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.

2017/2018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壳幔过渡带，该区域被认为是世界上最大、暴露最好、研究最多的部分。暴露在地面的海洋岩石圈的岩心长 400 m (CM1) 和 300 m (CM2)，是用近乎100% 的成功率，使它们成为岩石学、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中获得连贯的剖面。 -阿曼古地壳的地幔转变，提供了最下层的辉长岩、块状沙丘、斜长岩和韦尔岩的连贯长部分，而没有该项目可以被视为了解岩浆过程和深部地壳增生模式的罗塞塔石碑，该深度窗口迄今为止在近代海洋中无法实现。该项目重点关注遵循两种不同方法论的几个科学目标。方法：（1）在一项实验研究中，我们的目标是模拟母体 MORB 型系统中的平衡和分步结晶，该系统与“干”（如东太平洋海隆）和“湿”之间过渡时俯冲带的启动设置相关。 “ “ 状况（Izu-Bonin-Mariana 弧型地壳）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) 第二种方法侧重于 CM1 和 CM1 岩石的岩石学和地球化学研究。 CM2钻探岩心旨在阐明壳幔过渡过程中块状纯橄榄岩的形成机制，并建立最下地壳内分异/分异的精确模式。两种互补方法的结果将为深部研究提供基础。了解初始俯冲环境中快速扩张的地壳底部的磁性过程，并将提供有关快速扩张的海洋地壳增生的地球动力学的基础知识。