Deformation of Rocks Frank Press • Raymond Siever • John Grotzinger • Thomas H

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Deformation of Rocks Frank Press • Raymond Siever • John Grotzinger • Thomas H. Jordan • Folds and faults are geologic Understanding Earth structures caused by Fourth Edition deformation. Chapter 11: • Structural geology is the study of Folds, Faults, and other Records of Rock Deformation the deformation of rocks and its effects. Lecture Slides prepared by Peter Copeland • Bill Dupré Copyright © 2004 by W. H. Freeman & Company Orientation of Deformed Rocks We need some way to describe the distribution of geologic structures. So we use the terms strike and dip. Strike: compass direction of a rock layer as it intersects with a horizontal surface. Dip: acute angle between the rock layer and the horizontal surface, measured perpendicular to strike. Fig. 11.1 Strike and Dip on a Rooftop Fig. 11.4 Fig. 11.3 Types of Deformation Joints • elastic Cracks in rocks along which • ductile (plastic) there has been no appreciable displacement. • brittle (rupture) Faults Fractures in rocks created by earthquakes. • Dip-slip faults normal reverse • Strike-slip faults • Oblique-slip faults Fig. 11.9 • Hanging Wall: Term used by miners. They could “hang” their light on this side of the fault because it was above them. • Footwall: Also from the miners, this side of the wall upon which they could stand below the hanging wall. Fig. 11.2 Normal Fault hanging wall footwall Fig. 11.11 cross section Normal Fault Reverse Fault hanging wall hanging wall footwall footwall Cross section cross section San Andreas Fault Strike-slip Faults Motion of the fault blocks is parallel to the strike direction. Fig. 11.10 Left-lateral Strike Slip Fault Right-lateral Strike Slip Fault aerial (map) view aerial (map) view Folding of Rocks • Produced by horizontal or vertical forces • Scale can be from cm to 100’s of km Fig. Story 11.16a Fold Terminology axial plane: the plane of mirror symmetry dividing the fold into two limbs axis: the line formed by the intersection of the axial plane and a bedding plane horizontal fold: fold where the axis is horizontal plunging fold: fold where the axis is not horizontal Fig. Story 11.16b More Fold Terminology syncline: a sequence of folded rocks with the youngest rocks on the inside of the fold anticline: a sequence of folded rocks with the oldest rocks on the inside of the fold Fig. Story 11.16 Fig. 11.17 Fig. 11.18 And More Fold Terminology dome: a sequence of folded rocks in which all the beds dip away from a central point basin: a sequence of folded rocks in which all the beds dip towards a central point Fig. 11.19 Fig. 11.19 Fig. 11.20.

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