Chemistry of gabbroic rocks of ODP Hole 118-735B

We present results of a microprobe investigation of fresh and least-deformed and metamorphosed gabbroic rocks from Leg 118, Hole 735B, drilled on the east side of the Atlantis II Fracture Zone, Southwest Indian Ridge. This rock collection comprises cumulates ranging from troctolites to olivine-gabbro and olivine-gabbronorite to ilmenite-rich ferrogabbros and ferrogabbronorites. As expected, the mineral chemistry is variable and considerably expands the usual oceanic reference spectrum. Olivine, plagioclase, and clinopyroxene are present in all the studied samples. Orthopyroxene and ilmenite, although not rare, are not ubiquitous. Olivine compositions range from Fo85 to Fo30, while plagioclase compositions vary from An70 to An27. Mg/(Mg + Fe2+) of clinopyroxene (mostly diopside to augite) varies from 0.88 to 0.54. Mg/(Mg + Fe2+) of orthopyroxene varies from 0.84 to 0.50. These minerals are not significantly zoned. All mineralogical data indicate that fractional crystallization is an important factor for the formation of cumulates. However, sharp contacts, interpreted as layering boundaries or intrusion margins, suggest polycyclic fractionation of several magma batches of limited volumes. Calculated compositions of magmas in equilibrium with the most magnesian mineral samples at the bottom of the hole represent fractionated liquids through separation of olivine, plagioclase, and clinopyroxene at moderate to low pressures (less than 9 kb). Crystallization of orthopyroxene and ilmenite occurs in the most differentiated liquids. Mixing of magmas having various compositions before entering the cumulate zone is another mechanism necessary to explain extremely differentiated iron-rich gabbros formed in this slow-spreading ridge environment.

Hydrographic measurements from C.S.S. Hudson Cruise 82-002, Canadian Technical Report of Hydrography and Ocean Sciences No. 118, 112 pp (digital version)

This archive consists of the hydrographic data collected on Cruise 82-002 of C.S.S. Hudson, April 11 to May 2, 1982. 78 stations were occupied on a line running near 48°N from the mouth of the English Channel to the Grand Banks of Newfoundland. Pressure, temperature and salinity were measured by a Guildline digital CTP system. Salinity, dissolved oxygen, silicate, nitrate and phosphate were measured from water samples collected on the CTP upcasts. CTP and discrete bottle data and associated derived parameters are tabulated at standard levels. This is the digital version of the printed report (of 1989, see further details), published in 2006 with the information system Pangaea.