Re-fertilizing the Earth´s mantle: crust-mantle interaction in (ultra)high pressure settings

地球地幔的再肥沃：（超）高压环境下的壳幔相互作用

• 批准号: 438201206
• 负责人: Professor Dr. Silvio Ferrero
• 金额: --
• 依托单位: Università degli Studi di Cagliari
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2020
• 资助国家: 德国
• 起止时间: 2019-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/438201206?language=en
• 关键词: Re; fertilizing; Earth; mantle; crust

Understanding the chemical evolution of the lithosphere in collisional settings means to understand and quantify the exchange of material between crust and lithospheric mantle. Such exchange is a complex, two-way process: melts and fluids released from both lithospheric mantle and subducted rocks infiltrate the crust, causing anatexis, element redistribution, and thus crustal differentiation, while at the same time, subducted crustal material re-fertilizes the depleted mantle, renewing its capability for production of basaltic magmas. Crust-mantle interaction processes can be directly investigated in orogenic peridotites, portions of lithospheric mantle embedded in collisional orogens. Orogenic peridotites clearly show evidence of mantle heterogeneity, reflected by the presence of centimetric to metric bodies of pyroxenite and eclogite. Experimental studies suggest that mantle heterogeneity contributes substantially to the variability in composition of basalts, both MORB and OIB. Hence, understanding melt-related processes involving pyroxenite and eclogite is the most direct way to unravel the link between crust-mantle interaction, collisional settings, and mantle-related magmatism.Preserved glassy and crystallized melt inclusions (MI) were recently discovered for the first time in pyroxenites in orogenic peridotites and in eclogites in diamond-bearing metasediments of the Bohemian Massif. The melt in the pyroxenites has granitoid composition, with a clear subduction-related trace element signature, whereas preliminary data on the eclogites show a granitic melt generated at depth >100 km. However, mantle (peridotite) melting is expected to generate basalts, whereas eclogite melting mainly produces melts in the Trondhejmite-Tonalite-Granodiorite (TTG) series. Thus the presence of a granitoid melt during peak metamorphism at mantle depth in these rock types is completely unexpected and, to date, unexplained. Our project aims to solve this enigma with a multidisciplinary approach integrating MI studies in pyroxenites and eclogites, experimental petrology, phase equilibria modeling, and isotopic studies. We will identify melt-producing reactions and source of melts, and describe how the physicochemical parameters at the source region influence melt chemistry. Isotope studies will provide solid constraints to define the timeframe in which these melt-related processes occurred, as well as on the chemical affinity of the melt. We will define which chemical tracers can be used to identify and quantify the different contributions from mantle and crust to magmatism in collisional settings. In conclusion, our ambitious project will merge a wealth of novel geochemical data from natural MI in pyroxenites and eclogites with results from experiments and thermodynamic calculations to clarify lithosphere evolution in collisional settings, providing a complete portrait of how crust-mantle interaction processes shape the orogenic roots of the continental crust.

了解碰撞背景下岩石圈的化学演化意味着了解和量化地壳与岩石圈地幔之间的物质交换。这种交换是一个复杂的双向过程：从岩石圈地幔和俯冲岩石中释放的熔体和流体渗入地壳，引起深熔作用，元素重新分配，从而导致地壳分异，而与此同时，俯冲地壳物质重新滋养亏损的地幔，恢复其产生玄武岩浆的能力。壳幔相互作用过程可以在造山橄榄岩中直接研究，橄榄岩是嵌在碰撞造山带中的岩石圈地幔的一部分。造山带橄榄岩清楚地表明地幔不均匀性的证据，反映在厘米到公制机构的辉石岩和榴辉岩的存在。实验研究表明，地幔的不均匀性在很大程度上有助于玄武岩，MORB和OIB组成的变化。因此，了解熔体相关的过程，涉及辉石岩和榴辉岩是最直接的方式来解开壳幔相互作用，碰撞设置，和地幔相关的岩浆mammatization.Preserved玻璃和结晶熔体包裹体（MI）最近首次发现在辉石中的造山橄榄岩和榴辉岩中的金刚石变质沉积的波希米亚地块。辉石岩中的熔体具有花岗岩成分，具有明显的俯冲相关微量元素特征，而榴辉岩的初步数据显示，花岗岩熔体产生于>100 km的深度。然而，地幔（橄榄岩）熔融预计将产生玄武岩，而榴辉岩熔融主要产生熔体中的Trondhejmite-Tonalite-Granodiomite（TTG）系列。因此，在这些岩石类型中，在地幔深度的峰期变质作用期间存在花岗岩类熔体是完全出乎意料的，并且迄今为止无法解释。我们的项目旨在解决这个谜与多学科的方法集成MI研究辉石和榴辉岩，实验岩石学，相平衡建模，同位素研究。我们将确定熔体产生反应和熔体的来源，并描述如何在源区的物理化学参数影响熔体化学。同位素研究将提供坚实的约束，以确定这些熔化相关过程发生的时间范围，以及对熔体的化学亲和力。我们将定义哪些化学示踪剂可用于识别和量化地幔和地壳在碰撞背景下对岩浆活动的不同贡献。总之，我们雄心勃勃的项目将合并丰富的新的地球化学数据，从自然MI的辉石岩和榴辉岩的实验和热力学计算的结果，以澄清岩石圈演化碰撞设置，提供一个完整的肖像壳幔相互作用过程如何塑造大陆地壳的造山根源。