Seismic crustal structure beneath the Safford Basin and Pinaleiio Mountains: Implications for Cenozoic extension and metamorphic core complex uplift in SE Arizona

Persistent Link:
http://hdl.handle.net/10150/187557
Title:
Seismic crustal structure beneath the Safford Basin and Pinaleiio Mountains: Implications for Cenozoic extension and metamorphic core complex uplift in SE Arizona
Author:
Kruger, Joseph Michael
Issue Date:
1991
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:
Geologic relationships and reflection seismic data in the Safford basin and Pinaleiio Mountains metamorphic core complex suggest the northwest-trending core complex is formed along a mid-Tertiary detachment fault system that extends from a breakaway near the northeast flank of the Galiuro Mountains, to a depth of -15 km (-5 s) where it flattens beneath the Gila-Peloncillo Mountains. Top-to-the-northeast mid-Tertiary and late Cenozoic extension along this system caused isostatic uplift of the core complex, and warping of the detachment-fault system by unloading due to tectonic denudation of the upper crust and other mechanisms. The Safford basin is a northwest-trending, southwest-dipping half-graben containing a maximum of 4.5 km of late Cenozoic basin fill. Formation of this basin, and renewed uplift of the core complex, began in the middle Miocene (17 Ma 7) with partial reactivation of the detachment fault system on the northeast flank of the core complex, and extension along a 50°-20° northeast-dipping listric range-bounding fault which merges with or cuts the detachment fault. An increase in basement seismic reflectivity forms a convex-upward arch-shaped zone with an apex beneath the northeast flank of the core complex at a depth of -4 km (-1.9 s) in the vicinity of Eagle Pass. The top of this arch-shaped zone extends along the base of the inferred detachment fault beneath the Safford basin, but separates from the detachment fault near the apex, dipping to the southwest and flattening at -13.5 km (-4.8 s) beneath the northeast flank of the Gila Mountains. The reflective fabric of this arch-shaped zone probably formed below -13 km as a ductile continuation of the detachment fault and a regional, subhorizontal shear zone associated with differential movement across a major brittle-ductile transition. Crustal extension was accommodated by brittle detachment faulting and block faulting above the transition, and ductile pure shear or anastomosing shear zones below. Uplift of the fabric during and after formation resulted from core complex development. Crustal reflectivity within and below the arch-shaped zone is divided into domains of variable reflection amplitude and continuity, possibly caused by variations in compositional layering, ductile strain, and partial melts. The Moho beneath the Safford basin is indicated by a series of strong reflections or decrease in reflectivity, and occurs at depths of -29-31 km (-9.5-10.5 s), apparently increasing towards the Pinalefio Mountains. Sparse mantle reflections at -11-11.3 s may be from intrusions or partial melts.
Type:
text; Dissertation-Reproduction (electronic)
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Geosciences; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Johnson, Roy A.
Committee Chair:
Johnson, Roy A.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleSeismic crustal structure beneath the Safford Basin and Pinaleiio Mountains: Implications for Cenozoic extension and metamorphic core complex uplift in SE Arizonaen_US
dc.creatorKruger, Joseph Michaelen_US
dc.contributor.authorKruger, Joseph Michaelen_US
dc.date.issued1991en_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.abstractGeologic relationships and reflection seismic data in the Safford basin and Pinaleiio Mountains metamorphic core complex suggest the northwest-trending core complex is formed along a mid-Tertiary detachment fault system that extends from a breakaway near the northeast flank of the Galiuro Mountains, to a depth of -15 km (-5 s) where it flattens beneath the Gila-Peloncillo Mountains. Top-to-the-northeast mid-Tertiary and late Cenozoic extension along this system caused isostatic uplift of the core complex, and warping of the detachment-fault system by unloading due to tectonic denudation of the upper crust and other mechanisms. The Safford basin is a northwest-trending, southwest-dipping half-graben containing a maximum of 4.5 km of late Cenozoic basin fill. Formation of this basin, and renewed uplift of the core complex, began in the middle Miocene (17 Ma 7) with partial reactivation of the detachment fault system on the northeast flank of the core complex, and extension along a 50°-20° northeast-dipping listric range-bounding fault which merges with or cuts the detachment fault. An increase in basement seismic reflectivity forms a convex-upward arch-shaped zone with an apex beneath the northeast flank of the core complex at a depth of -4 km (-1.9 s) in the vicinity of Eagle Pass. The top of this arch-shaped zone extends along the base of the inferred detachment fault beneath the Safford basin, but separates from the detachment fault near the apex, dipping to the southwest and flattening at -13.5 km (-4.8 s) beneath the northeast flank of the Gila Mountains. The reflective fabric of this arch-shaped zone probably formed below -13 km as a ductile continuation of the detachment fault and a regional, subhorizontal shear zone associated with differential movement across a major brittle-ductile transition. Crustal extension was accommodated by brittle detachment faulting and block faulting above the transition, and ductile pure shear or anastomosing shear zones below. Uplift of the fabric during and after formation resulted from core complex development. Crustal reflectivity within and below the arch-shaped zone is divided into domains of variable reflection amplitude and continuity, possibly caused by variations in compositional layering, ductile strain, and partial melts. The Moho beneath the Safford basin is indicated by a series of strong reflections or decrease in reflectivity, and occurs at depths of -29-31 km (-9.5-10.5 s), apparently increasing towards the Pinalefio Mountains. Sparse mantle reflections at -11-11.3 s may be from intrusions or partial melts.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)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.advisorJohnson, Roy A.en_US
dc.contributor.chairJohnson, Roy A.en_US
dc.contributor.committeememberWallace, Terryen_US
dc.contributor.committeememberGehrels, George E.en_US
dc.contributor.committeememberConey, Peter J.en_US
dc.contributor.committeememberChase, Clement G.en_US
dc.identifier.proquest9210306en_US
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