Basaltic melts of Ocean Islands (OIB) and their sources estimated from the investigation of melt inclusions and quenched glasses of rocks

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Abstract

Using our updated database of published analyses of mineral-hosted melt inclusions and glasses from volcanic rocks, the compositions of mafic melts of ocean islands (OIB) were considered. Mean contents of major, trace, and volatile elements were calculated for the complete data array and some particular comprehensively studied complexes: Iceland, Hawaii, Canaries, Galapagos, and Reunion. It was found that the mean contents of most elements fall between the compositions of magmas from mid-ocean ridges (most depleted) and intraplate continental environments (most enriched). A detailed analysis of element ratios in the magmatic complexes showed that they could be approximated as mixtures of magmas from one depleted and two enriched reservoirs. The contents of trace elements in the supposed mantle sources were calculated. The depleted source is best manifested in Iceland and almost exactly matches the composition of the depleted mantle, from which mid-ocean ridge basalts were derived.

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About the authors

V. B. Naumov

Vernadsky Institute of Geochemistry and Analytical Chemistry

Author for correspondence.
Email: naumov@geokhi.ru
Russian Federation, Moscow

A. V. Girnis

Institute for Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences

Email: girnis@igem.ru
Russian Federation, Moscow

V. A. Dorofeeva

Vernadsky Institute of Geochemistry and Analytical Chemistry

Email: naumov@geokhi.ru
Russian Federation, Moscow

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Supplementary files

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2. Fig. 1. Average element contents in mafic melts normalized to the composition of the primitive mantle (Palme and O’Neill, 2014). MORB and CONT are the mafic melts of mid-ocean ridges and intraplate continental complexes, respectively, estimated in our previous works based on the compositions of melt inclusions and rock glasses (Naumov et al., 2023). OIB is the average composition of all mafic melts of oceanic islands. Average compositions of some individual complexes for which about 1000 or more analyses are available are also shown: HAW – Hawaii, GAL – Galapagos Islands, REU – Reunion Island, CAN – Canary Islands and ICE – Iceland.

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3. Fig. 2. Alkali–silica classification diagram for melt compositions from oceanic islands: Iceland (ICE), Hawaii (HAW), Reunion Island (REU), Galapagos Islands (GAL), and Canary Islands (CAN) (Table 2). Rock fields (Le Maitre et al., 2002): PB – picrobasalt, B – basalt, AB – basaltic andesite, TAB – basaltic trachyandesite, TB – trachybasalt, B–T – basanite and tephrite, PT – phonotephrite, TP – tephriphonolite, F – foidite.

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4. Fig. 3. Variations in TiO2 depending on the MgO content in melts of oceanic islands. Arrows point to the composition of olivine, the main mineral in melts with a high MgO content. At MgO content < 10 wt. %, the dependences become steeper, which is primarily due to the crystallization of minerals with a lower MgO content (pyroxenes, plagioclase). See Fig. 2 for legend.

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5. Fig. 4. Variations in Sr content as a function of MgO in oceanic island melts. The diagram clearly distinguishes groups of melts with low and high Sr contents, with a boundary between them at ~260 ppm Sr. The histograms show that all melts from the Hawaiian Islands (HAW) and Reunion Island (REU) are characterized by high Sr contents, while a bimodal distribution is observed for Iceland and the Galapagos Islands. In what follows, we consider separately the low-Sr and high-Sr compositions of Iceland (ICE¹ and ICE², respectively) and the Galapagos Islands (GAL¹ and GAL², respectively). Melts from the Canary Islands (CAN) are not shown in this figure, since almost all of them are characterized by high Sr contents (>500 ppm).

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6. Fig. 5. Variations of smoothed TiO₂ values ​​as a function of MgO for different groups of melt compositions. The diagram is based on the same input data as Fig. 3. Smoothing consisted of calculating median TiO₂ values ​​for MgO values ​​with an interval of 1 wt.% and a window of ± 1 wt.%. For the HAW and ICE¹ compositions, the interquartile ranges (first and third quartiles) are also shown.

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7. Fig. 6. Examples of variations in smoothed ratios of different elements in oceanic island melts. The diagrams show variations in the behavior of element ratios with different degrees of coherence. PM and DM are the compositions of the primitive and depleted mantle according to (Palme, O’Neill, 2013) and (Salters, Stracke, 2004), respectively.

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8. Fig. 7. Calculated compositions of three ocean island magma sources normalized to the primitive mantle content (Palme, O’Neill, 2014). Vertical lines are standard errors (2σ). The composition of the depleted mantle, the source of mid-ocean ridge basaltic melts (DM according to Salters, Stracke, 2004), is also shown.

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