Plume-Associated Ultramafic Magmas of Phanerozoic Age |
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Authors: | HERZBERG C; O'HARA M J |
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Institution: | 1DEPARTMENT OF GEOLOGICAL SCIENCES, RUTGERS UNIVERSITY, NEW BRUNSWICK, NJ 08903, USA
2DEPARTMENT OF EARTH SCIENCES, CARDIFF UNIVERSITY, PO BOX 914, CARDIFF CF10 3YE, UK |
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Abstract: | A parameterization of experimental data in the 0·27·0GPa pressure range constrains both forward models of potentialprimary magma compositions that exit the melting regime in themantle and inverse models for computing the effects of olivinefractionation for any olivine-phyric lava suite. This is usedto infer the MgO contents of primary magmas from Gorgona, Hawaii,Baffin Island and West Greenland. They typically contain 1820%MgO for wide variations in assumed peridotite source compositions,but MgO can drop to 1417% for Fe-enriched sources, andincrease to 2426% for fractional melts from Gorgona.Primary magmas with 1820% MgO have potential temperaturesof 15201570°C. For Gorgona picrites with 24% MgO,the potential temperature and initial melting pressure wereabout 1700°C and 8·0 GPa, respectively; melting washot and deep, consistent with the plume model. There are importantrestrictions to magma mixing in mantle plumes. Primary magmasthat exit the melting regime are both well-mixed aggregate fractionalmelts and isolated fractional melts. The latter can originatefrom a hot plume axis and be in equilibrium with olivines havingmg-numbers of 93·093·6, but they have MgOcontents and thermal characteristics that are difficult to constrain. KEY WORDS: komatiite; picrite; basalt; MORB; olivine; mantle plumes; primary magmas; equilibrium melting; accumulated fractional melting |
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