The Mid-Atlantic Ridge, particularly its segments in the Arctic Ocean north of Iceland, produce new crust that has a trace element-rich geochemical signature that differs from normal mid-ocean ridge basalts. This unusual chemistry is an enigma and its origins are disputed, with some evidence indicating that the lavas are of hotspot origin, but not related to the closest known hotspot which is under Iceland, and other evidence pointing to the melting of trapped subcontinental material resulting from the geologically recent opening of the Greenland Basin 53-55 million years ago. Resolution of this question impacts our understanding of the mantle with implications for other regions along the mid-ocean ridge system that experience anomalous volcanism such as the Azores and Ascension. This research examines geochemically anomalous lavas from Jan Mayen Island on the Kolbeinsey Ridge near Iceland to determine their source and the timing and mechanisms of melt generation and transport. Both in-hand samples and those to be collected on a German high-resolution field mapping cruise to the area will be analyzed for radiogenic isotopes (Sr, Nd, Pb, and Hf) and U-series isotopes. A better understanding of the region under investigation will provide important information about how melting occurs at depth and leads to volcanic activity. Broader impacts of the work include support of an early-career investigator from a group under-represented in the sciences at a women's liberal arts college and training of female undergraduate students in state-of-the-art high-end Uranium series dating techniques. The work also involves extensive international collaboration with Swedish, UK, and German scientists and cross training of students in other laboratories as well as having them participate in an international oceanographic cruise to the Arctic.
"Magma genesis is one of the most fundamental dynamic processes on Earth. Most of the Earth’s surface features, internal structure, atmosphere and oceans are a manifestation of the magmatic processes that occur within" (Sims, PhD Thesis). The broad objective of this research was to better understand melt generation at mid-ocean ridges, the Earth's biggest magmatic system. Understanding mid-ocean ridge magmatism is critical for understanding ocean crust formation and mantle dynamics. Mid-ocean ridge basalts also provide essential information about the Earth's chemical composition and how the Earth's mantle has changed as our planet has evolved. The specific objectives of this research were two fold: 1) Better understand melt generation along arctic mid-ocean ridges. Arctic mid-ocean ridges vary significantly in spreading rate, angle of divergence, segment length, axial depth, crustal thickness, and extent of magmatism (Elkins et al., 2014), such that they provide an important perspective on how these different variables affect the extent of mantle melting and the compositions of erupted magmas. 2) Determine the source/causes of anomalously high magma supply along the ultraslow-spreading ridges adjacent to Jan Mayen Island in the North Atlantic basin. Namely, is there a mantle plume beneath Jan Mayen, or is some other dynamical explanation required for the volcanism there? To address these questions, we conducted high-resolution mapping and more precise and detailed sampling of the Jan Mayen area, particularly the Eggvin Bank, an area with shallow seafloor in the center of the Northern Kolbeinsey Ridge. To reach the field area at sea, we worked with collaborators from GEOMAR in Kiel, Germany aboard the RV Poseidon, a German research vessel. After mapping the bathymetry of the seafloor along the Northern Kolbeinsey Ridge and collecting fresh basaltic rock samples, we measured major elements, trace elements, radiogenic isotopes, and U-Th-Ra isotopes on a full sample suite for the region. Our main results are: 1) Our ultraslow-spreading ridge data support a model in which global MORB (230Th/238U) is broadly controlled by mantle temperature, but also affected by local and regional variations in a number of factors, including mixing of melts from different depths, efficiency of melt extraction, melt-rock reaction, solid upwelling rate, residual melt porosity, and the presence and compositional range of heterogeneities in the source (Elkins et al., 2014, GCA, 127, 140-170, doi.org/10.1016/j.gca.2013.11.031.) 2) We show that Jan Mayen Island volcanism is the surface expression of a small mantle plume, which exerts significant influence on nearby mid-ocean ridge tectonics and volcanism. Radially-diluted Jan Mayen geochemical signatures are observed in lava samples from hotspot-adjacent ridge segments, where they are spatially associated with morphological indicators of enhanced magma supply. This plume-source geochemical anomaly overprints a regional mantle geochemical discontinuity underlying the Jan Mayen Fracture Zone and demonstrates the importance of even small mantle plumes in modifying the local expression of tectonic boundaries (Elkins et al., in prep). Our broader impacts have been: 1) Contributing to the larger perspective of mid-ocean ridge petrogenesis and ocean crustal construction. 2) Refinement of mass spectrometric techniques for the measurement of radiogenic isotopes and U-series disequilibria. 3) Training of graduate and undergraduate students. This research grant contributed to the training of one PhD student at the University of Wyoming and four undergraduate students from Bryn Mawr College, a women's college. We note that women are an underrepresented minority in geocience and in the sciences in general.
