Cratonic granulite, pyroxenite and eclogite xenoliths: Archives of continental crust evolution and terrestrial trace element cycling

克拉通麻粒岩、辉石岩和榴辉岩捕虏体：大陆地壳演化和陆地微量元素循环档案

基本信息

批准号：
243877522
负责人：
Dr. Sonja Aulbach
金额：
--
依托单位：
Abteilung Petrologie und Geochemie
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2013
资助国家：
德国
起止时间：
2012-12-31 至 2018-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/243877522?language=en
关键词：
Cratonic granulite pyroxenite eclogite xenoliths

项目摘要

The processes of forming, stabilising, modifying and recycling continental crust (CC) through time are fundamental to understanding the differentiation of the Earth, global geochemical cycling and geodynamics. While the composition and origin of the upper CC are reasonably well known, those of the largely inaccessible lower CC remain enigmatic. Granulites and pyroxenites are actual samples of cratonic lower CC that are sporadically entrained as xenoliths during rare kimberlite or basaltic magmatism. Moreover, some mantle eclogites may represent residues complementary to the early upper CC, while others crystallised near the crust-mantle boundary from mafic melts during later events. Thus, all these lithologies offer important insights into processes attending the formation and modification of the CC, such as crustal differentiation and mass transfer between the crust and mantle at the Moho. I propose to comprehensively study the major-element, trace-element and isotopic composition (U-Pb, Hf-Nd-Sr, O and multiple S isotopes) and redox state of granulite, pyroxenite and eclogite xenoliths from four cratons to constrain (1) the processes, sources, conditions and timing of lower CC formation, modification and growth; (2) the thermophysical properties of granulites and pyroxenites and the resultant thermal and gravitational stability of lower CC; (3) the role of cratonic mantle eclogites in continent formation and their relationship to the lower CC; (4) the abundances, distribution and mobility of high field-strength, chalcophile and siderophile elements, with a focus on accessory rutile, ilmenite and sulphide. Taken together, these studies will have implications for Archaean geodynamics, terrestrial trace-element cycling, and geochemical processes relevant to continent formation.

随着时间的推移，大陆地壳 (CC) 的形成、稳定、改变和循环过程对于理解地球的分异、全球地球化学循环和地球动力学至关重要。虽然上层 CC 的组成和起源已广为人知，但基本上难以接近的下层 CC 的组成和起源仍然是个谜。麻粒岩和辉石岩是克拉通下部 CC 的实际样本，它们在罕见的金伯利岩或玄武岩岩浆作用期间作为捕虏体零星夹带。此外，一些地幔榴辉岩可能代表了早期上CC的残留物，而另一些则在后期事件中从镁铁质熔体中在壳幔边界附近结晶。因此，所有这些岩性都为了解 CC 的形成和改造过程提供了重要的见解，例如莫霍面的地壳分异和地壳与地幔之间的质量传递。我建议全面研究四个克拉通麻粒岩、辉石岩和榴辉岩捕虏体的主量元素、微量元素和同位素组成（U-Pb、Hf-Nd-Sr、O和多种S同位素）和氧化还原状态，以约束（1 ) 低等CC形成、修饰和生长的过程、来源、条件和时间； (2) 麻粒岩和辉石岩的热物理性质以及由此产生的较低CC的热稳定性和重力稳定性； (3) 克拉通地幔榴辉岩在大陆形成中的作用及其与下CC的关系； (4) 高场强、亲铜和亲铁元素的丰度、分布和流动性，重点是副金红石、钛铁矿和硫化物。总而言之，这些研究将对太古代地球动力学、陆地微量元素循环以及与大陆形成相关的地球化学过程产生影响。