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Newman, S., Finkel, R.C. and MacDougall, J.D. (1984). Comparison of (super 230) Th- (super 238) U disequilibrium systematics in lavas from three hot spot regions; Hawaii, Prince Edward and Samoa. Geochimica et Cosmochimica Acta 48(2): 315-324. doi: 10.1016/0016-7037(84)90253-9. |
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(super 230) Th- (super 238) U disequilibrium systematics reveal several important characteristics of the mantle source regions and petrogenesis of volcanic rocks in the presumed hot spots of Hawaii, Marion Island (Prince Edward hot spot), and Samoa. The ( (super 230) Th/ (super 232) Th) activity ratios of lavas from these three hot spots (1.06 + or - 0.07, 1.04 + or - 0.08, and 0.81 + or - 0.06, respectively) imply that the source regions are each nearly homogeneous with Th/U weight ratios of 2.9, 3.0, and 3.8. For Marion Island and Mauna Kea, Hawaii, negligible secular variation occurs in the ( (super 230) Th/ (super 232) Th) initial ratios. This supports other evidence for very short transfer time between source and surface. Significant residence time at depth prior to eruption cannot be ruled out for the Samoan lavas we have studied; however, the data for one of these flows deviate from the proposed ( (super 230) Th/ (super 232) Th)- (super 87) Sr/ (super 86) Sr correlation in the opposite sense from that expected for such residence. If it is assumed that the measured ( (super 230) Th/ (super 232) Th) ratios of the young lavas reflect Th/U in their mantle sources, then the observed variations among these three hot spots, combined with those reported by other workers for Iceland, the Azores and Tristan de Cunha, suggest that these sources are characterized by Th/U ratios ranging from values similar to that of MORB source ( approximately 2.5) to values similar to those of bulk earth ( approximately 3.8). Mixing of different proportions of depleted and enriched mantle may be responsible for the observed range. |
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Keywords
actinides; alkaline earth metals; East Pacific Ocean Islands;, geochemistry; Hawaii; hot spots; Indian Ocean; Indian Ocean, Islands; isotopes; lava; Marion Island; metals; Oceania;, Polynesia; Prince Edward hot spot; radioactive isotopes; ratios;, Samoa; Sr-87/Sr-86; stable isotopes; strontium; Th-232/Th-230;, thorium; U-238/Th-230; United States; uranium, 02D, Isotope geochemistry |
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Elsevier Science
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