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;