Loading...
Proterozoic geology of the northern half of the Mount Evans 7.5-minute quadrangle, The
Powell, Logan
Powell, Logan
Citations
Altmetric:
Advisor
Editor
Date
Date Issued
2020
Date Submitted
Keywords
Collections
Research Projects
Organizational Units
Journal Issue
Embargo Expires
2021-07-03
Abstract
The Picuris orogeny was a 1450 Ma to 1360 Ma convergent tectonic event that left a deeply rooted orogenic belt across central Arizona, northern New Mexico, and Colorado. Mechanisms for the Picuris orogeny are debated, in large part due to early Mesoproterozoic plutonism that emplaced a belt of generally felsic, `anorogenic' intrusions spanning presentday North America from southern California to Newfoundland. While the majority of these intrusions do have geochemical signatures indicative of mantle upwelling and crustal extension, several plutons in the southwestern United States have major element geochemistry classically associated with arc magmatism, among them the metaluminous, calc-alkaline, magnesian, 1440 Ma Mount Evans batholith in the central Colorado Front Range. Numerous tectonic settings, including subduction, have been proposed for the Picuris orogeny, but specic plutons that may represent a relic Picuris magmatic arc have not been identied within that context. The purpose of this contribution was to unravel the structural history in and around the Mount Evans batholith and document the extent and nature of the Picuris orogeny in this region, using LA-ICP-MS zircon geochronology and 1:24,000 scale eld mapping from the northern half of the Mount Evans 7.5-minute quadrangle. A previously undated quartz monzonite gneiss and a monzogranite phase of the Mount Evans batholith yielded U-Pb ages of 1764:9 5:4 Ma and 1444:6 7:3 Ma, respectively. Inherited core analyses yielded 1900 Ma to 1500 Ma ages. Results from structural mapping of metasedimentary and metaignous rock units illuminate a complex polyphase Proterozoic deformation history. Observed isoclinal F1 folds and mineral lineations (D1) likely represent earliest deformation during the Paleoproterozoic growth of Laurentia. The absolute timing of open to close, commonly chevron F2 folds, open to close, north-plunging, upright F3 folds, and gentle to close, west-plunging, upright F4 folds is unknown, but can be constrained to the Paleoproterozoic and/or early Mesoproterozoic based on the regional geologic history. Defor- mation at 1440 Ma includes northwest-directed regional strain, based on the hypersolidus foliation of the Mount Evans batholith and sinistral-normal shear along a north-trending batholith/wall rock contact. Regional strain during crystallization and spatiotemporal association with orogenesis are key diagnostic characteristics of syn-tectonic plutons, both of which are met by the 1440 Ma Mount Evans batholith within the milieu of the 1450 Ma to 1360 Ma Picuris orogeny. The results of this study, in concert with published research suggesting geochemical arc-anity of the Mount Evans batholith, allude to the presence of a previously unrecognized, Mesoproterozoic magmatic arc.
Associated Publications
Rights
Copyright of the original work is retained by the author.