Identifying clinopyroxene-sulphide co-precipitation, rejuvenation mechanisms and platinum-group element fractionation processes in young continental mantle roots

利用激光烧蚀电感耦合等离子体质谱（LA-ICP-MS）技术研究年轻次大陆岩石圈地幔（SCLM）中硫化物的铂族元素（PGE）系统。我们的目的是为大陆岩石圈复兴提供一个亲铁的视角：一个以橄榄石为代价引入辉石的过程。这种再生已被提议在轻度衰竭橄榄岩的预期成分范围内进行，似乎比以前预期的更相关。然而，这一返青概念并没有解决亲铁矿物的演化问题，因此也没有解决此类大陆地幔根的PGE含量问题。通过使用LAICP- MS分析一组特征良好的中阿特拉斯橄榄岩捕虏体的硫化物组分，这些捕虏体具有异常良好的全岩PGE， Cu和主要元素系统，经历了模态恢复，我们将能够(a)表征整个岩石PGE组成的硫化物矿物学特征；(b)确定耦合或解耦的硫化物-硅酸盐和-氧化物在脱水过程中的沉淀和消耗；(c)研究从SCLM中提取硫化物的PGE分馏的潜力。这一数据采集对于来自克拉通外大陆地幔根的橄榄岩来说是独一无二的，因此可以进一步得出岩浆过程中经济相关元素的流动性和岩石圈地幔中PGE系统的长期二分法的结论。

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) techniques shall be utilized to investigate platinum-group elements (PGE) systematics of sulphides in young subcontinental lithospheric mantle (SCLM). We aim at providing a siderophile perspective on continental lithosphere rejuvenation: a process of pyroxene introduction at the expense of olivine. This rejuvenation has been proposed to operate within the compositional range anticipated for mildly depleted peridotite and appears to be more relevant than previously anticipated. However, this rejuvenation concept does not address the evolution of siderophile minerals and thus the PGE content of such continental mantle roots. By analyzing the sulphide fraction for the PGE content using LAICP- MS from a suite of well-characterized Middle Atlas peridotite xenoliths with unusually well correlated whole-rock PGE, Cu and major element systematics that has experienced modal rejuvenation we will be able to (a) characterize the sulphide mineralogy responsible for the whole rock PGE composition, (b) identify coupled or decoupled sulphide-silicate and –oxide precipitation and consumption during metasomatism and (c) study the potential for PGE fractionation in sulphides from SCLM. This data acquisition will be unique for peridotites from off-cratonic continental mantle roots and thus will allow further conclusion on the mobility of economically relevant elements during magmatic processes and the secular dichotomy of PGE systematics in the lithospheric mantle.