Trace-element contents of postorogenic granites of the eastern Arabian Shield, Kingdom of Saudi Arabia

Open-File Report 86-261

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Trace-element contents for 46 postorogenic granitoids vary by as much as two orders of magnitude; most samples are strongly enriched in incompatible elements (such as the heavy rare earths, yttrium, niobium, and uranium) and depleted in the compatible elements (such as barium, strontium, scandium, europium, and cobalt). These trace-element characteristics are typical of A-type granites found in other areas of the world. In spite of the wide range in trace-element contents, no samples contained economically significant concentrations of a single element.

Samples range from peralkaline to strongly peraluminous; most are weakly peraluminous or metaluminous. All three subgroups (peralkaline, metaluminous, and peraluminous) are enriched in uranium and hafnium and are depleted in compatible elements. The peralkaline granites are generally enriched in yttrium and niobium - the strongly peraluminous granites in rubidium and tantalum; both groups are also somewhat enriched in the heavy-rare-earth elements. Several of the peraluminous granites are known to be tin-bearing and, like tin-bearing granites found elsewhere in the world, their chondrite-normalized, rare-earth-element patterns are flat and have large negative europium anomalies.

Samples from several plutons have very anomalous ratios for geochemically similar elements such as yttrium and holmium, niobium and tantalum, and zirconium and hafnium. These ratios may reflect differential complexing with a halogen-rich aqueous phase that may be characteristic of plutons that have been subjected to an ore-forming process. A program to test these hypotheses, through study of known mineralized areas and laboratory experiments, should be implemented.

The regional trends for the chemical data and geochemical correlations over the large area sampled, suggest that the postorogenic granites were derived from a single protolith that formed by the mixing of oceanic sediments from the west, continental sediments from the east.

Study Area

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USGS Numbered Series
Trace-element contents of postorogenic granites of the eastern Arabian Shield, Kingdom of Saudi Arabia
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Open-File Report
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U.S. Geological Survey
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Reston, VA
i, 49 p. :ill., maps ;28 cm.
Saudi Arabia
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