A large-scale isotope anomaly in the Southern Hemisphere mantle
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...1982; Palacz & Saunders 1986), mantle enrichment through melt migration from the LVZ into oceanic and continental lithosphere (eg Sun 1980; Hart et al. 1986) or derivation of OIBs from the lower mantle which has lost lead by continuous core formation (eg Vidal & Dosso 1978). However, Newsom et al. (1986) showed that St Helena basalts have the same molybdenum (highly chalcophile) to praseodymium (highly lithophile) abundance ratios as MORBs and other OIBs, effectively arguing against continuous core formation. The EM-type character is generally considered to be related to processes associated with convergent margins, such as the recycling of sediments with oceanic crust (eg Hawkesworth et al. 1979; Cohen & O'Nions 1982; White 1985; Weaver et al. 1986). The formation of these OIB sources from remobilization or delamination of metasomatized enriched continental lithosphere has also been proposed (eg Richardson et al. 1982; McKenzie & O'Nions 1983; Hawkesworth et al. 1986). Multiple origins for EM-type mantle is likely, including superposition of different processes. Menzies (1983) suggested that EM1 could be related to enrichment by the introduction of CO2-rich silicate melt (eg kimberlite, nephelinite) whereas the high Rb/Sr, 878r/86Sr character of EM2 is similar to some modern island arc basalts (eg White 1985)....
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...More recently, Hart et al. (1986) pointed out that HIMU and EM1...
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...Schematic diagram of the ENd versus 87Sr/S6Sr plot for OIB data to show the fields of different types of oceanic basalts and the end-member assigned by Zindler & Hart (1986). Modified from Hart et al. (1986)....
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...Zindler & Hart (1986) used different terminology to define the characteristics of mantle end-members: DMM (depleted MORB mantle), PREMA (prevalent mantle, including Iceland, Galapagos, the Easter Islands of White's MORB group and the Hawaiian islands), HIMU (long-term high U/Pb in the source, including St Helena, Tubuai, Mangaia), EM1 (enriched mantle type 1 for the Kerguelen type) and EM2 (enriched mantle type 2 for the Society Island type)....
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...Schematic diagram of the ENd versus 87Sr/S6Sr plot for OIB data to show the fields of different types of oceanic basalts and the end-member assigned by Zindler & Hart (1986). Modified from Hart et al....
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...For comparison, oceanic regression line (ORL) is that of Tilton (1983); northern hemisphere Pb reference line (NHRL) is that of Hart (1984) ; S-K is the average crustal Pb-evolution curve of Stacey and Kramers (1975); field of Nazca plate basalts is from Unruh and Tatsumoto (1976); and field of Nazca plate sediments is constructed from Unruh and Tatsumoto (1976), Dasch (1981), and Tilton (1983)...
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