Funds are provided to support the U.S. contribution to a collaborative program with Norwegian investigators to sample the extinct Aegir Ridge, followed by onshore geochemical analyses and geodynamic modeling. Norwegian co-PIs have extensive experience in geophysical field work and geologic sampling in this region and will provide ~10 days of ship time as well as the necessary equipment to dredge the exposed scarps of the Aegir ridge axis. Major- and trace-elements studies, as well as isotope (Pb, Nd, Hf, Sr) analyses will be performed and 3D numerical models of continental rift-hotspot interaction will be developed which will define the physical conditions needed to explain the data, including quantitatively testing of the possible geologic scenarios.
The project provides training for students and promotes international collaboration.
The Iceland-Faeroes volcanic ridge is surrounded by extensive volcanism on the European and Greenland margins. The magma-starved basin formed by the extinct Aegir Ridge (active from ~53-25 Ma) appears as a major gap or "hole" in the North Atlantic large igneous province, created by the Iceland hotspot. The enigma of such weak or non-existent hotspot influenced volcanism during a time of extensive volcanic eruption, associated with the Iceland Plume and it’s interaction with the Mid-Atlantic Ridge, provides a unique opportunity to learn about problems related to dynamics of hotspot-rift interaction, the composition of plume-like mantle upwellings, and the concomitant geochemical evolution of ambient upper mantle mid-ocean ridge basalt source. The proposal supported the U.S. contribution (San Diego State University and the University of Hawaii) to a collaborative program with Norwegian investigators from the Universities of Bergen and the University of Oslo to sample the extinct Aegir Ridge, followed by onshore geochemical analyses at SDSU and geodynamic modeling at UH. Our Norwegian colleagues have extensive experience in doing geophysical field work and geologic sampling in these waters and provided ~10 days of ship time as well as the necessary equipment to dredge the exposed scarps of the Aegir Ridge axis. The San Diego State University team obtained Pb, Nd, and Hf isotope compositions, major and trace element analyses and, Ar-Ar geochronology on selected samples recovered by dredging. The University of Hawaii team led development of 3D numerical models for continental rift-hotspot interaction, which defined the physical conditions needed to explain the data, including quantitatively testing of the possible geologic scenarios. Dredges returned Mn crust, erratic cobbles, hyaloclastite, and basalt diabase. The diabase rocks are irregular shaped and appear to have been broken from the scarp target rather than having the rounded shape of an erratic cobble. Ten relatively fresh samples were selected, based upon petrographic examination and X-ray diffraction results, for geochemistry and Pb, Nd, Sr, and Hf isotopes, and Ar-Ar age determinations. The trace element analyses and Ar-Ar age data allowed for the identification of samples that truly represent the volcanism that occurred along the now extinct Aegir Ridge. The rocks erupted at the Ageir Ridge have Pb, Hf and Nd isotope compositions that show that at this time the ambient N-Atlantic upper mantle was relatively uncontaminated by the Iceland Plume, but significantly polluted by continental material, presumably during the early opening of the N-Atlantic Ocean Basin.
