Eggins, SM and Green, DH and Falloon, TJ, The Tasmantid Seamounts: shallow melting and contamination of an EM1 mantle plume, Earth and Planetary Science Letters, 107, (3-4) pp. 448-462. ISSN 0012-821X (1991) [Refereed Article]
Copyright 1991 Elsevier Science
Primitive basalts (Mg# ∼ 61–70;Ni= 232–322 ppm) dredged from the Tasmantid Seamounts range between incompatible element-rich alkali-olivine basalt and incompatible element-poor tholeiite compositions. They are primary and near-primary magma candidates, consistent with a decrease in depth of magma segregation from ∼ 2.5 GPa (for alkali-olivine basalts) to ∼ 1 GPa (for tholeiites). Variation in geochemical and isotopic data in these basalts indicates mixing involving two distinct mantle sources: (1) an EM1 mantle source dominating the tholeiitic basalts (Ba/Nd 15, 87/Sr 86/Sr 0.7050,εNd < −3.5) and (2) a "long-term depleted" upper mantle source dominating the alkali-olivine basalts (Ba/Nd < 8,87Sr/86Sr< 0.7035,εNd > +3). This mixing can be explained by the interaction of a deeply derived EM1 mantle plume (or diapirs) with surrounding upper mantle (asthenosphere or oceanic lithosphere). The hot plume core penetrates to shallow levels to generate tholeiitic magmas, whereas the plume margins interact with surrounding upper mantle, resulting in cooler temperatures, smaller degrees of melting, and the formation of alkaline magmas.
The fractionated REE patterns (i.e. Dy/Yb chondrites) of the tholeiitic and transitional basalts imply melting in the presence of residual garnet but are inconsistent with the low-pressure segregation of these magmas. This may be resolved if small melt fractions, generated in the presence of garnet, have been added to the tholeiitic magma source volume. This requires a melt segregation process where small melt fractions migrate from relatively deep levels within the plume and its margins to enrich the plume core at shallow levels. Alternatively, the plume could incorporate incompatible-element enriched oceanic lithosphere, formed through addition of small melt fractions derived from underlying garnet-bearing asthenosphere prior to Tasmantid magmatism.
|Item Type:||Refereed Article|
|Keywords:||Tasmantid Seamounts, OIB, EM1, intraplate volcanism, alkaline basalts, tholeiites, mantle plumes, RV Franklin|
|Research Division:||Earth Sciences|
|Research Field:||Igneous and metamorphic petrology|
|Objective Division:||Expanding Knowledge|
|Objective Group:||Expanding knowledge|
|Objective Field:||Expanding knowledge in the earth sciences|
|UTAS Author:||Green, DH (Professor David Green)|
|UTAS Author:||Falloon, TJ (Dr Trevor Falloon)|
|Web of Science® Times Cited:||20|
|Deposited By:||Earth Sciences|
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