Variations in deformation fields during development of a large-volume magmatic arc, central Sierra Nevada, California

Research Article| February 01, 1995 Variations in deformation fields during development of a large-volume magmatic arc, central Sierra Nevada, California Othmar T. Tobisch; Othmar T. Tobisch 1Earth Sciences Department, 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 94115 Search for other works by this author on: GSW Google Scholar Paul R. Renne; Paul R. Renne 3Institute of Human Origins, Geochronology Department, 2453 Ridge Road, Berkeley, California 94709 Search for other works by this author on: GSW Google Scholar Brendan McNulty; Brendan McNulty 4Earth Science Department, University of California, Santa Cruz, California 95064 Search for other works by this author on: GSW Google Scholar Weixing Tong Weixing Tong 4Earth Science Department, University of California, Santa Cruz, California 95064 Search for other works by this author on: GSW Google Scholar Author and Article Information Othmar T. Tobisch 1Earth Sciences Department, University of California, Santa Cruz, California 95064 Jason B. Saleeby 2Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 94115 Paul R. Renne 3Institute of Human Origins, Geochronology Department, 2453 Ridge Road, Berkeley, California 94709 Brendan McNulty 4Earth Science Department, University of California, Santa Cruz, California 95064 Weixing Tong 4Earth Science Department, University of California, Santa Cruz, California 95064 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1995) 107 (2): 148–166. https://doi.org/10.1130/0016-7606(1995)107<0148:VIDFDD>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 Email Permissions Search Site Citation Othmar T. Tobisch, Jason B. Saleeby, Paul R. Renne, Brendan McNulty, Weixing Tong; Variations in deformation fields during development of a large-volume magmatic arc, central Sierra Nevada, California. GSA Bulletin 1995;; 107 (2): 148–166. doi: https://doi.org/10.1130/0016-7606(1995)107<0148:VIDFDD>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 Mid- to Late Cretaceous plutons in the central Sierra Nevada magmatic arc show widely preserved magmatic foliation, whereas regionally developed solid-state foliation is absent. Relatively slow cooling of these plutons and expected strain rates (10−14) suggest that the plutons were emplaced in a neutral or weakly extensional deformation regime. Domains of solid-state ductile shear of only slightly younger age than the plutons, on the other hand, indicate a contractional regime. Timing of pluton emplacement and movement on the shear zones have been constrained using Pb-U (zircon) and 40Ar/39Ar (hornblende and biotite) geochronology. Both plutons and ductile shear zones become younger toward the east. The four more westerly shear zones, which were active between ca. 100 and 90 Ma, show steeply plunging stretching lineations, whereas the most easterly and/or youngest zones, active between ca. 88 and 78 Ma, show mostly oblique and/or subhorizontal stretching lineations, indicating a change in kinematics at ca. 90 Ma.The above events define a complex deformation pattern in which strain regimes fluctuated in time and space between neutral or weak extensional and contractional. We propose a tectonic model in which thenospheric mantle corner flow produced eddy pairs in the mantle corner that transmitted a neutral or weak extensional regime to the overlying crust and facilitated the movement of granitic magma to midand upper levels, probably as dikes via fractures. Slab flattening caused the neutral or weak extensional regime to move eastward away from the trench. Increased coupling between upper and lower plates induced by the slab flattening promoted contractional strain in the cooling plutons, and domains of ductile shear formed in progressively younger plutons to the east.The above events were accompanied by an oblique convergence vector between North America and Farallon plates (Engebretson et al., 1985), which imposed a relatively small component of right-lateral shear onto the arc that increased with time. We estimate that at ca. 100 Ma the convergence vector made an angle (Φobl) ≈ 20° to the arc normal, and we suggest that around ca. 90 Ma Φobl passed through a critical value, conceivably (20° < Φoblcrit < 30°). At this juncture, the component of right-lateral shear became sufficiently large to induce significant arc-parallel strike-slip movement on the most easterly shear zones; these kinematics continued as the dominant scheme, possibly as late as ca. 78 Ma. 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.