Skip to Main Content
Book Chapter

Structure of syn-Nevadan dikes and their relationship to deformation of the Galice Formation, western Klamath terrane, northwestern California

By
Gregory D. Harper
Gregory D. Harper
1
Department of Geological Sciences, State University of New York Albany, 1400 Washington Avenue, Albany, New York 12222, USA
Search for other works by this author on:
Published:
January 01, 2006

The Galice Formation is characterized by slaty cleavage, overturned tight-to-isoclinal folds having variable hingeline orientations, and a south–southeast-trending stretching lineation formed during the Nevadan orogeny. Calc-alkaline dikes and sills (151–146 Ma) that intruded the Galice Formation and its basement (Josephine ophiolite) are regionally metamorphosed, and some are deformed; however, some plutons of this age also overprint slaty cleavage, suggesting syntectonic intrusion. Amoeboid margins on some sills suggest intrusion began prior to lithification of the Galice Formation. Some dikes are intruded into pre-existing small thrust faults that predate the slaty cleavage. Dikes show a wide range of orientations, and poles to dikes are consistently oriented at a high angle to poles to extension veins and to the stretching lineation in the Galice Formation. Poles to dikes define two quadrants on an equal-area, lower-hemisphere projection separated by planes oriented at right angles. These planes are analogous to nodal planes of a fault-plane solution, and thus allow determination of P- and T-axes. Restoration of structures to their original (Nevadan) orientation results in the P- and T-axes, stretching lineations, poles to extension veins, poles to small syn-cleavage faults, and poles to cleavage all being essentially coplanar with the “movement plane” that strikes to the northwest and dips steeply. The “fault-plane solution” derived from dike orientations indicates northwest-southeast contraction, consistent with slip directions for most small faults having slickenfibers. A wide range of fold hingeline orientations and slip directions on small pre-cleavage faults, however, may record early west-directed shortening.

You do not currently have access to this article.

Figures & Tables

Contents

GSA Special Papers

Geological Studies in the Klamath Mountains Province, California and Oregon: A volume in honor of William P. Irwin

Arthur W. Snoke
Arthur W. Snoke
Search for other works by this author on:
Calvin G. Barnes
Calvin G. Barnes
Search for other works by this author on:
Geological Society of America
Volume
410
ISBN print:
9780813724102
Publication date:
January 01, 2006

References

Related

Citing Books via

Related Book Content
Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal