Joints, tensile strength and preferred fracture orientation in sandstones. New Brunswick and Prince Edward Island, Canada
DOI :
https://doi.org/10.4138/1377Résumé
The orientations of tensile fractures in Upper Devonian, Carboniferous and Lower Permian sandstones of southern New Brunswick and Prince Edward Island show correlation at the submicroscopic scale of microcrack alignments, the macroscopic scale of joints, and the megascopic scale of airphoto lineaments. Planes of minimum tensile strength and planes of preferred fracture, induced in visibly unfractured sandstone test-samples by line-loading and point-loading tests, are identified as microcrack alignments. The joints and airphoto lineaments have microcrack alignments parallel to them, but not all microcrack alignments are represented at the macroscopic and megascopic scales. Deformed Carboniferous sandstones east of Saint John have two prominent orthogonal Joint systems with microcrack alignments parallel to the four joint sets. The airphoto lineaments are parallel to only three joint sets. Southeast and northeast striking joints in one orthogonal system are tentatively interpreted as planes of extension and release respectively, related to the direction of compression during the Variscan-Appalachian orogeny. The other orthogonal system, with joint sets striking close to 010° and 100°, is interpreted as post-Triassic in age, possibly related to the presently acting crustal stresses in eastern North America. RÉSUMÉ Il y a correspondance dans les grès du Dévonien supérieur, du Carbonifère et du Permien inférieur du aud du Nouveau-Brunswick et de l'ile du Prince-Edouard entre l'orientation des fractures de tension à diverses échelles: microscopique — alignement des microfissures; macroscopique — dis-clases; et megascopique — linéaments observes à partir de photographies aériennes. On reconnait comrae alignements de microfissures les plans de force de traction minimale et les plans de fracture préférentlelle occasionnés par des essais de charges linéaires et ponctuelles sur des échantillons types de grès préalablement exempts de fractures apparentes. Bien que parallèlement aux diaclases et aux linéaments on retrouve des alignements de microfissures, ce ne sont pas tous les alignements de microfissures qui s'expriment aux échelles macroscopique et megascopique. À l'est de Saint-Jean, les grès déformes du Carbonifère possèdent deux systèmes distincts de diaclases orthogonales accompagnes d'alignements de microfissures parallèles aux quatre ensembles de diaclases. Les linéaments observes sur photographié aérienne ne sont parallèles qu'a trois ensembles de diaclases. On interprète provisoirement les diaclases de direction sud-est et nord-est dans l'un des systèmes orthogonaux comme, respectlvement, des plans d'extension et de relâchement reliés à la direction de compression durant l'orogenèse varisque-appalachienne. Des orientations se rapprochant de 010" et 100° caractérisent l'autre système orthogonal qui serait d'Sge post-triasique et peut être relié aux forces de tension contemporaines agissant sur l’écorce terrestre dans l'est de l'Amèrique du Nord. [Traduit par le journal]Téléchargements
Publié-e
1981-05-05
Comment citer
Lajtai, E., & Stringer, P. (1981). Joints, tensile strength and preferred fracture orientation in sandstones. New Brunswick and Prince Edward Island, Canada. Atlantic Geoscience, 17(2). https://doi.org/10.4138/1377
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