folding of shale-sandstone sequence, kings canyon, california folds and thrust which deformation and...
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Folding of Shale-Sandstone sequence, Kings Canyon, California
FOLDS and thrust
Which deformationand stresses
cause theses structures ?
… Compression…Shortening
The fold is like a Thrust defined
by its orientation
Parts of a fold:
–axial plane – limbs–“hinge”
Hinge
Types of Folds
• Anticline = arch
• Syncline = trough
• Monocline = stair step
• Dome or Basin
Chevron Fold, Laurel Mt., CA
Syncline
syncline, Israel
Youngest rocks in middle
Anticline
Virgin anticline, southern Utah
Oldest rocks in middle
Domes & Basins
Think of an Egg Carton!
Chernicoff and Whitney
Grenville Dome: Sinclair, WY
Map from Topozone.com
Syncline-AnticlinePairs + Domes: ZagrosMts, Iran
NASA “Earth as Art” web page
Monocline
Fold
Classification
Fold in Glacier, Antarctica
Folds axis are perpendicular to the main direction of compression
Little Shuteye, S
ierra Nevada, C
A
David Rogers
Casey Moore, UCSC
Domes are not produced by horizontal but vertical compression
Minor Folds and Foliation Are Clues to Much Larger
Structures
Foliation
Pre
ssur
e
– pressure flattens and/or aligns minerals in a rock
– platy or sheet-like structure reflects the direction in which pressure was applied
– Slate, schist, and gneiss foliated
Microscope Image of Foliated Garnet Schist, VT
1 mm
FoliationIn every case, the
foliation is:
In the direction of least resistance
at right angles to the direction of greatest compression.
Fold And Foliation
Folds and Foliation
How Geologists Use These Clues
• Here's an outcrop that might be seen in the field.
Minor Folds and foliations can be used to determine the axe of the fold
Pay attentionit migth look like folds
• K = Cretaceous• J = Jurassic• Tr = triassic• At X, we have
younger rocks surrounded by older rock
But it is produced by differential errosion on a thrust
• Dark green is older rock, thrust over the younger yellow rock
• The Klippe (K)
• W is a Fenster or Window
Folds and and Thrust are often associated
The overturned fold in the upper diagram may break, yielding an overthrust fold or thrust fault
Folds and thrust have the same
origin
Small thrust fault, Las Vegas, NV,Source: M. Miller, U. of Oregon
ReverseFault
Thrust Faults in Snow
fold-thrust complex developed in Upper Jurassic limestones in the Haut
Giffre area of the Subalpine thrust belt (Morcles nappe in France)
R.W.H. Butler
Folds and thrust are both responsible for the orogens
Folded Appalachians
Near Harrisburg, PA, Source: NASA
Folding in Malaspina Glacier, AK, 1969
Oil and Gas Concentrate in Domes
Chernicoff and Whitney
Growth of Minerals
Bohlen et al., 1987
Folded Amphibolite in Marble, Warrensburg(K. Hollocher, NYSGA field photo)
Small Scale Structures Mimic Large Scale Structures!!
Mulwaree fault zone, Australia, Tullis et al.Foliated Gneiss, Nunavut,S. Tella Photo.
Foliated Slate, Shelburne, VT, UVM
Foliation Macroscopic and Microscopic
Feldspar (strong)
Quartz (weak)
Mulwaree fault zone, Australia
Pressure
K. Hamblin
A. Kronenberg
Cararra MarbleDeformationExperiments
Brittle Ductile
Continental Extension
Chernicoff and Whitney
Nevada Bureau of Mines and Geology
Basin and Range
Extension
– Crust Thins Ductile
– Faulting Brittle
Shearing
– lateral slip creates faults
– common at transform boundaries
Faults – result from brittle deformation
– rocks offset across fault
– Sides referred to as “hanging wall” and “footwall”
– 3 types of fault
Hanging Wall
Footwall
Strike & Dip
– Describe fault orientation
– Direction of slip determines kind of fault: “dip-slip” or “strike-slip” Chernicoff and Whitney
Normal Fault, Lamb Canyon, CA
NormalFault
Strike-slip fault near Las Vegas, NV,Source: M. Miller, U. of Oregon
Strike-SlipFault
Strike-slip fault displacement in orchard
Joints
• Brittle “cracks” in rocks
• Form near surface
• Regular spatial distribution
• No offset
Calcite veins in joints of marble, Laurel Mt., CA
Preferential weathering of joints in Sandstone;