Comment on "isotopic and incompatible element constraints on the genesis of island arc volcanics from Cold Bay and Amak Island, Aleutians, and implications for mantle structure" by J. D. Morris and S. R. Hart

Details Comment on "isotopic and incompatible element constraints on the genesis of island arc volcanics from Cold Bay and Amak Island, Aleutians, and implications for mantle structure" by J. D. Morris and S. R. Hart Comment on "isotopic and incompatible element constraints on the genesis of island arc volcanics from Cold Bay and Amak Island, Aleutians, and implications for mantle structure" by J. D. Morris and S. R. Hart

Mar 1986

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986gecoa..50..477p&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 50, Issue 3, pp.477-481

Computer Science

9

Scientific paper

Similarities between incompatible element ratios and isotopic characteristics of oceanic island basalts (OIB) and andesites from Cold Bay and Amak Island have led and (1983) to suggest that Aleutian Island and arc magmas in general are derived from mantle sources similar to those which produce OIB. We suggest that shallow-level fractionation can substantially affect certain LIL-element ratios in evolved arc rocks and therefore such ratios are not indicative of the source values. We also debate their modal melting model which relies on an incompatible element-rich residual phase and an enriched mantle source in order to produce typical arc-type enrichments ( e.g. Ba / La ) from OIB sources. Furthermore, typical metasomatism associated with alkaline volcanic rocks cannot be relied upon to selectively produce Cs enrichments in arc volcanics. The broad overlaps in OIB and arc isotopic values cannot be used to define a unique mixture of sources as Morris and Hart suggest. Rather, we suggest that the range and variability of arc isotopic values are characteristic of individual arcs and reflects a melt / fluid signature from the slab. Recent studies of short-lived isotopes in Aleutian volcanic rocks have also indicated they could have been derived from MORB-type sources contaminated by slab-derived components. Theories suggesting that enrichments in OIB sources are ultimately a consequence of subduction are currently in vogue. Differences between localized melt / dehydration processes beneath arcs and more complete, long-term fusion at deeper levels in the mantle are invoked to account for significant differences in major and trace element compositions between island arc basalt (IAB) and OIB magmas.

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