Pop-Up Structures and the Fracture Pattern in the Balsam Lake Area, Southern Ontario
Andrea L. Rutty
Alexander R. Cruden
ABSTRACT
An examination of topographic lineaments detectable in Landsat TM images and measurement of joints in outcrop in the Balsam Lake area reveals a systematic bedrock fracture pattern with three principal sets oriented 091°, 027°, and 152°. The 027° trend is parallel to a major aeromagnetic anomaly, the Niagara-Pickering Linear Zone (NPLZ), which underlies the Balsam Lake area and is thought to mark the sub-Paleozoic continuation of the Proterozoic Central Metasedimentary Belt Boundary Zone (CMBBZ). Possible origins of the main joint sets due to Acadian (091° set), Alleghanian (152° set) and St. Lawrence rift system tectonics (091° and 027° sets) are discussed. En-echelon pop-up structures have a mean principal trend of 118°. They displace Lake Algonquin paleobeaches, suggesting formation less than 12,500 years ago. The orientation of the pop-up structures is subnormal to the current in situ maximum horizontal stress direction, SHmax (020°), and is parallel to members of the 091° joint set, indicating possible nuclea-tion on favourably-oriented pre-existing joints. These pop-ups are the only features in the Balsam Lake area with strong evidence for a neotectonic age.
RÉSUMÉ
Les structures de soulèvement (pop-ups) ef le réseau de fissures dans la région de Balsam Lake, au sud de l’Ontario
L'examen des linéaments topographiques repérables sur les images Landsat (TM) et la mesure des diaclases dans un affleurement de la région de Balsam Lake révèle la présence d'un réseau de fractures dont l'orientation des trois principaux ensembles est 091°, 027° et 152°. La direction 027° est parallèle à une anomalie aéromagnétique majeure, la zone linéaire Niagara-Pickering, présente sous la région de Balsam Lake; on croit qu'elle identifie le prolongement sub-paléozoïque de l'aire limite de la zone méta-sédimentaire centrale protérozoïque. On traite des origines possibles des principaux ensembles de fractures attribuables aux systèmes acadien (091°), alléghanien (152°) et du rift du Saint-Laurent (091 °et 027°). La direction des structures de soulèvement en échelon est de 118°. Elles ont déplacé des paléo-plages du Lac Algonquin, indiquant ainsi une formation postérieure à 12 500 ans. L'orientation des structures de soulèvement est subnormale à la direction de la contrainte horizontale maximale actuelle, SHmax(020°), et est parallèle à des éléments de l'ensemble des fractures de direction 091°, montrant ainsi leur formation possible dans des fractures existantes bien orientées. Ces structures de soulèvement sont les seuls éléments de la région démontrant un âge néotectonique.
ZUSAMMENFASSUNG
Hebungsstrukturen und Bruchmuster im Gebiet des Balsam Lake, südliches Ontario
Eine Untersuchung der topographischen Lineamente die in Landsat TM-Bildern nachweisbar sind und Messungen der Fugen in den Aufschlùssen des Balsam Lake-Gebiets lassen ein systematisches Bruchmuster des anstehenden Gesteins erkennen mit drei nach 091°, 027° und 152° ausgerichteten Haupteinheiten. Die Ausrichtung nach 027° ist parallel zu einer wichtigen aeromagnetischen Anomalie, der linearen Zone von Niagara-Pickering, die unter dem Balsam Lake-Gebiet liegt; man halt sie fur eine subpalàozoische Fortfùhrung des Grenz-bereichs der proterozoischen zentralen metasedimentàren Gùrtel-zone. Man diskutiert môgliche Ursprùnge der Hauptfugen-systeme, die auf die akadische (091° System), alleghanische (152° System) und Sankt-Lorenz-Spaltensystem Tektonik (091° und 027° System) zurùckgefùhrt werden. Die gestaffelten Hebungsstrukturen haben eine durchschnittliche Hauptrichtung von 118°. Sie haben Palào-Strànde vom Lake Algonquin versetzt, und weisen so auf eine Bildung vor weniger als 12,500 Jahren. Die Orientierung der Hebungsstrukturen ist subnormal zu der gegenwàrtigen maximalen horizontalen Stressrichtung, S"m" (020°) und parallel zu Elementen des 091° Fugen-systems, was auf ihre môgliche Bildung auf gùnstig orientierten schon vorhandenen Fugen weist. Dièse Hebungen sind die einzi-gen Strukturen im Balsm Lake-Gebiet, welche deutlich ein neotektonisches Alter belegen.
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| Autores : | Andrea L. Rutty y Alexander R. Cruden |
|---|---|
| Título : | Pop-Up Structures and the Fracture Pattern in the Balsam Lake Area, Southern Ontario |
| Revista : | Géographie physique et Quaternaire, Volumen 47, número 3, 1993, p. 379-388 |
| URI : | http://id.erudit.org/iderudit/032965ar |
| DOI : | 10.7202/032965ar |
Tous droits réservés © Les Presses de l'Université de Montréal, 1993