OS22C-03
Seafloor Hydrothermal Activity in the Southern Gulf of California

Tuesday, 15 December 2015: 10:50
3018 (Moscone West)
Jennifer Brophy Paduan1, David A Clague2, David W Caress2, Lonny Lundsten2, Robert A Zierenberg3, Giancarlo Troni2, Charles Geoffrey Wheat4 and Ronald Michael Spelz5, (1)Monterey Bay Aquarium Res Inst, Moss Landing, CA, United States, (2)Monterey Bay Aquarium Research Institute, Watsonville, CA, United States, (3)University of California Davis, Earth and Planetary Sciences, Davis, CA, United States, (4)University of Alaska Fairbanks, Fairbanks, AK, United States, (5)Autonomous University of Baja California, Mexicali, Mexico
Abstract:
Active hydrothermal venting was previously unknown between Guaymas Basin and 21°N on the East Pacific Rise. MBARI AUV surveys and ROV dives in 2012 and 2015 discovered 7 hydrothermal vent sites with diverse and varied vent communities within that gap. One field in the Pescadero Basin vents clear shimmering fluids at 3685 m depth and four vigorous black smoker fields and several extinct chimney fields are between 2225 and 2400 m depth on the Alarcón Rise. Low-temperature vent sites are present on both of the Pescadero and Tamayo Transforms. The chimneys were discovered in 1-m resolution AUV bathymetric data, with some indicated to be active based on temperature anomalies in the AUV CTD data and confirmed during later ROV dives. The low-temperature vent sites on the transform faults were found on ROV dives while exploring young lava flows and sediment hills uplifted by sill intrusions.

Pescadero Basin is a deep extensional basin in the southern Gulf. The smooth, subtly faulted floor is filled with at least 150 m of sediment, as determined from sub-bottom profiles collected by the AUV. Three large chimneys (named Auka by our Mexican collaborators) and several broad mounds are located on the SW margin of the basin. Temperatures to 290°C were measured, the fluids are clear, neutral pH, and contain elevated Na. The chimneys are delicate, white, predominantly Ca-carbonate; barite, sparse sulfides, and some aromatic hydrocarbons are also present.

Three active vent fields (Ja Sít, Pericú, and Meyibó) at Alarcón Rise are located near the eruptive fissure of an extensive young sheet flow. The fourth field (Tzab-ek) is 1.1 km NW of the axis on older pillow lavas. The largest chimneys are in the Tzab-ek field: 31 and 33 m tall, with flanges and upside-down waterfalls. They rise from a sulfide mound, suggesting a long-lived hydrothermal system, in contrast to the near-axis fields where the chimneys grow directly on basalt. The Alarcón chimneys are Zn and Cu-rich sulfides. The fluids are acidic, with elevated Na and temperatures of 330-359°C.

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