Appendix I - Cruise Summary
Sonar Mapping, Dredging, Seafloor Camera Surveys, and CTD Sampling on the
Submarine Flanks of Fernandina and Isabela Islands, Galapagos Islands
Mark D. Kurz, Daniel J. Fornari, Dennis Geist
This research cruise will focus on the mantle geochemistry and submarine volcanic construction of the Galapagos Archipelago, by studying the submarine flanks and rift zones of the two western-most islands, Fernandina and Isabela. These two islands host two of the most active volcanoes in the Galapagos - Fernandina and Cerro Azul [see map, Appendix II]. Fernandina is considered to be at the leading edge of the Galapagos hotspot, and the study of its submarine western flank and the rift zones which extend westward offer the opportunity to sample undegassed lavas erupted from the leading edge of the hotspot. Similarly, Cerro Azul is at the western edge of the Galapagos platform and samples from its submarine slopes/rift zones will provide a comparison to Fernandina. Significant portions of Cerro Azul appear to be scarps, created by mass-wasting of the unbuttressed flank of the volcano, which may expose older lavas that cannot be sampled above sea level. The overall goal of the project is to identify the tectonic and magmatic processes responsible for the earliest submarine phases of Galapagos volcanism, and to compare the geochemistry of submarine lavas with that of the previously sampled subaerial lavas from both islands, and also from other oceanic islands such as Hawaii.
During the field program, on the Scripps Institution of Oceanography vessel R/V Revelle, we will make detailed maps of the submarine flanks and rift zones of Fernandina and Isabela, using the MR-1 side-scan sonar system of the University of Hawaii, Simrad multibeam sonar, and WHOI towed digital camera system. These tools will allow us to identify areas of volcanic construction and study the relationships between structural and volcanic features on the seafloor. Areas of inferred recent volcanic activity will be identified as highly reflective, unsedimented, young submarine lava flows. These maps will then be used to collect a comprehensive suite of submarine lava samples around Fernandina and Isabela over a wide depth range [from ~500 m down to ~3500 m depth] that will be subjected to a full-suite of geochemical analyses. Deep sea camera tows will be deployed in several areas around Fernandina and Isabela as indicated by the shipboard analysis of the MR-1 sonar data to be regions of important volcanic contacts. We also plan to carry out several CTD (conductivity, temperature, depth) casts to collect water samples from areas that are suspected of being hydrothermally active. The data from these geological and geochemical studies will address several important questions related to hotspot-upper mantle interactions, mantle geochemistry, volcanology, and the geologic history of the Galapagos including their origin as submarine volcanoes.
Use of the mapping tools will allow identification of constructional volcanic features and possible volcanic vents (cones); evaluation of sediment cover (as a rough indicator of relative age), and identification of possible lava flow contacts and landslide features. Post-cruise efforts will include a full suite of geochemical analyses on submarine lava samples and analysis of the sonar and camera tow photographic data. One of the main goals of the cruise will be to recover glassy basalt suitable for noble gas measurements. Preliminary results from the Melville 2000 cruise show that the submarine Fernandina lavas are relatively undegassed and are characterized by very 3He/4He ratios, making them ideal for the noble gas studies. The leading hypothesis to explain high 3He/4He ratios at Fernandina is that the Galapagos hotspot is derived from the lower mantle, and that Fernandina is the center of the upwelling region. The results will be made available as a Preliminary Report within 90 days following the end of the cruise. A Final Report will be provided within 12 months of the end of the cruise. Results of the field and laboratory analytical programs will be published as scientific papers in refereed international scientific journals.