Transtension is the oblique divergence between bounding plates or blocks that combines a coaxial orthogonal extension with a deformation zone boundary-parallel, noncoaxial, component, which generates a bulk constrictional strain. The coaxial component determines the rate and amount of crustal/lithospheric thinning and part of the horizontal extension. The non-coaxial component controls the vorticity, the horizontal shortening, and part of the horizontal extension. The instantaneous stretching direction bisects the angle between the direction of divergence (transport direction) and the zone boundary orthogonal. In the brittle regime, normal fault arrays accommodate vertical shortening and horizontal extension whereas simultaneous wrench fault arrays allow horizontal shortening. All faults, except those that are vertical and parallel with the zone boundary, rotate either with or against vorticity, depending on their orientation with respect to the transport direction and the zone boundary. Block rotation co...

Transtension in Arcs and Orogens

The Humber Arm and Hare Bay Allochthons of Western Newfoundland are made up of a variety of sedimentary rocks and volcanic and plutonic rocks that originated toward the east and record the evolution and destruction of the ancient continental margin of Eastern North America Five contrasting rock assemblages that constitute different structural slices are defined and delineated in the Humber Arm Allochthon Six contrasting rock assemblages constitute the Hare Bay Allochthon In each allochthon, the lower structural slices consist of sedimentary rocks and the highest structural slice consists of the ophiolite suite The stacking order and mode of assembly indicate that progressively higher slices travelled increasingly greater distances, so that their present vertical superposition represents a former west-to-east juxtapositionMost of the transported rocks have direct lithic correlatives in central Newfoundland These occur west of the Dunnage Melange, so that if the Dunnage marks the vestige of a North Am

Structural Succession, Nomenclature, and Interpretation of Transported Rocks in Western Newfoundland

It has long been recognized in North America that orogens represent deformed ancient continental margins, although the basic concepts have changed greatly from the early views of Hall, Dana, and Schuchert to later ones of Kay, Drake, and Dietz. This North American view stemmed from the fact that on this continent all the Phanerozoic orogens are at or near the present edge of the continent. The doctrine that geosynclines are open toward the ocean (one-sided) and that continents grow by the outward addition of younger orogenic belts was popular in North America during the 1950s and early 1960s, and it was enhanced by the interpretation of Paleozoic volcanic belts as island-arc complexes (Kay, 1951). The doctrine was further supported by early oceanographic studies at the present Atlantic margin, e.g., Drake et al. (1959), and by the models of Dietz (1963) and Dietz and Holden (1966) based upon actual comparisons between ancient and modern continental margins.

The Ancient Continental Margin of Eastern North America

Publisher Summary Although prior to 20 years ago, greenstones were thought to represent an Archean phenomenon, it is now clear that greenstones have formed throughout geologic time. It seems to be equally clear that all greenstones do not represent the same tectonic setting, nor do the proportions of preserved greenstones of a given age and tectonic setting necessarily reflect the original proportions of that tectonic setting. To better understand the tectonic settings of greenstones and their role in the history of continents and ocean basins, it is of interest to compare greenstones through time. Some studies have compared the geochemistry of greenstone volcanics of different ages with emphasis on basalts, and have recognized secular changes, especially at the Archean Proterozoic (A&’) boundary. Others have focused on granitoids associated with greenstones, and have reported secular geochemical changes, again with the most prominent changes at the A/P boundary.

Chapter 3 Greenstones Through Time

Trondhjemitic rocks are recognized in two ophiolitic assemblages in western Newfoundland. Regional geological considerations suggest that one of these assemblages, the Little Port Complex, represents the basement of an island arc assemblage, whilst the other, the Bay of Islands Complex, is an undeformed ophiolite and represents oceanic lithosphere. The origin of trondhjemites differs in these two complexes. In one it appears that the trondhjemites are a result of partial fusion of amphibolites; in the other a result of differentiation of basaltic magma. Chemical differences are recorded and might be used in other instances to determine the origin of trondhjemitic liquids.

Two Contrasting Trondhjemite Associations from Transported Ophiolites in Western Newfoundland: Initial Report

In the Moretons Harbour area, at the eastern end of the Lushs Bight terrane of central Newfoundland, the volcanic rocks of the "Lushs Bight Supergroup" are divided into two new groups, viz, the Mor...

D. F. Strong

Papers

Early Paleozoic Volcanism and Metamorphism of the Moretons Harbour–Twillingate Area, Newfoundland