Kilometer-scale recumbent folding, tectonic attenuation, and rotational shear in the western Anaconda Range, southwestern Montana, USA

dc.contributor.authorNeal, Bryce A.
dc.contributor.authorLaskowski, Andrew K.
dc.contributor.authorLonn, Jeffrey D.
dc.contributor.authorBurrell, William B.
dc.date.accessioned2023-12-04T22:50:19Z
dc.date.available2023-12-04T22:50:19Z
dc.date.issued2023-10
dc.description.abstractThe Eocene Anaconda metamorphic core complex is the most recently documented metamorphic core complex in the North American Cordillera. While much work has focused on constraining the nature and timing of core complex extension, earlier deformation preserved in its footwall is not as well understood. The Anaconda metamorphic core complex footwall contains an anomalously thin, lower- to uppermost-amphibolite-facies section of Mesoproterozoic Belt Supergroup and Paleozoic metasedimentary strata. While the tectonic nature of this thinning is generally accepted, the mechanisms behind it remain enigmatic. Previous workers have hypothesized that footwall strata were attenuated along the upper limb of the Late Cretaceous Fishtrap recumbent anticline, a kilometer-scale, NW-vergent, recumbent fold exposed throughout the west-central metamorphic core complex footwall. New geologic mapping in the west-central Anaconda Range better constrains the nature and timing of tectonic attenuation in this structurally complex area. Two generations of folds were recognized: (1) F1 recumbent isoclines associated with the Fishtrap recumbent anticline and (2) F2 W-vergent asymmetric folds associated with map-scale N-plunging folds. F1 folds, axial planar S1 transposition fabrics, and bedding-parallel faults and shear zones boudinage, transpose, and omit strata of the Belt Supergroup. We suggest that the Fishtrap recumbent anticline tectonically attenuated the Belt Supergroup through Paleozoic section of the west-central Anaconda metamorphic core complex footwall, and we propose that it is a kilometer-scale, regionally significant structure. We further propose that the fold may have developed in response to rotational shear and sinistral transpression along the Lewis and Clark Line, which was further driven by accretion of outboard terranes along the western margin of North America during Late Cretaceous time.en_US
dc.identifier.citationBryce A. Neal, Andrew K. Laskowski, Jeffrey D. Lonn, William B. Burrell; Kilometer-scale recumbent folding, tectonic attenuation, and rotational shear in the western Anaconda Range, southwestern Montana, USA. Geosphere 2023;; 19 (6): 1616–1639. doi: https://doi.org/10.1130/GES02595.1en_US
dc.identifier.issn1553-040X
dc.identifier.urihttps://scholarworks.montana.edu/handle/1/18240
dc.language.isoen_USen_US
dc.publisherGeological Society of Americaen_US
dc.rightscc-by-ncen_US
dc.rights.urihttps://creativecommons.org/licenses/by-nc/4.0/en_US
dc.subjectEocene Anacondaen_US
dc.subjectAnaconda metamorphic coreen_US
dc.subjectNorth American Cordilleraen_US
dc.subjecttectonic attenuationen_US
dc.subjectsouthwestern Montanaen_US
dc.titleKilometer-scale recumbent folding, tectonic attenuation, and rotational shear in the western Anaconda Range, southwestern Montana, USAen_US
dc.typeArticleen_US
mus.citation.extentfirstpage1en_US
mus.citation.extentlastpage24en_US
mus.citation.journaltitleGeosphereen_US
mus.data.thumbpage3en_US
mus.identifier.doi10.1130/GES02595.1en_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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