Nature of serpentinization of ultramafic rocks from Hero Fracture Zone, Antarctic: Constraints from stable isotopes

Serpentinites from the Hero Fracture Zone, Drake Passage, Antarctica, contain serpentine, amphibole, talc, chlorite, and magnetite as well as relict olivine, pyroxene, and spinel from a spinel peridotite precursor. Two episodes of serpentinization are recognized. The first event produced lizardite and antigorite, whereas the second produced only lizardite. The initial and subsequent serpentinization events occurred at about 178–283 °C and 170–298 °C, respectively. Calculated water/rock ratios of the serpentinization events are less than 5 for the initial event and greater than 5 for the subsequent event. A model involving deep seawater infiltration in the fracture zone, followed by serpentinization of mantle peridotite and buoyancy-driven uplift controlled by relatively small-scale faults and not by a large-scale detachment fault, is invoked to explain the emplacement of serpentinite on the surface.