The Icelandic Mantle Plume: A 62 Million Year Record of the Deep Mantle
Abstract
The Icelandic mantle plume has plumbed the high-3He/4He deep mantle for over sixty million years, starting with the Baffin Island flood basalts. The Baffin Island lavas are geochemically important because they host the highest observed terrestrial-mantle-derived 3He/4He (Stuart et al., 2003; Starkey et al., 2009) and also have 182W anomalies indicating an early Hadean origin (Rizo et al., 2016). This study provides a comprehensive geochemical data set—He-Pb-Sr-Nd-Hf-O isotopic compositions, as well as major and trace element concentrations—for a suite of 18 Baffin Island lavas, and draws on extensive literature data for this province and the genetically and temporally related West Greenland picrites (e.g., Larsen and Pedersen, 2009). Baffin Island lavas transited through, and assimilated variable degrees of, Precambrian continental basement, thereby potentially obscuring the primary mantle signature carried by these key lavas. We use trace element ratios sensitive to continental crust assimilation—including Ce/Pb and Nb/Th—to identify the least crustally-contaminated lavas in the suite. To investigate the Icelandic plume source, and to evaluate whether the high-3He/4He domain in the plume exhibits a continuous composition over time, the isotopic compositions of the least contaminated Baffin Island lavas are compared to mid-Miocene and neovolcanic lavas from Iceland. While the lithophile radiogenic isotopes in the least contaminated Baffin Island lavas exhibit some similarities with MORB, important petrological differences stand out. We show that major element differences between Baffin Island lavas and MORB imply different melting conditions for the plume-derived flood basalts (higher pressure, temperature, and melt fraction) compared to conditions of ambient MORB melting. Signatures of high-temperature and -pressure melting in plume-derived lavas support the contention that the high-3He/4He source is sampled only by the hottest and most buoyant plumes.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.V11A..02W
- Keywords:
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- 1037 Magma genesis and partial melting;
- GEOCHEMISTRYDE: 1038 Mantle processes;
- GEOCHEMISTRYDE: 1040 Radiogenic isotope geochemistry;
- GEOCHEMISTRYDE: 1065 Major and trace element geochemistry;
- GEOCHEMISTRY