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

了解碰撞环境下岩石圈的化学演化意味着了解和量化地壳和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释放的熔体和流体渗入地壳，导致深熔、元素重新分配，从而导致地壳分异，同时，俯冲的地壳物质使枯竭的地幔重新肥沃，恢复其产生玄武岩岩浆的能力。壳幔相互作用过程可以在造山橄榄岩中直接研究，造山橄榄岩是埋藏在碰撞造山带中的岩石圈地幔的一部分。造山橄榄岩清楚地显示出地幔的不均一性，反映在辉石岩和榴辉岩的厘米到公制岩体的存在上。实验研究表明，地幔的非均质性对玄武岩成分的变化有很大的贡献，无论是MORB还是OIB。因此，了解辉石岩和榴辉岩的熔体相关过程是揭示壳幔相互作用、碰撞环境和与地幔有关的岩浆岩之间联系的最直接途径。最近，在造山橄榄岩中的辉石岩和波西米亚地块含金刚石变质岩中的榴辉岩中首次发现了保存完好的玻璃状和结晶熔体包裹体(MI)。辉石岩中的熔体具有花岗岩类成分，具有明显的与俯冲有关的微量元素特征，而榴辉岩的初步数据显示，在&gt；100公里深处产生了花岗岩熔体。然而，地幔(橄榄岩)熔融预计会产生玄武岩，而榴辉岩熔融主要产生Trondhejmite-Tonalite-GranoDiorite(TTG)系列的熔体。因此，在这些岩石类型中，在地幔深处的峰期变质过程中，花岗岩类熔体的存在是完全出乎意料的，到目前为止，也无法解释。我们的项目旨在通过整合辉石岩和榴辉岩的MI研究、实验岩石学、相平衡模拟和同位素研究的多学科方法来解决这个谜团。我们将确定熔体的产生反应和熔体的来源，并描述来源区域的物理化学参数如何影响熔体化学。同位素研究将提供坚实的约束，以确定这些熔体相关过程发生的时间框架，以及熔体的化学亲和力。我们将确定哪些化学示踪剂可以用来识别和量化地幔和地壳对碰撞环境中岩浆活动的不同贡献。总之，我们雄心勃勃的项目将把辉石岩和榴辉岩中天然MI的大量新的地球化学数据与实验和热力学计算的结果结合起来，以阐明碰撞环境下的岩石圈演化，提供壳幔相互作用过程如何塑造大陆地壳造山根的完整图景。

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.