Research Article| May 01, 2000 Pluton emplacement by sheeting and vertical ballooning in part of the southeast Coast Plutonic Complex, British Columbia E.H. Brown; E.H. Brown 1Department of Geology, Western Washington University, Bellingham, Washington 98225, USA Search for other works by this author on: GSW Google Scholar W.C. McClelland W.C. McClelland 2Department of Geology and Geological Engineering, University of Idaho, Moscow, Idaho 83844, USA Search for other works by this author on: GSW Google Scholar Author and Article Information E.H. Brown 1Department of Geology, Western Washington University, Bellingham, Washington 98225, USA W.C. McClelland 2Department of Geology and Geological Engineering, University of Idaho, Moscow, Idaho 83844, USA Publisher: Geological Society of America Received: 30 Oct 1998 Revision Received: 19 Jul 1999 Accepted: 27 Jul 1999 First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2000) 112 (5): 708–719. https://doi.org/10.1130/0016-7606(2000)112<708:PEBSAV>2.0.CO;2 Article history Received: 30 Oct 1998 Revision Received: 19 Jul 1999 Accepted: 27 Jul 1999 First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation E.H. Brown, W.C. McClelland; Pluton emplacement by sheeting and vertical ballooning in part of the southeast Coast Plutonic Complex, British Columbia. GSA Bulletin 2000;; 112 (5): 708–719. doi: https://doi.org/10.1130/0016-7606(2000)112<708:PEBSAV>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 Batholiths of the Coast Plutonic Complex, in the area of Harrison Lake, British Columbia, are interpreted to have formed by horizontal sheeting and vertical inflation. Zoned ovoid batholiths exhibit sheeted margins as thick as 3 km. Shallow floors are indicated by moderately to gently inward dipping magmatic foliations, the observed trace of floor contacts across topography, and a published deep seismic reflection transect. Mineralogic aureoles under the floors preserve a paragenetic record of increasing pressure during aureole crystallization. Initial pressures of <3.0 kilobars are indicated by an early assemblage of andalusite + biotite. Garnet thermobarometry of late-stage aureole assemblages that overprint the andalusite indicates peak pressures of 5–6.5 kilobars, equating to an added load more than 7–12 km thick. The mode of emplacement of the ovoid batholiths is interpreted from these features to be a sequential process of (1) initial intrusion of a relatively shallow horizontal sheeted complex fed by a dike system, followed by (2) inflation vertically by multiple injections or ballooning of the original sheets to accommodate a high volume of magma. The floor of the initial sheets was pushed down and rotated into steeper dips at the pluton margins as the bottom sagged and the magma body assumed a bowl or tub shape. In this process, magma ascended via fractures, and space was made for the plutons primarily by downward displacement of country rock and concomitant depression of the Moho. U-Pb zircon dating reveals crystallization periods of as much as 8 m.y. for individual batholiths, a likely consequence of construction by episodic pulses of magma. This model finds accordance with observations of many workers in other orogenic belts. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
The Coast Mountains orogen in central southeastern Alaska records intra-arc mid-Cretaceous underthrusting of the Alexander terrane and Gravina belt beneath metamorphic rocks correlative with the Yukon-Tanana terrane followed by evolution of the Late Cretaceous and early Tertiary Coast shear zone. U-Pb geochronologic data from the Bradfield Canal and Stikine River regions demonstrate that arc-related plutonism continued from mid-Cretaceous to Eocene time, synchronous with deformational evolution of the orogen. The southwest-vergent mid-Cretaceous Sumdum fault separates the Gravina belt from the Yukon-Tanana terrane, which in this region is dominated by a Middle to Late Devonian arc assemblage. Mid-Cretaceous plutons that crosscut this structure suggest that juxtaposition of the Yukon-Tanana terrane and Gravina belt occurred prior to ca. 90 Ma. Structures related to mid-Cretaceous contraction and pluton emplacement are truncated and overprinted by the Coast shear zone along the western flank of the Coast Mountains. Complex domainal kinematic relationships associated with ductile fabrics of the shear zone indicate a complex and protracted west- and east-side-up and possible dextral strike-slip displacement history. Simple geometric considerations and kinematic observations support a model in which this structure accommodated buoyancy-driven Late Cretaceous exhumation of the underthrust Alexander terrane followed by Paleocene-Eocene exhumation of rocks within the Coast Mountains. This younger exhumation was synchronous with tonalite and granodiorite pluton emplacement within and east of the shear zone. Limited kinematic data support a strike-slip origin for the shear zone. The shear zone likely evolved between 80 and 85 Ma and deformation continued at least through 57 Ma but ceased prior to 50 Ma.
