me about the Continental drift hypothesis?
Super continental called Pangae breaks apart 200 million years ago
What are the evidences that support continental drift hypothesis?
- fit of the continents
- fossil evidence
- rock types
- paleoclimatic
Who proposed seafloor spreading hypothesis?
Harry Hess 1960
Geomagnetic reversal
- The North pole is transformed into a South pole and the South pole becomes a North pole.
- Recorded in the ocean crust
What was the msot convincing evidence to support continental drift and sea floor spreading?
Paleomagnetism
Earths major plates
- strong, rigid outer layer
- uppermost crust
-overlies a weaker region in the mantle; asthenosphere - in motion and continous change
- largest plate is the pacific
- 7 major litospheric plates
- plates moves 5 centimeter (2 in) per year
types of boundaries (plates)
- divergent
- convergent
- transform fault
divergent plates
- most are located along the crest of oceanic ridges
- la forma en que se mueven es como si se despegaran unas de otras
continental rifting
- Split landmass I to two smaller segment along a continental rift
- example: east African rift and Rhine valley
- produced by extensional forces on lithosphere
Convergent plate
- old portion of oceanic plates are returned to the mantle
- surface expression of the descending plate is an ocean trench
- called subduction zones
- angle of subduction= 45º
Types of convergent boundaries
- Oceanic-continental convergence
- Oceanic-oceanic convergence
- Continental-continental convergence
Oceanic-continental convergence
- continental volcanic arc
- along descending plate melting of mantle rock generates magma
- denser oceanic slab sink into the asthenosphere
convergent margins
- Subduction creates magma, produces volcanoes and igneous rocks.
- Subduction creates trenches and basins where sediments are deposited and buried to form sedimentary rocks.
Continental-continental convergence
- Continued subduction can bring two continents together
- less dense
- resulting collision of two continentals produce mountains (himalayas)
Oceanic-oceanic convergence
- When two oceanic slabs converge, one descends beneath the other
- forms volcanoes on the ocean floor
- if volcanoes emerge as island , a volcanic island arc is formed (japan, tonga island
Transform fault
- Plates slide past one another and no new lithosphere is created or destroyed
- fracture zones: segment of a mid -ocean ridge along breaks in the oceanic crust
example: san andreas and alpine new Zealand
evidence from ocean drilling
Has come by drilling directly into ocean floor sediment
- age of deep sediments
- thicness of ocean floor
Hot spots
- caused by rising plumes of mantle
- volcanoes can form over them (hawaiian island chain)
mantle plumes
- long lived structured
- originate at great depth, perhaps mantle core boundary
paleomagnetism and plate motion
- stored in rocks on the ocean floor provides method to determine plate motion
- direction and rate of seafloor spreading can be established
Measuring plate velocities from space
- VLBI
-GPS
What drives plate motions
convective flow in the mantle
Forces that drive plate motion
Slab-pull
Ridge-push
Slab suction
importance of plate tectonics
- Earth’s major surface processes
- geologic distribution of earthquakes, volcanoes, and mountains
- The distribution of ancient organisms and mineral deposits
Minerals
- naturally occur
- inorganic
- solid
- crystaline structure
- chemical composition
rocks
- mass of minerals that occur naturally
atoms
- smallest particle of matter
- composed of:
protons
neutrons
electron
composition of minerals
- covalent bonding
- metallic bonding
- hybrids bond
how minerals form?
- precipitation of minerals matter
- crystallization of molten rock
- deposition as a result of biological process
physical properties of minerals
- lusster : light reflected of mineral
metallic
nonmetallic - ability to transmit light
- color
- streak: color in is powered form
- crystal shape
- tenacity: resistent to breaking or deforming
-hardness: resistance of scratching - cleavage: smooth surface ex; muscovite, feldspar, fluorite, hornblende
- fracture: irregular fracture
- density: mass per unit volume
- specific gravity
-taste - feel
- magnetism
other properties
- calcite has double refraction
- carbonates effervesce in acid
carbonates
- calcite
- dolomite
nonsilicate minerals have economic value
gypsum: building materials
halite: salt
how igneous rocks is formed?
- as molten rock (magma) cools and solidifies
characteristics of magma
- parent material of igneous rocks
- formed from partial melting rocks
- magma at surface is lava
nature of magma: components
- liquid portion =melt
- solid
- volatiles: dissolved gases in the melt (ex: h20, co2, so2)
crystallization
-cooling of magma resulting in the systematic arrangement of ions into orderly patterns
- silicone and oxygen together is the building block of silicate minerals)
igneous processes
- magma crystallizes at depth forms plutonic or intrusive igneous rocks ( this rocks are in the surface)
- solification of lava forms volcanic or extrusive igneous rocks
composition of igneous rocks
- composed of silicate minerals
- dark silicates: have iron and magnesium ( ex: olivine, pyroxene, amphibole, biotite)
- light silicate: pottassium, sodium , calcium (ex: quartz, muscovite, feldspar)
felsic vs mafic
- felsic:
+ light colored
+ compossed of quartz and potassium feldspar
+ high silica SiO2
+ major constitute of continental crust - mafic:
+ dark silicate, calcium feldspar
+ higher density
+ comprise ocean floor and volcanic islands
other composition of igneous: intermediate and ultramafic
- intermediate:
+ 25% more dark silicate minerals
+ associated wwith volcanic island arc - ultramafic:
+ composition mostly olivine and pyroxene
+ almost entirely ferromagnesium (dark) minerals (ex: peridotite [main constitute of the upper mantle])
common igneous rocks
- felsic: granite, rhyolite
- intermediate: diorite, andesite
- mafic: gabbro, basalt
- ultramafic: peridotite, komatite
how the chemical makeup of igneous rocks can be inferred?
