Geochemistry and mineralogy of garnet grains from ODP Sample 183-1137A-33R-3,50-53

On Elan Bank, a southwestern promontory of the Kerguelen Plateau in the southern Indian Ocean, we cored an interval of conglomerate and minor sandstone within a thick section of Cretaceous flood basalts. Most of the detritus in these sedimentary rocks is volcanic with the exception of a small amount of conspicuous material of probable continental derivation. The anomalous clasts include several pebbles of gneiss (Nicolaysen et al., 2001, doi:10.1130/0091-7613(2001)029<0235:POPGBG>2.0.CO;2) and garnet sand grains. The presence of continental material on the plateau bears significantly on the interpretation of Indian Ocean basalts (Weis et al., 2001, doi:10.1130/0091-7613(2001)029<0147:OOCCII>2.0.CO;2). The purpose of the present study was to determine the composition of the garnets to provide additional constraints on the nature of the source area.在南印度洋凯尔盖朗高原（Kerguelen Plateau）西南端的埃兰滩（Elan Bank）上，我们在一套厚层白垩纪溢流玄武岩地层中钻取了一段砾岩夹少量砂岩的岩心。这套沉积岩中的绝大多数碎屑均为火山成因，仅含少量特征显著的疑似陆源物质。本次发现的异常碎屑包括若干片麻岩（gneiss）砾石（Nicolaysen等，2001，doi:10.1130/0091-7613(2001)029<0235:POPGBG>2.0.CO;2）与石榴石（garnet）砂粒。该高原上陆源物质的产出，对印度洋玄武岩的成因解释具有重要意义（Weis等，2001，doi:10.1130/0091-7613(2001)029<0147:OOCCII>2.0.CO;2）。本研究旨在测定石榴石的化学成分，以进一步约束物源区的性质。