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Assimilation, contamination and felsic melt generation at the top of the axial melt lens at fast-spreading oceanic crust: Combined geochemical and experimental investigations at the dike/gabbro transition from IODP Site 1256 (East Pacific Rise)

快速扩张的洋壳轴向熔体透镜体顶部的同化、污染和长英质熔体生成：对 IODP 站点 1256（东太平洋海隆）的岩脉/辉长岩转变进行地球化学和实验联合研究

基本信息

批准号：
224563012
负责人：
Professor Dr. Jürgen Koepke
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：
2012
资助国家：
德国
起止时间：
2011-12-31 至 2015-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/224563012?language=en
关键词：
Assimilation contamination felsic melt generation

项目摘要

The formation and evolution of oceanic lithosphere at mid-ocean ridges is one of the dominant processes in the chemical differentiation and physical evolution of our planet. The about 60.000 km long mountain chain of mid-ocean ridges is associated with 90% of Earth´s volcanism and about 25 % of heat release of the Earth. Although so important, major issues on the mode of magmatic accretion, the way how the lower crust is hydrothermal cooled, or the geological meaning of the seismic Layer 2-3 boundary are still poorly understood. To solve critical questions related to the geodynamics of fast-spreading mid-ocean ridge systems, the IODP drilling campaign "Superfast Spreading Crust" (Leg 206, Expeditions 309, 312, 335) at Site 1256 was initiated. Site 1256 is located on 15 million year old crust formed at the East Pacific Rise during an episode of superfast ocean spreading (>200 mm/yr full rate). It is one of the major achievements of this campaign that, for the first time in IODP, a complete section through intact crust from lavas via sheeted dikes into the uppermost gabbros was drilled. One characteristic of the lowermost sheeted dikes as well as in the gabbroic section of the 1256 drill core, is the abundance of felsic rocks which show significant differences in compositions, modes of emplacement, and relations to the various background rocks. They provide the key for understanding the complex and intimate coupling between magmatic, metamorphic and hydrothermal processes at the top of the axial melt lens in fast-spreading mid-ocean ridge systems. In order to understand the different mechanisms of evolved melt formation within a spectrum of magmatic processes from MORB differentiation to assimilation-partial melting of previously hydrothermally altered material and its role in contaminating MORB, we attempt to start a systematic investigation on the geochemistry and petrology of these rocks. For this, major and trace element geochemical methods will be applied to bulk rocks as well as to mineral phases. The results will enable us to unravel the principal magmatic endmember processes involved, and their role as contaminator for primary MORB. In a second part of the project we plan to apply experimental techniques - crystallization and partial melting experiments using natural systems recovered at Site 1256 - in order to test, confirm, or modify those models derived by our geochemical and petrological results. The combination of both approaches will offer considerable insight into the complex interfering magmatic, metamorphic, and hydrothermal processes ongoing at the top of axial melt lens in fast-spreading mid-ocean ridge systems. Details on this are poorly known up to now, and the exceptional rocks of the dike-gabbro transition at Site1256 drilled by IODP provide the key for improving our understanding.

大洋中脊岩石圈的形成和演化是地球化学分异和物理演化的主导过程之一。大约60.000公里长的海洋中脊山脉与地球90%的火山活动和大约25%的地球热量释放有关。虽然如此重要，但关于岩浆增生模式、下地壳如何热液冷却或地震层2-3边界的地质意义等主要问题仍然知之甚少。为了解决与快速扩展的洋中脊系统的地球动力学有关的关键问题，在1256号站点启动了IODP钻探活动“超快速扩展地壳”（第206航次，第309、312、335次考察）。1256号地点位于东太平洋海隆1500万年前的地壳上，是在一次超高速海洋扩张（>200毫米/年）期间形成的。这是该活动的主要成就之一，在IODP中，第一次钻取了从熔岩通过席状岩脉到最上部辉长岩的完整地壳。最下面的席状岩脉以及1256号岩芯的辉长岩段的一个特征是长英质岩的丰度，长英质岩在成分、侵位方式以及与各种背景岩的关系方面表现出显著差异。它们为理解快速扩张的洋中脊系统中轴向熔融透镜顶部的岩浆、变质和热液过程之间复杂而密切的耦合提供了关键。为了了解不同的机制内的岩浆过程从MORB分化同化部分熔融以前的热液蚀变物质和它的作用，污染MORB的演化熔体形成的光谱，我们试图开始对这些岩石的地球化学和岩石学的系统调查。为此，主量元素和微量元素地球化学方法将应用于大块岩石以及矿物相。这些结果将使我们能够解开主要的岩浆端元过程中所涉及的，和他们的作用作为污染物的初级MORB。在该项目的第二部分，我们计划应用实验技术-结晶和部分熔融实验，使用自然系统恢复在站点1256 -为了测试，确认，或修改这些模型，我们的地球化学和岩石学的结果。这两种方法的结合将提供相当多的洞察复杂的干扰岩浆，变质，和热液过程中正在进行的顶部轴向熔体透镜在快速扩展的洋中脊系统。关于这一点的详细资料至今知之甚少，而IODP钻探的1256站点脉岩-辉长岩过渡带的特殊岩石为我们提供了提高认识的关键。

项目成果

期刊论文数量（4）

专著数量（0）

科研奖励数量（0）

会议论文数量（0）

专利数量（0）

Trace elements in anatectic products at the roof of mid-ocean ridge magma chambers: An experimental study

DOI：
10.1016/j.chemgeo.2017.03.004
发表时间：
2017-05
期刊：
Chemical Geology
影响因子：
3.9
作者：
M. Erdmann;L. Fischer;E. Deloule;J. Koepke
通讯作者：
M. Erdmann;L. Fischer;E. Deloule;J. Koepke

Apatite in the dike-gabbro transition zone of mid-ocean ridge: Evidence for brine assimilation by axial melt lens

DOI：
10.2138/am-2017-5906
发表时间：
2017-03
期刊：
American Mineralogist
影响因子：
3.1
作者：
Chao Zhang;J. Koepke;M. Albrecht;I. Horn;F. Holtz
通讯作者：
Chao Zhang;J. Koepke;M. Albrecht;I. Horn;F. Holtz

A Practical Method for Accurate Measurement of Trace Level Fluorine in Mg‐ and Fe‐Bearing Minerals and Glasses Using Electron Probe Microanalysis

DOI：
10.1111/j.1751-908x.2015.00390.x
发表时间：
2016-09
期刊：
Geostandards and Geoanalytical Research
影响因子：
3.8
作者：
C. Zhang;J. Koepke;Lian-Xun Wang;Paul Eric Wolff;S. Wilke;A. Stechern;R. Almeev;F. Holtz
通讯作者：
C. Zhang;J. Koepke;Lian-Xun Wang;Paul Eric Wolff;S. Wilke;A. Stechern;R. Almeev;F. Holtz

Felsic Plutonic Rocks from IODP Hole 1256D, Eastern Pacific: Implications for the Nature of the Axial Melt Lens at Fast-Spreading Mid-Ocean Ridges