The origin of serpentinite from Hero Fracture zone in Drake passage, Antartic

Abstract

Serpentinites from Hero Fracture zone in Antarctic contain serpentine, amphibole, talc, chlorite, and magnetite as well as olivine, pyroxene, and spinel as relict minerals. Fosterite compositions of olivines in serpentinites are 89 - 90. Cr-numbers and Mg-numbers of spinels in serpentinites are similar to those of spinels in abyssal peridotite. Serpentinites from Hero Fracture zone in Drake Passage have undergone two serpentinization events by oceanic water;first serpentinization event and second serpentinization event. First serpentinization part includes lizardite and antigorite, but second serpentinization part includes only lizardite. First serpentinization event occurred at deeper part (150 - 450oC) than second serpentinization event. During serpentinization, MgO and FeO in olivine are decreased, and those in orthopyroxene and clinopyroxene are increased. The protholith of serpentinites is upper mantle spinel peridotite because of mineral assemblage, Fo89-90 composition in olivines, and Cr-number and Mg-number in spinels. Moreover, the values of (HREE)n (0.3 - 1.6) and no Eu anomaly in serpentinites from Hero Fracture zone indicate that the protholith of serpentinites is upper mantle spinel peridotite.