Fluid flow, mineralization and deformation in an oceanic detachment fault: Microtextural, geochemical and isotopic evidence from pyrite at 13°30’N on the Mid-Atlantic Ridge
Fluid flow, mineralization and deformation in an oceanic detachment fault: Microtextural, geochemical and isotopic evidence from pyrite at 13°30’N on the Mid-Atlantic Ridge Andrew J. Martin1*, John W. Jamieson2, Sven Petersen3, Mostafa Fayek4, Javier Escartin5 1 Geoscience, University of Nevada, Las Vegas, 89154, USA 2 Department of Earth Sciences, Memorial University of Newfoundland, A1B 1L9, Canada 3 GEOMAR, Helmholtz Centre for Ocean Research Keil, 24128, Germany 4Department of Earth Sciences, University of Manitoba, R3T 2N2, Canada 5Laboratoire de Géologie (CNRS UMR8538), Ecole Normale Supérieure de Paris, PSL University, Paris, France * Corresponding author: Andrew.email@example.com Geochemical and isotopic dataset for the above manuscript.
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Whole-rock geochemistry Powdered in an agate mill (Pulerisette 5 by Frisch), and analyzed commercially at ACTLABS (Ancaster, Canada) for their major and trace element composition using a combination of methods, including inductively coupled plasma-atomic emission spectroscopy, inductively coupled plasma-mass spectrometry, and instrumental neutron activation (Supporting Information 1, T1). High-purity burnt and acid-treated quartz-sand, iso-2-propanol and deionized water were used for cleaning in between samples. In order to control the accuracy of the measurements, two certified international reference materials (standards CCu-1c and CZn-3; Supporting Information 1, T1) were prepared and analyzed as unknown samples along with the other samples. Laser Ablation ICP-MS GeoLas 193 nm laser coupled to a Thermo-Finnigan Element XR ICP-MS. Analysis employed a spot diameter of 40 μm at a frequency of 5 Hz and a fluence of 3 J/cm2. Each analysis lasted 50 s and a gas blank was measured for 30 s prior to each analysis. Lines were conducted under the same analytical parameters as spot analyses and the sample translated relative to the laser at 15µm/sec. Iron-57 was used as an internal standard for all analyses and a stoichiometric Fe content of 46.5% was assumed for pyrite. External calibration was performed using USGS MASS-1 and NIST 610. Precision was monitored through the repeat analysis of MASS-1 (n= 26) that yielded a relative standard deviation (RSD) for Bi, Pb, As, Zn, Cu and Mn of <10%, and <13% for V, Cr, Ni, Ga, Ge, Mo, Ag, Cd, In, Sn, Sb and Au. Only Te, Se, and Co showed a higher RSD, reaching 18, 13 and 18%, respectively (see Supporting Information 1, T2). Subtraction of gas blanks and calculation of detection limits was performed using Iolite software. Sulfur isotope analysis Secondary ion mass spectrometry (SIMS) microanalysis in three polished mounts. Samples were mounted in epoxy resin with aluminum retaining rings, polished, and then coated with 300Å of Au to mitigate charging of the sample during ion bombardment. Analyses were performed using a Cameca IMS 7f SIMS instrument equipped with a ETP 133H electron multiplier at the University of Manitoba (Canada). Each sample was bombarded with a primary ion beam of 3 nA of Cs+ accelerated through a potential voltage of 10 KeV and focused into a 10 μm spot. Negatively charged secondary ions were accelerated into the mass spectrometer using a potential of +8.7 KeV. Each spot was pre-sputtered for 120-180 s prior to analysis to exclude sulfur contamination from the sample surface. Reproducibility of results was calculated based on the repeat analysis of standard reference material Balmat Pyrite (15.1‰) (Crowe and Vaughn, 1996), and to correct for instrumental mass fractionation. The spot-to-spot reproducibility was better than ±0.3‰ (Supporting Information 1, T3). All analyses are reported in standard delta notation (δ34S, ‰) relative to Vienna-Canyon Diablo Troilite (V-CDT).