Tectonics and basin deformation in the Cabot Strait area and implications for the late Paleozoic development of the Appalachians in the St. Lawrence promontory.

摘要

The Cabot Strait lies astride the Cabot Fault system at the eastern extent of the Magdalen Basin, a pull-apart structure which was the depocentre of the regional Maritimes successor basin during the late Devonian to early Permian development of the Canadian Appalachians. Under the Cabot Strait two linear grabens parallel the major fault trends and preserve up to 6 km of Devonian to Carboniferous sedimentary rocks.; In Part I of this study these strata have been mapped using conventional reflection seismic data, with support from potential field and onshore geological data. A series of major dextral strike-slip faults, including the Cape Ray Fault, the Hollow-St. George's Bay Fault, and the Red Island Fault parallel the regional trend, and define a wrench borderland geometry with the Cabot Fault as the master fault. The Cape Ray Fault is shown to have played a role in middle to late Devonian basin formation as well as Carboniferous deformation, while the others were active only in the Carboniferous. Four unconformities yield timing of movement along the faults and allow correlations to be made with regional deformation. Classic wrench-related features such as restraining bends, flower structures and inversion profiles are present in the Cabot Strait-Bay St. George area.; In Part II, the middle Devonian and later modification of the orogen at the St. Lawrence Promontory is examined through a series of crustal profiles, terrane configuration sketches, and paleogeographic reconstructions. Data pertaining to the Salinic and Acadian events are compiled, and evidence is presented for the development of the pre-Horton/Horton basins as extensional collapse features associated with the overthickening of the crust at the collision of two promontories. Overstepping, mainly post-Tournaisian basin development is seen primarily as a consequence of dextral strike-slip. Both of the above processes were enhanced and overprinted in Newfoundland by tectonic ejection of crustal blocks away from the St. Lawrence Promontory. Localized terrestrial basins such as the Deer Lake Basin are related mainly to this latter process. The reconstructions further reveal that the distribution of pre-existing lower Paleozoic terranes can be explained by an evolving series of dextral strike-slip faults centered on the Cabot Fault system.; Part III consists of a series of paleogeographic reconstructions of lands bordering the North Atlantic, which allow conclusions of the foregoing chapters to be projected on a regional scale. The Silurian-early Devonian tectonic development of the St. Lawrence Promontory is visualized as a process of sinistral terrane accretion, featuring a continuum of terrane sizes, ranging from slivers to microplates. For the mid-Devonian and later, arguments are made for tectonic processes which have been accepted for some time in Europe, but which have not been fully evaluated in the Canadian Appalachians, such as tectonic indentation (wedging), tectonic escape and extensional collapse. The Maritimes Basin is interpreted to have evolved in two phases, the first related to Appalachian crustal overthickening and collapse, and the second related to Variscan foreland strike-slip. This latter transcurrent faulting is attributed to the action of the Iberian indentor and consequent escape of West Avalonia, and not to large scale rotation of the combined Laurentia + Baltica plate.