VITIAZ – The Life Cycle of the Vitiaz-Kermadec Arc / Backarc System: from Arc Initiation to Splitting and Backarc Basin Formation

The R/V SONNE expedition SO255 is part of the research project VITIAZ, conducted in close cooperation with New Zealandic, U.S. American, and Japanese scientists. The overarching goal of VITIAZ is to elucidate the physical and chemical conditions that control the development of subduction zones, including subduction initiation, evolution of mature arc systems, and the transition from arc splitting to backarc basin generation. This approach should also provide basic data for a better evaluation of the impact of subduction volcanism on the environment. Cruise SO255 mapped and sampled magmatic structures at the Kermadec Fore Arc, the Kermadec Ridge, the Havre Trough, and the Colville Ridge (SW-Pacific) using Kongsberg EM122 and EM710 multi-beam echo sounding systems, an Atlas PARASOUND DS P-70 sub-bottom profiler, and chain bag dredges. Besides extensive profiling, a total of 165 dredge hauls in an average water depth of 2,500 m were carried out on SO255. Of these, 137 (= 83%) delivered in situ samples of which 102 obtained lava or subvolcanic rocks, 69 volcaniclastics, and 30 sedimentary rocks. No equipment was lost or seriously damaged. The on shore work program at GEOMAR and cooperating institutions will include volcanological, geochronological, petrological and geochemical studies on igneous samples obtained during the cruise. The results of VITIAZ will be integrated with those of previous campaigns (e.g. SO249 BERING), and work carried out within the GeoPRISMS initiative.

The geological program of the cruise has been completed by biological investigations intending (1) to collect planktonic gastropod specimens for morphological and molecular analysis to understand their taxonomy, biogeography and evolution; (2) to use water samples to study degradation processes in the deep sea; and (3) to describe the benthic diversity of deep-sea invertebrates in the working area by collecting macro benthos from the dredged rocks.