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doi:10.2204/iodp.proc.344.201.2015

Data report: strontium isotope analyses of pore fluids from the CRISP-A transect drilled during Expeditions 334 and 344¹

Nathan Ross,² Marta E. Torres,² Brian A. Haley,² Evan A. Solomon,³ and Miriam Kastner⁴

Abstract

We report on the Sr isotopic composition of pore fluids recovered during Integrated Ocean Drilling Program Costa Rica Seismogenesis Project Expeditions 334 and 344. Pore fluid samples were acidified and loaded directly onto columns containing EICHROM Sr-Spec resin, followed by analyses using a NU multicollector inductively coupled plasma–mass spectrometer at the Keck Collaboratory, Oregon State University.

Sites drilled on the upper plate exhibited a decrease in the ⁸⁷Sr/⁸⁶Sr ratio to values as low as 0.70762 in the upper 200–300 m of the sediment column, suggesting the role of ash alteration. The unconformity between the slope sediment sequence and underlying framework rock, sampled at Sites U1378–U1380, is characterized by intense fracturing. The fluids sampled within the unconformity at these sites have ⁸⁷Sr/⁸⁶Sr ratios ranging from 0.70834 to 0.70844.

Fluids sampled from the incoming plate sediment show evidence of ash alteration and carbonate diagenesis, but the deepest sediment here may also be modified by diffusion of fluids from the underlying oceanic crust. Intense carbonate recrystallization in the lower 66 m of Site U1414 results in Sr concentrations that are almost an order of magnitude higher than those measured at the base of Site U1381. The deepest pore fluid sample measured at both Sites U1381 and U1414 has a ⁸⁷Sr/⁸⁶Sr ratio of 0.7086.

The strontium systematics in this margin, used in the context of other ongoing studies, may be used to unravel processes at this margin, such as carbonate diagenesis, ash alteration, fluid migration, and diffusive exchange with the underlying oceanic crust.

¹ Ross, N., Torres, M.E., Haley, B.A., Solomon, E.A., and Kastner, M., 2015. Data report: strontium isotope analyses of pore fluids from the CRISP-A transect drilled during Expeditions 334 and 344. In Harris, R.N., Sakaguchi, A., Petronotis, K., and the Expedition 344 Scientists, Proc. IODP, 344: College Station, TX (Integrated Ocean Drilling Program). doi:10.2204/iodp.proc.344.201.2015

² 104 CEOAS Administration Building, Oregon State University, Corvallis OR 97331, USA. Correspondence author: mtorres@coas.oregonstate.edu

³ School of Oceanography, University of Washington, Seattle WA 98195, USA.

⁴ Scripps Institution of Oceanography, University of California, San Diego, La Jolla CA 92093-0212, USA.

Initial receipt: 4 March 2014
Acceptance: 17 February 2015
Publication: 18 May 2015
MS 344-201

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