Understanding axial melt lens dynamics and lower crust accretion at fast-spreading mid-ocean ridges: new insights from drill cores obtained by the ICDP Oman Drilling Project

2016/17年冬季，ICDP钻井项目“阿曼钻井项目”（OmanDP）成功穿透了阿曼蛇绿岩的下古地壳，这是世界上最大、暴露程度最高、研究最多的海底暴露海洋岩石圈部分。岩心长400米，恢复成功率接近100%，使其成为岩石学，岩石学，地球化学和构造研究的独特宝贵资源，并确保在快速扩张的海洋地壳的关键区域：最底部的层状辉长岩（岩心GT1），层状到片理辉长岩过渡（岩心GT2）和辉长岩/岩脉过渡（岩心GT3）中获得连贯剖面。钻穿阿曼古地壳深部地壳的横断面可以被视为了解覆盖地球约三分之一的快速扩张的海洋地壳的吸积和冷却模式的罗塞塔石碑。该项目主要有四个主要的科学目标：(1)探索辉长岩/岩脉过渡的轴向熔融透镜动力学；(2)研究中地壳层状辉长岩与片理辉长岩过渡的性质；(3)了解深层层状地壳的成层过程机制；(4)验证岩浆变质体系中形成的含角闪岩斑块/脉是深部地壳初始冷却的结果。我们计划将岩相学、岩石学、地球化学和微结构工作（利用电子后向散射衍射的晶格优选方向）整合到层状、片理和变质辉长岩中。这些结果将为深入了解岩浆和初始热液过程在轴向熔融透镜和周围的晶体糊内建立基础，这些晶体糊形成了中洋脊下熔融柱末端的岩浆房。

In winter 2016/17, the ICDP drilling initiative "Oman Drilling Project" (OmanDP) successfully penetrated the lower paleocrust of the Oman ophiolite, the world’s largest, best-exposed, and most-studied section of subaerially exposed oceanic lithosphere. The cores are 400 m long and were recovered with a nearly 100 % success rate, making them a uniquely valuable resource for petrographical, petrological, geochemical and structural study and ensuring access to coherent sections throughout critical zones of a fast-spreading oceanic crust: the lowermost layered gabbros (core GT1), the layered to foliated gabbro transition (core GT2), and the gabbro/dike transition (core GT3). The drilled transects through the plutonic crust of the Oman paleocrust can be regarded as a Rosetta Stone for understanding the mode of accretion and cooling of fast-spread oceanic crust that covers about one third of our planet. The proposed project focuses on four main scientific targets: (1) exploring of axial melt lens dynamics at the gabbro/dike transition, (2) investigating the nature of the transition between layered and foliated gabbro in the mid-crust (3) understanding the mechanisms of layer-forming processes in the deep, layered crust, and (4) testing the hypothesis that amphibole-bearing patches/veins formed in the magmatic-metamorphic regime are the results of initial cooling of the deep crust. We plan to integrate petrographical, petrological, geochemical and micro-structural work (lattice preferred orientation using electron backscattering diffraction) on layered, foliated and varitextured gabbros. The results will establish the basis for a deep understanding of the magmatic and initial hydrothermal processes within the axial melt lens and surrounding crystal mush, which form the magma chambers at the end of the melting column beneath mid-ocean ridges.