Evidence for Polyphase Exhumation of the Harcuvar Metamorphic Core Complex, Western Arizona

Walsh, Emily O.; Wong, Martin S.; Singleton, John S.; Wrobel, Alexander J.; Weiss, Thomas G.; Christensen, K.-E.

doi:10.1130/abs/2016am-287659

Cited by 2 publications

(8 citation statements)

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“…However, Walsh et al. (2016) reported preliminary thermobarometry and monazite geochronology on rare pelitic garnet ± kyanite schists from the Harcuvar footwall that suggests Late Cretaceous (76–70 Ma) garnet growth during decompression from pressures as high at ∼10 kbar to as low as ∼4 kbar during that time. These data suggest a major exhumational event of ∼4–6 kbar occurred during the Late Cretaceous.…”

Section: Discussionmentioning

confidence: 99%

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Late Cretaceous‐Early Paleogene Extensional Ancestry of the Harcuvar and Buckskin‐Rawhide Metamorphic Core Complexes, Western Arizona

et al. 2023

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Metamorphic core complexes in the western North American Cordillera are commonly interpreted as the result of a single phase of large‐magnitude extension during the middle to late Cenozoic. We present evidence that mylonitic shear zones in the Harcuvar and Buckskin‐Rawhide core complexes in west‐central Arizona also accommodated an earlier phase of extension during the Late Cretaceous to early Paleocene. Microstructural data indicate substantial top‐NE mylonitization occurred at amphibolite‐facies, and 40Ar/39Ar thermochronology documents post‐tectonic footwall cooling to <500°C by the Paleocene to mid‐Eocene. Amphibolite‐facies mylonites are spatially associated with voluminous and variably deformed footwall leucogranites that were emplaced from ca. 74–64 Ma, and a late kinematic ca. 63 Ma dike indicates this phase of mylonitization had waned by the early Paleocene. Reconstruction of the footwall architecture indicates that this latest Cretaceous—early Paleocene deformation occurred within a NE‐dipping extensional shear zone. The leucogranites were likely the result of crustal melting due to orogenic thickening, consistent with a model whereby crustal heating triggered gravitational collapse of overthickened crust. Other tectonic processes, such as the Laramide underplating of Orocopia Schist or mantle delamination, may have also contributed to this episode of orogenic extension. Miocene large‐magnitude extension was superimposed on this older shear zone and had similar kinematics, suggesting that the location and geometry of Miocene extension was strongly influenced by tectonic inheritance. We speculate that other Cordilleran core complexes also experienced a more complex and polyphase extensional history than previously recognized, but in many cases the evidence may be obscured by later Miocene overprinting.

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Section: Discussionmentioning

confidence: 99%

“…In addition, preliminary thermobarometry and monazite geochronology on rare pelitic garnet ± kyanite schists from the Harcuvar Mountains suggests that Late Cretaceous metamorphism occurred at 6–10 kbar pressures at ca. 76–70 Ma (Walsh et al., 2016). Although Spencer et al.…”

Section: Discussionmentioning

confidence: 99%

Late Cretaceous‐Early Paleogene Extensional Ancestry of the Harcuvar and Buckskin‐Rawhide Metamorphic Core Complexes, Western Arizona

et al. 2023

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“…This exhumation may record Laramide extensional unroofing. Similarly, Walsh et al (2016) reported preliminary thermobarometry and monazite geochronology on rare pelitic garnet ± kyanite schists from the Harcuvar footwall that suggests Late Cretaceous (76-70 Ma) garnet growth during decompression from pressures as high at ~10 kbar to as low as ~4 kbar during that time. These data suggest a major exhumational event of ~4-6 kbar occurred during the Late Cretaceous.…”

Section: Evidence For Late Cretaceous Extensionmentioning

confidence: 91%

“…Cretaceous metamorphism occurred at 6-10 kbar pressures (Walsh et al, 2016), suggesting that the footwall had been deeply buried. We calculate temperatures using a pressure range of 4-6 kbar (Table 1), with calculated temperatures shifting by ~15°C per kbar under these conditions.…”

Section: Ti-in-quartz Thermometrymentioning

confidence: 99%

“…However, Chapman et al (2020) that Late Cretaceous metamorphism occurred at 6-10 kbar pressures at ca. 76-70 Ma (Walsh et al, 2016). Although Spencer et al (2018) argued that any crustal welt in the region may have been tectonically removed from the base of the crust as a result of Laramide emplacement of the Orocopia Schist (Jacobson et al, 2017;Seymour et al, 2018;Strickland et al, 2018) during lowangle subduction, it is unclear that schist emplacement requires the removal of a Cretaceous crustal welt.…”

Section: Regional Tectonic Implicationsmentioning

confidence: 99%

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Late Cretaceous-early Paleogene extensional ancestry of the Harcuvar and Buckskin-Rawhide metamorphic core complexes, western Arizona

Wong

Singleton

Seymour

et al. 2022

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Metamorphic core complexes in the western North American Cordillera are commonly interpreted as the result of a single phase of large-magnitude extension during the middle to late Cenozoic. We present evidence that mylonitic shear zones inthe Harcuvar and Buckskin-Rawhide core complexes in west-central Arizona also accommodated an earlier phase of extension during the Late Cretaceous to early Paleocene. Microstructural data indicate substantial top-NE mylonitization occurred at amphibolitefacies, and 40 Ar/ 39 Ar thermochronology documents post-tectonic footwall cooling to <500°C by the Paleocene to mid-Eocene. Amphibolite-facies mylonites are spatially associated with voluminous and variably deformed footwall leucogranites that were emplaced from ca. 74-64 Ma, and a late kinematic ca. 63 Ma dike indicates this phase of mylonitization had waned by the early Paleogene. Reconstruction of the footwall architecture indicates that this latest Cretaceous -early Paleocene deformation occurred within a NE-dipping extensional shear zone. The leucogranites were likely the result of crustal melting due to orogenic thickening, implying a model whereby crustal heating triggered gravitational collapse of overthickened crust. Other tectonic processes, such as the Laramide underplating of Orocopia Schist or mantle delamination, may have also contributed to this episode of orogenic extension. Miocene large-magnitude extension was superimposed on this older shear zone and had similar kinematics, suggesting that the location and geometry of Miocene extension was strongly influenced by tectonic inheritance.We speculate that other Cordilleran core complexes also experienced a more complex and polyphase extensional history than previously recognized, but in many cases the evidence may be obscured by later Miocene overprinting.

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Evidence for Polyphase Exhumation of the Harcuvar Metamorphic Core Complex, Western Arizona

Cited by 2 publications

References 0 publications

Late Cretaceous‐Early Paleogene Extensional Ancestry of the Harcuvar and Buckskin‐Rawhide Metamorphic Core Complexes, Western Arizona

Late Cretaceous‐Early Paleogene Extensional Ancestry of the Harcuvar and Buckskin‐Rawhide Metamorphic Core Complexes, Western Arizona

Late Cretaceous-early Paleogene extensional ancestry of the Harcuvar and Buckskin-Rawhide metamorphic core complexes, western Arizona

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