Tectonic origin of supra-subduction zone ophiolites from the three-dimensional geochemical structure of the lava pile

蛇绿岩是保存在陆地上的洋壳碎片，经常被用来推断洋壳的内部结构和形成过程。然而，大多数蛇绿岩并不是在典型的大洋中脊环境中形成的，而是在靠近以前的俯冲带形成的。它们形成的确切构造环境已经争论了40多年。如果蛇绿岩代表俯冲启动事件期间形成的弧前地壳，那么它们为俯冲带的启动提供了洞察，这是板块构造中一个悬而未决的问题。如果蛇绿岩形成于弧后或板块边缘环境，它们可能是洋壳内部结构的有用类似物。如果它们形成于海脊-海沟-海沟或海脊-海沟-变换三重结合部，则可以用来研究地幔楔形结构和过程。不同的构造模型预测了蛇绿岩熔岩的地球化学随时间和空间的不同变化。我们将绘制塞浦路斯特罗多斯蛇绿岩的3D化学结构图，它是保存最完好、暴露最好的蛇绿岩之一。我们将对新鲜的火山玻璃进行常量和微量元素的微量分析，以避免蚀变的影响。蛇绿岩北缘和南缘特罗多斯火山剖面的详细高分辨率取样将被用来确定岩浆作用的化学演化。来自特罗多斯熔岩序列不同地层的熔岩的新的39Ar-40Ar年龄将用于确定火山活动的年龄和持续时间，以及岩浆活动的化学演化速率随时间的变化。我们新的地球化学和年代学数据将被用来检验特罗多斯蛇绿岩构造起源的假说。

Ophiolites are fragments of oceanic crust preserved on land, and are often used to infer the internal structure of the oceanic crust and the processes by which it is formed. However, most ophiolites were not formed in typical mid-ocean ridge settings, and instead appear to have formed close to former subduction zones. The exact tectonic setting in which they were formed has been debated for over 40 years. If ophiolites represent fore-arc crust formed during subduction initiation events, then they provide insights into the initiation of subduction zones, an outstanding unresolved question in plate tectonics. If ophiolites were formed in back-arc or plate edge settings they may represent useful analogues for the internal structure of oceanic crust. If they were formed at a ridge-trench-trench or ridge-trench-transform triple junction then they could be used to investigate mantle wedge structure and processes. Different tectonic models predict different geochemical variations in ophiolite lavas with space and time. We will map out the 3D gechemical structure of the Troodos Ophiolite of Cyprus, one of the best preserved and exposed ophiolites. We will use major and trace element microanaysis of fresh volcanic glass in order to avoid the effects of alteration. Detailed high resolution sampling of sections through the Troodos volcanic section on both the northern and southern margins of the ophiolite will be used to determine the chemical evolution of magmatism. New 39Ar-40Ar ages for lavas from different stratigraphic levels in the Troodos lava sequence will be used to determine the age and duration of the volcanism, and rates of chemical evolution of magmatism with time. Our new geochemical and geochronological data will be used to test hypotheses for the tectonic origin of the Troodos ophiolite.