| 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. |
| Genre: | Article |
| ProdID: | 70014878 |
| Citation Author: | Dodge, F. C. W.; Calk, L. C.; Kistler, R. W. |
| Citation Contributing Office: | |
| Citation Datum: | |
| Citation Day: | |
| Citation Edition: | |
| Citation Editor: | |
| Citation End Page: | 1304 |
| Citation Issue: | 6 |
| Citation Keywords: | |
| Citation Language: | English |
| Citation Larger Work Title: | Journal of Petrology |
| Citation LatN: | |
| Citation LatS: | |
| Citation LonE: | |
| Citation LonW: | |
| Citation Month: | |
| Citation No Pagination: | |
| Citation Number Of Pages: | 28 |
| Citation Online Only Flag: | |
| Citation Phsyical Description: | |
| Citation Projection: | |
| Citation Public Comments: | |
| Citation Publisher: | |
| Citation Series: | |
| Citation Series Code: | |
| Citation Series Number: | |
| Citation Search Results Text: | Lower crustal xenoliths, Chinese Peak lava flow, central Sierra Nevada.; 1986; Article; Journal; Journal of Petrology; Dodge, F. C. W.; Calk, L. C.; Kistler, R. W. |
| Citation Start Page: | 1277 |
| Citation Volume: | 27 |
| Citation Year: | 1986 |
| Type: | citation/reference |
| Text: | Lower crustal xenoliths, Chinese Peak lava flow, central Sierra Nevada.; 1986; Article; Journal; Journal of Petrology; Dodge, F. C. W.; Calk, L. C.; Kistler, R. W. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| Date Other: | Wed, 1 Jan 1986 00:00 -0600 |
| Publisher: | |
