Lower crustal xenoliths, Chinese Peak lava flow, central Sierra Nevada.
Journal of Petrology
By: F. C. W. Dodge, L. C. Calk, and R. W. Kistler
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Abstract
This assemblage of pyroxenite, peridotite and mafic granulite xenoliths in the toe of a 10 m.y. trachybasalt flow remnant overlying late Cretaceous granitic rocks, indicates the presence of a mafic-ultramafic complex beneath this part of central California; orthopyroxenites, websterites and clinopyroxenites are dominant. A few of the xenoliths contain ovoid opaque patches that are apparently pseudomorphs after garnet and have pyralspite garnet compositions; using a garnet-orthopyroxene geobarometer, they indicate a lower crustal depth of approx 40 km. Abundant mafic granulites can be subdivided into those with Al2O3 = or <12% and chemically gradational with pyroxenites, and others with Al2O3 > 15% and showing considerable scatter on oxide variation diagrams. The high-alumina granulite xenoliths have relatively low 87Rb/86Sr but high 87Sr/86Sr, whereas the low-alumina and ultramafic xenoliths have a wide range of 87Rb/86Sr, but lower 87Sr/86Sr; the isotopic data indicate roughly the same age as that of overlying granitic plutons (approx 100 m.y.). However, the granitic rocks have initial 87Sr/86Sr ratios intermediate between those of the high-alumina and ultramafic xenoliths, suggesting that they result from the mixing of basaltic magma (represented by the ultramafic rocks) and crustal materials, with subsequent crystal fractionation.-R.A.H.
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Lower crustal xenoliths, Chinese Peak lava flow, central Sierra Nevada. |
| Series title | Journal of Petrology |
| Volume | 27 |
| Issue | 6 |
| Year Published | 1986 |
| Language | English |
| Larger Work Type | Article |
| Larger Work Subtype | Journal Article |
| Larger Work Title | Journal of Petrology |
| First page | 1277 |
| Last page | 1304 |
| Google Analytic Metrics | Metrics page |