Nature and timing of deformation in the Foothills terrane, central Sierra Nevada, California: Its bearing on orogenesis

Abstract

Research Article| March 01, 1989 Nature and timing of deformation in the Foothills terrane, central Sierra Nevada, California: Its bearing on orogenesis OTHMAR T. TOBISCH; OTHMAR T. TOBISCH 1Earth Science Board Applied Science Building, University of California, Santa Cruz, California 95064 Search for other works by this author on: GSW Google Scholar SCOTT R. PATERSON; SCOTT R. PATERSON 1Earth Science Board Applied Science Building, University of California, Santa Cruz, California 95064 Search for other works by this author on: GSW Google Scholar JASON B. SALEEBY; JASON B. SALEEBY 2Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125 Search for other works by this author on: GSW Google Scholar EDWARD E. GEARY EDWARD E. GEARY 3Department of Geology; San Jose State University, San Jose, California 95192 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1989) 101 (3): 401–413. https://doi.org/10.1130/0016-7606(1989)101<0401:NATODI>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation OTHMAR T. TOBISCH, SCOTT R. PATERSON, JASON B. SALEEBY, EDWARD E. GEARY; Nature and timing of deformation in the Foothills terrane, central Sierra Nevada, California: Its bearing on orogenesis. GSA Bulletin 1989;; 101 (3): 401–413. doi: https://doi.org/10.1130/0016-7606(1989)101<0401:NATODI>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Detailed mapping and structural analysis combined with new age dates, using U-Pb and 40Ar/39Ar techniques, have allowed us to constrain the timing of pre-ductile and ductile deformation in the Foothills terrane of the central Sierra Nevada. By using strain and other data, it can be shown that rigid rotation of beds (folding/faulting) predated the onset of ductile deformation and probably occurred between 160 and 151 Ma. Ductile structures, consisting of continuous and secondary cleavages and associated folds and lineations, started forming ca. 151 Ma in the Bear Mountains fault zone and then ca. 145 Ma, began moving away from the fault zone, forming diachronously over an ∼30-m.y. period. The last documented ductile structure formed ca. 123 Ma, although some secondary structures may be younger.Metamorphism of these rocks is generally upper greenschist facies, although higher-grade belts (one bearing staurolite, andalusite, and sillimanite) are present. Strain was preferentially partitioned into one of these belts of higher metamorphic grade (and sporadically elsewhere). The structural history here is much more complex, and at least one and locally two complete transpositions of the original cleavage have occurred. In these zones of complex deformation, it is in most cases possible only to identify a composite foliation consisting of new continuous cleavage and relicts of earlier phases, all lying mutually parallel.Timing constraints indicate that the pre-ductile structures may correspond to a very late stage of the Nevadan orogeny (that is, 155 ± 3 Ma), but the ductile structures postdate that orogeny (as defined) by as much as about 25-30 m.y. Models which relate the ductile structures in the central Foothills terrane to Nevadan plate-tectonic events are untenable. In addition, recent work indicates that Late Cretaceous ductile deformation in the central and southern Sierra Nevada may be relatively widespread, indicating that tectonic models for the Sierra Nevada need to be reassessed. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.