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蛇绿岩是陆地上最大、暴露最好和研究最多的海洋岩石圈。它是ICDP钻探计划“阿曼钻探项目”的目标，该项目将提高我们对创建和修改大洋地壳和浅地幔的过程范围的了解，从其在海底的起源到其在山脉的现代环境。阿曼。在这一国际综合发展项目倡议的范围内，本项目以阿曼南部蛇绿岩Wadi Gideah三个不同地点的钻探样品为基础，重点研究快速扩张的洋壳热液冷却造成的增生、演化和蚀变机制。为了达到这一目标，我们将在微观和宏观尺度上研究连贯的部分。这是唯一的方法来测试现有的，地壳增生，MORB分异和深部热液冷却的理论模型，通过比较成分与。深度剖面与模型的预测。结合详细的岩相调查，我们将使用广泛的分析方法，对主要和微量元素以及多种硫、锶和氧同位素进行大宗岩石和矿物分析。在该项目中，我们解决了四个具体目标：（1）地壳增生和分异机制。我们的初步研究结果指出，显着的原位结晶的深度，这是在对比常见的“辉长岩冰川”模型的地壳增生。GT 1和GT 2的钻探将穿透下地壳更深处的关键区域，致力于为这一复杂问题提供新的认识。(2)临界岩墙/辉长岩过渡期内的岩浆/变质/热液过程。变质岩中代表夹在轴向熔融透镜和席状岩脉之间的导电边界层的特征矿物环带将使我们能够提取轴向熔融透镜的地球动力学的时间尺度。穿透轴向熔化透镜层位的站点GT 3致力于提供该问题的关键部分。(3)系统地横切辉长岩剖面的热液化断裂带的作用。详细的岩相学和分析研究将表明，这些区域是否代表通道的海水衍生流体渗透在非常高的温度下的地壳深部，从而提供了一个有效的散热机制。钻孔GT 1和GT 2将被精确定位以穿透这些区域。(4)海水衍生流体引起的下地壳岩石蚀变的强度、温度和范围。GT 1 -3钻孔将提供适当的样本材料来解决这个复杂的问题。多种硫、氧和锶同位素组成的变化将使我们能够量化背景蚀变过程的强度，以及可以追踪海水衍生流体的循环深度。