The project will use the submersible ALVIN and the AUV SENTRY to obtain samples on-and off-axis at the intermediate-spreading Galapagos Spreading Center to study the effects of variable magma supply on volcanic processes at the intermediate-spreading Galapagos Spreading Center. The project will obtain important new constraints on the relationships between magma supply, magma chamber properties and processes, eruption dynamics and the development of volcanic landforms at this intermediate-spreading mid-ocean ridge.
This collaborative project was designed to examine the relationships between variable magma supply and volcanic and tectonic processes and mid-ocean ridges. Mid-ocean ridges are where new ocean crust is created by long chains of volcanoes that encircle the globe on ocean floors. As the amount of magma available to these volcanoes varies, do the size, frequency, and nature of eruptions also vary? The Galapagos Spreading Center (GSC) was chosen as a natural laboratory because it experiences decreasing magma supply with increasing distance from the nearby Galapagos hotspot. Two contrasting sites on the GSC were mapped using high-resolution swath bathymetry (to produce topographic maps), submersible observations, and camera tow photography. Additionally, rock samples and local magnetic field measurements were collected via submersible. To evaluate how flow volume, frequency, duration, and chemical heterogeneity vary with increasing magma supply at near constant spreading rate, it is necessary to develop a chronology for the observed and sampled flow units. The primary goal of the work carried out at University of Minnesota (and University of Wisconsin – Milwaukee) was to place age constraints on volcanic flows using variations in the strength of the geomagnetic field (i.e., paleointensity) produced in Earth’s core. Variations in paleointensity are recorded in volcanic glass that forms when hot magma is rapidly quenched by contact with seawater. This method of absolute and relative age dating has been successfully used in the past on flows along the north-south trending East Pacific Rise. The east-west geometry and high-iron content of the GSC flows make this technique more challenging in the present study, where highly magnetic preexisting lava flows may produce a magnetic field that locally distorts the core-produced field. The work funded by this grant was intended serve as a feasibility study of the technique in this region. Results of this work show that in regions with relatively large locally-produced anomalies, it is necessary to collect a large number of samples (at least 15-20) to adequately represent the within-flow scatter in paleointensity. If this is done, it may be possible to properly estimate the flow mean paleointensity and place some age constraints on mapped flow units. In order to do this, however, one must first 1) identify flow boundaries based on independent information (paleointensity alone cannot be used to determine whether or not a single sample belongs in one flow-field or another); and 2) determine whether or not locally-produced anomalies are expected to have zero mean. The broader impacts of this grant include contributions to the training of the next generation of geoscientists by providing laboratory research experience to four undergraduate students. Students participated in the project by splitting and processing sediment cores, and measuring their magnetic properties; preparing rock samples for paleointensity analysis, making most of the measurements for these experiments; participating in the processing and interpretation of the data; and carrying out experiments designed to understand how the magnetic properties of volcanic glass vary with age. Additionally, increasing our understanding of volcanic eruption frequency may help to estimate volcanic hazards in some parts of the world.
