Ancient refractory asthenosphere revealed by mantle re-melting at the Arctic Mid Atlantic Ridge

A Highly Depleted and Subduction‐Modified Mantle Beneath the Slow‐Spreading Mohns Ridge

“…Because of this, the mantle has experienced hydrous melting, likely in an arc‐type setting, leading to anomalously depleted peridotite compositions. Our results add to a growing body of literature trying to better constrain and understand the mantle segmentation and evolution in the Arctic region (Goldstein et al., 2008; Neumann & Schilling, 1984; Richter et al., 2020; Sanfilippo et al., 2021; Yang et al., 2021).…”

“…If the anomalous depleted mantle source was affected during the re-melting of a mantle depleted in enriched components because of a recent ridge jump (Sanfilippo et al, 2021), we might expect to see differences in the isotopic composition between the ridge basalts and basalts formed 4-5 Myr. However, the Sr and Nd isotopic ratios of the basalts (Table S1) are similar to those of the present-day spreading axis (Figures 4 and 5), implying that they have either (a) been derived from a similar source, or (b) been mixed and homogenized to such a degree that source compositions have been masked.…”

“…From a regional perspective, less than 8% of all studied mid‐ocean ridge peridotites come from the Arctic Mid‐Ocean Ridges (AMOR) and no peridotites have been reported from the Mohns and Knipovich Ridges. On a broader scale, the 550 km long Mohns Ridge is of special interest because of its very slow spreading rate and reported ultra‐refractory, subduction‐influenced mantle composition (Blichert‐Toft et al., 2005; Sanfilippo et al., 2021; Yang et al., 2021). Specifically, it has some of the most radiogenic Hf isotopes seen in mid‐ocean ridge basalts indicating a mantle‐source that is ultra‐depleted (Sanfilippo et al., 2021).…”

Chemical Geodynamics Insights From a Machine Learning Approach

“…However, the excess buoyancy of the actively upwelling mantle under most OIB locations may, in part, derive from its residual nature (e.g., Matthews et al., 2016, 2021; Shorttle et al., 2014, 2020; Stracke et al., 2019), that is, the upwelling mantle contains a large proportion of mantle that has previously been melted and has thus become very incompatible element depleted, but also less dense (e.g., Afonso and Schutt, 2012; Schutt and Lesher, 2006). Such residual mantle can still produce considerable amounts of melts (e.g., Byerly and Lassiter, 2014; Sanfilippo et al., 2021), because incompatible elements are almost quantitatively extracted for small extents of melts exctraction (∼1–5%), but it takes up to 20% of melt etxration to exhaust clinopyroxene, and thus considerably lower melt producitivity (e.g., Asimow et al., 1997). Hence residual mantle contributes little to the incompatible element budget, and therefore to the Sr‐Nd‐Hf‐Pb isotope ratios of the erupted melts, which are a weighted average of melts from all source constituents (e.g., Rudge et al., 2013; Stracke, 2021a, 2021b; Stracke and Bourdon, 2009; Stracke et al., 2011; Willig et al., 2020).…”

“…However, the excess buoyancy of the actively upwelling mantle under most OIB locations may, in part, derive from its residual nature (e.g., Matthews et al, 2016Matthews et al, , 2021Shorttle et al, 2014Shorttle et al, , 2020Stracke et al, 2019), that is, the upwelling mantle contains a large proportion of mantle that has previously been melted and has thus become very incompatible element depleted, but also less dense (e.g., Afonso and Schutt, 2012;Schutt and Lesher, 2006). Such residual mantle can still produce considerable amounts of melts (e.g., Byerly and Lassiter, 2014;Sanfilippo et al, 2021), because incompatible elements are almost quantitatively extracted for S1). S1).…”