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Geology Seminar Series - Jordan Deane, PhD Candidate - Stratigraphy and Geochemistry of the Waugh Lake Group, Southern Taltson Orogen

Wed., Apr. 5, 2023 4:00 p.m. - Wed., Apr. 5, 2023 5:00 p.m.

Location: CW 237.1 and Zoom

Please join us for this PhD student seminar which you can attend in person or on Zoom. All are welcome!

Topic: Stratigraphy and Geochemistry of the Waugh Lake Group, Southern Taltson Orogen

Date and Time: Wednesday, April 5, 2023 at 4:00 PM

Location: College West Room 237.1

Zoom Link: https://uregina-ca.zoom.us/j/97101090599?pwd=WlovMThjZEVubVpSUzFzOGVxcDN3dz09

( Meeting ID: 971 0109 0599 - - - - Passcode: 255875)

Presenter: Jordan Deane, PhD Student, Dept. of Geology, University of Regina

Abstract:

Arc-related volcanic rocks are rarely preserved within Paleoproterozoic orogens; instead, we commonly just see their deeper-level (intrusive) equivalents. The Waugh Lake group (WLg), a 2.02-1.97 Ga greenschist-facies supracrustal succession, is potentially one such rare occurrence. This group was previously interpreted as the remnant of an intra-arc basin, or alternatively a back-arc, that formed on the SW margin of the Rae craton during the 2.0-1.93 Ga Taltson orogeny. It is preserved in a small synformal outlier, bordering the Taltson magmatic zone spanning the Alberta-Saskatchewan border. Its lower sequence comprises a spatially extensive turbiditic package with locally observed younging reversals, unconformably overlain by a thin unit of strongly foliated polymictic conglomerate with flattened clasts of impure quartzite, granitoid, rhyolite, basalt, and sandstone in a schistose matrix. These are in turn overlain by the upper sequence, comprising two cycles of variably sheared pebbly arkosic subarenite units each overlain by units of intermediate-felsic volcanic-volcaniclastic rocks with discernible primary textures such as phenocrysts and lapilli. The two paired siliciclastic-volcanic cycles are separated by a distinctively green unit of mafic-intermediate tuff interbedded with lithic wacke. At the top of the upper sequence is a unit of mafic-intermediate volcanic rocks with local autoclastic breccia. All WLg units are intruded by a suite of ca. 1.97 Ga Taltson granitoids and folded along NNE-trending axes. Preliminary geochemical analyses of upper sequence volcanic rocks indicate calc-alkaline affinity with compositions ranging from basalt to dacite. All units have strongly fractionated REE (La/YbN = 12.6-26.2) with a minimally to moderately negative Eu anomaly (Eu/Eu* = 0.62-0.90) and more strongly fractionated LREE (La/SmN = 3.5-5.0) relative to HREE (Gd/YbN = 1.5-3.2). Furthermore, when normalized to N-MORB, all units exhibit high Th and Ce relative to Nb, Ti, Y, and Yb, and when plotted on tectonic discrimination diagrams, all are diagnostic of an arc environment. The basal unit of the upper sequence, marked by pebbly arkosic rocks, indicates a sharp change in depositional environment (i.e., increase in continentally-derived detritus) from lower sequence turbidites, and points to a continental arc setting. This, together with the early phase of folding in the lower sequence and variable, locally intense, strain in the upper sequence suggests contrasting tectonic histories, and a potential age gap; which will be tested with future geochronological and isotopic study.