CTG Online Series
The Canadian Tectonics Group (CTG) Online Series will be held in Fall and Winter 2020/2021, starting in late September 2020 in Zoom. The Zoom link will be available only to the CTG members or those ones who are subscribed to the CTG Mailing List. If you are interested in giving a talk in the upcoming series, please contact Nadia Mohammadi at Nadia.mohammadi@unb.ca or Gabriel Sombini Dos Santos (Gabriel.santos@uwaterloo.ca).
TALKS AVAILABLE AT THE OFFICIAL CTG YOUTUBE CHANNEL
The Canadian Tectonics Group (CTG) Online Series will be held in Fall and Winter 2020/2021, starting in late September 2020 in Zoom. The Zoom link will be available only to the CTG members or those ones who are subscribed to the CTG Mailing List. If you are interested in giving a talk in the upcoming series, please contact Nadia Mohammadi at Nadia.mohammadi@unb.ca or Gabriel Sombini Dos Santos (Gabriel.santos@uwaterloo.ca).
TALKS AVAILABLE AT THE OFFICIAL CTG YOUTUBE CHANNEL
UPCOMING 2021 CTG ONLINE SEMINAR SERIES:
January 26th, 2021, 1 Pm (EST): TBA
February 23rd, 2021, 1 Pm (EST): Eric Thiessen, Laurentian University
March 09th, 2021, 1 Pm (EST): Cees van Staal, Geological Survey of Canada
March 30th, 2021, 1Pm (EST): Claire Currie, University of Alberta
April 20th, 2021, 1 Pm (EST): Camille Patin, University of Saskatchewan
CTG 2020 AUTUMN SEMINAR SERIES:
Nicolas Piette-Lauzière (PhD student, University of British Columbia_Okanagan): "Impact of Metasomatism on Shear Zone Rheology: An Example from the Pocologan Harbour Granitoid Belt, Canadian Appalachians", December 9th, 2020 @ 1:00 PM EST.
Website: ResearchGate
Email: nicolas.piette-lauziere@alumni.ubc.ca
Abstract
Nicolas Piette-Lauzière, Kyle P. Larson, Dawn A. Kellett, Rüdiger Kilian, Michael Stipp, Riccardo Graziani and Isabelle Therriault
Active faults and shear zones form the plumbing of fluid circulation in the upper and middle continental crust, allowing surface water to percolate to depth and metamorphic and/or hydrothermal fluids to migrate into upper crustal levels. The strain history of a thermodynamically metastable host rock is commonly linked with the fluids it may react with: Net transfer reactions or hydration reactions have the potential to either promote shear zone widening or induce strain localization. While most effects of fluid-rock interaction on deformation have been established across continuous outcrops or through laboratory experiments, much less work has been carried out to quantify them at the regional scale. To do so, we use benchtop µXRF data to quantify major element mass changes and phase distributions within representative specimens from across the strain gradient associated with regional shear zones. Furthermore, we quantify the fabric anisotropy from phase maps with quantitative image analysis. We tested this method on the Pocologan-Kennebecasis shear zone (PKSZ) in New Brunswick where we quantified the compositional changes of the shear zone host rocks and the contribution of phase transitions to the anisotropy of the thin section-scale fabric.
The PKSZ is located within the Ganderia microcontinent at the contact between the Pocologan Harbour granitoid belt and the Pocologan metamorphic suite. The latter reached amphibolite facies conditions during the Acadian Orogeny. Both units recorded dextral strike-slip ductile deformation during the Neoacadian Orogeny and were subsequently folded and faulted during an episode of orogen-oblique extension that lasted until the Carboniferous. Within the granite, monzonite, and quartz-diorite orthogneiss of the Pocologan Harbour granitoid belt, the foliation is defined by three mineral assemblages: chlorite + zoisite, muscovite, or muscovite + potassium-feldspar. Whole rock compositions of the deformed specimens show significant element mobility compared to undeformed specimens. Assuming that Ti was the least mobile major element, specimens with an assemblage of muscovite + potassium-feldspar are significantly enriched in Na, K, and Si (> 300 wt%) while being depleted of Mg (>90%). Because of the low chlorite-carbonate-pyrite alteration index, we interpret the compositional changes to relate to metasomatism instead to variations of protolith compositions or hydrothermal alteration. The deformation gradient across the PKSZ is best approximated by the shape anisotropy of quartz, plagioclase, biotite and muscovite aggregates, with the least altered specimens displaying equivalent or greater phase aggregate anisotropy than the most altered specimens. Interestingly, the increase in mica modal proportion is not correlated with greater fabric anisotropy.
Jillian Kendrick (PhD student, University of Waterloo): "Modelling TTG petrogenesis: Recent Advances and a Case Study from the Kapuskasing Uplift, Ontario", November 17th, 2020 @1 PM EST.
Abstract
Tonalite-trondhjemite-granodiorite (TTG) suites are the dominant component of Archean continental crust, but their origin remains debated. The trace element composition of TTGs is commonly used as a proxy of the tectonic setting of their basaltic source; elevated Sr/Y and La/Yb ratios are interpreted as evidence of high-pressure anatexis of subducted oceanic crust. However, non-subduction models for TTG genesis have also been proposed. Investigating the petrogenesis of TTGs can therefore provide crucial insight into the tectonic regime that operated on early Earth and gave rise to the first continents. Increasingly sophisticated thermodynamic models have become powerful tools in this field of research, as they allow for forward modelling of the metabasite source and calculation of expected TTG chemical compositions. Different scenarios may be tested, including the general effects of petrological processes on TTG composition and regional studies linking TTGs to possible sources.
