“Petit Spot” Rejuvenated Volcanism Superimposed on Plume‐Derived Samoan Shield Volcanoes: Evidence From a 645‐m Drill Core From Tutuila Island, American Samoa

Abstract

In 2015 a geothermal exploration well was drilled on the island of Tutuila, American Samoa. The sample suite from the drill core provides 645 m of volcanic stratigraphy from a Samoan volcano, spanning 1.45 million years of volcanic history. In the Tutuila drill core, shield lavas with an EM2 (enriched mantle 2) signature are observed at depth, spanning 1.46 to 1.44 Ma. These are overlain by younger (1.35 to 1.17 Ma) shield lavas with a primordial “common” (focus zone) component interlayered with lavas that sample a depleted mantle component. Following ~1.15 Myr of volcanic quiescence, rejuvenated volcanism initiated at 24.3 ka and samples an EM1 (enriched mantle 1) component. The timing of the initiation of rejuvenated volcanism on Tutuila suggests that rejuvenated volcanism may be tectonically driven, as Samoan hotspot volcanoes approach the northern terminus of the Tonga Trench. This is consistent with a model where the timing of rejuvenated volcanism at Tutuila and at other Samoan volcanoes relates to their distance from the Tonga Trench. Notably, the Samoan rejuvenated lavas have EM1 isotopic compositions distinct from shield lavas that are geochemically similar to “petit spot” lavas erupted outboard of the Japan Trench and late stage lavas erupted at Christmas Island located outboard of the Sunda Trench. Therefore, like the Samoan rejuvenated lavas, petit spot volcanism in general appears to be related to tectonic uplift outboard of subduction zones, and existing geochemical data suggest that petit spots share similar EM1 isotopic signatures.

EM1‐Signature in the North Fiji Basin: Evidence for Stagnant Slab‐Derived Mantle Upwelling Beneath the Trench‐Distal Back‐Arc Basin

“… Diagram of the principal component analysis (PCA) of geochemical proxies used in Figures 5, 6 and 9 (Sr‐Nd‐Pb‐He isotopes, Ba/Th, Ba/Ta, La/Ta, Zr/Hf, and Zr/Th in right panel). Samples from the shield‐stage and rejuvenated Samoa (open symbols represent data from Konter & Jackson, 2012; filled symbols represent data from Reinhard et al., 2019) and the Pitcairn (Eisele et al., 2002) are included in a source data for the PCA. The enriched CSR basalts have high Ba/Th and Ba/Ta ratios similar to the South Pandora Ridge and Wallis samples.…”

“…no depletion of HFSE such as Nb and Ta, Figure 3) cannot be attributed to the typical sub-arc mantle, Instead, the Ba-rich characteristic of the enriched CSR basalts is similar to those of the Gaussberg lamproite in Antarctica and the Cenozoic alkaline basalts in NE China, which is considered to have originated from the OH ET AL. Reinhard et al (2019), and (c) Ba/Ta versus La/Ta modified from Gorring et al (2003). Symbols are the same as in Figure 1c.…”

“…The long-term (ca. 2 Ga) recycled bulk oceanic crust components (basalt + sediment) calculated by Kimura et al (2016) can describe the enriched CSR samples with the component in a range of 20%-30% of sediment (Figure 5 Konter & Jackson, 2012; filled symbols represent data from Reinhard et al, 2019) and the Pitcairn (Eisele et al, 2002) are included in a source data for the PCA. The enriched CSR basalts have high Ba/Th and Ba/Ta ratios similar to the South Pandora Ridge and Wallis samples.…”

Sulfur Isotope Evidence for a Geochemical Zonation of the Samoan Mantle Plume

“…At Samoa, subaerial rejuvenated volcanism occurs on the islands of Savai‘i, Upolu, and Tutuila, which are located >180 km from the current location of the Samoan mantle plume (which is inferred to lie below the volcanically active Vailulu‘u seamount). The source of rejuvenated volcanism at Samoa is not well understood, but has been discussed elsewhere (Konter & Jackson, 2012; Natland, 1980; Workman et al., 2004; Reinhard et al., 2019). It has been proposed that rejuvenated volcanism at Samoa may be driven by mantle melting from plate flexure of the lithosphere due to subduction at the Tonga Trench (Konter & Jackson, 2012; Natland, 1980).…”

Simplifying Age Progressions within the Cook‐Austral Islands using ARGUS‐VI High‐Resolution 40Ar/39Ar Incremental Heating Ages

“…Second, Samoa is located near the Tonga Trench, and there is evidence for interaction between the Samoan plume and this subducting zone that could influence the age progression recorded at this location (Hart et al, 2004;Koppers et al, 2008). Here chemical interactions between the Samoan plume and the down going slab have been linked to late-stage volcanism on Samoa (Konter & Jackson, 2012;Price et al, 2016;Reinhard et al, 2019). Modeling has shown that tectonic interactions in the Tonga Trench may be causing plate tearing that allows for magma to penetrate the lithosphere (Govers & Wortel, 2005) as well as distortions in local mantle flow (Druken et al, 2014) that both may cause different volcanic surface expressions compared to the traditional mantle plume theory.…”