LOCALIZED BINARY MIXING OF MANTLE COMPONENTS ALONG THE NORTH RIFT ZONE, NE ICELAND

The Icelandic plume is thought to be comprised of numerous chemically distinct components. However, the precise nature and spatial arrangement of these components is highly debated. It has only been since routine, high-precision, analyses of isotopic systems that the arrangement and scale of plume-heterogeneity can be resolved. Here, we report new Sr-Nd-Hf-Pb isotopic analyses for a suite of post-, inter-, and intra-glacial lavas collected from the Krafla, Fremri-Námur, Askja, and Kverkfjöll eruptive centres of the Northern Rift Zone (NRZ), Iceland. In general, all samples are chemically distinct from lavas of the Western Rift Zone and the Reykjanes Peninsula, lying along a shallower trend in Sr-Nd isotopic space. However, with the use of high-precision, double-spike corrected, Pb-isotopic analyses, subtle differences within the overall trend of the NRZ lavas can be distinguished. In particular, lavas from Krafla, Fremri-Námur, and Askja all form negative Δ ²⁰⁷Pb – ²⁰⁶Pb/²⁰⁴Pb correlations, suggesting that localized binary mixing is dominant at individual eruptive centres the length of the rift zone. These trends are sub-parallel to the Öræfajökull/Snæfell off-rift array. Previous studies have shown that the off-rift trend is the result of small contributions of recycled-sediment into local, well-blended, end-members (e.g., Manning and Thirlwall, Contib. Mineral. Petr. 2014). Thus, the sub-parallel trends identified for the NRZ, suggests that the influence of recycled-sediment is also present along the NRZ, contributing to local pseudo- binary end-members. In particular, the trends identified for each eruptive centre requires a decreasing contribution from the recycled-sediment component away from the plume head. In contrast, lavas from the Kverkfjöll eruptive centre define a trend that is at a high angle with respect to the Öræfajökull/Snæfell array. Similar relationships are hinted at for other central volcanoes that lie within the Vatnajökull ice sheet. This indicates that a significant shift in the tapping of mantle components occurs in this region, possibly related their proximity to the plume head.