In-situ U-Pb age dating and the oxygen isotopic composition of accessory minerals in jadeitites: investigating the timing of fluid release and fluid-rock interactions in subduction zones

原位 U-Pb 年龄测定和硬玉中副矿物的氧同位素组成：研究俯冲带中流体释放的时间和流体-岩石相互作用

• 批准号: 508778581
• 负责人: Dr. Andreas Hertwig
• 金额: --
• 依托单位: John de Laeter Research Centre
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2022
• 资助国家: 德国
• 起止时间: 2021-12-31 至 2023-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/508778581?language=en
• 关键词: situ; Pb; age; dating; oxygen

When crustal rocks return into Earth’s mantle at subduction zones, fluids released from subducted material initiate melting in the mantle wedge which ultimately leads to the build-up of new continental crust and venting of volcanic gases into the atmosphere. Since fluids act as major agents of mass and energy transfer in such a setting, understanding how and when fluids are released is of paramount importance for constructing a coherent picture of this ongoing global material recycling at subduction zones. Jadeitites – rocks composed mainly of the sodic clinopyroxene jadeite - either directly witnessed such subduction-zone fluids or represent crystallized portions of these fluids themselves. The timing of fluid release(s) could then be constrained by determining the formation ages of jadeitites by dating certain accessory minerals such as zircon. However, zircon has the ability to survive partial melting and high-grade metamorphism which leads to some ambiguity concerning its primary origin in jadeitites. In this study it is therefore proposed to perform in-situ U-Pb dating by secondary ion mass spectrometry (SIMS) of other common accessories in jadeitites including titanite, rutile, and apatite which can often be directly linked to the effect of fluids. In combination with SIMS oxygen isotope analysis of accessory phases, the proposed investigations can provide valuable information about jadeitite formation and, ultimately, fluid production in subduction zones.

当地壳岩石在俯冲带返回地球的地幔中时，从俯冲材料中释放出的烟道会在地幔楔中融化，最终导致新的连续地壳和火山气通向大气中。由于在这种环境中，烟道是质量和能量转移的主要代理，因此了解如何以及何时释放流体对于构建俯冲区域正在进行的全球材料回收的连贯图片至关重要。 Jadeitetes - 主要由Sodic clusteryroxene Jade组成的岩石 - 直接见证了这种俯冲区域的烟道或代表这些液体本身的结晶部分。然后，可以通过与某些辅助矿物（如锆石）的日期来确定玉式的形成年龄来限制流体释放的时间。然而，锆石具有在部分熔化和高级变质的能力中生存的能力，这导致了关于其主要起源在翡翠的歧义。因此，在这项研究中，提议通过二十离子质谱（SIM）（SIMS）进行原子u-PB，包括钛，金红石和磷灰石，通常可以与流体的效果直接相关。结合SIMS氧同位素分析辅助阶段，提出的研究可以提供有关翡翠形成以及最终在俯冲区中流体产生的宝贵信息。