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

陆壳的形成、稳定、改造和再循环过程是理解地球分异、全球地球化学循环和地球动力学的基础。虽然上CC的组成和成因是众所周知的，但基本上无法进入的下CC的组成和成因仍然是个谜。花岗岩和辉石岩是克拉通下部CC的实际样品，在罕见的金伯利岩或玄武岩岩浆作用期间零星地以捕虏体的形式夹带。此外，一些地幔榴辉岩可能代表了与早期上CC互补的残留物，而另一些榴辉岩则是在后期事件期间镁铁质熔体在壳幔边界附近结晶的。因此，所有这些岩性都为参与CC形成和改造的过程提供了重要的见解，如莫霍面的地壳分异和壳幔之间的物质转移。建议对4个克拉通的麻粒岩、辉石岩和榴辉岩包体的主量元素、微量元素和同位素组成(U-Pb、Hf-Ndsr、O和多个S同位素)和氧化还原状态进行综合研究，以约束(1)下CC形成、变质和生长的过程、来源、条件和时间；(2)麻粒岩和辉石岩的热物理性质及其形成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、亲硫、亲铁元素的丰度、分布和活动性，重点是副金红石、钛铁矿和硫化物。综上所述，这些研究将对太古宙地球动力学、陆地微量元素循环和与大陆形成相关的地球化学过程产生影响。

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.