Multistage emplacement of the Mount Givens pluton, central Sierra Nevada batholith, California

Abstract

Research Article| January 01, 2000 Multistage emplacement of the Mount Givens pluton, central Sierra Nevada batholith, California Brendan A. McNulty; Brendan A. McNulty 1Earth Science Department, University of California, Santa Cruz, California 95064 Search for other works by this author on: GSW Google Scholar Othmar T. Tobisch; Othmar T. Tobisch 1Earth Science Department, University of California, Santa Cruz, California 95064 Search for other works by this author on: GSW Google Scholar Alexander R. Cruden; Alexander R. Cruden 2Department of Geology, University of Toronto, Erindale Campus, Mississauga, Ontario L5L 1C6, Canada Search for other works by this author on: GSW Google Scholar Stuart Gilder Stuart Gilder 3Institut de Physique du Globe de Paris, Laboratoire de Paleomagnetisme, 4 place Jussieu, 75252 Paris Cedex 05, France Search for other works by this author on: GSW Google Scholar Author and Article Information Brendan A. McNulty 1Earth Science Department, University of California, Santa Cruz, California 95064 Othmar T. Tobisch 1Earth Science Department, University of California, Santa Cruz, California 95064 Alexander R. Cruden 2Department of Geology, University of Toronto, Erindale Campus, Mississauga, Ontario L5L 1C6, Canada Stuart Gilder 3Institut de Physique du Globe de Paris, Laboratoire de Paleomagnetisme, 4 place Jussieu, 75252 Paris Cedex 05, France Publisher: Geological Society of America Received: 11 Mar 1998 Revision Received: 11 Feb 1999 Accepted: 22 Apr 1999 First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2000) 112 (1): 119–135. https://doi.org/10.1130/0016-7606(2000)112<119:MEOTMG>2.0.CO;2 Article history Received: 11 Mar 1998 Revision Received: 11 Feb 1999 Accepted: 22 Apr 1999 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 Brendan A. McNulty, Othmar T. Tobisch, Alexander R. Cruden, Stuart Gilder; Multistage emplacement of the Mount Givens pluton, central Sierra Nevada batholith, California. GSA Bulletin 2000;; 112 (1): 119–135. doi: https://doi.org/10.1130/0016-7606(2000)112<119:MEOTMG>2.0.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 The ca. 90 Ma Mount Givens pluton is one of the largest granodioritic to granitic intrusions in the Sierra Nevada batholith of California. Emplacement of the pluton occurred during a critical time in the tectonic evolution of the central Sierra Nevada magmatic arc, marked by a transition from regional contraction to dextral transcurrent shear. A model for the emplacement of the intrusion is developed based on detailed mapping of the pluton and its wall rocks and characterization of its internal structure by measurements of the anisotropy of magnetic susceptibility (AMS) at 351 stations. One of the key results of the study is documentation of a strong correlation between petrologic and structural fabrics in the pluton, and determination that these fabrics reflect internal magma chamber dynamics more than regional tectonic strain.The ∼80-km-long, 15–30-km-wide pluton crystallized from a multiphase, three-segment magma chamber marked by a bulbous northern lobe and linear central and southern segments. The pluton is interpreted to be tabular in shape with a thickness of ∼5 km. Most of the space for the pluton was created by piecemeal block downdrop of the magma chamber floor along three principal fracture sets, the most important of which were steeply dipping, northwest-trending fractures formed parallel to the structural grain of the arc, and vertical, north-trending extension fractures formed in response to a component of arc-parallel dextral shear. Some of these fractures acted as magma conduits, episodically filling the pluton as source rocks became depleted in melt. An initial, voluminous intrusive event (stage 1) quickly filled the southern chamber with granodiorite magma, but only partially filled the northern and central chambers. Stage 2 magmatism involved underplating of megacrystic granite in the northern chamber and lateral flow of a large batch of this magma from the northern to the central chamber, the latter delineated by a 20-km-long belt of megacrystic granite containing subhorizontal magnetic lineations that connects the pluton segments. Floor downdrop eventually ceased to be an effective space-making process in the northern lobe, and renewed magmatism (stage 3) led to expansion and doming of the chamber. As the northern lobe cooled, a ring fault ruptured within the viscoelastic stage 1–2 carapace, allowing ring dike intrusion (stage 4) and sinking of a central flap of consolidated material. The temporal and spatial variations in emplacement mechanisms demonstrated for the Mount Givens pluton (i.e., fracture generation, floor downdrop, underplating, inflation, ring diking) suggest that end-member models (e.g., fracture vs. diapir) are oversimplifications of the pluton assembly process. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.