Sr and Nd isotopic composition of xenoliths from the Big Pine Volcanic Field, California
- Univ. of North Carolina, Chapel Hill, NC (United States). Dept. of Geology
Many continental basaltic rocks from the western USA, such as those from the Big Pine Volcanic Field (BPVF), California are interpreted to have been derived from enriched mantle (EM) based on their high [sup 87]Sr/[sup 86]Sr and low [sup 143]Nd/[sup 144]Nd ratios. However, samples of such mantle are rare, and some EM'' signatures probably result from contamination of magmas with depleted mantle (DM) characteristics. In order to determine the origin of the EM signature in the BPVF, The authors have begun a geochemical and isotopic study of xenoliths from the BPVF. Mantle xenolith-bearing mafic rocks from the BPVF have nearly the same Sr and Nd isotopic composition as xenolith-free lavas. If mantle xenoliths are a good discriminant for identifying crust-free lavas, then the Sr and Nd isotope systematic systematics of these lavas have not been greatly modified by crustal contamination, even though xenocrystic quartz and spongy plagioclase occur locally. An acid leached clinopyroxene from a spinel lherzolite xenolith from the BPVF has a measured [sup 87]Sr/[sup 86]Sr ratio of 0.7022 and an E[sub Nd] value of +12. Four bulk xenolith Sr and Nd isotopic analyses define mixing lines between their host lavas and the DM composition, as determined from the meticulously prepared clinopyroxene separate. The isotope ratios of the xenoliths are significantly different than the isotopic composition of the basalts, indicating that the xenoliths incorporated in the BPVF lavas are apparently not samples of the elusive EM that produced these lavas. Possible mechanisms to explain these data are described.
- OSTI ID:
- 5437324
- Report Number(s):
- CONF-9305259--
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Journal Name: Geological Society of America, Abstracts with Programs; (United States) Vol. 25:5; ISSN GAAPBC; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
580000* -- Geosciences
ALKALINE EARTH ISOTOPES
BASALT
CALIFORNIA
CHEMICAL COMPOSITION
COMPARATIVE EVALUATIONS
DEVELOPED COUNTRIES
EVALUATION
GEOLOGIC DEPOSITS
GEOLOGY
IGNEOUS ROCKS
ISOTOPE RATIO
ISOTOPES
MAGMA
MAGMATISM
NEODYMIUM ISOTOPES
NORTH AMERICA
PETROCHEMISTRY
PETROGENESIS
PETROLOGY
ROCKS
STRONTIUM ISOTOPES
USA
VOLCANIC ROCKS