The geology of ophiolitic and adjoining rocks of Chagnon Mountain, southern Quebec

• Main Author: Harris, Janet M.
• Format: Text
• Language: unknown
• Published: Scholars Archive 1984
• Subjects: Chagnon Mountain; St. Daniel Formation; sedimentation; Peasley Pond Conglomerate; Geology; Sedimentology; Tectonics and Structure; Baie Verte
• Online Access: https://scholarsarchive.library.albany.edu/cas_daes_geology_etd/33; https://scholarsarchive.library.albany.edu/context/cas_daes_geology_etd/article/1032/viewcontent/harrisms.pdf; https://scholarsarchive.library.albany.edu/context/cas_daes_geology_etd/article/1032/filename/0/type/additional/viewcontent/HarrisChagnonMt.pdf

Chagnon Mountain is located near the southern end of the Baie Verte-Brompton Line in the Eastern Townships of southern Quebec. The lithologic units in the area of study, from west to east and going up structure, are: gabbro, quartz-diorite, diabase, volcanics, the St. Daniel Formation and the Peasley Pond Conglomerate of the Glenbrooke Group. All these rocks have been metamorphosed to the greenschist facies. Contacts between the plutonic rocks are irregular and gradational indicating only one parent magma. Diabase dikes are present in the diabase unit and in the volcanics indicating the dikes acted as feeders to the volcanics. Geochemical analyses on several samples supports a tholeiitic origin for the mafic rocks and infer this magma to be from an ocean floor setting. The St. Daniel Formation lies structurally above the volcanics with the contact in some places conformable and in others, unconformable. The contact between the two could be a normal fault or set of faults which would give rise to a situation where sedimentation of muds would occur onto surfaces existing before faulting in some places and onto degrading fault scarps in others. The Peasley Pond Conglomerate was deposited after emplacement of the Baldface-Orford-Chagnon (BOC) ophiolites. It is a basal conglomerate which unconformably overlies the volcanic rocks and the St. Daniel Formation in the Chagnon Mountain area. The sediments of this unit contain chromite grains and silicic volcanic clasts indicating sources both the northeast (BOC source) and southwest (Ascot-Weedon source).