Proposed Sites | Table of Contents


The overall aim of Leg 193 is to delineate, effectively in three dimensions, the subsurface volcanic architecture, the structural and hydrologic characteristics, and the deep-seated mineralization and alteration patterns of the PACMANUS hydrothermal field (Fig. 8). From these data and subsequent laboratory analyses of samples and structural data, the following specific scientific objectives will be pursued. Unlike ODP legs in sedimentary sequences, we are less able to predict in detail the lithologies and structures that will be encountered; hence, we must stand prepared to "expect the unexpected."

  1. Assess the manner in which fluids and metals derived from underlying magmatic sources, and from leaching of wall rocks by circulated seawater, respectively, have combined within the PACMANUS hydrothermal system. This will be approached by applying geochemical and isotopic modeling to the vertical and lateral variations in hydrothermal alteration styles and sulfide mineral occurrences including subsurface massive sulfide deposits established by the drilling. Related subsidiary objectives include comparison of exhalative and subhalative mineralizing processes, assessing the consequences of fluid phase separation, and seeking explanations for the elevated contents of Cu, Zn, Ag, and Au in massive sulfide chimneys at the PACMANUS seafloor.

  2. Delineate probable fluid pathways within the system and establish a hydrological model by measuring and interpreting variations in physical properties and fracture patterns of fresh and altered bedrocks.

  3. Determine whether the construction of Pual Ridge is simple "layer cake," with potential older exhalative or subhalative massive sulfide horizons concealed by younger lavas or, alternatively, whether inflation of the volcanic edifice by lava domes or shallow intrusions is the predominant process in this submarine felsic volcanic environment.

  4. Develop a petrogenetic model for Pual Ridge igneous rocks and seek evidence pertaining to the nature of the possible underlying source for magmatic components in the hydrothermal fluids.

  5. By combining the above models, develop an integrated understanding of the relationship between volcanological, structural, and hydrothermal phenomena in the PACMANUS system for comparison with equivalent hydrothermal phenomena at midocean ridges and for providing a new basis for interpreting ancient ore environments.

  6. Establish the nature, extent, and habitat controls of microbial activity within the hydrothermal system, and interpret the differences encountered in diversity and biomass in terms of nutrient supplies and environmental habitats interpreted in the context of the geochemical and hydrologic understanding of the total hydrothermal system.

Proposed Sites | Table of Contents