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Chemical and isotopic diversity in basalts dredged from the East Pacific Rise at 10??S, the fossil Galapagos Rise and the Nazca plate

Marine Geology

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Abstract

We present petrographic, chemical and isotopic data for fresh lava samples dredged from three regions: (1) the fossil Galapagos Rise; (2) an elongate volcano near this extinct spreading center; and (3) the East Pacific Rise at 10??S. The samples from the Galapagos Rise are among the first samples from any fossil spreading center to be analyzed. Alkalic picrites from the elongate seamount and transitional basalts from the East Pacific Rise are both somewhat unusual rock types considering their respective tectonic environments. The dredges from the East Pacific Rise at about 10??S recovered unusual transitional, light rare-earth element (LREE) enriched basalts which show a range of fractionation. On the basis of their chemical and isotopic abundances, it is unlikely that the lavas are related by a single simple process of magmatic differentiation. We suggest that the mantle source region of these basalts was chemically and isotopically heterogeneous. The chemistry of LREE-depleted tholeiitic basalt dredged from near the axis of the extinct Galapagos Rise indicates complex petrogenesis and differentiation. The presence of tholeiitic basalts here indicates that unlike the Guadalupe and Mathematician fossil ridges, the Galapagos Rise has not been the site of voluminous post-abandonment alkalic volcanism. Alkalic basalts of picritic bulk composition dredged from an elongate seamount near the Galapagos Rise do not represent liquid compositions. Instead, we suggest that these alkalic liquids contain added olivine and plagioclase xenocrysts. Although most of the samples analyzed are very fresh, a few have been altered. The latter exhibit characteristic chemical and isotopic effects of seawater alteration. ?? 1982.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Chemical and isotopic diversity in basalts dredged from the East Pacific Rise at 10??S, the fossil Galapagos Rise and the Nazca plate
Series title:
Marine Geology
Volume
49
Issue:
1-2
Year Published:
1982
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Marine Geology
First page:
115
Last page:
132
Number of Pages:
18