Investigating the Influence of Magmatic Volatile Input and Seawater Entrainment on Vent Deposit Morphology and Composition in Manus Basin (Back-arc) Hydrothermal Systems
Abstract
In August 2006, hydrothermal activity within the eastern Manus Basin north of Papua New Guinea was investigated using a combination of mapping (SeaBeam from the R/V Melville, near-bottom multi-beam sonar and magnetometer from AUV ABE and ROV Jason-2) and sampling (fluids and solids using ROV Jason-2). Objectives included identifying tectonic/geologic settings, examining interactions of seawater with felsic rocks that constitute the high silica end-member in the range of basement compositions, determining the extent of volatile magmatic inputs into these systems, and examining the evolution of hydrothermal activity through time. At the PACMANUS (Papua New Guinea Australia Canada Manus) area five previously discovered vent fields were mapped and sampled, and a new very active field, Fenway, was located south of the Satanic Mills field. The core of the Fenway field is a 40 m diameter two-tiered mound. A large black smoker complex venting boiling (356C, 172 bar) fluids forms the upper tier, with the lower tier composed of sulfide debris, massive anhydrite-sulfide deposits, and anhydrite sand. At the DESMOS Caldera hyaloclastites and extensive patches of bleached and stained substrate were mapped and sampled, as were diffuse (72C) and focused (119C) acidic fluids with a pH (25C) of 1.0; no sulfide deposits were observed in the area. At the North Su vent field within the SuSu Knolls area even lower pH fluids were sampled (see Seewald et al., this session). Hydrothermal activity includes venting of white sulfur-rich fluids through cracks and sediments, formation of native sulfur flanges, diffuse venting through spires, and black smoker activity (324C). Anhydrite cement is also present. The abundance of massive anhydrite at Fenway and presence of anhydrite cement at North Su is consistent with significant local entrainment and heating of seawater. The extremely low pH (less than 2) of some vent fluids supports previous hypotheses that fluids in this area contain significant input of magmatic volatiles (e.g., Gamo et al. 1997, Geology 25). During the cruise, 104 black, gray, and clear fluids were sampled using gas-tight and major samplers, and 198 vent sulfide deposit, 83 altered substrate, and 43 fresh lava samples were recovered. Geophysical maps and geochemical data for solids and fluids will be used to determine the styles of mixing and reaction occurring beneath the vent fields, estimate subsurface mineral deposition, and investigate the extent to which input of magmatic fluids is occurring within each system.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.B34A..01T
- Keywords:
-
- 0450 Hydrothermal systems (1034;
- 3017;
- 3616;
- 4832;
- 8135;
- 8424);
- 3001 Back-arc basin processes;
- 3017 Hydrothermal systems (0450;
- 1034;
- 3616;
- 4832;
- 8135;
- 8424);
- 4832 Hydrothermal systems (0450;
- 1034;
- 3017;
- 3616;
- 8135;
- 8424);
- 8135 Hydrothermal systems (0450;
- 1034;
- 3017;
- 3616;
- 4832;
- 8424)