Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by MacPherson, G. J. Articles by Phipps, S. P. Search for Related Content GeoRef GeoRef Citation

Tectonic implications of diverse igneous blocks in Franciscan mélange, Northern California and southwestern Oregon

¹ Department of Mineral Sciences, U.S. National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560, U.S.A.
² Department of Physics and Geology, California State University at Stanislaus, Turlock, California 95382, U.S.A.
³ Department of Earth and Environmental Science, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6316, U.S.A.

Correspondence: ^* E-mail: glenn{at}volcano.si.edu

More than 50% of the igneous blocks from mélanges of the Franciscan subduction complex in northernmost California and from the equivalent Dothan Formation of southwestern Oregon are more silica-rich than basalt, and some contain supra-subduction zone geochemical signatures such as elevated Th/Ta ratios. In contrast, blocks from more southerly parts of the Franciscan mélange belt are more commonly mid-ocean ridge and ocean island/seamount basalts. The data indicate a north-south variation in the block population, due to differences in source terrane, or in the processes that provided the blocks and transported them into the mélange, or both. We suggest that, in the northern Franciscan, a relatively greater fraction of igneous mélange blocks was emplaced by block slumping from the forearc crust into the trench than was the case to the south.

Key Words: Franciscan • igneous blocks • mélange • geochemistry

This article has been cited by other articles:

				W.G. Ernst, C. A. Snow, and H. H. Scherer Contrasting early and late Mesozoic petrotectonic evolution of northern California GSA Bulletin, January 1, 2008; 120(1-2): 179 - 194. [Abstract] [Full Text] [PDF]