Geochemistry of boninite and harzburgite of ODP Leg 125 basement samples@en

Holes drilled into the volcanic and ultrabasic basement of the Izu-Ogasawara and Mariana forearc terranes during Leg 125 provide data on some of the earliest lithosphere created after the start of Eocene subduction in the Western Pacific. The volcanic basement contains three boninite series and one tholeiite series. (1) Eocene low-Ca boninite and low-Ca bronzite andesite pillow lavas and dikes dominate the lowermost part of the deep crustal section through the outer-arc high at Site 786. (2) Eocene intermediate-Ca boninite and its fractionation products (bronzite andesite, andesite, dacite, and rhyolite) make up the main part of the boninitic edifice at Site 786. (3) Early Oligocene intermediate-Ca to high-Ca boninite sills or dikes intrude the edifice and perhaps feed an uppermost breccia unit at Site 786. (4) Eocene or Early Oligocene tholeiitic andesite, dacite, and rhyolite form […]

本数据集依托大洋钻探第125航次（Leg 125），在伊豆-小笠原（Izu-Ogasawara）与马里亚纳（Mariana）弧前地体（forearc terranes）的火山及超基性基底中钻进获取的岩心数据，可为西太平洋始新世俯冲作用启动后形成的部分最古老岩石圈（lithosphere）提供研究资料。该火山基底包含3个玻安岩（boninite）系列与1个拉斑玄武岩（tholeiite）系列：
(1) 786号站位外弧高地的深地壳剖面最底部，以始新世低钙玻安岩、低钙古铜安山岩枕状熔岩及岩脉为主；
(2) 786号站位玻安岩建造的主体部分，由始新世中钙玻安岩及其分异产物（古铜安山岩、安山岩、英安岩与流纹岩）构成；
(3) 786号站位的火山建造中侵入有早渐新世中钙至高钙玻安岩岩床或岩脉，其可能为该站位最上部角砾岩单元的物源；
(4) 始新世或早渐新世拉斑质安山岩、英安岩及流纹岩构成[...]