Long in-situ sections in the Wadi Gideah, Oman ophiolite: The key for understanding the mechanism of accretion, magmatic evolution and cooling of lower fast-spread oceanic crust

阿曼蛇绿岩 Wadi Gideah 的长原位剖面：了解下部快速扩张洋壳的增生、岩浆演化和冷却机制的关键

• 批准号: 270849521
• 负责人: Dr. Carl-Dieter Garbe-Schönberg
• 金额: --
• 依托单位: Institut für Mineralogie
• 依托单位国家: 德国
• 项目类别: Infrastructure Priority Programmes
• 财政年份: 2015
• 资助国家: 德国
• 起止时间: 2014-12-31 至 2019-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/270849521?language=en
• 关键词: Long; situ; sections; Wadi; Gideah

The Samail ophiolite in the Sultanate Oman and the United Arab Emirates is the largest, best-exposed, and most-studied piece of oceanic lithosphere on land. It is the target for an ICDP drilling initiative, "the Oman Drilling Project", which will improve our understanding of the spectrum of processes that create and modify the oceanic crust and shallow mantle from its origin on the ocean floor to its modern setting in the mountains of Oman. Embedded within this ICDP initiative, the project presented here focuses on the mechanisms of accretion, evolution and alteration by hydrothermal cooling of fast-spreading oceanic crust, based on samples to be drilled at three different sites in the Wadi Gideah in the southern Oman ophiolite. To reach this goal we will investigate coherent sections on a micro- and macro-scale. This is the only way to test the available, theoretical models for crustal accretion, MORB differentiation, and deep hydrothermal cooling by comparing composition-vs.-depth profiles with the predictions of the models. In combination with detailed petrographic surveys, we will use a wide spectrum of analytical methods for bulk rock and mineral analysis of major and trace elements as well as multiple sulfur, strontium and oxygen isotopes. Within the project we address four specific objectives:(1) Crustal accretion and mechanisms of differentiation. Our preliminary results point to significant in-situ crystallization in the depth which is in contrast to the common "gabbro glacier" model for crustal accretion. The drilling at sites GT1 and GT2 will penetrate critical zones in the deeper parts of the lower crust, dedicated to shed new light on this complex issue.(2) Magmatic/metamorphic/hydrothermal processes within the critical dike/gabbro transition. Characteristic mineral zoning in metamorphic rocks representing the conducting boundary layer sandwiched between the axial melt lens and the sheeted dikes will enable us to extract time scales of the geodynamics of the axial melt lens. Site GT3, penetrating the axial melt lens horizon, is dedicated to provide key sections for this issue.(3) Role of hydrothermalized fault zones crosscutting the gabbro section in a systematic way. Detailed petrographic and analytical studies will show whether these zones represent pathways where channeled seawater-derived fluids penetrated at very high temperatures the deep crust, thereby providing an efficient mechanism of heat removal. The drilling GT1 and GT2 will be precisely sited to penetrate such zones.(4) Intensity, temperature, and extent of lower crustal rock alteration by seawater-derived fluids. The drillings GT1-3 will provide appropriate sample material to address this complex issue. Variation of the compositions of multiple sulfur, oxygen, and strontium isotopes will enable us to quantify the intensity of background alteration processes and how deep the circulation of a seawater-derived fluid can be traced.

阿曼苏丹国和阿拉伯联合酋长国的Samail Ophiolite是陆地上最大的，最大，最受欢迎的海洋岩石圈。它是ICDP钻探计划“阿曼钻探项目”的目标，它将提高我们对创建和修改海洋壳和浅层地幔的过程的理解阿曼山。此处介绍的项目嵌入了该ICDP计划中，重点介绍了通过快速扩张的海洋地壳的水热冷却的机制，基于在南部奥曼属岩的Wadi Gideah的三个不同地点进行钻探的样品。为了达到这个目标，我们将研究微观和宏观尺度上的连贯部分。这是测试可用的构图，医疗差异和深水热冷却的可用理论模型，通过比较组合-VS.深入的剖面与模型的预测。结合详细的岩石学调查，我们将使用广泛的分析方法来进行大量岩石以及对主要元素和痕量元素以及多种硫，跨质和氧同位素的矿物分析。在项目中，我们解决了四个特定目标：（1）分化的地壳积聚和机制。我们的初步结果表明，深度的明显原位结晶与地壳积聚的常见“ Gabbro冰川”模型形成鲜明对比。位点GT1和GT2的钻孔将穿透下层地壳更深的部分的关键区域，专门为这一复杂问题提供了新的启示。（2）岩浆/变质/变质/水热过程中关键的堤坝/GABBRO过渡过程中。代表夹杂在轴向熔体透镜和薄堤之间的导电边界层的变质岩石中的特征矿物分区将使我们能够提取轴向熔体透镜的地球动力学的时间尺度。穿透轴向熔体透镜层的位点GT3专门为此问题提供关键部分。（3）水热断层区的作用以系统的方式交叉GABBRO部分。详细的岩石学和分析研究将显示这些区域是否代表在非常高温下渗透的海水衍生的流体在深层外壳中渗透的途径，从而提供了有效的去除热量机制。钻孔GT1和GT2将精确地渗透到此类区域。（4）海水衍生的流体改变地壳岩石改变的强度，温度和程度。钻探GT1-3将提供适当的样品材料来解决这一复杂问题。多种硫，氧和锶同位素的组成的变化将使我们能够量化背景改变过程的强度以及可以追溯到海水衍生的流体的循环深度。