Deep mantle processes and core-mantle interaction: a novel geochemical perspective

对深地幔过程和核-幔相互作用的量化必须依赖于地球物理证据和间接示踪物，如来自地幔柱的火山岩的地球化学。在过去的几年里，高精度测量地球岩石中的短寿命放射性和核合成同位素异常已经彻底改变了我们对深部地幔过程的认识。地幔柱源新生代玄武岩中放射成因的182 W和142 Nd同位素异常（半衰期分别为900万年和10300万年）表明，地球上的冥古宙（> 4.0Ga）分异作用的遗迹在整个地球历史中一直存在于地幔深部。同样，地球的原始，前晚期单板地幔可以显示出小的核合成同位素过剩的100钌。在地球动力学的背景下，这两个新的发现现在第一次允许明确地确定在地球历史的大部分时间里被隔离的地幔深处的原始域。此外，这些示踪剂的组合现在允许识别核幔相互作用。在DeepDyn的背景下，我们建议使用这些新的化学示踪剂来（1）更好地理解核幔相互作用和地幔柱根的结构，（2）重建地幔柱成分在古地磁超年代的可能变化。为了实现这些目标，我们提出了一个组合的高精度182 W-142 Nd-100 Ru研究选定的，羽状相关的镁铁-超镁铁岩套的新生代年龄（130马及年轻），补充传统的长寿命放射性同位素数据。在我们以前的工作的基础上，结合同位素测量将涵盖经典的地幔柱的地方，在那里很好的交叉羽截面可用于研究其空间结构。利用白垩纪以来的原始火成岩样品研究与白垩纪超时有关的深部地幔成分的可能变化。130至65 Ma的大型火成岩省和白垩纪金伯利岩。这一结果不仅为地幔柱的组成和来源提供了新的线索，而且也将为下地幔非均匀性（如LLSVP和ULVZ）的起源和演化提供一般性的结论。此外，拟议的研究将为地球物理模型提供有价值的输入参数。

Quantifying deep mantle processes and core mantle interaction has to rely on geophysical evidence and indirect tracers such as the geochemistry of volcanic rocks that are derived from mantle plumes. In the past years, high precision measurements of short-lived radiogenic and nucleosynthetic isotope anomalies in terrestrial rocks have revolutionized our understanding of deep mantle processes. Widespread isotope anomalies of radiogenic 182W and 142Nd, the decay products of long extinct 182Hf and 146Sm (half lifes of 9 Myrs and 103 Myrs, respectively) in plume-derived Cenozoic basalts could show that vestiges of Hadean (> 4.0 Ga) differentiation processes on Earth have survived in the deep mantle throughout Earth history. Likewise, Earth’s primordial, pre-late veneer mantle could be shown to exhibit small nucelosynthetic isotope excesses of 100Ru. In a geodynamic context, both of these new findings now allow for the first time to unambiguously identify primordial domains in the deep mantle that have been isolated through most of Earth’s history. Furthermore, the combination of these tracers now allows identifyng core-mantle interaction. In the context of DeepDyn, we propose to employ these novel chemical tracers to (1) better understand core-mantle interaction and the structure of roots of mantle plumes and (2) reconstruct possible changes of mantle plume compositions across paleomagnetic superchrons. To achieve these goals, we propose a combined high precision 182W-142Nd-100Ru study on selected, plume-related mafic-ultramafic rock suites of Cretaceous-Cenozoic age (130 Ma and younger), complemented by conventional long-lived radiogenic isotope data. Building on our previous work, the combined isotope measurements will cover classical mantle-plume localities, where good cross-plume sections are available to study their spatial structure. Possible changes in deep mantle composition related to the Cretaceous superchron will be studied using primitive igneous samples from ca. 130 to 65 Ma old large igneous provinces and Cretaceous kimberlites. The results will not only provide new clues on the composition and sources of mantle plumes, but will also allow general conclusions on the origin and evolution of lower mantle heterogeneities such as LLSVPs and ULVZs. Furthermore, the proposed study will provide valuable input parameters for geophysical models.