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Timing of extension in the Pioneer metamorphic core complex with implications for the spatial-temporal pattern of Cenozoic extension and exhumation in the northern U.S. Cordillera

Vogl, James; Foster, David; Fanning, Christopher; Kent, K. Allen; Rodgers, David W.; Diedesch, Timothy

Description

The Pioneer core complex (PCC) in central Idaho lies along a transition between Early Eocene and ca. 40 Ma core complexes to the north and south, respectively. Thus, the age of extensional development of the PCC is important in understanding the spatial-temporal patterns of core-complex development in the North American Cordillera. New results, including structural observations and U-Pb zircon (SHRIMP and ICPMS) geochronology, constrain the early extensional history of the footwall for the...[Show more]

dc.contributor.authorVogl, James
dc.contributor.authorFoster, David
dc.contributor.authorFanning, Christopher
dc.contributor.authorKent, K. Allen
dc.contributor.authorRodgers, David W.
dc.contributor.authorDiedesch, Timothy
dc.date.accessioned2015-12-10T22:21:41Z
dc.identifier.issn0278-7407
dc.identifier.urihttp://hdl.handle.net/1885/52323
dc.description.abstractThe Pioneer core complex (PCC) in central Idaho lies along a transition between Early Eocene and ca. 40 Ma core complexes to the north and south, respectively. Thus, the age of extensional development of the PCC is important in understanding the spatial-temporal patterns of core-complex development in the North American Cordillera. New results, including structural observations and U-Pb zircon (SHRIMP and ICPMS) geochronology, constrain the early extensional history of the footwall for the first time. High-temperature strain with a top-WNW shear-sense is pervasive throughout metamorphic rocks of the northwestern footwall. An isoclinally folded dike yields a crystallization age of ∼48-47 Ma, whereas a crosscutting dike yielded an age of 46 Ma. Metamorphic rocks are also intruded by the ∼50-48 Ma Pioneer intrusive suite (PIS), a W-dipping granodiorite sheet displaying a magmatic fabric. Northwest-trending lineations are locally visible and also defined by anisotropy of magnetic susceptibility, indicating that during emplacement, the PIS was undergoing similarly oriented extensional strain as the enclosing metamorphic rocks. Therefore, WNW-directed extension spanning this structural section occurred between ∼50 and 46 Ma. Following emplacement of crosscutting 46 Ma dikes, deformation was partitioned into the WNW-directed Wildhorse detachment. Motion on the detachment occurred between ∼38 and 33 Ma, as documented by previous 40Ar/ 39Ar thermochronology. It is not clear, however, whether extension was continuous through the interval between these two time periods. Although Early Eocene extension in the PCC was synchronous with extension in core complexes to the north, rates of footwall exhumation in central Idaho were much lower. This southward slowing is compatible with N-S differences in inferred subduction zone geometry/kinematics and in the internal character of the orogenic wedge.
dc.publisherAmerican Geophysical Union
dc.rightsAuthor/s retain copyright
dc.sourceTectonics
dc.subjectKeywords: Anisotropy of magnetic susceptibility; Cenozoic extension; Core complex; Crystallization age; Extensional strain; Granodiorite; High temperature; Magmatic fabrics; Metamorphic core complex; New results; North American; Orogenic wedge; Spatial temporals; S
dc.titleTiming of extension in the Pioneer metamorphic core complex with implications for the spatial-temporal pattern of Cenozoic extension and exhumation in the northern U.S. Cordillera
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume31
dc.date.issued2011
local.identifier.absfor040312 - Structural Geology
local.identifier.absfor040313 - Tectonics
local.identifier.absfor040303 - Geochronology
local.identifier.ariespublicationu4027924xPUB244
local.type.statusPublished Version
local.contributor.affiliationVogl, James, University of Florida
local.contributor.affiliationFoster, David, University of Florida
local.contributor.affiliationFanning, Christopher, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationKent, K. Allen, University of Florida
local.contributor.affiliationRodgers, David W., Idaho State University
local.contributor.affiliationDiedesch, Timothy, University of Tennessee
local.bibliographicCitation.startpage1
local.bibliographicCitation.lastpage22
local.identifier.doi10.1029/2011TC002981
local.identifier.absseo970104 - Expanding Knowledge in the Earth Sciences
dc.date.updated2016-02-24T10:29:15Z
local.identifier.scopusID2-s2.0-84857070541
local.identifier.thomsonID000300236800002
dcterms.accessRightsOpen Access
CollectionsANU Research Publications

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