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P. C. Bateman

Publications and source records attributed to P. C. Bateman.

27 records · Page 2Linked to original sources
USGS1965

Isotopic ages of minerals from granitic rocks of the central Sierra Nevada and Inyo Mountains, California

Potassium-argon ages of biotite and hornblende from specimens of 17 granitic plutons in the central Sierra Nevada and the western Inyo Mountains, California, range from 69 to 183 m. y. The Mount Givens, Lamarck. and Round Valley Peak Granodiorites and related younger and more felsic quartz monzonites represent a pulse of magma emplaced in the general time interval of 80-90 million years ago, during Cretaceous time. Mineral ages of granitic rocks that flank these plutons on both the east and the west have been reduced during the emplacement of the Cretaceous intrusive rocks and are minimum ages for the time of crystallization. The ages of hornblende from the Tinemaha Granodiorite (150 to 180 m. y.) may approach crystallization dates. In conjunction with ages for other intrusive rocks in the Sierra Nevada and adjacent desert ranges they strongly suggest a magmatic episode during the Early Jurassic.

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USGS1965

Investigation of initial Sr87/Sr86 ratios in the Sierra Nevada Plutonic Province

One to three whole-rock samples from each of more than a dozen discrete plutonic intrusions in the east-central Sierra Nevada batholith have been analyzed for Sr 87 /Sr 86 and Rb/Sr ratios to obtain information on initial Sr 87 abundances. The initial Sr 87 /Sr 86 ratios in the rock magmas forming this province appear to have been in the range 0.7073 ± .0010 in the majority of cases. This range is definitely higher than that found for modern alkali-type and tholeiite-type basalt magmas of oceanic regions, which commonly range between 0.703 and 0.705. However, it is much lower than the average Sr 87 /Sr 86 ratios found in Precambrian sialic regions which range from 0.71 to 0.73. It seems clear therefore that the Sierra Nevada magmas were not derived solely either from the typical source regions of oceanic basalt or from the melting of ancient crustal sial. It is possible that these magmas represent a mixture of oceanic basalt and crustal sial, as would be the case of anatexis in a geosyncline containing much volcanic material of fairly recent origin and some terrigenous sialic detritus. They may instead be of mantle derivation with admixtures of crustal material assimilated during their rise. The whole-rock Rb-Sr age results derivec from the study indicate that the Lamarck and Mount Givens Granodiorites and the alaskite of Evolution Basin and porphyritic biotite granite of Dinkey Lakes form a younger group of intrusive rocks of 90 ± 10 m.y. Although the sampling was not designed for isochron age studies, it appears that most of the remaining rock units are considerably older.

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