Distinguishing Volcanic Contributions to the Overlapping Samoan and Cook-Austral Hotspot Tracks

Abstract

To deconvolve contributions from the four overlapping hotspots that form the “hotspot highway” on the Pacific plate—Samoa, Rarotonga, Arago-Rurutu, and Macdonald—we geochemically characterize and/or date (by the 40Ar/39Ar method) a suite of lavas sampled from the “downstream” Samoan hotspot track. We find that Papatua seamount, located ~60 km south of the axis of the Samoan hotspot track, has lavas with both a HIMU composition (206Pb/204Pb = 20.0), previously linked to one of the Cook-Austral hotspots, and an EM1 composition, which we interpret to be rejuvenated and Samoan in origin. We show that these EM1 rejuvenated lavas are geochemically similar to rejuvenated volcanism on Samoan volcanoes, and suggest that flexural uplift, caused by tectonic forces associated with the nearby Tonga trench, triggered a new episode of melting of Samoan mantle material that had previously flattened and spread laterally along the base of the Pacific plate under Papatua, resulting in volcanism that capped the previous HIMU edifice. We argue that this process generated Samoan rejuvenated volcanism on the older Cook-Austral volcano of Papatua. We also study Waterwitch seamount, located ~820 km WNW of the Samoan hotspot, and provide an age (10.49 ± 0.09 Ma) which places it on the Samoan hotspot trend, showing that it is genetically Samoan and not related to the Cook-Austral hotspots as previously suggested. Consequently, with the possible exception of the HIMU stage of Papatua seamount, there are currently no known Arago-Rurutu plume-derived lava flows sampled along the swath of Pacific seafloor that stretches between Rose seamount (~25 Ma) and East Niulakita seamount (~45 Ma), located 1400 km to the west. The “missing” ~20-million-year segment of the Arago-Rurutu hotspot track may have been subducted into the northern Tonga trench, or perhaps was covered by subsequent volcanism from the overlapping Samoan hotspot, and has thus eluded sampling. Finally, we explore tectonic reactivation as a cause for anomalously young volcanism present within the western end of the Samoan hotspot track.

Breaking Up Is Hard to Do: Magmatism During Oceanic Arc Breakup, Subduction Reversal, and Cessation

“…A. Price et al., 2022, 2017); OTJ, Ontong Java Plateau (Tejeda et al., 2004, without age correction); the Manus Basin (Woodhead et al., 2001); and the Knipovich segment of the Arctic Mid‐Atlantic Ridge (Sanfilippo et al., 2021). Data for volcanic rocks with SiO 2 >60% are excluded.…”

“…Turner et al, 1997). Those with the lowest 206 Pb/ 204 Pb ratios, in the high-K basalts of southern Lomaiviti and Lau, are most similar to the Alexa-type seamounts (Hart et al, 2004;A. A.…”

“…Price et al. (2022), we refer to them as Alexa‐type; they are a subset of what was called WESAM by Hart et al. (2004).…”

“…Price et al. (2022). Their basalts are more depleted isotopically than those farther east in the Samoan chain, having 87 Sr/ 86 Sr < 0.7044, 143 Nd/ 144 Nd > 0.5128, and 206 Pb/ 204 Pb < 19.05.…”

“…A. Price et al (2022), we refer to them as Alexa-type; they are a subset of what was called WESAM by Hart et al (2004). From west to east, the six for which geochemical data are published are Alexa, Niulakita, Nukulaelae, Bustard, Bayonaise, and Tuscarora.…”