Transcript Thrust Faults

THRUST FAULTS:
ASSOCIATED
STRUCTURES AND
IMPLICATIONS IN
HYDROCARBONS TRAPS
STRUCTURE AND HYDROCARBON PROSPECTIVITY OF BASINS
James Moore
Alex Nyombi
Christian Hidalgo
Adekunle Odutola 1
Aims & Objectives
1. A brief introduction to Thrust Faults
2. Define Tectonics Settings involving Thrust
Faults formation
3. Review structures associated with Thrust
Faults
4. Highlight two examples of Hydrocarbon
Traps associated with Thrust Faults
5. Summarise
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Why Study Thrust Faults ?
• The are very damaging. Host of the largest
and potentially most destructive earthquakes
• Associated with mountain building and
collisional tectonics
• Influence positions of ore deposits and
hydrocarbons
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What Are Thrust Faults ?
• They are reverse faults with low dip that
form in layered sequences where horizontal
stress is greater than vertical stress.
• They are formed by compressive stresses
• Thrust faults are dip-slip faults
• They have dip less than 45°
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What Are Thrust Faults ?
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Major Types of Thrust Faults
1.
Thin-Skinned Thrusts
• Thin skinned thrusts developed within sedimentary
basins
• Basement may act as a basal detachment
• Basement is not involved
• Typical of leading edges of compressive orogens
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Major Types of Thrust Faults
2. Thick-Skinned Thrusts
• Thick skinned thrusts cut
upward through the
basement and propagate
through the sediment
• Thick skinned thrusts
usually steepen upwards
and are covered by drape
folds
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Rules For Thrust Development
• Thrust always cut up-section in the direction
of transport
• Thrust always place older over younger
rocks
• Higher thrust develop first
• Thrusting proceeds from higher to lower and
from hinterland towards foreland
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Dynamics of Thrust Motion
Conditions for thrust movement include overcoming:
• Frictional resistance to sliding on the basal fault
surface
• Gravitational forces resulting from the mass of the
sheet
Hypothesis supporting thrust movement include:
• Gravity sliding hypothesis
• Fluid pressure hypothesis
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Mechanisms of Thrusting
• They are formed by compressive
tectonic stresses and occur at
convergent plate boundaries.
• Ϭ1 is horizontal and Ϭ3 is vertical.
• The two sets of thrust faults
intersect along the horizontal Ϭ2
axis with dip less that 45°.
• Horizontal contraction parallel to
Ϭ1 and vertical extension parallel
to Ϭ3
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Components of a Thrust System
• Foreland is the area in front of the thrust belt
• Hinterland is the area behind the thrust belt
• Imbricate fan: Individual thrust sheets overlap like roofing
tiles
• Duplex: system of imbricate thrusts that branch off from a
single fault below and merge with a thrust fault above. The rock
body bounded by faults above and below is called a horse
• Ramps & Flats: Faults consist of flats parallel to bedding
(surface of weakness) and ramps where the fault cuts across
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the bedding
Components Of Thrust Faults
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Tectonic Setting of Thrust Fault
• Thrust faults accommodate shortening of the earth's
crust
• Most big mountain ranges are fold-and-thrust belts
• Consists of a set of folds and thrust faults that
extend for 10s to 100s of kilometres along strike
• Usually shortening takes place near the plate
boundary in convergent margins: (Himalayas, Alps,
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Appalachians, Urals)
Formation of Duplex Structure
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Formation of Thrust Duplex
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Structures Associated with Thrust Faults
Foreland thrust and fold belts
• Belts of deformed sedimentary rock in which the
layers are folded and duplicated by thrust faults
are common at the edges of orogens
• Folds and thrust faults are the dominant structures
• Results in the formation of foreland basin and
“piggy- back basin”
• Classic examples occur in: the Main Ranges,
Valley and Ridge province of the Appalachians,
and the Jura Mountains in the Alps
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Foreland Thrust And Fold Belt
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Folds Associated with Thrust Faults
• Fault bend folds
• Detachment folds
• Fault
propagation fold
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Thrust Faults as Hydrocarbon Traps:
Hypothetical Example
Thrust Faults:
This example
shows sediment
deposited by a
glacier 10,000
years ago.
 When the glacier moved back over the sediments,
faulting occurred. A glacial ‘readvance.’
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Thrust Faults as Hydrocarbon Traps:
Hypothetical Example
 Hypothetical
situation set up
below.
 Sandstone:
source rock,
Shale: seal
rock.
 Rock sequence is thrusted: creates a possible
hydrocarbon trap.
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Thrust Faults as Hydrocarbon Traps:
Nepal
Location of Nepal
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Thrust Faults as Hydrocarbon Traps:
Nepal
 Traps can be
seen in the Siwalk
Fold Belt.
 A blind thrust is
also seen. This can
also act as a
trapping
mechanism.
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Thrust Faults as Hydrocarbon Traps:
Moose Mountain, Canada
McConnell Thrust
Moose Mountain
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Thrust Faults as Hydrocarbon Traps:
Moose Mountain, Canada
 “Moose Mountain”
thrust sheet is defined
as the uppermost thrust
sheet which strata are
exposed at the surface.
This thrust essentially
placed a single repetition of the entire Cambrian through
Cretaceous sequence in the hanging wall, over the footwall.
 Strata in the footwall of the Moose Mountain thrust range from
Paleozoic to the Lower Cretaceous.
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Summary
• They are found in compressional settings
like orogenic belts, salt domes and diapiric
structures in general
• Repeat stratigraphy, puts older rocks on top
of younger rocks and contracts layering
• They closely associated with folds and
thrust belts
• 2 major types of Thrust faults: Thin-Skinned
Thrusts and Thick-Skinned Thrusts.
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Summary
• Components of a Thrust System : Foreland,
Hinterland, Imbricate fans, Duplexes, Ramps
& Flats
• When rock sequence is trusted: creates a
possible hydrocarbon trap
• Two examples of thrust faults forming a
structural trap for hydrocarbons: Nepal,
Moose Mountains
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Questions ?
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References
• Park, R.G. Foundations of Structural Geology, Chapman & Hall. pp
95 – 96, 1997.
• Twiss, R. J. and E. M. Moores, Structural Geology, W. H. Freeman &
Co., New York, 256p, 1992.
• http://vle.leeds.ac.uk/site/nbodington/earthscience/fifth/msc_struc/
• http://ic.ucsc.edu/~casey/eart150/Lectures/4ThrustFlts/4thrustfaults.ht
m
• http://courses.eas.ualberta.ca/eas421/lecturepages/thrust.html
• http://earth.leeds.ac.uk/faults/thrust/tipline/fbfold.htm
• http://www.colorado.edu/geolsci/courses/GEOL3120/3120lect_13.pdf
 (Taken from
http://www.cseg.ca/conferences/2000/2000abstracts/505.PDF)
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