Ocean-Ridge System in Northwest America

Abstract

Two actively tectonic systems affect the earth's surface. The first is a chain of island arcs and arcuate mountain ranges which borders the Pacific Ocean and extends from Indonesia via the Himalayas to the European Alps. The system of arcs is distinct from the ocean-ridge tectonic system in having deep-seated seismicity, free-air anomalies an order of magnitude greater than those associated with the ocean ridges, and comparatively low values of heat flow. In addition the chain of tectonic arcs is associated with the formation of foredeeps, whereas the ocean-ridge system is associated with the formation of rifts. The most richly endowed petroleum provinces (those in which major fields tend to be concentrated) are located in foredeeps formed by the belt of arcs. This is true because these features are the sites of heavy sedimentation, fertilization of phytoplankton by nutrient salts, and restricted water circulation. The second global tectonic system is the ocean ridges. This system affects the continents in fewer localities than the system of arcs, but where it does, it also is the locus of the formation of basins favorable to hydrocarbon production and preservation. The East Pacific Rise is the segment of the ocean-ridge system which enters the North American continent through the Gulf of California. The tectonic development of this rise created the Tertiary architecture of the Los Angeles basin and the Great Valley of California. The question here considered concerns the northern extremity of the East Pacific Rise. Geophysical and geological evidence indicates that at the latitude of Yukon Territory the East Pacific Rise strikes into the continent. Its extension crosses the Yukon, from which it traverses the Arctic Archipelago by way of the delta of the Mackenzie River. During the Mesozoic a segment of the ocean-ridge system developed in the area now occupied by the Arctic Beaufort Sea. Consequent upon the development during the Tertiary of the East Pacific Rise, the Franklin Rise is extending into Yukon Territory, connecting the East Pacific Rise to the polar extension of the Mid-Atlantic Ridge. The Franklin Rise is the site of contemporary tectonism which is observable in a band extending from Chatham Strait to Ellesmere Island. Hydrocarbon exploration of this region must be based on premises different from those used in regions affected by the system of arcs.