silica content
silica content influence magma behavior
- granitic magma have high silica content, are thick and erupt at lower temp.
- basaltic magma have lower silica, more fluidike, erupt at higher temp
igneous texture
- appearance of the rock , size, shape, mineral grains
factors affecting crystal size
- rate of cooling : slow rate=larger crystals, fast rate= small crystals
- amount of silica
- amount of dissolved gases
types of igneous textures:
- aphanitic
+ rapid cooling
+ microscopic crystals - phaneritic
+ slow cooling
+ large crystals - porphyritic
+ minerals can grow large before others
+ magma moves to diferent enviroment and minerals form quickly
+ large crystals and small crystals - vesicular
+ rocks with voids by gas bubbles in lava (extrusives igneous) ex Scoria - glassy
+ rapid cooling
+ ions frozen , no ordenly structure
ex : Obsidian - pyroclastic
+ consolidation of individuals rock fragment ejected by explosive eruption - pegmatic
+coarse grained
+ form in late stage of crystallization of magma
+ rocks are called pegmatites
clasificattion igneous rocks
based on texture and composition, minerals
granitic igneous: granite
- phaneritic
- best known igneous rock
- abundant
- natural beauty
- small dark silicate
granitic igneous: rhyolite
- extrusive
- light colored silicate
- buff to pink or light gray
- less common
- felsic
granitic igneous: pumice
- form by large amount of gas escape from lava
- voids
- found with obsidian
- will float in water
- felsic
granitic igneous: obsidian
- glassy, dark colored
- silica lava cools quickly
- similar composition of granite
- dark color = small metallic ions
- felsic
intermediate igneous rocks
- andesite:
+ medium gray
+ volcanic origin
+ porphyritic texture - diorite:
+ intrusive
+ coarse grained
+ looks like gray , but lacks visible quartz crystals
+ salt and pepper apearance
mafic igneous rocks: basalt
- dark green to black
- composed of pyroxene and calcium
- most common extrusive
- upper layer of oceanic crust is composed of basalt
mafic igneous rock: gabbro
- intrusive
- dark to green
- uncommon on continental crust , but significant on oceanic crust
ultramafic rock: peridotite
- dark silicate minerals olivine and pyroxene
- rich in magnesium and iron
- typical rock of mantle
pyroclastic rocks: tuff
- common pyroclastic
- composed of ash cemented together
pyroclastic rock: welded tuff
- ash particles are hot to fuse together
- walnut sized pieces of pumice and rocks fragments
origin of magma
- earth crust and mantle are composed of solid rocks
- magma is generated in the uppermost mantle
+ big amount are produced at divergent plate
+ lesser amount are produced at subduction zones
+ also produced when crustal rocks heated
geothermal gradient
- temp. in upper crust increase 25ºC
- rocks in lower crust are near melting point
decompression melting
- melting occurs at higher temp.
- reducing pressure lowers melting temp.
addition of water when generating magma from solid rock
- occurs at subduction zones
- addition of water lowers the melting temp
3 ways to create magma
- decrease in preasure
- introduction of water
- heating crustal rocks above their melting point
bowen reaction series
- Minerals crystallize in a systematic fashion based on their melting points
- As minerals crystallize, the composition of the liquid portion of the magma continually changes
crystal settling
- minerals are denser than the liquid portion of magma and sink to the base of magma chamber.
magmatic differentiation
- formation of one or more secondary magmas from a single parent magma
assimilation
magma migrates to the crust, it incorporate some of the surrounding rock
magma mixing
when ascent of two different magma bodies, the more buoyant mass may overtake the slower rising body
partial melting
- produce more magma
- melt enriched in ions from minerals
basaltic magma
- most magma that erupt is mafic
- originate from partial melting at oceanic ridges
andesitic magma
- form when basaltic magmas assimilate crustal rock
granitic magma
- form when basaltic ponds beneath continental crust
clasiffication of pluton (intrusive)
- tabular
- discordant
- concordant
- massive
tabular: dike
discordant pluton
tabular: sill
concordant pluton
columnar jointing
when igneous rocks cool and develope shrinkage fractures
batholith
- largest intrusive
- less than 10 km thick
xenoliths
suspended blocks of country rocks found in pluton
laccoliths
-Forcibly injected between sedimentary strata
- Causes the overlying strata to arch upward
