Radioactivity of the rocks of the batholith of southern California

Esper S. Larsen; N.B. Keevil

doi:10.1130/0016-7606(1947)58[483:rotrot]2.0.co;2

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Radioactivity of the rocks of the batholith of southern California

Esper S. Larsen·N.B. Keevil

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Abstract

Determination of radioactivity has been made on 43 rocks, carefully selected from the different mapped units of the complex Cretaceous batholith of Southern California; they range from gabbro to granite. The activity of the gabbro averages about 0.3 alphas/mg./hr., that of the tonalites, 0.8, the granodiorite 1.3, and the granites over 2.0. The activity of the average rock of the batholith is about 0.9 alphas/mg./hr. Most of the rocks have been analyzed, and modal compositions are given. The radioactivity and the percentages of K 2 O, SiO 2 and PbO are plotted on a variation diagram. The variation curve for activity nearly parallels that for K 2 O, and the ratio of activity to K 2 O is about 0.5. The radioactivities of some rocks fall far from the variation curve, and degree of activity correlates with K 2 O content. A less-marked correlation between activity SiO 2 and PbO was also noted. The K 2 O, SiO 2 , PbO, and radioactivity concentrate in the residual liquid during crystallization and differentiation. PbO follows K 2 O closely, as it is concentrated in the K 2 O minerals, but radioactivity is very low in the K 2 O minerals and is greatly concentrated in the accessory minerals.

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Source-reported bounding extent: 32.62087018318113° to 36.98500309285596° latitude; -121.77246093750001° to -114.169921875° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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Esper S. Larsen, N.B. Keevil. 1947. Radioactivity of the rocks of the batholith of southern California. https://doi.org/10.1130/0016-7606(1947)58%5B483%3Arotrot%5D2.0.co%3B2

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