Dick, Henry J B; Ozawa, Kazuhito; Meyer, Peter S; Niu, Yaoling; Robinson, Paul T; Constantin, Marc; Hébert, Rejean; Maeda, Jinichiro; Natland, James H; Hirth, James Gregory; Mackie, Suzie (2002): Mineralogy and geochemistry of ODP Hole 176-735B minerals [dataset publication series]. PANGAEA, https://doi.org/10.1594/PANGAEA.787522,

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Supplement to: Dick, HJB et al. (2002): Primary silicate mineral chemistry of a 1.5-km section of very slow spreading lower ocean crust: ODP Hole 735B, Southwest Indian Ridge. In: Natland, JH; Dick, HJB; Miller, DJ; Von Herzen, RP (eds.) Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 176, 1-61, https://doi.org/10.2973/odp.proc.sr.176.001.2002

We present a synthesis of some 20,504 mineral analyses of ~500 Hole 735B gabbros, including 10,236 new analyses conducted for this paper. These are used to construct a mineral stratigraphy for 1.5-km-deep Hole 735B, the only long section of the lower crust drilled in situ in the oceans. At long wavelengths, generally >200 m, there is a good chemical correlation among the principal silicate phases, consistent with the in situ crystallization of three or four distinct olivine gabbro bodies, representing at least two major cycles of intrusion. Initial cooling and crystallization of these bodies must have been fairly rapid to form a crystal mush, followed by subsequent compaction and migration of late iron-titanium-rich liquids into shear zones and fractures through which they were emplaced to higher levels in the lower crust where they crystallized and reacted with the olivine gabbro host rock to form a wide variety of ferrogabbros. At the wave lengths of the individual intrusions, as represented by the several olivine gabbro sequences, there is a general upward trend of iron and sodium enrichment but a poor correlation between the compositions of the major silicate phases. This, together with a wide range in minor incompatible and compatible element concentrations in olivine and pyroxene at a given Mg#, is consistent with widespread permeable flow of late melt through these intrusions, in contrast to what has been documented for a 600-m section of reputedly fast-spreading ocean crust in the Oman Ophiolite. This unexpected finding could be related to enhanced compaction and deformation-controlled late-stage melt migration at the scale of intrusion at a slow-spreading ocean ridge, compared to the relatively static environment in the lower crust at fast-spreading ridges.

Only newly obtained data by the authors (labelled 'DCK' in the Source field) is presented here. More data on Hole 176-735B can be found in the following datasets: Alt et al. (2001, doi:10.1594/PANGAEA.787369), Niu et al. (2001, doi:10.1594/PANGAEA.787448), Holm et al. (2001, doi:10.1594/PANGAEA.787387), Maeda et al. (2002, doi:10.1594/PANGAEA.787397), Robinson et al. (2002, doi:10.1594/PANGAEA.787475) and Hertogen et al. (2002, doi:10.1594/PANGAEA.787422).