Geochemistry of Etendeka magmatism: Spatial heterogeneity in the Tristan-Gough plume head

Geochemical Constraints on the Structure of the Earth's Deep Mantle and the Origin of the LLSVPs

“…Global seismic tomography models reveal that many mantle plumes are rooted within, or at the margins of the LLSVPs, indicating that these regions represent "plume nurseries" (Figure 1; Doubrovine et al, 2016;French & Romanowicz, 2015;Jackson et al, 2018). Furthermore, several mantle plumes worldwide display bilateral asymmetry; where isotopically enriched signals are assigned to melting of upwelling LLSVP material, and isotopically depleted compositions are related to melting of the surrounding peridotitic mantle (Harpp, Hall, & Jackson, 2014;Harpp & Weis, 2020;Hoernle et al, 2015;Huang et al, 2011;Weis et al, 2011;Zhou et al, 2020). Therefore, a critical analysis of the compositional variability displayed by one such mantle plume, considering all available isotopic, trace element and major element data, has the potential to reveal new insights into the origin of the LLSVPs, with implications for the evolution of the solid Earth over billion-year timescales.…”

From Continent to Ocean: Investigating the Multi-Element and Precious Metal Geochemistry of the Paraná-Etendeka Large Igneous Province Using Machine Learning Tools

“…Finally, Etendeka samples show a strong trend towards MgO, Ni and Cr eigenvectors (Figure 4B) and embedding sectors (Figures 5, 6), a multi-element association also identified in NAIP lavas (Hughes et al, 2015;Lindsay et al, 2021a). Etendeka is the only locality to be classified in Group 6 (Figure 8C; Table 3), a multi-element end-member that likely represents high degree partial melts with predominant asthenospheric signatures (e.g., Gibson et al, 2005;Zhou et al, 2020). The literature suggests that many basalts from the Etendeka CFBs were particularly enriched in MgO due to higher temperature melting (e.g., Jennings et al, 2017;Natali et al, 2017;Jennings et al, 2019;Beccaluva et al, 2020), producing different magma compositions to the entire Paraná CFB sequence, which is less primitive in terms of MgO concentrations in comparison (Figure 3).…”

“…This end-member also features enrichment in incompatible elements like Zr, Hf, Rb, and LREE. High-Ti Paraná basalts are typically interpreted to be from a more enriched mantle source in the literature, often connected to OIB Tristan plume signatures more than lower-Ti South American CFBs (e.g., Peate, 1997;Rämö et al, 2016;Weit et al, 2017;Beccaluva et al, 2020;Zhou et al, 2020).…”

“…This may reflect the rapidly shifting geodynamic conditions in the (now) PELIP during the Creataceous period and the knock-on effect this has on melting processes. For the onshore portions, the High-/Low-Ti split is commonly thought to represent geochemical zonation in the plume (i.e., lavas produced in line with the plume head focus, and lavas that are more peripheral, respectively) (e.g., Gibson et al, 1999;Zhou et al, 2020). This led to localised heterogeneous melting processes producing distinct multi-element signatures as a net effect (as per Rämö et al, 2016).…”

“…Despite a common regional rifting event in the opening of the South Atlantic, centred roughly on the Tristan plume, the multielement geochemistry of PELIP lavas on the South American and African plates are different in terms of endmembers identified using MLA (summarised in Figure 8) and PGE concentrations (Figure 9). In both Paraná and Etendeka, the High-Ti lava types are the products of partial melting of a mantle source enriched in incompatible elements and LREE (Rämö et al, 2016;Jennings et al, 2019;Zhou et al, 2020) suggest that this likely represents a deeper asthenospheric source undergoing low-degrees of partial melting under a thick lithosphere lid. Similar signatures are observed in Walvis Ridge and contemporary Tristan da Cunha lavas (Gibson et al, 2005).…”