In northern British Columbia, the Sylvester Allochthon of the Slide Mountain terrane is the most inboard of Cordilleran suspect terranes, resting as a vast klippe upon miogeoclinal strata of the Cassiar Platform. The Sylvester is oceanic; it comprises gabbro, pillowed and massive basalt, banded chert, carbonate, argillite, ultramafics and minor arenite, which range in age from Late Devonian to Late Triassic. Internal structure in the Sylvester Allochthon is characterized as a stack of innumerable interleaved tectonic slices, bounded by subhorizontal, layer-parallel faults. These lithotectonic units are an order of magnitude smaller than the terrane itself and may consist of only a single or a few repeated rock types. The internal structure of the Sylvester is complex but not chaotic; small numbers of slices occur together in larger second-order packages which are also fault-bounded and lensoidal. However, tectonic juxtaposition of unrelated lithologies and older-over-younger faults are common. The "stratigraphy" of the Sylvester assemblage is thus tectonic. Sliver-bounding faulting within the Sylvester is known to have, at least in part, predated its post-Triassic, pre-mid Cretaceous emplacement. The Sylvester was emplaced onto North America as the roof thrust to a foreland-style duplex within underlying North American strata. vii viii The Sylvester Allochthon is the most inboard of accreted terranes, however it does not represent a simple marginal basin. New microfossil dating demonstrates that most rock types occur through the complete range of Sylvester ages. Coeval but depositionally incompatable lithologies must have accumulated in separate ocean floor paleoenvironments. Lithologies of the allochthon derive almost exclusively from layer 1, only the surface of oceanic crust. Thus, Sylvester slices are telescoped remnants detached from a vast area of ocean crust which ranged in age and width through the upper Paleozoic but which is now otherwise entirely consumed. Similarities of rock type, internal structure, age range, and regional tectonic setting have identified the Sylvester Allochthon as broadly correlative with a discontinuous series of terranes extending the length of the Cordillera. Together, these terranes may represent the remnants of what was once the late Paleozoic proto-Pacific ocean floor.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/187539 |
| Date | January 1986 |
| Creators | Harms, Tekla Ann, Harms, Tekla Ann |
| Publisher | The University of Arizona. |
| Source Sets | University of Arizona |
| Language | English |
| Detected Language | English |
| Type | text, Dissertation-Reproduction (electronic), maps |
| Rights | Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. |
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