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TitlePtarmigan Fiord basement-cover thrust imbricates, Baffin Island, Nunavut
AuthorChadwick, T C; St-Onge, M R; Weller, O M; Dyck, B J
SourceCanada-Nunavut Geoscience Office, Summary of Activities 2015 p. 61-72 Open Access logo Open Access
Alt SeriesEarth Sciences Sector, Contribution Series 20150289
PublisherCanada-Nunavut Geoscience Office
File formatpdf
NTS26B/09; 26B/10; 26B/15; 26B/16
AreaBaffin Island; Ptarmigan Fiord; Hall Peninsula
Lat/Long WENS -67.0000 -66.0000 65.0000 64.5000
Subjectsgeneral geology; igneous and metamorphic petrology; regional geology; structural geology; systematic stratigraphy; bedrock geology; imbricate structures; metamorphic environment; metamorphic rocks; metamorphic petrology; deformation; faults, thrust; gneisses; meta-semipelites; metapelites; migmatites
Illustrationslocation maps; photographs; tables
ProgramGEM2: Geo-mapping for Energy and Minerals Baffin Bedrock Mapping
Released2015 01 01
AbstractThe rocks at Ptarmigan Fiord on theHall Peninsula ofBaffin Island underwentmidcrustal deformation during the formation of the Paleoproterozoic Trans-Hudson Orogen. The structural style in the region is dominated by imbricate panels of Archean basement orthogneiss and Paleoproterozoic supracrustal strata, interpreted to have been deformed by thickskinned ductile thrusting. Basement rocks comprise amphibolite-faciesmetatonalite,metagranodiorite,metaquartz-diorite and metamonzogranite, and cover rocks comprise amphibolite-facies migmatitic pelitic and semipelitic schist, psammitic schist, amphibolite, calcsilicate and quartzite. The S1a penetrative foliation is variably present in basement rocks and consistently present in cover rocks, and is defined by alignment of biotite, sillimanite and leucogranite that formed before and during the thermalmetamorphic peak. The S1a foliation was deformed by F1b isoclinal folds with an amplitude of 100m. These structures are interpreted as forming during a D1 east-west crustal shortening event. Basement and cover imbrication occurred after the thermal metamorphic peak and is interpreted as D2 thick-skinned ductile thrusting. Ductile thrust faults at the base of seven basement-cover slices are identified on the basis of repetition of units and strain localization, and are interpreted as predominantly south-to-southeast verging on the basis of shear-sense indicators. There are two structural panels of D2 thrust imbricates, one in the northwestern part of the map area and one in the eastern part of the map area. Map-scale crosscutting relationships indicate that the northwestern panel overthrusted the eastern panel on a southeasterly T2c-directed thrust fault, following a F2b folding event that folded the T2a basement-cover thrust imbricates in the eastern panel. The Ptarmigan Fiord area contains a world-class exposure of thick-skinned structures as they are spectacularly delineated by belts of distinctive grey-weathering Archean basement rocks and brown- to black-weathering Paleoproterozoic supracrustal rocks.
Summary(Plain Language Summary, not published)
Ptarmigan Fiord, located on Hall Peninsula, southeast Baffin Island, is a spectacular location to observe rocks that were involved in the collision of two continents. In order to accommodate the intense deformation, rocks in the collision zone break along planes of weakness and ride on top of one another as large sheets, in a process known as thrusting. As these rock sheets pile up, the mountain belt develops. At Ptarmigan Fiord, cliff faces expose layers of granite (light coloured rocks) that have been thrust on top of layers of metasedimentary rocks (brown coloured rocks), creating a striped appearance to the landscape. These stacked sheets were also later folded, creating a geologically complex area. During August 2015, geological observations, measurements and samples were collected for the purpose of compiling a new map of the area, and determining the number and timing of deformation events. This study has economic implications due to the close proximity of diamond transporting rock known as kimberlite south of Ptarmigan Fiord.

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