ABSTRACT
During the interval between Devonian collision and Triassic
rifting, the Northern Appalachians were the site of a wide,
strike-slip plate boundary zone. Episodic motion on northeast- and
east-trending faults resulted in the relative displacement of the
Avalon and Meguma Terranes with respect to North America, and at
the same time caused the subsidence and later deformation of about
25 more-or-less distinct sedimentary basins. The result is an
exceedingly complex rock record characterized by along- and
across-strike variations through regimes of pure strike slip,
rapid and continuous basin subsidence, and local, compressional
deformation.
A large body of geologic evidence (first synthesized by Webb,
1969) shows that during Carboniferous times, the sense of
displacement was dextral, and its magnitude was in the range of a
few hundred kilometers. On the other hand, recent paleomagnetic
work (e.g. Kent and Opdyke, 1978) has suggested that about 2000 km
of sinistral motion occurred in the Northern Appalachians during
this interval. Accordingly, the first purpose of this study was to
reexamine the geologic evidence bearing on the sense-of-motion
question. Results of this analysis (Chapter 2) show (as Webb
believed) that displacement (1) was dominantly dextral and (2)
probably amounted to a few hundred kilometers. These dextral
faults were moving precisely during that interval when the
paleomagnetic evidence implies sinistral faulting. Furthermore,
although Kent and Opdyke's interpretation of the paleomagnetic
data absolutely requires the existence of a major left lateral
fault, geologic links across all known faults in Newfoundland and
New Brunswick show that none can have accomodated even a
significant fraction of the required left-lateral motion. Another
explanation of the paleomagnetic data must therefore be sought.
One of the most striking features of this transform is the extent
to which strike slip faulting was accompanied by basin subsidence.
A survey of the 25 major sedimentary basins (Chapter 3 and
Appendix 1) reveals a population of (1) pull-apart basins,
including those that underwent late thermal subsidence (Magdalen),
and those disrupted by later strike slip (Moncton); (2) basins
bounded in part by thrust faults (Cumberland); (3) basins at
strike slip fault intersections (Deer Lake); and (4) basins of
unknown origin (Narragansett).
Field studies of two Carboniferous sedimentary basins in Cape
Breton Island (Chapters 4 and 5) are consistent with regional
evidence that basin subsidence was driven by dextral faulting.
Mapping at 1:10,000 in the Big Pond Basin indicates that it is a
dextral pull apart that formed during Visean times at a right step
in the newly recognized Big Pond fault zone. Although the origin
of the Bay St. Lawrence Basin is less obvious, 1:12,000 mapping
along the eastern margin shows that subsidence in early and medial
Carboniferous was associated with at least 3 km of dextral slip on
the St. Lawrence fault.
The ultimate goal in a strike slip system such as this is the
construction of a set of palinspastic, paleogeographic maps
illustrating the evolving relationships between faulting and
sedimentation (Chapter 6). While the displacement histories of
most faults in the Canadian Appalachians are still inadequately
understood, this goal will be within reach after a few well
focussed field seasons.
Bradley, D.C., 1984. Late Paleozoic strike slip tectonics of the
Northern Appalachians. Unpublished PhD dissertation, State
University of New York at Albany. 286pp., +xiv; 3 folded plates
(maps)
University at Albany Science Library call number: SCIENCE
MIC Film QE 40 Z899 1984 B72
Copies of this PhD dissertation can be ordered
from Proquest UMI
Front matter (title,
table of contents, abstract, acknowledgements) - 0.4MB pdf
file
Photo pages in dissertation
(greyscale
photos with captions): - 7MB pdf file
Plate 1 (1.1) - Geologic/tectonic
map
of
the Upper Paleozoic of the Northern Appalachians
(uncoloured geological map,
scale 1:1,000,000)
Plate 2 (4.1) - Geologic
map
of
the
Big Pond Basin, Cape Breton Island
(uncoloured geological
outcrop map and cross sections, scale 1:10,000)
Plate 3 (5.1) - Geologic
map
of
the
Bay St. Lawrence Basin, Cape Breton Island, Nova Scotia
(uncoloured geological
outcrop map and cross sections, scale 1:12,300)
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