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H. R. Cornwall

Publications and source records attributed to H. R. Cornwall.

10 recordsLinked to original sources
USGS1976

Geochronology of the Arabian Shield, western Saudi Arabia: K-Ar results

An orogenic event, correlated with the Pan-African event in eastern Africa, affected the Arabian Peninsula between 510 and 610 m.y. ago and is well-recorded geochronologically. The event probably included two thermal pulses or maxima, the first occurring between 560 and 610 m.y. ago and the second between 510 and 540 m.y. ago. The earlier pulse, the more severe one, included the majority of the igneous activity and metamorphism. During the last part of the 510- to 610-m.y. period, left-lateral strike-slip faulting occurred along a set of northwest-trending en echelon fracture zones, whose composite displacement may be as large as 240 km. At least one and probably more orogenic events affected the Arabian Peninsula before the Pan-African event, but only minimum ages can be assigned to these, because thermal effects of the 510- to 610-m.y. event have reset K-Ar ages. Major diorite-granite batholiths, however, formed before 760 m.y. ago.

Arabian Shield↗
USGS1957

Minor elements in Keweenawan lavas, Michigan

The distribution of minor elements in three basaltic flows of the Keweenawan series, of Michigan, is related to differentiation in the flows. Thus, nickel is most abundant in the early differentiates; nickel, chromium, and barium are generally deficient in the pegmatites, which formed late; whereas copper, vanadium, yttrium, and other minor elements are concentrated in the pegmatites. The minor-element content of individual minerals in the Greenstone flow varies markedly from one mineral to another and seems to depend primarily on the presence or absence in the minerals of major elements for which the minor elements can substitute. Minor elements have substituted most readily for those major elements with similar ionic radii. Valence and electronegativity also seem to influence the ease of substitution. The distribution of other minor elements in copper-bearing lodes of the Michigan copper district shows no apparent relation to copper mineralization.

Michigan↗