The accretionary history of the Alexander terrane and structural evolution of the Coast Mountains batholith: Evidence from geologic, geochronologic, and thermobarometric studies in the Petersburg region, central southeastern Alaska.

Persistent Link:
http://hdl.handle.net/10150/185033
Title:
The accretionary history of the Alexander terrane and structural evolution of the Coast Mountains batholith: Evidence from geologic, geochronologic, and thermobarometric studies in the Petersburg region, central southeastern Alaska.
Author:
McClelland, William Cabell.
Issue Date:
1990
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
Rocks west of the Coast Mountains batholith in central southeastern Alaska include the Alexander terrane, Gravina belt, Taku terrane, and newly defined Ruth assemblage. Geologic, geochronologic and thermobarometric studies of these rocks in the Petersburg region provide new constraints on the accretionary history of the Alexander terrane and structural evolution of the Coast Mountains batholith. Paleozoic and Upper Triassic strata of the Alexander terrane were deformed within the Duncan Canal shear zone. Dextral shear in this zone during Early or Middle Jurassic time is inferred to reflect deformation along the eastern margin of the Alexander terrane and record the juxtaposition of the Alexander terrane with the North American margin. Deposition of the Upper Jurassic-Lower Cretaceous Gravina belt occurred within a transtensional back-arc to intra-arc basin that evolved during the northward translation of the Alexander terrane. The Ruth assemblage and Taku terrane were structurally emplaced over the Gravina belt and Alexander terrane along the Sumdum-Fanshaw fault system during mid-Cretaceous time. West-vergent thrusting of the Ruth assemblage was accompanied by metamorphic P,T conditions of 6.8 kb, < 450°C in the Gravina belt and 6.9 to > 7.4 kb, > 550°C in the Ruth assemblage. The age of deformation is constrained by syntectonic and post tectonic intrusive bodies that yield U-Pb lower intercept apparent ages of 92.3 ± 3 Ma and 91.3 ± 6.3 Ma, respectively. Late Devonian-Mississippian orthogneiss and felsic metavolcanic rocks in the Ruth assemblage suggest correlation of the assemblage with continental margin rocks of the Yukon-Tanana and Nisling terranes east of the Coast Mountains batholith. Thus the mid-Cretaceous Sumdum-Fanshow fault system marks the fundamental boundary between the Alexander terrane and inboard fragments. This deformation records the final structural accretion of the Alexander, Wrangellia, and Peninsular terranes to the western margin of North America. The mid-Cretaceous thrust system is truncated to the east by the LeConte Bay shear zone: a complex zone of Late Cretaceous-early Tertiary fabrics that occur within and west of the Coast Mountains batholith. This zone has apparently accommodated both west-side-up and east-side-up displacement during the collapse of the overthickened crust developed during mid-Cretaceous time.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Batholiths -- Alaska -- Petersburg Region; Geology, Structural -- Alaska -- Petersburg Region; Geology, Stratigraphic -- Jurassic; Geology -- Alaska -- Petersburg Region.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Geosciences; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Gehrels, George E.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleThe accretionary history of the Alexander terrane and structural evolution of the Coast Mountains batholith: Evidence from geologic, geochronologic, and thermobarometric studies in the Petersburg region, central southeastern Alaska.en_US
dc.creatorMcClelland, William Cabell.en_US
dc.contributor.authorMcClelland, William Cabell.en_US
dc.date.issued1990en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractRocks west of the Coast Mountains batholith in central southeastern Alaska include the Alexander terrane, Gravina belt, Taku terrane, and newly defined Ruth assemblage. Geologic, geochronologic and thermobarometric studies of these rocks in the Petersburg region provide new constraints on the accretionary history of the Alexander terrane and structural evolution of the Coast Mountains batholith. Paleozoic and Upper Triassic strata of the Alexander terrane were deformed within the Duncan Canal shear zone. Dextral shear in this zone during Early or Middle Jurassic time is inferred to reflect deformation along the eastern margin of the Alexander terrane and record the juxtaposition of the Alexander terrane with the North American margin. Deposition of the Upper Jurassic-Lower Cretaceous Gravina belt occurred within a transtensional back-arc to intra-arc basin that evolved during the northward translation of the Alexander terrane. The Ruth assemblage and Taku terrane were structurally emplaced over the Gravina belt and Alexander terrane along the Sumdum-Fanshaw fault system during mid-Cretaceous time. West-vergent thrusting of the Ruth assemblage was accompanied by metamorphic P,T conditions of 6.8 kb, < 450°C in the Gravina belt and 6.9 to > 7.4 kb, > 550°C in the Ruth assemblage. The age of deformation is constrained by syntectonic and post tectonic intrusive bodies that yield U-Pb lower intercept apparent ages of 92.3 ± 3 Ma and 91.3 ± 6.3 Ma, respectively. Late Devonian-Mississippian orthogneiss and felsic metavolcanic rocks in the Ruth assemblage suggest correlation of the assemblage with continental margin rocks of the Yukon-Tanana and Nisling terranes east of the Coast Mountains batholith. Thus the mid-Cretaceous Sumdum-Fanshow fault system marks the fundamental boundary between the Alexander terrane and inboard fragments. This deformation records the final structural accretion of the Alexander, Wrangellia, and Peninsular terranes to the western margin of North America. The mid-Cretaceous thrust system is truncated to the east by the LeConte Bay shear zone: a complex zone of Late Cretaceous-early Tertiary fabrics that occur within and west of the Coast Mountains batholith. This zone has apparently accommodated both west-side-up and east-side-up displacement during the collapse of the overthickened crust developed during mid-Cretaceous time.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectBatholiths -- Alaska -- Petersburg Regionen_US
dc.subjectGeology, Structural -- Alaska -- Petersburg Regionen_US
dc.subjectGeology, Stratigraphic -- Jurassicen_US
dc.subjectGeology -- Alaska -- Petersburg Region.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGeosciencesen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorGehrels, George E.en_US
dc.contributor.committeememberConey, Peter J.en_US
dc.contributor.committeememberPatchett, P. Jonathan.en_US
dc.contributor.committeememberButler, Robert F.en_US
dc.contributor.committeememberChase, Clementen_US
dc.identifier.proquest9024652en_US
dc.identifier.oclc704353470en_US
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