l1 l2 part 1 basic geology
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CALIFORNIAGEOLOGY
Earth109
ProfessorBusby
INTRODUCTIONAND
CHAPTER1
SimplifiedgeologicmapofCalifornia,bythe
CaliforniaGeological
Survey-
Seeinsidebookcoverof
yourtextbook:California Geology,
Deborah R. Harden,
2nd Edition
REQUIRED
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I have been researching and teaching about California geology ever since I was
an undergraduate at Berkeley, a PhD student at Princeton, and for 28 years as
a professor here at UCSB.
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READ YOUR SYLLABUS CAREFULLY AND REFER TO IT OFTEN!
HUGE range in the educational backgrounds of class members.
To get everyone on the same page, the class will spend the first 6 weeks of the quarter
studying the textbook.
The last 4 weeks will go beyond the book, using pdfs of my powerpoints, to be posted
on Gaucho Space.
Foreach class meeting, you will prepare a neatly drawn 3-page maximum cheat
sheetin pencil , and be prepared to go to the board and answer any given question.
You will bring these cheat sheets on the field trip and to both exams.
GRADING:
First exam (including quality of cheat sheets): 45% of grade - Feb 15 IN
CLASS.Second exam (including quality of cheat sheets): 45% of grade - March 13
IN CLASS. NO EXAM DURING FINALS WEEK.
Participation (preparation for class answers, as well as field exercise
participation): 10% of grade.
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REQUIRED Field Exercise: 7:00 am Friday March 2 to 9:00 pm Monday
March 5.
You will be barced $150 lab fee for the trip.
This is an elective class; do not take the class if you have conflict for those dates
(be it personal or class conflict). The only excuse for missing the trip will be a
doctors letter saying you were too ill to attend.
Each stop on the field trip will have questions for you to answer, with sketches. You
will turn in your field notes at the last stop of the field trip, and I will return them toyou with comments at the next class meeting so you can revise them for the final.
There is no limit to the length of your field exercise cheat sheet.
WEEK 1: Review of Basic Geology. Reading: Chapters 1-4
GET STARTED TODAY!
ANSWER WEEK 1 QUESTIONS BY WEDNESDAY.
ANSWER WEEK 2 QUESTIONS BEFORE NEXT MONDAYS CLASS.
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WEEK 1: Review of Basic Geology
Can you label the major plates?
Do you know what these three symbols mean?
SimilartoFigure1-1inyourbook5
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Queson1a-TheLayeredEarth:rightsideshowslayeringby
COMPOSITION,getsdenserinward.
Iron-rich (metallic) core (9 - 16 X the density of water)
Stony mantle (~ 6 - 3X the density of water) - more Fe and Mg, less Si thancrust.
Stony crust,less dense than mantle (~2.7 - 3.2X the density of water)
Similar to
Figure 1-2 of
your book
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Inner core is solid,Outer core is liquid with convection currents,responsible for Earths magnetic field.
Mesosphere and asthenosphere are plastic.
Lithosph,ere is brittle, and makes the tectonic plates.
Question 1b - left side shows layering by STRENGTH
Similar to Figure
1-2 of your book
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Tectonic (or
lithospheric) plate -
May include:
continental crust
(lightest, thicker),
oceanic crust
(denser, thinner),and the uppermost
part of the mantle
(densest).
These float on theplastic
asthenosphere by a
process called
isostacy (see next
slide).
Question 1c - Similar to Figure 1-3 of your book:
Oceanic crust is made of basalt, formed by sea-
floor spreading.
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Isostasy(Question 1c)
Less dense materials float
higher than more dense
materials, like an iceberg
floating in the ocean.
Continental crust floats
highest, with a thick
hidden root - thecontinent is the tip of
the iceberg.
Oceanic crust is denser and
floats lower than the
continents - that is what
makes the ocean basins,
which hold most of the
water on earth.
A thicker continent sticks up
higher.
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Question 2a - Divergent plate boundary on the sea floor.
Figure 1-5 of your
book:Sea-floor spreading =
injection of mantle-
derived melts into the
crack created as two
plates are pulled apart.
The process repeats
over and over. Sea floor
is created by this
process.The asthenosphere is virtually at thesurface at a mid-ocean ridge.
Transform faults accommodate right
or left steps along the mid-ocean
ridge.
How do we know this?
MAGNETIC
STRIPING OF THE
SEA FLOOR.10
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What is MAGNETIC STRIPING OF THE SEA FLOOR?
Earthsmagnecfieldactslikegiantbarmagnet,
withnorthendneartheNorthPoleandsouth
endneartheSouthPole(causedbydynamoin
liquidoutercore).
