Understanding the crust-mantle transition from fast-spreading mid-ocean ridges: experiments and analytical studies using ICDP OmanDP drill core samples

了解快速扩张的大洋中脊的壳幔转变：使用 ICDP OmanDP 钻芯样本进行实验和分析研究

• 批准号: 439183043
• 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
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/439183043?language=en
• 关键词: Understanding; crust; mantle; transition; fast

In winter 2017/18, the ICDP drilling initiative "Oman Drilling Project" (OmanDP) successfully penetrated the paleo-crust-mantle transition of the Oman ophiolite, which is regarded as the world’s largest, best-exposed, and most-studied section of subaerially exposed oceanic lithosphere. The cores are 400 m (CM1) and 300 m (CM2) long and were recovered with a nearly 100 % success rate, making them a uniquely valuable resource for petrographical, petrological, and geochemical study and ensuring access to coherent sections throughout the enigmatic transition between the uppermost mantle and the lowermost crust of fast-spreading ridge systems. The drilled transects through the crust-mantle transition of the Oman paleo-crust, provide coherent long sections of the lowermost layered gabbros, massive dunites, troctolites, and wehrlites without any gaps, and can be regarded as a Rosetta Stone for understanding the magmatic processes and the mode of deep crustal accretion, in a depth window that was not accessible in recent oceans so far. The proposed project focuses on several scientific targets following two different methodological approaches: (1) In an experimental study we aim to simulate equilibrium and fractional crystallization in a parental MORB-type system relevant for a setting of initiation of a subduction zone at the transition between "dry" (like East Pacific Rise) and "wet" conditions (Izu-Bonin-Mariana arc-type crust). In a subproject we aim to quantify the trace element distribution between spinel/chromite and MORB melt. (2) The second approach focus on petrological and geochemical investigations on the rocks from the CM1 and CM2 drill cores in order to clarify the mechanism of massive dunite formation in the crust-mantle transition, and establish the exact mode of differentiation/fractionation within the lowermost crust. The results of both complementary approaches will provide a basis for a deep understanding of the magmatic processes at the base of fast-spreading crust in an environment of initial subduction, and will provide fundamental knowledge about the geodynamics of accretion of fast-spreading oceanic crust.

在2017/18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古地壳-地幔过渡，该蛇绿岩被认为是世界上最大，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（CM 1）和300米（CM 2），成功率接近100%，使其成为岩石学、岩石学和地球化学研究的独特宝贵资源，并确保在快速扩张的山脊系统的最上地幔和最下地壳之间的神秘过渡期间获得连贯的剖面。通过阿曼古地壳的壳幔过渡钻孔断面，提供连贯的最低分层辉长岩，块状纯橄榄岩，troctolites，和wehrlites没有任何差距的长段，并可以被视为罗塞塔石碑了解岩浆过程和深地壳增生的模式，在深度窗口，这是目前为止在现代海洋不可访问。拟议的项目侧重于几个科学目标，采用两种不同的方法：（1）在一项实验研究中，我们的目标是模拟平衡和分离结晶的母MORB型系统有关的设置开始俯冲带之间的“干”（如东太平洋隆起）和“湿”条件（伊豆-小笠-马里亚纳弧型地壳）。在一个子项目中，我们的目标是量化尖晶石/铬铁矿和MORB熔体之间的微量元素分布。(2)第二种方法是通过对CM 1和CM 2岩心岩石的岩石学和地球化学研究，阐明壳幔过渡期块状纯橄榄岩的形成机制，并建立最低地壳分异/分馏的精确模式。这两种互补方法的结果将为深入了解初始俯冲环境中快速扩张地壳底部的岩浆过程提供基础，并将提供关于快速扩张洋壳增生地球动力学的基本知识。