File:Collected reprints - Atlantic Oceanographic and Meteorological Laboratories (and) Pacific Oceanographic Laboratories (1968) (20672110621).jpg

Title: Collected reprints / Atlantic Oceanographic and Meteorological Laboratories (and) Pacific Oceanographic Laboratories
Identifier: collectedreprin1972v2atla (find matches)
Year: 1968 (1960s)
Authors: Atlantic Oceanographic and Meteorological Laboratories; Pacific Oceanographic Laboratories; United States. Environmental Science Services Administration. Research Laboratories; Environmental Research Laboratories (U. S. )
Subjects: Oceanography Periodicals.
Publisher: Washington, D. C. : U. S. Dept. of Commerce, Environmental Science Services Administration, Research Laboratories : For sale by Supt. of Docs. U. S. G. P. O.
Contributing Library: Penn State University
Digitizing Sponsor: LYRASIS Members and Sloan Foundation

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NICKEL IRRUPTIVE A WHITEWATER SERIES ')j-T; GNEISS ANO GRANITE I 1 VOLCANICS, SEDIMENTS. I 1 BASIC INTRUSIVES /-» COPPER-NICKEL w OCCURRENCES i% DEPOSITS DESCRIBED IN TEXT Figure 5: Geologic map of the Sudbury lopolith showing fifty-one occurrences of copper-nickel sulphide lodes along the Irruptive contact (after Souch and Podolsky, 1969). to be undifferentiated primordial substances. The difference appears to be negligible.) A grand average of seventeen samples analyzed by Thode (1963) shows a plus 1.3 per milSS^4 value, or one which is close to the primordial meteoritic standard. Thus, a meteoritic origin for the Sudbury sulphur is at least permissible. On the other hand, it cannot be construed as proof, as many magmatic sulphide bodies which are obviously of terrestrial origin also have isotopic ratios that are close to the Canyon Diablo troilite standard. In principle, the lead isotope values also should be useful, as their ratios in meteorites are distinctive. However, the lead content of a siderite is exceedingly low - only about 1/25 of that present in the earth's crust. Any interpretation of the lead isotope ratios as a criterion for cosmic origin is probably vitiated by contamination with terrestrial lead. SUDBURY"MOON" As noted above, the Sudbury bolide would have had a diameter of 4 km. This is calculated from the basic assumptions that the impact velocity was 15 km/sec (a typical asteroidal velocity), that the original crater diameter was 40 km, and that the object was an iron meteorite of density 7.8. In turn, the original apparent crater depth was 12,500 ft, which is the sum of the true depth of 8,500 ft plus a rim height of 4,000 ft (Dietz, 1964). We may classify possible giant cosmic bodies into two types, (1) comet heads and (2) Apollo asteroids — i.e., those whose orbits cross the Earth's. Comet heads, because of their extreme hypervelocity and low density (circa 0.8, owing to their composition of ice and free radicals), probably explode surficially. This shallow focus of burst creates a shallow crater with a prominent central uplift (Sun, 1968). Quite likely, comet heads caused most of the known astroblemes, as, unlike Sudbury, these impact scars typically display a central dome. In contrast, an asteroidal siderite, owing to its low hypervelocity and high density (circa 7.8), penetrates the rock strata to a depth of one bolide diameter or more, causing a deep focus explosion. A bowl-shaped crater results without any central uplift, as exemplified by the Barringer Meteor Crater. A similar geomorphic style is found at other modern craters with associated siderite fragments (e.g., Henbury, Wolf Creek, etc.). The lack of any known central uplift at Sudbury suggests that this basin was caused by a low-velocity high-density asteroid rather than a comet head. This type of impact may also account for the extensive melting at Sudbury, making it a remarkably "wet" astrobleme. It should be mentioned, however, that Dence (1968) offers quite a different explanation for simple bowl craters and the large complex craters with central uplifts and peripheral annular depressions. A pure siderite would hardly qualify as the proposed Sudbury "moon." A differentiated meteorite is required, most plausibly one that contains a mix of both a chalcophyllic phase (to supply the copper and sulphur) and a siderophyllic phase (to supply the iron, nickel, cobalt, and Pt-metals). The ratio of iron to nickel in the Sudbury sulphides is about 10:1, 510

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