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

在2016/17年冬季，ICDP钻探计划“阿曼钻探项目”（OmanDP）成功穿透了阿曼蛇绿岩的下部古结壳，这是世界上最大，暴露最好，研究最多的海底暴露海洋岩石圈部分。这些岩心长400米，成功率接近100%，是进行岩相学、岩石学、地球化学和结构研究的独特宝贵资源，并确保能够获得快速扩张的洋壳关键区域的连贯剖面：最下层辉长岩（岩心GT 1）、层状辉长岩向片理化辉长岩过渡（岩心GT 2）和辉长岩/岩脉过渡（岩心GT3）。通过阿曼古地壳的深成地壳钻孔断面可以被视为罗塞塔石碑，用于了解覆盖地球约三分之一的快速扩展的海洋地壳的吸积和冷却模式。拟议的项目侧重于四个主要科学目标：（1）探讨辉长岩/岩墙过渡带轴向熔融透镜动力学;（2）研究中地壳层状辉长岩与片理化辉长岩过渡带的性质;（3）了解深部层状地壳成层机制;（4）验证了含角闪石斑（脉）形成于岩浆-变质体系是地壳深部初始冷却的结果这一假说。我们计划整合岩石学，岩石学，地球化学和微观结构的工作（晶格优先取向，使用电子背散射衍射）分层，叶理和变纹理辉长岩。研究结果将为深入了解轴向熔融透镜和周围晶体泥内的岩浆和初始热液过程奠定基础，这些晶体泥在洋中脊下熔融柱的末端形成岩浆室。

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.