Lithoprobe onshore seismic reflection transects across the Newfoundland Appalachians

Abstract

Vibroseis seismic reflection data have been recorded to 18 s two-way traveltime along three transects across the island of Newfoundland. The upper crust has both steep and subhorizontal reflectors consistent with a ramp–flat style of deformation, whereas the middle and lower crust are largely free of regional flats. Reflectors descend through ca. 20 km of vertical section in the middle and lower crust to flatten into the Moho or perhaps cut through it in places. The Moho is interpreted to be no younger than the dipping reflectors. Reflection fabrics, interpreted to be indicators of dominantly Mid-Ordovician to Mid-Silurian strain, show consistent orientations among the transects and divide the crust into two blocks. A northwestern block is characterized by upper and middle crustal reflectors dipping mostly southeast at variable angles. This block is underlain to the southeast by supposedly younger and dominantly northwesterly dipping reflectors that define a northwest-tapering, wedge-shaped block floored by the Moho. This latter block is cut by isolated southeast-dipping, upper crustal reflectors near the southeast ends of the seismic transects. One of these reflectors is spatially correlated with the Bay d'Est Fault, on which the last ductile motion was south over north thrusting of Mid-Silurian age. The two crustal blocks are proposed to represent the Laurentian and Gondwanan plates juxtaposed during closure of the Iapetus Ocean. The Gondwanan plate appears to be underthrust westward beneath the Laurentian plate, perhaps by as much as 200 km.

Provenance of tectonic history of the Gander Zone in the Caledonian/Appalachian Orogen: Implications for the origin and assembly of Avalon

“…The seismically defined lower crustal block underneath the Gander Zone (Marillier et al, 1989;Stockmal et al, 1990) thus probably represents its original basement. Quinlan et al (1992) recently argued on the basis of continuity of seismic reflectors that the lower crustal block is similar to the basement of the Hermitage Flexure (Bras d'Or-Brookville belt) in southwestern Newfoundland (Fig. 1).…”

Logan Medallist 2. Geophysics and Geology: An Essential Combination Illustrated by LITHOPROBE Interpretations–Part 1, Lithospheric Examples

“…Accessing available roads, the northern profile crossed the wide part of the Central Mobile belt and the southern one crossed the narrower part. Quinlan et al (1992) presented an initial interpretation of the contractor-processed data set and Hall et al (1998) included a more comprehensive interpretation that also considered the wide-angle reflection/refraction and potential field studies that were carried out. The data quality for these interpretations was not particularly good.…”

New age data refine extent and duration of Paleozoic and Neoproterozoic plutonism at Ganderia–Avalonia boundary, Newfoundland

“…2). It has been interpreted as the continuation of the Ganderia-Avalonia boundary (e.g., Blackwood and O'Driscoll 1976), but has a more subtle expression in seismic reflection data (Quinlan et al 1992).…”