Full Title: The Taconide Zone and the laconic Orogeny in the Western Part of the Northern Appalachian Orogen
Author: E-an Zen
From the original introduction: Geologists studying the bedrock of the northern Appalachian region have long been aware of the existence of a line of major lithostratigraphic and structural discontinuity along the western front of the folded Appalachians. This is Logan's Line (for history, see Osborne, 1956, p. 168); it follows the St. Lawrence River from Gaspé Peninsula to Quebec City, thence south-southwest to the east shore of Lake Champlain; from here it trends almost due south to the upper end of that lake. (Compass directions used in this paper are present-day directions. They are used for convenience of reference and do not necessarily indicate the correct early Paleozoic compass orientations). Recent geologic and geophysical studies show that Logan's Line is not simply a trace of a surface of discontinuity in the bedrock, but the composite western limit of a zone characterized by distinctive early Paleozoic sedimentary and tectonic history. This paper is an attempt to describe and summarize some of this geologic history. The rocks of the Paleozoic Appalachian belt that mostly have been affected only by the Taconic orogeny will be called the Taconides. As the term is used in this paper, the Taconide belt is bordered on the north and west by Logan's Line where the line has been defined; otherwise, the northwest limit of the belt is the southeast limit of the foreland of the Taconic orogeny. On the southeast side of the Taconide belt, our discussion will be restricted to the area north and west of the Cabot fault zone in Newfoundland, the Shickshock Range on the Gaspé Peninsula, the axial region of the Notre Dame Mountain-Sutton Mountain anticlinorium in the Eastern Townships of Quebec, and the Hinesburg thrust in Vermont. The eastern limit of the Taconide belt then follows the Green Mountain and Berkshire massifs of Precambrian rocks (hereafter called the Precambrian massifs). The Taconide belt is some 100 km wide and over 2,000 km long; yet within this narrow belt many important Paleozoic geologic phenomena are persistent: a fundamental lateral change in sedimentary facies, the location of both detachment and receiving sites of major gravity slides and other thrust sheets, a persistent pair of large Bouguer gravity anomalies, and a possible change from continental to oceanic crust (which has since become altered by tectonic, plutonic, and metamorphic activities). In the first section of this paper, we describe the geologic features that seem to characterize the Taconides. The second section describes individual geologic terranes; because of uneven amount of published work and the writer's own familiarity in these areas, the description is necessarily uneven in detail. The final section of the paper will attempt to interpret the origin and history of the Taconides.
Published: 6/05/1972
ISBN Number: 0813721350
Pages: 80
Product Category: EBooks