Petrologic-Tectonic Evolution of the Lau Basin

几十年来，弧后盆地的成因一直是海洋地质学家、地球物理学家和岩石学家感兴趣的话题，也是一个有争议的话题。引起这种兴趣的部分原因是它们靠近岛弧，在那里不同类型的岩浆与弧后盆地地壳的形成同步喷发。弧后盆地的热和应力机制令人感兴趣，因为它们代表了伸展构造、陡峭的温度梯度和地幔上涌和熔融，这些地区总体上以古老和冷沉积以及地壳岩石在地幔内相当深的挤压和俯冲为主。本奖项将支持对位于西南太平洋汤加海沟和汤加海脊以西的刘盆地形成的地质和地球化学研究。刘盆地在最近几百万年内开始裂谷，玄武岩化学逐渐从与岛弧有关的玄武岩为主向更正常的弧后盆地玄武岩转变。这种变化意味着玄武岩喷发的地幔源区发生了演化。现场计划将研究混合玄武岩喷发的过渡区和目前部署正常盆地地壳的扩张山脊。随后对回收的样品进行的实验室分析应充分确定弧后熔融制度，并将刘盆地与更充分研究的马里亚纳斯弧后盆地进行比较。来自现场项目的数据还将有助于确定海洋钻探的潜在地点。

The origin of backarc basins has been a topic of much interest and some controversy to marine geologists, geophysicists and petrologists for several decades. This interest stems in part because of their location close to island arcs where different magma types are erupted synchronously with formation of the backarc basin crust. The thermal and stress regimes of backarc basins are of interest because they represent extensional tectonics, steep thermal gradients and mantle upwelling and melting in regions which are dominated overall by compression and subduction of old and cold sediments and crustal rocks to considerable depth within the mantle. The present award will support a geologic and geochemical study of the formation of the Lau Basin which lies to the west of the Tonga Trench and Tonga Ridge in the southwest Pacific. The Lau Basin began rifting within the last few million years and has shown a progressive change in basalt chemistry from a dominance of island arc related basalts to more normal backarc basin basalts. Such a change implies an evolution in the mantle source region from which the basalts are erupted. The field program will examine both the transition regions where mixed basalts have been erupted and the spreading ridge where normal basin crust is presently being emplaced. Subsequent laboratory analyses of recovered samples should fully define the backarc melting regime and allow a comparison of the Lau Basin with the more fully studied Marianas back arc basin. Data from the field program will also aid in defining potential sites for ocean drilling.