Temporal evolution of primordial tungsten-182 and 3He/4He signatures in the Iceland mantle plume

Hot and Heterogenous High‐3He/4He Components: New Constraints From Proto‐Iceland Plume Lavas From Baffin Island

“…However, Kruijer and Kleine (2018) proposed a potential nuclear field shift effect as the origin of the large μ 182 W found in an Ontong Java Plateau drill core sample (Rizo et al, 2016), leading to these authors speculating about the validity of the large positive μ 182 W anomaly measured in the Baffin Island sample from the same study. The Rizo et al (2016) result contrasts with recent results of Mundl-Petermeier et al (2019), which show slightly negative 182 W anomalies in genetically related West Greenland picrites. Given the susceptibility of 182 W in primitive Baffin Island and West Greenland lavas (≤62 ppb W; Mundl-Petermeier et al, 2019;Rizo et al, 2016) to being overprinted by continental crust (1,000 ppb W; Rudnick & Gao, 2003), additional 182 W analyses from Baffin Island lavas, specifically targeting lavas that are identified as being least crustally contaminated, will be critical for evaluating the presence of μ 182 W anomalies in the mantle source of Baffin Island lavas.…”

“…Hence, a core contribution to mantle plumes would be observed as negative 182 W anomalies in hotspot lavas. Mundl et al () and Mundl‐Petermeier et al () reported negative 182 W anomalies in high‐ 3 He/ 4 He Iceland lavas, consistent with a core contribution, whereas Rizo et al () reported positive 182 W anomalies in Baffin Island lavas. However, Kruijer and Kleine () proposed a potential nuclear field shift effect as the origin of the large μ 182 W found in an Ontong Java Plateau drill core sample (Rizo et al, ), leading to these authors speculating about the validity of the large positive μ 182 W anomaly measured in the Baffin Island sample from the same study.…”

“…More importantly for this study, the juxtaposition (and possible mixing) of ancient high-3 He/ 4 He and recycled domains in the plume source could explain the isotopic heterogeneity in the Iceland plume through time. Moreover, ultralow velocity zones (ULVZ; Garnero et al, 2016;McNamara et al, 2010;Rost et al, 2005), which have even slower shear wave velocity anomalies than LLSVPs, provide a second potential long-term storage site for primitive geochemical signatures (Herzberg et al, 2013;Mundl et al, 2017); the three hotspots observed to have 182 W anomalies-Hawaii, Iceland, and Samoa-are all associated with ULVZs (Mundl et al, 2017;Mundl-Petermeier et al, 2019). (Note that 182 W data are not yet available for Galápagos lavas.)…”

Tungsten Isotope Composition of Archean Crustal Reservoirs and Implications for Terrestrial μ182W Evolution

“…Instead, our data, together with the literature data, show that the Archean mantle maintained a heterogeneous distribution of μ 182 W values throughout much of the Archean, with values ranging from approximately +18 to −10 in komatiite samples (Figure 5). The known range in μ 182 W in the Archean is only slightly smaller than in modern mantle‐derived rocks, though in modern rocks, the range is shifted to substantially lower values, from +5 to −20 (Mundl et al, 2017; Mundl‐Petermeier et al, 2020, 2019; Rizo et al, 2019). The timing of late accretion is relatively early in solar system history (0 to 20 Ma after the last magma ocean; Walker, 2016), and relatively rapid mantle‐mixing timescales on the early Earth are demonstrated by the diminution of 142 Nd/ 144 Nd variability by the end of the Archean.…”

The142Nd/144Nd variations in mantle-derived rocks provide constraints on the stirring rate of the mantle from the Hadean to the present

“…Heterogeneities in 142 Nd/ 144 Nd appear to be rare in modernday igneous rocks (2,5,7,11,13,(25)(26)(27), to the degree they occur for 182 W/ 184 W (30,31), which sometimes occur in the samples with lack of 142 Nd/ 144 Nd variability (32). Although the short-lived Sm-Nd and Hf-W systems are affected during silicate-mantle differentiation, the lack of isotopic variability in one system over the other, suggests the decoupling of the two systems owing to different processes involved in the generation of heterogeneity.…”