North American alkaline rock and carbonatite distribution and their relationship to rifts and suture zones: Testing the Wilson cycle model.

摘要

Nepheline syenites, their volcanic equivalents, and Carbonatites (ARCs) are commonly associated with intra-continental rifts that can develop into Atlantic-type continental margins. ARCs may be preserved on those margins. When an ocean basin closes, a suture forms and the ARCs become DARCs (Deformed ARCs). The site of the suture is then also the site of an older rifted continental margin. The presence of DARCs on suture zones indicates that a Wilson Cycle has been completed. The use of GIS to compile the spatial and temporal distribution of rifts, sutures, ARCs, and DARCs facilitates the testing of the ideas that: (1) Evidence of completed Wilson Cycles can be discerned within continents from ARC/DARC distribution and (2) Intra-continental rifts commonly form over older sutures in which new ARCs form by partial melting of underlying DARCs. To test these two ideas for North America, part of a set of newly digitized and updated world-wide maps of rifts and sutures, has been used with a digitized database constructed by extracting 259 ARCs and DARCs from a published alkaline rock database. The primary product of the research is a new map of North American rifts, sutures, ARCs and DARCs. Twelve regions in North America were identified in which ARC/DARC distribution was linkable to rifts and/or sutures. Four areas in (1) East Greenland, (2) on either shore of the Labrador Sea, (3) in the Monteregian Hill region of the Grenville Province of Canada and (4) in the Keewenawan/Kapuskasing region of Lake Superior proved particularly important because they contained evidence serving to improve general understanding of the operation of Rift/Suture/ARC/DARC relations.