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doi:10.2204/iodp.proc.345.106.2014

Inorganic geochemistry

One gabbronorite was selected in Hole U1415E (Sample 345-U1415E-1R-1, 44–47 cm) for geochemical analysis. Sample selection was based on discussion among representatives from all expertise groups within the shipboard scientific party. Inductively coupled plasma–atomic emission spectroscopy (ICP-AES) was used to determine major and trace element concentrations, and gas chromatography was used for S, H₂O, and CO₂ quantifications. Results are reported in Table T1 in the “Geochemistry summary” chapter (Gillis et al., 2014c). Major and trace elements are reported on a volatile-free basis.

Sample 345-U1415E-1R-1, 44–47 cm, is characterized by low volatile contents, with a 0.44 wt% loss on ignition, 0.95 wt% H₂O, and 0.09 wt% CO₂. These values are consistent with the moderate degree of alteration of the analyzed sample (~10%; see “Metamorphic petrology” and Hole U1415E thin section descriptions in “Core descriptions”). The sample has an Mg# (cationic Mg/[Mg + Fe]; all Fe as Fe²⁺) of 73; relatively high SiO₂ (51 wt%), Fe₂O₃^(T) (7.7 wt%), and TiO₂ (0.5 wt%) content; and low Cr (123 ppm) and Ni (67 ppm) concentrations, overlapping in composition with gabbronorite previously sampled at ODP Site 894 and along the Northern Escarpment of the Hess Deep Rift. This gabbronorite plots at the most primitive end of the field of the Hess Deep gabbro and gabbronorite (Gillis, Mével, Allan, et al., 1993; Pedersen, et al, 1996; Natland and Dick, 1996; Hanna, 2004; Kirchner and Gillis, 2012).

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