Variable sampling of distinct ancient mantle domains by the Iceland mantle plume over its 62 Ma eruption history

Abstract

Mantle plumes produce geochemically diverse lavas over their lifetime, some of which preserve compositions derived from Earth's earliest events. Most studies of plume-related lavas in this context have focused on modern ocean island basalts (OIB), primarily because these are relatively free of geochemical influences from crustal assimilation that may obscure the compositions of their mantle sources. Notwithstanding, there is no a priori reason why a mantle plume should consistently tap the same mantle domain over geological time, which means that early plume-related magmas may preserve a perspective on the early Earth that complements that of modern OIB. This study expands a previous investigation of picrites with high ³He/⁴He ratios, a likely indicator for ancient, less degassed mantle domains, with new ¹⁴²Nd/¹⁴⁴Nd (n = 7) and ¹⁸²W/¹⁸⁴W (n = 2) data that, together with literature data, comprise a detailed short-lived radiogenic isotope database for the Iceland hotspot. Heterogeneous ¹⁴²Nd/¹⁴⁴Nd ratios in lavas from different stages of the Iceland plume imply that it has tapped a variety of early-formed mantle domains, in particular that the head of the Iceland plume rapidly shifted between tapping domains with distinct histories. This behavior may reflect both the higher buoyancy flux of plume heads as well as the petrological and physical properties of these domains. Together, these data highlight the importance of developing comprehensive, high-precision short-lived radiogenic isotope datasets for all stages of plume magmatism, since the geochemical compositions of modern OIB reflect only one set of mantle domains that can be potentially tapped by mantle plumes.