HR: 1340h
AN: V43B-1577    [Abstracts]
TI: Palagonitization of Mauna Kea Sideromelane: New Insights From in-situ Micro Mass Spectrometry
AU: * Pauly, B
EM: pauly@geology.ucdavis.edu
AF: Dept. of Geology, University of California, Davis, 1 Shields Ave., Davis, CA 95616 United States
AU: Schiffman, P
V43B-1577 AF: Dept. of Geology, University of California, Davis, 1 Shields Ave., Davis, CA 95616 United States
AU: Hervig, R
V43B-1577 AF: Dept. of Geological Sciences, Arizona State University, Box 871404, Tempe, AZ 85287 United States
AU: Yin, Q
V43B-1577 AF: Dept. of Geology, University of California, Davis, 1 Shields Ave., Davis, CA 95616 United States
AU: Zierenberg, R
V43B-1577 AF: Dept. of Geology, University of California, Davis, 1 Shields Ave., Davis, CA 95616 United States
AB: The process of palagonitization remains incompletely understood largely because of the difficulty in physically separating adjacent fresh and palagonitized sideromelane. We have used integrated LA-ICPMS (quadrupole and multicollector) and SIMS analysis to investigate palagonitization in a hyaloclastite recovered from a depth of 2847 m in the Hawaii Scientific Drilling Project's 3 km-deep corehole. The LA-ICPMS (quadruple) at UCDavis was used to analyze trace elements along a contact-perpendicular traverse from palagonite into adjacent sideromelane. Trace elements analyzed in palagonite show both enrichment and depletion relative to sideromelane. Enrichment gradients were observed in the palagonite (more enriched further from the contact) for Cr, Cu, and Zr. Ba and Rb are increasingly depleted with distance from the contact. Sc, V, Co, and Zn showed no gradient. The REE pattern in palagonite has the same slope as for the adjacent sideromelane (smooth, LREE-enriched), but REE concentrations are enriched relative to sideromelane. A pronounced REE gradient (more enriched further from the contact) was observed in the palagonite. The LA-ICPMS (multi-collector) at UCDavis was used to analyze Sr concentration and ^87/86Sr along a similar traverse. A concentration gradient was observed for Sr, with the highest concentration nearest the contact. ^87/86Sr values were highest at the outer palagonite rim, decreasing inward toward the contact. These concentration and isotopic data fit a simple Sr mixing model using sideromelane and seawater as end-members, and indicate that water circulation decreased from the outer palagonite rim toward the contact during palagonitization (based on textural evidence that the palagonitization reaction front moved inward). The Cameca 3F SIMS at Arizona State University was used to analyze B concentration, δ¹¹B, and δ¹⁸O along similar traverses. B concentration within palagonite increased from the sideromelane (less than 0.25 ppm) outwards toward the seawater interface (3.5 ppm). Simple mixture modeling for B concentration yields water circulation results similar to those obtained for the Sr mixing model. δ¹¹B was approximately 14 per mil throughout the palagonite, a value intermediate between basalt and seawater. δ¹⁸O values were constant in sideromelane and adjacent palagonite, with the palagonite values 4 per mil heavier than sideromelane. Absolute δ¹⁸O measurements will require the creation of a palagonite δ¹⁸O standard.
DE: 1034 Hydrothermal systems (0450, 3017, 3616, 4832, 8135, 8424)
DE: 1039 Alteration and weathering processes (3617)
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1065 Major and trace element geochemistry
DE: 8427 Subaqueous volcanism
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005