thumbnail

Olivine and chromian spinel in primitive calc-alkaline and tholeiitic lavas from the southernmost cascade range, California: A reflection of relative fertility of the source

Canadian Mineralogist

By:
and

Links

  • The Publications Warehouse does not have links to digital versions of this publication at this time
  • Download citation as: RIS

Abstract

Chromian spinel and coexisting olivine phenocrysts from a geochemically diverse suite of primitive tholeiitic and calc-alkaline basalts and magnesian andesites from the Lassen region, in the southernmost Cascade Range, in California, show that the sub-arc mantle is zoned. Depleted calc-alkaline basalts and magnesian andesites erupt in the forearc region, and calc-alkaline basalts contain increasing abundances of incompatible elements toward the backarc. High-alumina olivine tholeiites erupt from the arc and backarc areas. Olivine from all these lavas displays a limited compositional range, from Fo86 to Fo91, and crystallized at high temperature, generally 1225-1275??C. Chromian spinel trapped in the olivine phenocrysts displays a large range of composition: Cr# values span the range 9-76. Excess Al in the spinel relative to that in 1-atm spinel suggests that it crystallized at elevated pressure. The phenocrysts in these lavas are in equilibrium with their host liquids. The full range of Cr# of the spinel compositions cannot be explained by differentiation or variable pressure, variations in f(O2), subsolidus equilibration or variations in degree of partial melting of a single peridotitic source. Rather, the systematic compositional differences among phenocrysts in these primitive lavas result from bulk chemical variability in their mantle sources. Correlations between spinel and host-rock compositions support the assertion that the geochemical diversity of Lassen basalts reflects the relative fertility of their mantle sources.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Olivine and chromian spinel in primitive calc-alkaline and tholeiitic lavas from the southernmost cascade range, California: A reflection of relative fertility of the source
Series title:
Canadian Mineralogist
Volume
35
Issue:
2
Year Published:
1997
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Canadian Mineralogist
First page:
453
Last page:
472
Number of Pages:
20