Fig. 2: Trace element chemistry.
From: Evidence for simple volcanic rifting not complex subduction initiation in the Laxmi Basin
a N-MORB normalized multi-element spider diagrams for the LB lavas. Water-mobile elements are plotted left of Ba, with immobile elements on the right side of the plot starting at Nb. Compatibility in mantle phases increases to the right within the immobile elements. N-MORB values are from Gale et al.15. b Nb/Yb–Th/Yb discrimination diagram16 highlights variable input from subduction, AFC processes, inheritance, and mantle source enrichment that can displace rock compositions from and along the MORB-OIB array. Data were filtered prior to plotting to remove fractionated samples with >55 wt% SiO2, significant crystallized oxides (Ti/Ti* < 0.85) and strong crustal contamination (Th/Nb > 0.2) following Pearce et al.16. Open symbols identify LB lavas and IBM boninites that do not meet these requirements. Analytical uncertainties are within the size of the plotted symbols. Negative Nb anomalies, common in rocks formed in subduction zones, result in compositions to be displaced sub-vertically from MORB. Many basalts unrelated to subduction can carry apparent subduction signatures as a result of crustal assimilation and inheritance and may similarly plot in the volcanic arc array. c The Nb/Yb–TiO2/Yb diagram16 can further help discriminate intra-plate from plate margin basalts as it is less sensitive to crustal input. Volcanic rifted margins, LB lavas and the Réunion plume plot along a steep diagonal from the OIB to MORB array. Increased extension and attenuation of continental lithosphere drives compositions from the OIB to MORB field as depth of melting shallows. Subduction-influenced rocks, such as basalts and boninites from the IBM, that involve higher degrees of fluid-flux melting under MORB-like temperatures, remain and evolve along the MORB array. Field labels from Pearce et al.16. Data compiled from GEOROC, IBM9, and Nauret et al.17. Alk alkaline; BABB back-arc basin, B-FAB boninitic forearc basalt, Bon boninite, BTP British Tertiary Province, E enriched type, E-MORB Enriched Mid-Ocean Ridge Basalt, FAB forearc, IBM Izu-Bonin-Mariana, LB Laxmi basin, MORB mid-ocean ridge basalt, N normal type, N. Atlantic North Atlantic margin, OIB Ocean Island Basalt. Data plotted in these figures are provided in Supplementary Data 1 and from the Mendeley databank at https://doi.org/10.17632/723c5d795r.1.
