Sr and Nd isotopic compositions of individual olivine-hosted melt inclusions from Hawai'i and Samoa: Implications for the origin of isotopic heterogeneity in melt inclusions from OIB lavas

Abstract

ReuseThis article is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs (CC BY-NC-ND) licence. This licence only allows you to download this work and share it with others as long as you credit the authors, but you can't change the article in any way or use it commercially. More information and the full terms of the licence here: https://creativecommons.org/licenses/ TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. ABSTRACTGeochemical investigations of mantle heterogeneity as sampled by ocean island basalts (OIB) have long relied on isotopic analyses of whole rock lavas. However, recent work has shown that significant isotopic disequilibrium can exist between the phases (groundmass and phenocrysts) of a single OIB lava. In this study, we target individual olivine hosted melt inclusions from two lavas-one Samoan and one Hawaiian-with melt inclusion 87 Sr/ 86 Sr heterogeneity previously observed using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). We report 87 Sr/ 86 Sr and 143 Nd/ 144 Nd in individual melt inclusions using thermal ionization mass spectrometry (TIMS). In melt inclusions from Samoan sample AVON3-71-2, we find highly heterogeneous (935 ppm) 87 Sr/ 86 Sr (0.705193 -0.705853, N=6), consistent with previously identified 87 Sr/ 86 Sr heterogeneity (~2030 ppm) by laser ablation multicollector ICP-MS (0.70459 -0.70602, N=12). In contrast, we find very little (251 ppm) 87 Sr/ 86 Sr Cabral et al., 2014;Rose-Koga et al., 2012 and Sr (Jackson and Hart, 2006;Harlou et al., 2009;Sobolev et al., 2011) isotopic compositions that span much of the variability observed in oceanic lavas globally. Despite their volumetrically minor contribution to the whole rock lava, the isotopic diversity preserved in melt inclusions provides important information about mantle melting and the processes that operate in magma chambers. The origin of the chemical and isotopic diversity in melt inclusions remains the source of debate, but has most often been attributed to either assimilation of oceanic crust or mixing of isotopically heterogeneous pristine mantle melts (e.Only a handful of studies have examined Sr isotopic compositions of olivine hosted melt inclusions from ocean island basalt (OIB) lavas. Jackson and Hart (2006) were the first to target individual olivine-hosted melt inclusions for Sr isotopic analysis, utilizing laser ablation multicollector inductively coupled plasma mass spectrometry (ICP-MS) to analyze melt inclusions from Samoan picrites. Jackson and Hart (2006) found 87 Sr/ 86 Sr variability within olivine-hosted melt inclusions from a single basalt as large as 3400 ppm, which is 13% of the total range observed in the lavas from the ocean basins (i.e., 0.7021 [Schilling et al., 1994;Fontignie and Schilling, 1996] to 0.7205 [Jackson et al., 2007]). This result was reinforced by the work of ...

Isotopic analysis of sub‐nanogram neodymium loads using new ATONA™ amplifiers

“…In recent years the ability to measure precise Nd isotopic ratios in increasingly small samples has become of great interest to not only the geological community, but also anthropologists and forensic scientists. For geologists the 143 Nd/ 144 Nd ratio of small samples is being used for Sm‐Nd geochronology in small or partially dissolved garnets and mineral inclusions in diamonds 25,32 and in olivine hosted melt inclusions for studying earth's mantle processes 2,3,33 . The ATONA™ amplifier technology has the potential to provide higher precision results for these types of studies, allowing more nuanced conclusions to be reached about geologic systems with lower age or 143 Nd/ 144 Nd variability.…”

“…For geologists the 143 Nd/ 144 Nd ratio of small samples is being used for Sm-Nd geochronology in small or partially dissolved garnets and mineral inclusions in diamonds 25,32 and in olivine hosted melt inclusions for studying earth's mantle processes. 2,3,33 The ATONA™ amplifier technology has the potential to provide higher precision results for these types of studies, allowing more nuanced conclusions to be reached about geologic systems with lower age or 143 Nd/ 144 Nd variability. Furthermore, archaeologists are using ultratrace 143 Nd/ 144 Nd measurements in dental enamel which contains very little Nd for provenance studies, 34,35 and for "non-invasive"…”

“…These improvements have been exploited in studies of the isotopic compositions of mineral inclusions, 2,3 and in U-Pb geochronology. 4,5 However, the design of the RTIA has remained fundamentally unchanged over the last 40 years and suffers from a number of drawbacks.…”

Trachytic Melt Inclusions Hosted in Clinopyroxene Offer a Glimpse Into Samoan EM2‐Endmember Melts

“…They present compositional snapshots in time, although following entrapment MI compositions may be modified by post‐entrapment crystallization (PEC) or by post‐entrapment diffusive exchange (PED) with their host crystal. MIs often reveal highly heterogenous compositions, or distinct compositions not realized by the associated erupted products (e.g., Kamenetsky, 1996; Kamenetsky et al., 1997; Kent et al., 1999; Maclennan, 2008; Reinhard et al., 2018; Rowe et al., 2011; Saal et al., 1998; Sobolev et al., 2000; Sobolev & Shimizu, 1993; Sours‐Page et al., 1999; Wallace, 2005). Compared with the whole rock, these differences in composition are likely a direct result of sampling different time frames during melting and mixing processes, or even different mantle sources than are present in whole rock lavas (e.g., Jackson & Hart, 2006; Saal et al., 1998; Sobolev, 2007).…”

“…ADAMS ET AL. Maclennan, 2008;Reinhard et al, 2018;Rowe et al, 2011;Saal et al, 1998;Sobolev et al, 2000;Sobolev & Shimizu, 1993;Sours-Page et al, 1999;Wallace, 2005). Compared with the whole rock, these differences in composition are likely a direct result of sampling different time frames during melting and mixing processes, or even different mantle sources than are present in whole rock lavas (e.g., Jackson & Hart, 2006;Saal et al, 1998;Sobolev, 2007).…”