The composition and distribution of the rejuvenated component across the Hawaiian plume: Hf‐Nd‐Sr‐Pb isotope systematics of Kaula lavas and pyroxenite xenoliths

Abstract

Rejuvenated volcanism refers to the reemergence of volcanism after a hiatus of 0.5–2 Ma following the voluminous shield building stage of Hawaiian volcanoes. The composition of the rejuvenated source and its distribution relative to the center of the plume provide important constraints on the origin of rejuvenated volcanism. Near‐contemporaneous lavas from the Kaula‐Niihau‐Kauai ridge and the North Arch volcanic field that are aligned approximately orthogonally to the plume track can constrain the lateral geochemical heterogeneity and distribution of the rejuvenated source across the volcanic chain. Nephelinites, phonolites and pyroxenite xenoliths from Kaula Island have radiogenic Hf, Nd and unradiogenic Sr isotope compositions consistent with a time‐integrated depleted mantle source. The pyroxenites and nephelinites extend to the lowest 208Pb/204Pb reported in Hawaiian rocks. These data, along with new Pb isotope data from pyroxenites from the Salt Lake Crater (Oahu) redefine the composition of the depleted end‐member of the Hawaiian rejuvenated source at 208Pb/204Pb=37.35±0.05, 206Pb/204Pb = 17.75±0.03, εNd = 9–10, εHf ∼16–17 and 87Sr/88Sr <0.70305. The revised isotope composition also suggests that this depleted component may contribute to LOA and KEA trend shield stage Hawaiian lavas, consistent with the rejuvenated source being part of the Hawaiian plume and not entrained upper mantle. The isotope systematics of rejuvenated magmas along the Kaula‐Niihau‐Kauai‐North Arch transect are consistent with a larger proportion of the rejuvenated depleted component in the periphery of the plume track rather than along its axis.

Keywords

• pyroxenite
• xenolith
• rejuvenated volcanism
• mantle plume
• Kaula
• plume structure