Magmatism and Extension in the Anaconda Metamorphic Core Complex of Western Montana and Relation to Regional Tectonics

dc.contributor.authorHowlett, Caden J.
dc.contributor.authorReynolds, Aislin N.
dc.contributor.authorLaskowski, Andrew K.
dc.date.accessioned2021-12-13T19:51:36Z
dc.date.available2021-12-13T19:51:36Z
dc.date.issued2021-09
dc.description.abstractMetamorphic core complexes (MCCs) are a product of crustal extension, but their dynamics are still debated. Early research suggests that the formation of MCCs in the western United States was due to gravitational collapse of crust that had been thickened during Cordilleran orogenesis. However, the instability of overthickened crust alone cannot explain the diachronous formation of core complexes with a strong spatial dependency, as there was relatively uniform crustal thickness along strike of the Cordillera. For this reason, there is an interest in what role other lithospheric processes (such as subducted slab removal) play in the evolution of MCCs. We investigate the role of such processes by determining the temporal relation between magmatism and extension in the Anaconda MCC (AMCC) of western Montana. Geologic mapping, zircon U-Pb geochronology, and zircon (U-Th)/He thermochronology reveal that the initiation of extension in the AMCC in the Eocene (∼53 Ma) began at least 3 Myr after the emplacement of voluminous Paleocene two-mica plutons. We interpret that the AMCC is an example of a core complex that was primed for extension by magmatic thermal weakening and suggest that foundering of the Farallon flat slab and the onset of the ignimbrite flareup in western Montana was responsible for the initiation of AMCC extension. An updated compilation of MCC cooling ages and Cenozoic volcanic activity across the western United States supports previous interpretations that the removal of Farallon oceanic lithosphere likely initiated MCC exhumation in some regions.en_US
dc.identifier.citationHowlett, Caden J., Aislin N. Reynolds, and Andrew K. Laskowski. “Magmatism and Extension in the Anaconda Metamorphic Core Complex of Western Montana and Relation to Regional Tectonics.” Tectonics 40, no. 9 (September 2021). doi:10.1029/2020tc006431.en_US
dc.identifier.issn1944-9194
dc.identifier.urihttps://scholarworks.montana.edu/handle/1/16582
dc.language.isoen_USen_US
dc.titleMagmatism and Extension in the Anaconda Metamorphic Core Complex of Western Montana and Relation to Regional Tectonicsen_US
dc.typeArticleen_US
mus.citation.issue9en_US
mus.citation.journaltitleTectonicsen_US
mus.citation.volume40en_US
mus.data.thumbpage3en_US
mus.identifier.doi10.1029/2020TC006431en_US
mus.relation.collegeCollege of Letters & Scienceen_US
mus.relation.departmentEarth Sciences.en_US
mus.relation.universityMontana State University - Bozemanen_US

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