A carbon, nitrogen, and multi-isotope study of basalt glasses near 14°N on the Mid-Atlantic Ridge. Part B: Mantle source heterogeneities

• DOI: 10.1016/j.gca.2023.12.017
• Publication Date: 2023-12-20T18:31:29Z
• Authors: D.V. Bekaert; P.H. Barry; J. Curtice; J. Blusztajn; M. Hudak; A. Seltzer; M.W. Broadley; J.A. Krantz; V.D. Wanless; S.A. Soule; E. Mittelstaedt; M.D. Kurz
• Keywords: Radiogenic nuclide; Isotopic signature

Geochemical variations along mid-ocean ridges reveal the heterogeneous nature of the convecting upper mantle and geodynamic evolution of our planet (e.g., Hofmann, 2007, Parai et al., 2012). Although the occurrence of incompatible element and isotopically enriched mid-ocean ridge basalts (E-MORB) commonly arises from interaction with nearby mantle plumes, the source of E-MORBs far from known hotspots is debated. A well-known example of an enigmatic geochemical enrichment is found at 14°N on the Mid-Atlantic ridge (MAR). This is also one of the few locations worldwide where volatile-saturated E-MORBs, often referred to as “popping rocks†(PR), have been recovered. Although the mechanism(s) involved in popping rock generation remain elusive, compressional regimes associated with the exhumation and formation of oceanic core complexes (OCC) may be required to produce popping rocks via protracted volatile accumulation. However, the geochemical signature of OCC samples and their potential relationship to local geochemical enrichments associated with popping rock-affiliated MORBs remain unknown. Here, we present a comprehensive volatile characterization of popping rocks and associated MORBs (n = 19) sampled at 14°N on the MAR, including (n = 2) normal MORBs (N-MORB) from an oceanic core complex (OCC) and (n = 17) E-MORBs (Bekaert et al., Part A). We use isotopic and abundance data for volatile (carbon, nitrogen, noble gases) and radiogenic (Pb, Sr, Nd) elements, as well as the abundances of major and trace elements, to elucidate on the source(s) of E-MORBs at 14°N and discuss the potential origin(s) of geochemical heterogeneities within the upper mantle. We observe co-variations of helium and radiogenic element isotopes, suggesting potential contributions from a young HIMU-type (high μ = time-integrated 238U/204Pb) component in the OCC mantle source. The mantle source of the OCC samples is clearly distinct from that of PR-affiliated samples, suggesting no genetic relationship between OCC samples and E-MORBs. In ...