Collaborative RUI: Uranium-Series Constraints on Melting in the Jan Mayen Region

Bryn Mawr College, Bryn Mawr PA

Investigators

Abstract

The Mid-Atlantic Ridge, particularly its segments in the Arctic Ocean north of Iceland, produce new crust at a relatively slow rate (~2 cm/yr.). Lavas from the Arctic ridge segment known as the Eggvin Bank have chemical and isotopic compositions that reflect a more trace element-rich source than normal ridge basalts. The Eggvin Bank, which is anomalously shallow, is adjacent to the volcanic Jan Mayen Island, whose origins are disputed: its trace element enriched lavas may suggest a hotspot origin, but the precise isotopic and chemical compositions of the lavas are distinct from the Iceland hotspot. Jan Mayen may instead overlie a chemically distinct mantle, containing trapped subcontinental material from the geologically recent opening of the Greenland Basin (53-55 million years ago). These characteristics raise a number of questions: is the Jan Mayen magma source heterogeneous, containing different rock types that each had different origins? Is it hydrated? Does it indeed contain pieces of subcontinental mantle? Is Jan Mayen a rapidly upwelling hotspot? Does anomalous mantle affect the depth and composition of the nearby Eggvin Bank? These questions impact our understanding of the mantle, with implications for other regions along the mid-ocean ridge system that experience anomalous volcanism (e.g. the Azores, Ascension). A better understanding of the region will provide important information about how melting occurs and leads to volcanic activity and about the dynamics of the Earth?s mantle-crust system. Using new multibeam backscatter bathymetry techniques, we will conduct the first high-resolution mapping of the Eggvin Bank, to characterize the nature of its volcanism and to precisely target new sampling. We will collect and compile fresh basaltic rocks from the Eggvin Bank, the adjacent Mohns Ridge to the north, and nearby Jan Mayen Island, selecting unaltered basaltic glass (an indication of very fresh lava material). We will measure uranium, thorium, and radium isotopes as indicators of mantle source composition, of the amount of melting occurring to produce the lavas, and of the precise timing of melting and melt transport. Constraining the timing of melting in this way provides insight into the melting dynamics, including the presence of hotspot activity. This work contributes to broad scientific efforts to better understand melt generation at ocean ridges and its implications for mantle dynamics. The research supports an early-career woman scientist and undergraduate students at a women?s liberal arts college. These students will have the opportunity to learn and receive training in state-of-the-art geochemical scientific research methods. This project seeks to examine geochemically anomalous lavas from the Kolbeinsey Ridge near Iceland for the presence of signatures of plumes and/or subcontinental lithospheric mantle. Although some samples from dredges are in hand, additional precisely located ROV samples will be collected on a German high-resolution field mapping cruise to the area. Samples will be analyzed for Sr, Nd, Pb, and Hf isotopes, as well as U-Th and Th-Ra. Goals will be to determine melt transport and timing and melt sources. Broader impacts of the work include support of an early-career incvestigator from a group under-represented in the sciences who is employed at a women?s liberal arts college where she will train undergraduate students in state-of-the-art analytical Uranium series dating techniques and serve as a mentor. Additional impacts also include international collaboration with UK and German scientists and allow students to cross train in other laboratories and participate in an international oceanographic cruise to the Arctic.