URANIUM AND THORIUM IN SELECTED SUITES OF IGNEOUS ROCKS
The uranium and thorium contents of 199 igneous rocks from a variety of petrographic provinces are here summarized. Data are given for the Mesozoic calcalkalic batholiths of the western United States; volcanic and hypabyssal rocks of the tholeiitic magma type from Hawaii and Virginia; and effusive calc- alkalic, alkalic, and subsilic-alkalic rocks from the western United States and Hawaii. The batholithic rocks show an increase of both uranium and thorium from gabbro to quantz-monzonite and granite. The more extreme differentiates, chiefly muscovite-quantz monzonites, contain considerably less uranium and thorium than the quartz monzonites and granites, although the Th/U ratios are nearly the same. The volcanic and hypabyssal rocks in general show a similar increase in both thorium and uranium toward the more felsic members. The alkalic basalts of the Honolulu volcanic series show an anomalous decrease in uranium and thorium toward the right on a variation diagram. The Th/U ratios remain fairly constant from the mafic to the felsic members of each series studied: each series also has a more or less characteristic Th/U ratio, ranging from 21/2 to 5. The scatter of thorium contents, uranium contents, and Th/U ratios is larger with increasing complexity of magmatic differentiation. The batholithic rocks have the greatest scatter, and have a significantly lower Th/U ratio in the gabbros than in the more felsic members. The data show no increasing loss of uranium relative to thorium from the magma during the later stages of crystallization. (auth)
- Research Organization:
- U.S. Geological Survey, Washington, D.C.
- NSA Number:
- NSA-14-013924
- OSTI ID:
- 4141929
- Journal Information:
- American Journal of Science (U.S.), Vol. Vol: 258-A; Other Information: Orig. Receipt Date: 31-DEC-60
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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