Magnecpolarityreverses
Everyseveralthousandtotensofmillionsof
years,theorientaOonofmagneOcfield
switchesfromnorth(normal)polarityto
south(reverse)polarity.
InclinaOonofmagneOclinescanalsobeusedto
inferwhatlatudetherockformedat
(determinepaleolaOtudinalposiOonsofthe
conOnents).
APrimeronEarthsMagnecField
Question 2a continued.11
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MagnezaonofVolcanicRocks:Whenlavacoolstobelow550oC(Curiepoint),atomsiniron-bearingminerals
lineupindirecOonofEarthsmagneOcfield,recordingbothpolarity(normal
vs.
reversed)andinclinaon(laOtudeatwhichthelavacooled).
Astackoflavaflowsmayrecordseveral
reversals,whichcanbedated
radiometrically.Bythismethoda
magneOcpolarityreversalOmescalecan
beconstructed.
Question 2a continued.12
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MagnezaonPaXernsontheSeafloors
ceanfloorisstripedbyparallelbandsofmagneOzedrockwith
alternaOngpolariOesStripesareparalleltomid-oceanridges,andpaXernofstripesis
symmetricalacrossmid-oceanridges(paXernononesideofridge
hasmirroroppositeonotherside)
VaryingwidthsofalternaOngpolaritystripesmatchlengthsofOme
betweensuccessivereversalsofEarthsmagneOcfield
Question 2a continued.13
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MagnezaonPaXernsontheSeafloors
Magmaisinjectedintotheoceanridgestocoolandformnew
rockimprintedwiththeEarthsmagneOcfieldSeaflooristhenpulledawayfromoceanridgeliketwolarge
conveyorbeltsgoinginoppositedirecOonsseafloor
spreadingCross sectional
view
Question 2a, divergent plate boundary, continued.
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Question 2a, divergent plate boundary on the sea floor, continued:
ceanfloordepthsincreasesystemaOcallywithseafloorage,moving
awayfrommid-oceanridges.WHY?
Theplategetsthicker,byslowcoolingofoceaniccrustand
uppermostmantle,andbecomesdenser,thereforesinkingaliXle
lowerintomantleasthenosphere.
SedimentslowlypilesupwithOme(thickeronolderseafloor)andits
weightonplatealsocauseittosinkaliXleintomantle
Well talk about divergent plate boundaries on continents later.15
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Question 2b - CONVERGENT PLATE BOUNDARY with oceanic
plate subducting under a continent.Figure 1-6 of your book:
UPPERPLATE (over-
riding plate)LOWER
PLATE (going
back down intothe mantle)
The Benioff zone is
defined by earthquakes
where the lower
(subducting) plate grinds
under the upper plate.
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Question 2b - CONVERGENT PLATE BOUNDARY - what
happens where light crust gets carried into the subduction zone?
Ocean-continentconvergence (top): oceanic
plate is subducted,
but when a piece of light
continental crust getsbrought in on the subducting
slab,
it cant subduct (toobouyant), and
continental upheaval results.
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Question 2b - CONVERGENT PLATE BOUNDARY
India moved 2,000 km north toward Asia
by subduction of Indian Ocean plates.
Pre-collision, Indian and Asian crusts were
35 km thick.
Crust under Tibetan plateau is now 70 km
thick, highest continental area on Earth.
India is still
shoving
under Asia.
Some muchsmaller parts
of California
were
accreted in a
similar way.19
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Question 2c - TRANSFORM PLATE BOUNDARY
Figure 1-7 of your book,
illustrating right-lateral slip
along the San Andreas fault and
the Hayward fault. Below: map
view.
This fault shows left-lateral slip.
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Strike-slip faults: horizontal movement
When straddling a fault, if
right-hand side moved
towards you, it is a right-lateral fault
When straddling a fault, if
the left-hand side has moved
towards you, it is a left-lateral fault
Convention works in either
direction
Question 2c - TRANSFORM PLATE BOUNDARY continued.
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Question 2 summary: Tectoniccycle(takesabout250millionyears): Meltedasthenosphereflowsupwardasmagma
Coolstoformnewoceanfloor(lithosphere)
Newoceaniclithosphere(slab)divergesfromzoneofformaOonatopasthenosphere(seafloorspreading)andcoolsasitisraedaway.
Whenslabofoceaniclithospherecollideswithanotheryounger,warmerslab,theolder,
colder,denserslabsubductsandisreabsorbedintothemantle
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Question 4 - Fixed hot spot rising up through the mantle under the Pacificplate, which is moving toward the NW - so Hawaiian Islands are older toward
north, and sink under their own weight.
Figure 1-7 of your book
Hot spot track records plate
motion directions for the
last 80 million years.
