Melting in the Deep Earth (NERC grants NE/I010734/1 and NE/I010947/1)

Published paper from grant NE/I010734/1, Modeling the melting of multicomponent systems: the case of MgSiO3 perovskite under lower mantle conditions by Cono Di Paola and John P. Brodholt doi: 10.1038%2Fsrep29830 Two published papers from NERC grant NE/I010947/; Thomson et al AmMin 2014 Experimental Determination of Melting in the systems Enstatite-Magnesite and Magnesite-Calcite from 15 to 80 GPa http://dx.doi.org/10.2138/am.2014.4735 Lord et al EPSL 2014 The Melting Curve of Ni to 1 Mbar http://dx.doi.org/10.1016/j.epsl.2014.09.046 Grant Abstract: Melting in the Earth has a huge effect on its chemical and physical state. For instance, the chemistry of the crust, the mantle and the atmosphere are largely controlled by melting and crystalisation at mid-ocean ridges, hotspots or island arcs. There has, therefore, been an enormous effort in the last decades to understand these shallow melting processes. Yet much deeper melts may have been equally influential in the evolution of the Earth. For instance, it is generally accepted that a deep magma ocean perhaps extending to the Earth's centre, existed early its history. This was the result of multiple impacts as the Earth accreted. From this magma ocean, iron melts separated from silicate melts to form the core, volatiles degassed to form an early atmosphere, and a proto-crust may have formed. It is also accepted that the Earth was hit by a Mars-sized body to create the moon; this too would have caused enormous amounts of melting in the deep Earth. Moreover, there is some evidence for melting in the deep Earth now. It is possible, therefore, that melts in the deepest Earth have existed throughout Earth's history. However, many basic data on the physical and chemical properties of deep melting do not exist. For instance, we don't know the melting curves for mantle minerals and rocks at the pressure and temperatures of the deep Earth. We don't know which minerals crystalise from these melts first (the liquidus phases). We don't know the composition of partial melts of deep mantle rocks or rocks which have been subducted. We don't know the relative densities of the rocks and their melts, and so we do not even know whether minerals float of sink in these deep melts. This lack of data has led to much speculation on the effect of deep melts on the Earth's evolution. For instance, it has been suggested that geophysical and geochemical anomalies in the Earth's mantle have deep early melts as their origin. But these models depend of the chemical and physical properties of the melts and crystalline solids, properties that are simply not known. This project will use novel experiments in conjunction with ab initio modelling obtain these data. The data will provide the chemical and physical foundation on which all future models of the Earths early crystallization and subsequent evolution will be based.

出版于资助项目NE/I010734/1的研究论文，探讨了多组分体系熔融模型：在下地幔条件下对MgSiO3钙钛矿的熔融过程研究，作者为Cono Di Paola与John P. Brodholt，文献编号doi: 10.1038%2Fsrep29830。此外，NERC资助项目NE/I010947/资助下发表的两篇论文：Thomson等人的《从15至80 GPa实验测定Enstatite-Magnesite和Magnesite-Calcite体系的熔融》发表于AmMin 2014年，文献编号http://dx.doi.org/10.2138/am.2014.4735；Lord等人的《Ni至1 Mbar的熔融曲线》发表于EPSL 2014年，文献编号http://dx.doi.org/10.1016/j.epsl.2014.09.046。项目摘要：地球内部的熔融过程对地球的化学与物理状态具有深远影响。例如，地壳、地幔及大气层的化学组成主要受中洋脊、热点或岛弧处的熔融与结晶作用控制。因此，在过去的几十年中，科研人员投入了巨大努力以理解这些浅层熔融过程。然而，更深层的熔融过程可能对地球的演化同样具有举足轻重的作用。例如，普遍认为地球早期历史中可能存在一个可能延伸至地球中心的深部岩浆洋，这是地球凝聚过程中多次撞击的结果。从这个岩浆洋中，铁熔融物从硅酸盐熔融物中分离出来，形成了地核，挥发性物质逸出形成了早期大气，而原始地壳可能也由此形成。同时，普遍认为地球曾遭受火星大小天体的撞击，形成了月球；这一事件同样在深部地球中引发了巨大的熔融。此外，目前也有一些证据表明深部地球存在熔融现象。因此，深部地球中可能自地球形成以来就存在着熔融物。然而，关于深部熔融的物理和化学性质的基本数据尚不充足。例如，我们并不了解地幔矿物和岩石在深部地球的压力和温度条件下的熔融曲线。我们不清楚哪些矿物会首先从这些熔融物中结晶（即液相）。我们不知道深部地幔岩石或俯冲岩石的局部熔融物的组成。我们不清楚岩石及其熔融物的相对密度，因此我们甚至不知道矿物在深部熔融物中是上浮还是下沉。这种数据的缺失导致了关于深部熔融对地球演化影响的诸多推测。例如，有人提出地球地幔中的地球物理和地球化学异常可能源于深部早期的熔融。但这些模型依赖于熔融物和结晶固体的化学与物理性质，而这些性质我们尚不清楚。本项目将通过结合新颖的实验与原位建模来获取这些数据。这些数据将为地球早期结晶及其随后演化的所有未来模型提供化学和物理基础。