Distribution of elements in biotite-hornblende pairs and in an orthopyroxene-clinopyroxene pair from zoned plutons, northern Sierra Nevada, California
✍ Scribed by Anna Hietanen
- Book ID
- 104745867
- Publisher
- Springer
- Year
- 1971
- Tongue
- English
- Weight
- 904 KB
- Volume
- 30
- Category
- Article
- ISSN
- 0010-7999
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✦ Synopsis
Distribution of major and minor elements has been determined for five hornblendebiotite pairs from hornblende-biotite quartz diorite and monzotonalite and for a clinopyroxeneorthopyroxene pair from pyroxene diorite collected from the border zones and centers of zoned plutons in the northern Sierra Nevada, California. The distribution coefficients K D [Mg/Fe] for biotite/hornblende are of the same magnitude (0.61-0.67) for both the mafic border zone and the silicic center.
For comparison, KD[Mg/Fe ] values for biotite/hornblende from plutonie rocks of the central Sierra Nevada and the southern California batholith were calculated from data published by others. Rocks of the oldest age group (ca. 150 m.y.) in the central Sierra Nevada have an average distribution coefficient, KD, of 0.64, close to the average K D in the study area, where K-Ar dates are 143 to 129 m.y. The intermediate age group has an average K D = 0.81, and the youngest group has K D -= 0.77. K D [Mg/Fe] for biotite/hornblende from the southern California batholith is 0.83, close to the average of the intermediate age group in the central Sierra Nevada. The calculated difference in pressure of crystallization between rocks of the Feather River area and the southern California batholith is 1 kb; the rocks of the Feather River area being crystallized at a higher pressure. This is in good agreement with the low-pressure contact metamorphism in the south (pyroxene hornfels facies), as compared with a medium-pressure metamorphism around the northern plutons, where andalusitesillimanite-cordierite and andalusite-staurolite subfacies of the amphibolite facies indicate pressures of about 4 kb.
Trace elements Cr, V, Ni, Co, Ga are distributed equally between biotite and hornblende, whereas Ba and possibly Cu are concentrated in biotite and Sr and Se and possibly Zr in hornblende.