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Question 5 - FAULTS - not fully discussed in book but you need to
know this.
How is a fault different from a joint in a rock?
Its a fracture in the Earth in which two sides move relative to each
other.
Jointing: brittle rocks fracture and crack but a there is no offset across a joint.
Examples of bedding offset by faults.
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Strike = intersection of the fault plane with the earths surface.
Above: the strike of the Alpine
fault in New Zealand is about10 degrees east of north.
Below: the San Andreas fault
here strikes about 30 degrees
west of north (see north arrow);
offset of a creek is right lateral.
Question 5 continued - Three-dimensional view of a fault plane:
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Question 5 - Three-dimensional view of a fault plane, continued:
Dip = angle between the earths surface and the fault plane. Example
shown on block diagram is about 45 degrees.
Above: these small faults
dip steeply (about 80
degrees). Below: faultplanes can be curved. This
fault flattens with depth:
from a dip of about 45
degrees, to a dip of about 20
degrees.
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Question 5 continued - What is the difference between a
hypocenter and an epicenter?
Stress builds up until rupture starts at the weakest point along the fault
plane -- this is called the hypocenter or focus
The spot on the earth directly above the place of initial rupture is the
epicenter
Rupture then spreads out along
the fault surface.
The surface rupture will occur
directly above the hypocenter
ONLY if the fault plane is
vertical.
Sometimes faults dont rupture
all the way to the surface, and
then there is no ground
breakage.27
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Question 5 continued -
FAULTS THAT ARE NOT VERTICAL are referred to as dip slip
faults, because they are dominated by vertical movement.
Miners refer to the
block beneath them
as the
footwall (block
beneath the fault)
because they stand
on it, and the block
above them as the
hanging wall (blockabove the fault)
because they hang
their lantern on it
(the roof).
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Question 5, continued.
Figure 1-13 from your book,
illustrating compression,
extension, and transform
motion.
Its a little confusing
because it shows the faultplane as being vertical in all
three cases.
What is much more common
is that the fault plane is onlyvertical for transform
motion,and is NOT vertical
for compression and
extension (see next slide).
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Question 5, continued.
Figure 1-15 from your
book:(a) reverse fault is a
dip slip fault that
forms by
compression,
(b) normal fault is a
dip, slip fault that
forms by extension,
and
(c) strike slip fault is a
vertical fault that
forms by transform
motionPrettier drawings on following
slides..
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Normal Fault : a dip slip fault
formed due to PULLING
APART = extensional.
Hanging wall moves downrelative to footwall.
Zone of omission - if you wanted to
drill down into the stippled bed to get
water or oil from it, you wouldnt find
it there.
Reverse Fault-a dip slip fault
formed due to PUSHING
TOGETHER = compressional.
Hanging wall moves up relative
to footwall.
Zone of omission - if you wanted to
drill down into the stippled bed to get
water or oil from it, you would hit it
twice!
Question 5, continued.
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Figure 1-14 from your
book illustrates how
compression not only
produces reverse faultsbut also may cause
folding, especially in
layered rocks.
Example of folding of rock
layers: these sedimentary
layers were deposited flat and
then they got crumpled up
along the San Andreas fault.
Photo along Highway 14 just
south of Palmdale (San
Andreas fault zone).
Question 5, continued.
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Figure 1-15 from yourbook illustrates how
extension not only
produces normal faults,
but can produce a graben
(left) or downsag (right).
A graben will be seen at
the surface as a basin or
valley.
Question 5, continued.
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Left bend in a right-lateral
fault
(or right step in left-lateral
fault, not shown):
THE TWO SIDES PUSH
TOGETHER
Compression, uplift,hills and mountains
Steps or bends in Strike-Slip Faults: Earth does not rupturealong planes that are perfectly straight and continue forever. Instead, the
faults bend or make steps to the left or right.
Question 5, continued.
TRANSPRESSION - see Figure 1-17
of your book. 34
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Right bend in a right-lateral fault
(or left bend in left-lateral
fault, not shown):
THE TWO SIDES PULL
APART
Extension, down-
dropping,
basins and valleys
Figure 3.14
Steps or bends in Strike-Slip Faults, continued:
TRANSTENSION - see Figure 1-17
of your book.
Question 5, continued.
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Strike-Slip Faults, continued:
A TRANSFORM FAULT is a strike-slip fault that forms a plateboundary.
Example shown here connects two spreading centers on the ocean
floor.
Question 5, continued.
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TRANSFORM FAULTScontinued:
Example shown here
(San Andreas fault)
connects spreading
centers in the Gulf ofCalifornia with the
subducting Juan de
Fuca plate.
It forms the plate
boundary between the
Pacific and North
American plates.
Question 5, continued.
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