Proposed Sites | Table of Contents
SCIENTIFIC OBJECTIVES
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."
- 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.
- 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.
- 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.
- 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.
- 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.
- 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