Major and trace element compositions and strontium, neodymium, and lead isotopic ratios of late Cenozoic mafic lavas from the northern Basin and Range

Lum, Clinton Chew Lun

Major and trace element compositions and strontium, neodymium, and lead isotopic ratios of late Cenozoic mafic lavas from the northern Basin and Range

Files

9234411.PDF (7.68 MB)

Date

1992

Authors

Lum, Clinton Chew Lun

Abstract

During the late Cenozoic mafic lavas were emplaced contemporaneously with Basin and Range extension near Battle Mountain, Nevada. They display wide ranges in major and trace elements contents and Sr, Nd, and Pb ratios. The temporal and compositional characteristics of the basalts indicate that the effects of crustal contamination on the compositions of the younger lavas has decreased relative to the older lavas. Assimilation and fractional crystallization (AFC) modeling suggests that their compositional heterogeneity cannot be attributed solely to crustal contamination, and instead most likely reflects their derivation from a heterogeneous mantle source region. Regional variations in the trace element ratios (Rb/La and Ba/Zr) and Sr, Nd and Pb isotopic compositions of mafic lavas from the western U.S. indicate they were derived from a heterogeneous lithospheric mantle. Crustal contamination and subduction related processes appear to be unable to reproduce the range in $\sp87$ Sr/ $\sp86$ Sr and low Rb/La of the lavas. Therefore, the variation in the basalts' isotopic ratios most likely reflects their derivation from a heterogeneous mantle source region. Plots of $\sp87$ Sr/ $\sp86$ Sr versus $\sp207$ Pb/ $\sp204$ Pb or $\sp207$ Pb/ $\sp207$ Pb clearly illustrates the compositional characteristics of their source regions. The Snake River Plain and southern Sierran Province basalts display elevated $\sp87$ Sr/ $\sp86$ Sr and varied Pb isotopic ratios indicating they were derived from a heterogeneous ancient lithospheric source with high time integrated Rb/Sr and U/Pb ratios. The low $\sp87$ Sr/ $\sp86$ Sr and Pb isotopic ratios of the suggest the Colorado Plateau-Eastern Transition Zone basalts were derived from a heterogeneous ancient lithospheric source with low time integrated Rb/Sr and U/Pb ratios. Basalts from the Basin and Range, Oregon Plateau, and northern Sierran Province display a positive correlation between their $\sp87$ Sr/ $\sp86$ Sr versus $\sp208$ Pb/ $\sp204$ Pb or $\sp207$ Pb/ $\sp204$ Pb ratios, which appears to reflect two component mixing between accreted depleted oceanic-type mantle and an enriched mantle component.

Advisor

Leeman, William P.

Degree

Doctor of Philosophy

Type

Thesis

Keywords

Geochemistry, Geology

Citation

Lum, Clinton Chew Lun. "Major and trace element compositions and strontium, neodymium, and lead isotopic ratios of late Cenozoic mafic lavas from the northern Basin and Range." (1992) Diss., Rice University. https://hdl.handle.net/1911/16558.

Rights

Copyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.

Citable link to this page

https://hdl.handle.net/1911/16558

Collections

Rice University Electronic Theses and Dissertations

Full item page