Mineralogy and textures of iron-titanium oxide gabbros and associated olivine gabbros from Hole 735B

Abstract

Abundant iron-titanium (Fe-Ti) oxide gabbro, olivine gabbro, and troctolite were drilled at Hole 735B adjacent to the Atlantis II Fracture Zone. The Fe-Ti oxide gabbro occurs as intrusive bodies into olivine gabbro with very sharp intrusive contacts. The size of the intrusive bodies varies from a millimeter to a few tens of meters. Mineralogical parameters, such as anorthite content of plagioclase and Mg/(Mg + Fe) ratios of mafic minerals exhibit bimodal distributions corresponding to olivine and Fe-Ti oxide gabbros, respectively. When the two major gabbro types are looked at separately, several downhole mineralogical cycles are recognized. The interlayered occurrence of evolved and primitive gabbros from Hole 735B represents a typical section of lower ocean crust formed at a very slow spreading ridge. -from Authors