I will discuss two TTG modelling studies that form part of my PhD thesis. The first tests the effect of three factors that may influence the composition of TTGs at their source: progressive loss of anatectic melt, fractionation of garnet cores from the system, and source metabasite composition. The results illustrate that the trace element signatures of TTGs can be linked to variables other than depth of melting. In the second study, thermodynamic modelling is used to test the genetic connection between TTGs and granulites in the Kapuskasing Uplift in the Superior Province. Two geochemical groups of TTGs are found, and preliminary modelling results indicate that the associated granulites may represent the source of one group. The other group, however, appears to be most consistent with a lower-T, higher-P eclogite-facies source. Integrating these results with geochronological data will be key to determining the significance of the TTG groups to the tectonic history of the Kapuskasing Uplift. As thermodynamic models are further refined, this technique will continue to provide valuable insights into the genesis of crustal rocks on Earth.
Dr. David Corrigan (Geological Survey of Canada): "Paleoproterozoic Earth: Setting a Template for Modern Tectonics and Related Geological Processes", October 20th, 2020 @1 PM EST.
This talk is available at the OFFICIAL CTG YOUTUBE CHANNEL; Click Here for the full presentation.
Abstract:
The Canadian Shield provides an unparalleled field laboratory for the study of secular changes in tectonic processes. Breaking up of continental crust that previously amalgamated during the Neoarchean produced new oceanic lithosphere, as well as thinned continental crust on which intracontinental and marginal basin formed, sequestring CO2, Ca, Mg, P, and other elements from the oceans in the process. Along the continental edges, tholeiitic magma provinces, including flood basalt, formed where mantle plumes impinged prior to breakup. After opening for about 155 Ma, which is similar in duration to the time span of the modern Atlantic, the main (Manikewan) ocean closed producing arcs and back-arc basins that were later accreted to continental margins. In the Labrador Trough, Fe released in ca. 1.88 Ga transtensional marginal basins precipitated in shallow, well-oxygenated near-shore waters, forming world-class iron-ore deposits of the Schefferville/ Labrador City areas. Fragments of the Manikewan paleo-ocean are now only preserved in the Watts Group of Cape Smith belt, where they are preserved in a klippe. Continental arc magmatism resulting from ocean lithosphere subducting beneath continental margins produced elongate batholiths and plutonic suites semi-continuous over distances of 2000 km or more, on scales comparable with Phanerozoic arcs. Accretion and collision following ocean closure resulted in the development of foreland and molasse basins, fed by modern-like fluvio-deltaic systems. In terms of collisional processes, many hallmarks observed in the Alpine-Himalayan orogenic system occurred, perhaps for the first time in Earth’s history, in the Superior-Churchill collision system (Trans-Hudson orogen). These processes include indenter tectonics, lower crustal flow, radial flow, formation of oroclines, and lateral extrusion. These observations suggest that thermal, petrological and mechanical parameters of the crust and mantle had attained states similar to those observed today by the Paleoproterozoic, roughly midway through Earth’s evolution.
Mike Duvall (University of Alberta, LinkedIn): "Active Faulting and Subsurface Structural Variability of the Himalayan Foreland Basin, Nepal", September 29th, 2020 @ 1:00 PM EST.
Abstract:
Foreland basin stratigraphy can be used to investigate the behaviour of basement features during continent-continent collision, and to test links between basement structure, along-strike segmentation of deformation, and lithospheric flexure in a developing orogen. The Himalayan orogen has been segmented along its strike at the scale of hundreds of kilometres. This segmentation is apparent from along-strike changes in earthquake rupture patterns, thickness changes, deformation styles, topographic gradients, thermal evolution, and faults at oblique angles to the orogen. Heterogeneities in the Indian plate, such as crustal scale basement faults and ridges, are possible controls on this lateral segmentation. Understanding the driving mechanisms of this longitudinal variability could further our understanding of the orogen, and potentially improve earthquake hazard assessment.
Using 2D seismic reflection data, we mapped several regional horizons to characterize the geometry of the Ganga Basin, Nepal. Our findings suggest that basement features have been inherited by the Himalayan foreland basin, controlling accommodation. These basement features likely play a key role in the spatial localization of active deformation and may influence seismicity patterns varying along strike of the orogen. We also demonstrate that Himalayan ruptures may pass under the present-day trace of the Main Frontal Thrust as blind faults inaccessible to trenching, and that paleoseismic studies may underestimate Holocene convergence.
CTG 2020 SUMMER SEMINAR SERIES:
August 11th, 1 Pm EST, Alissa Kotowski, McGill University, Structural petrology and petrochronology record subduction, underplating, and return flow in the Cycladic Blueschist Unit exposed on Syros Island, Greece
July 28th, 1 PM EST, Alana Hinchey, Geological Survey of Newfoundland and Labrador
Crustal recycling during the assembly of NUNA: Geochemical and isotopic constraints from felsic magmatism in the Makkovik Province, Labrador
June 30th, 1 PM EST, Spencer Fuston, University of Houston
Raising the Resurrection Plate from an Unfolded-Slab Plate Tectonic Reconstruction of the NW Cordillera since Early Cenozoic Time
June 2nd, 1 PM EST, Pascal Audet, University of Ottawa
Tectonics of the northern Canadian Cordillera from a geophysical perspective
June 16th, 1 PM EST, Clare Warren, Open University
From the bottom to the top: exploring the depths of the NW Bhutan Himalaya
May 19, 1 PM EST, Noah Phillips, Texas A&M
The geological record of slow to seismic slip from an exhumed shallow subduction zone
May 5, 1 PM EST, Sean Kelly, Dalhousie University
Enigmatic Himalayan-Tibetan evolution explained by mantle delamination of Tibetan accreted terranes