Reconstruction of Mid-Cenozoic Extension in the Rincon Mountains Area, Southeastern Arizona, USA, and Geodynamic Implications

Jon E. Spencer, Stephen M. Richard, Steven H. Lingrey, Bradford J. Johnson, Roy A Johnson, George E Gehrels

Research output: Contribution to journalArticle

Abstract

The Rincon Mountains metamorphic core complex, located east of Tucson, Arizona, consists of an arched footwall of foliated crystalline rocks bounded above by the generally outward dipping, Oligocene-Miocene San Pedro extensional detachment fault. The southwest trending axes of corrugations in the detachment fault, and in footwall foliation and lithologic layering, parallel mylonitic lineation, and inferred top-southwest displacement on the fault. An upper plate fault block within a synformal fault groove on the west side of the Rincon Mountains contains a thrust fault that is interpreted as displaced 34-38 km westward from an original position adjacent to a similar thrust in the footwall of the San Pedro detachment fault. Much of the footwall of the detachment fault in the eastern Rincon Mountains consists of metasedimentary tectonites derived largely from Paleozoic carbonates that were buried beneath Proterozoic crystalline rocks forming the hanging wall of the Laramide Wildhorse Mountain thrust. These tectonites were later exhumed by displacement on the San Pedro detachment fault. Structural reconstruction supports the interpretation that the carbonate tectonites localized extensional faulting along the San Pedro detachment fault at crustal depths where carbonates would be weak and deform by crystal plasticity while quartzo-feldspathic rocks would be strong and brittle. This weak zone is located adjacent to the greatest width of exposed extension-parallel mylonitic fabrics in southeastern Arizona and may have been associated with the earliest initiation of extension in the region. Domains of low-strength carbonates may be an underappreciated influence on extensional tectonics in cratonic southwestern North America.

Original languageEnglish (US)
JournalTectonics
DOIs
StatePublished - Jan 1 2019

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Geodynamics
detachment fault
Carbonates
geodynamics
detachment
mountains
Crystalline rocks
footwall
mountain
carbonates
carbonate
crystalline rock
rocks
thrust
Faulting
Tectonics
Plasticity
Rocks
extensional tectonics
hanging wall

Keywords

  • continental extension
  • core complex
  • detachment fault
  • Laramide tectonics
  • Rincon Mountains
  • San Pedro detachment

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

Cite this

Reconstruction of Mid-Cenozoic Extension in the Rincon Mountains Area, Southeastern Arizona, USA, and Geodynamic Implications. / Spencer, Jon E.; Richard, Stephen M.; Lingrey, Steven H.; Johnson, Bradford J.; Johnson, Roy A; Gehrels, George E.

In: Tectonics, 01.01.2019.

Research output: Contribution to journalArticle

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abstract = "The Rincon Mountains metamorphic core complex, located east of Tucson, Arizona, consists of an arched footwall of foliated crystalline rocks bounded above by the generally outward dipping, Oligocene-Miocene San Pedro extensional detachment fault. The southwest trending axes of corrugations in the detachment fault, and in footwall foliation and lithologic layering, parallel mylonitic lineation, and inferred top-southwest displacement on the fault. An upper plate fault block within a synformal fault groove on the west side of the Rincon Mountains contains a thrust fault that is interpreted as displaced 34-38 km westward from an original position adjacent to a similar thrust in the footwall of the San Pedro detachment fault. Much of the footwall of the detachment fault in the eastern Rincon Mountains consists of metasedimentary tectonites derived largely from Paleozoic carbonates that were buried beneath Proterozoic crystalline rocks forming the hanging wall of the Laramide Wildhorse Mountain thrust. These tectonites were later exhumed by displacement on the San Pedro detachment fault. Structural reconstruction supports the interpretation that the carbonate tectonites localized extensional faulting along the San Pedro detachment fault at crustal depths where carbonates would be weak and deform by crystal plasticity while quartzo-feldspathic rocks would be strong and brittle. This weak zone is located adjacent to the greatest width of exposed extension-parallel mylonitic fabrics in southeastern Arizona and may have been associated with the earliest initiation of extension in the region. Domains of low-strength carbonates may be an underappreciated influence on extensional tectonics in cratonic southwestern North America.",
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N2 - The Rincon Mountains metamorphic core complex, located east of Tucson, Arizona, consists of an arched footwall of foliated crystalline rocks bounded above by the generally outward dipping, Oligocene-Miocene San Pedro extensional detachment fault. The southwest trending axes of corrugations in the detachment fault, and in footwall foliation and lithologic layering, parallel mylonitic lineation, and inferred top-southwest displacement on the fault. An upper plate fault block within a synformal fault groove on the west side of the Rincon Mountains contains a thrust fault that is interpreted as displaced 34-38 km westward from an original position adjacent to a similar thrust in the footwall of the San Pedro detachment fault. Much of the footwall of the detachment fault in the eastern Rincon Mountains consists of metasedimentary tectonites derived largely from Paleozoic carbonates that were buried beneath Proterozoic crystalline rocks forming the hanging wall of the Laramide Wildhorse Mountain thrust. These tectonites were later exhumed by displacement on the San Pedro detachment fault. Structural reconstruction supports the interpretation that the carbonate tectonites localized extensional faulting along the San Pedro detachment fault at crustal depths where carbonates would be weak and deform by crystal plasticity while quartzo-feldspathic rocks would be strong and brittle. This weak zone is located adjacent to the greatest width of exposed extension-parallel mylonitic fabrics in southeastern Arizona and may have been associated with the earliest initiation of extension in the region. Domains of low-strength carbonates may be an underappreciated influence on extensional tectonics in cratonic southwestern North America.

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KW - San Pedro detachment

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