East Scotia Ridge unsecured

V polarstern cruise ps47 ant xvii with general dredge

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ed side-scan sonar and bathymetric data (Livermore et al., 1995; Fig. 2). In 1997–1998, sampling of segments E3–E7 was carried out using a drum-shaped dredge during R.V. Polarstern cruise PS47 (ANT XV/II), with general dredge direction along the spreading axis. Fresh volcanic material, e.g. pillow lavas, sheet flows and lava tubes, most of which preserved fresh glassy margins, were recovered during the 10 dredge deployments during cruise PS47 (Fig. 2). During R.R.S. James Clark Ross cruise JR39b in 1999, fresh volcanic glass fragments were obtained at 28 sites from segments E2 to E9 using a wax corer (Livermore et al., 1999). These fresh volcanic samples, when combined with previous high-density sampling of segment E2 (Leat et al., 2000) during cruise JR12, provide complete coverage of the East Scotia Ridge neo-volcanic zone (Fig. 2, coordinates listed in Table 1). ANALYTICAL METHODS Macroscopic criteria (vesicularity; size, abundance and variety of minerals) were used to select different rock types from each dredge haul, from which glassy pillow rims were separated under a binocular microscope and washed several times in ultra-pure water. Glass fragments in wax cups from the wax corer were removed from the wax with tweezers. The fragments were then placed into a beaker with water in a microwave oven for 2 min to melt the wax. The beaker was cooled and the wax removed. The sample was then washed several times in ultra-pure water. Analyses of minerals were made at the University of Kiel (Institut fur Geowissenschaften) with a Cameca ¨ CAMEBAX electron microprobe running at a beam current of 12·5 nA and acceleration voltage of 14–15 kV. Usually, the beam width was about 1–2 m, and was defocused for plagioclase analyses. Synthetic and natural standards were used to calibrate the microprobe. Repeat measurements show that the relative standard deviations are smaller than ±0·5%, indicating a good reproducibility for all major elements. The major element concentrations of the volcanic glass samples were determined with a Cameca SX50 electron microprobe at GEOMAR (Kiel) (Table 1). A beam current of 10 nA with an accelerating voltage of 15kV was used. The beam was defocused to 5 m to minimize Na loss during measurements. Glass analyses reported are the averages of more than five individual spot analyses (Table 1) with relative standard deviations smaller than ±0·5%. International glass standards ( JDF-D2, CFA47 2) were measured after every 20 analyses to check precision, which is better than ±0·7%. H2O analyses were obtained by Fourier transform infrared (FTIR) spectroscopy at the University of Kiel using the methods and calibration described by Stolper (1982). Double-polished glass thin sections, 100–250 m thick, were analysed with a Bruker IFS 66v/S FTIR spectrometer equipped with a Bruker A 590 Infrared Microscope with a mercury–cadmium–telluride detector. Optically clear areas of known thickness (±5 m) were measured with aperture size of 120 m diameter with 256 scans per spot. Concent...
View Full Document

This document was uploaded on 02/01/2014.

Ask a homework question - tutors are online