Global similarities in the spacing of east-west trending mantle-rooted structural discontinuities
published: Jan 1, 1998
ArtNo. ESP136000701008, Price: 19.00 €
My studies of structural control of ore deposits, carried out in different geological environments on five continents, reveal that within the individual ore districts the distribution of ore bodies and deposits is related to local stress distribution, but on a broad regional scale, the distribution of giant and supergiant ore deposits and major ore clusters is controlled by a pattern of mantle-rooted structural discontinuities and their intersections (especially in marginal parts of lithospheric plates, at intersection with orogenic belts, rift structures, and near corners of major blocks). In the present configuration of lithospheric plates, a major role in North America and Eurasia is played by EW-trending discontinuities. In China they are expressed as major latitudinal belts. In the United States, the EW-discontinuities belong to the least expressed ones in surface geology and geomorphology, but they are recognized by combination of geological, geophysical and geochemical data. The most important ones extend at latitudes close to 45°N, 40°N, and 35°N, with a spacing close to 600 km. This spacing is very similar to the size of the Ordos (Yishan) structural block (560 x 700 km) enclosed between the Yinshan-Tienshan and the Tsinling-Kunlun belts in China. The 400N discontinuity extends through the entire western U.S. (crossing, in Nevada, the former western edge of the Proterozoic North American craton). Major clusters of ore deposits of different type and age have developed in Colorado, Utah and Nevada near intersections of this EW-discontinuity with deep structures of other trends. This pattern guided the discovery of a new Mo-Cu porphyry and a new gold target in Pershing County, Nevada. These intersections are characterized by anomalous thickness of the crust, with upper mantle updoming in Utah and Nevada. In the eastern U.S. the spacing between EW-boundaries, enclosing major basins and uplifts, is about 550 and 460 km respectivel. One of these boundaries correlates with the biggest curvature of the Appalachian foldbelt. Within this intersection occurs an EW-belt of alkaline intrusives described by Ratcliffe. The spacing between the axes of E-trending North German-, North Danish-, and North Bohemian basins in Europe is about 300 km. In eastern South America the spacing of major NW-trending discontinuities (assuming their E-W orientation in the "pre-drift" position of the continent, before it separated from Africa), is about 750-800 km. The above similarities indicate a rather uniform stress distribution in the mantle at the time of the origin of major E-W discontinuities. This may give support to the theory of Stovas (1963), Stovickova (1966), Sun Dianqing & Gao Qinghua (1980), and others about global fracturing in relation to the changes in the speed of rotation of the Earth. It also endorses the conclusions by J.S. Lee (1962, 1984) about the importance of the EW-trending structures.