Nanogranites in migmatites: deciphering the chemical differentiation in the continental crust

混合岩中的纳米花岗岩：破译大陆地壳的化学分异

• 批准号: 279014837
• 负责人: Professor Dr. Patrick J. O' Brien, since 11/2021
• 金额: --
• 依托单位: Institut für Geowissenschaften
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/279014837?language=en
• 关键词: Nanogranites; migmatites; deciphering; chemical; differentiation

Chemical differentiation of the crust influences the evolution of our planet, it fuels the technological evolution of humankind by re-concentrating elements in ore deposits and it shapes the atmosphere by releasing volatiles. Such re-distribution process begins at depth when the continental crust melts, and the investigation of such deep melts is thus key to understand differentiation. Natural rocks which experienced melting, i.e. migmatites, still contain melt as micrometric inclusions of primary nature. Such melt inclusions (MI) -also called nanogranitoids- were proven in the last decade to represent the most reliable and robust tool to gauge the composition and evolution of melt at depth. In the last three year, the applicant jump-started and extensively developed the investigation of melting and melt-related processes in mafic/ultramafic systems by characterizing in detail two case studies of MI from melting of amphibolites and metagabbros. Moreover, within pyroxenites and eclogites the applicant and his collaborators also discovered the first "metasomatic" nanogranitoids, i.e. containing metasomatic melt originated outside the rock in which they can be currently found. Moreover, the enlargement of the MI database has clearly shown that the metastable polymorphs of quartz and plagioclase are far more common than originally expected, and often they coexist with new phases never reported before -all discoveries warranting more investigations.The renewal of the present project will allow the applicant to further our understanding of chemical differentiation by combining for the first time two powerful petrogenetic tools: nanogranitoids and zircon studies. Zircon is a robust geochronometer, a versatile petrogenetic tool to gauge the physicochemical conditions characteristic of deep processes, and unsurprisingly a very reliable inclusion container. The applicant will combine the information obtained via petrology of metamorphic zircon with a detailed study of the melt preserved in it as MI by means of nanogranitoids re-homogenization and in situ analyses studies – in terms of major and trace elements, volatiles and isotopes. A pilot experiment was successful in re-melting former nanogranitoids in zircon, paving the way for the present project. Such combined approach has the potential to produce significant advancements in our knowledge on deep melt-related processes, and it is at present an entirely unexplored asset in metamorphic petrology. Moreover, part of the project will be dedicated to investigate the crystallization prodcuts of the melt confined in inclusions, in particular synthesizing the polymorphs and characterizing the new phases recently identified.Overall, the present project will lead to take a significant leap forward toward a better understanding of how crustal differentiation at depth starts and evolve through time and how deep melts behave on crystallization.

地壳的化学分化影响了地球的演化，它通过在矿床中重新浓缩元素来推动人类的技术进化，并通过释放挥发物来塑造大气。这种重新分配过程始于大陆地壳融化时的深部，因此，对这种深部熔体的研究是理解分异的关键。经历了熔融的天然岩石，即混合岩，仍然含有熔体，作为原始性质的微量包裹体。这种熔体包裹体(MI)-也被称为纳米花岗岩-在过去十年中被证明是测量深部熔体成分和演化的最可靠和最强大的工具。在过去的三年里，申请人通过详细描述角闪岩和变长角闪岩熔融的两个案例，启动并广泛发展了镁铁质/超镁铁质系统中熔融和与熔融有关的过程的研究。此外，在辉石岩和榴辉岩中，申请人和他的合作者还发现了第一批“交代”纳米花岗岩，即含有交代熔体的岩石起源于目前可以找到它们的岩石之外。此外，MI数据库的扩大清楚地表明，石英和斜长石的亚稳多晶型比最初预期的要常见得多，而且它们经常与以前从未报道过的新相共存-所有这些发现都需要进行更多的研究。本项目的更新将使申请者首次结合两种强大的岩石成因工具：纳米花岗岩和锆石研究，进一步加深我们对化学分异的理解。锆石是一种坚固的地质计时仪，是一种多功能的岩石成因工具，可以测量深部过程的物理化学条件，并不令人惊讶地是非常可靠的包裹体容器。申请者将结合通过变质锆石岩石学获得的信息，通过纳米花岗岩再均一化和现场分析研究--主要和微量元素、挥发分和同位素--对其中保存为MI的熔体进行详细研究。一项中试实验成功地在锆石中重熔了以前的纳米花岗岩，为目前的项目铺平了道路。这种组合方法有可能大大提高我们对深熔相关过程的认识，目前它是变质岩石学中一项完全未被勘探的资产。此外，该项目的一部分将致力于研究限制在包裹体中的熔体的结晶过程，特别是合成多晶型并表征最近发现的新相。总体而言，本项目将导致重大飞跃，以更好地理解地壳深部分异是如何开始和随时间演化的，以及深熔体在结晶过程中的行为。