A Detailed Bathymetric Study of Tectonic and Magmatic Processes at the Extremely Slow-Spreading Gakkel Ridge

ABSTRACT Cochran OPP-0352642 Intellectual Merit: Gakkel Ridge, the mid-ocean ridge spreading center in the Arctic, is the slowest spreading portion of the global mid-ocean ridge (MOR) system. Mantle melting models predict that melt production and crustal thickness should decrease significantly at spreading rates of less than 15-20 mm/a. The extremely slow spreading rate and the gradient in spreading rate along the Gakkel Ridge make it an important end member constraining models of mantle melting and crustal generation. Extension at MORs involves both. The balance and interplay of magmatic and mechanical extension of accommodating plate separation varies as a function of spreading rate (and melt availability) to produce the differing ridge axis and ridge flank morphology. Thus, the low spreading rate and low melt production may affect the crustal thickness and along-axis distribution of volcanism and faulting. Recently the Gakkel Ridge was studied by two programs using very different platforms and instrumentation. The SCICEX program used a U.S. Navy submarine to obtain gravity, high-resolution sidescan and low- to moderate-resolution bathymetry data out to 50 km from the axis for 600 km along the Gakkel Ridge. The AMORE project used two icebreakers to obtain high-resolution bathymetry, rock samples and seismic refraction data at the Gakkel Ridge axis. The bathymetry data maps the ridge axis for ~1000 km, but is confined to the rift valley floor and walls. The Principal Investigator was invited by AMORE Principal Investigators to analyze and interpret the AMORE bathymetry data and to establish the detailed tectonic context of their rock samples. The project will be primarily based on the high-resolution AMORE swath-bathymetry data and the SCICEX sidescan data. The goals of the research are to determine and characterize volcanic and tectonic landforms within the Gakkel Ridge rift valley, relate the nature and distribution of the bathymetry to extensional processes, and to establish how these processes vary along the ridge and how they interact to accommodate plate separation at the extremely slow spreading rates of the Gakkel Ridge. Hypotheses to be addressed include: -What form does volcanic activity take at the extremely slow spreading Gakkel Ridge? Are there significant differences in the form, distribution and size of individual small scale volcanic features in the western volcanic zone where volcanism is widespread and the rest of the ridge where it occurs at widely spaced volcanic centers? -What form does tectonic activity take at the Gakkel Ridge? Are there differences in the dip, throw, length and spacing of faults along the axis? How does faulting differ between the western volcanic zone and the rest of the ridge where magmatism is rarer? In the eastern portion of the ridge, does the nature of faulting change approaching the volcanic centers and if so, how? Does the nature of faulting in areas where the ridge is orthogonal to the opening direction differ from where it is oblique? -How do volcanic and tectonic processes interact to produce the observed morphology along the Gakkel Ridge? How does extension and lithospheric creation occur in the absence of volcanism? Broader Impacts: Undergraduate students will be involved in this research through Lamont Doherty Earth Observatory (LDEO)'s Summer Internship program. This is an NSF-sponsored program in which undergraduates spend the summer working on a project under the mentorship of an LDEO scientist. At the end they write an abstract and present an American Geophysical Union (AGU) -type" talk on their research. Not infrequently, interns present their work at national meetings or coauthor papers with their mentors. This program has been very successful in introducing undergraduates to an academic research environment and the majority decide to go on graduate school in the Earth sciences.