Petrology and origin of basalts at DSDP Hole 66-487

The volcanism of Central America, according to current theory (Pichler and Weyl, 1973; Stoiber and Carr, 1974; Hey, 1977), is related to the subduction of the Cocos Plate under the North American lithospheric plate and the melting of ocean crust material in the subduction zone (Green and Ringwood, 1968; Dickinson, 1970, Fitton, 1971).
Since Cocos Plate subduction occurs at the rate of more than 7 cm/y. (Hey et al., 1977), basalts underlying upper Miocene sediments of the Middle America Trench outer slope, penetrated in Hole 487 (Fig. 1) during Leg 66 (Moore et al., 1979), should have formed far from their present position if current theory is accurate.
Present manifestations of basaltic magmatism in adjacent areas of the Pacific derive from the axial part of the East Pacific Rise, the Galapagos spreading center, and transform fracture zones.
The question arises: Are there analogs of the Middle America Trench basalts among magmatic cock associated with these modern features, or do the trench basalts have some other origin?

根据现有主流理论（Pichler与Weyl，1973；Stoiber与Carr，1974；Hey，1977），中美洲火山作用与科科斯板块（Cocos Plate）在北美岩石圈板块之下的俯冲过程，以及俯冲带内洋壳物质的熔融作用（Green与Ringwood，1968；Dickinson，1970；Fitton，1971）紧密相关。由于科科斯板块的俯冲速率超过7厘米/年（Hey等，1977），若该现有理论准确，则在第66航次（Moore等，1979）于487号钻孔（图1）钻获的中美洲海沟（Middle America Trench）外坡上中新统沉积物之下的玄武岩，其形成位置应当与当前所处位置相距甚远。太平洋毗邻区域现今的玄武质岩浆作用，均源自东太平洋海隆（East Pacific Rise）轴部、加拉帕戈斯扩张中心（Galapagos spreading center）以及转换断裂带（transform fracture zones）。由此引出一个核心问题：与这些现代地质特征相关的岩浆岩中，是否存在与中美洲海沟玄武岩类似的岩体？抑或海沟玄武岩另有成因？