Melting and Volatile Interactions in the 50-70 Kbar Mantle

在地球上地幔的岩浆和岩石中发现了少量的挥发性分子H2O和CO2。这些挥发物对岩浆的起源、地幔的熔融温度作为深度的函数、原始地幔中沿地热存在的熔体以及地幔的化学分异等问题都有重要影响。在过去的30年里，实验研究的重点是在压力高达35千巴的情况下回答这些问题，这些压力只涉及到最上层的地幔。上层压力很大程度上取决于仪器的限制。在过去三年中，由于多砧高压装置的出现，出现了70- 250kbar压力范围内的井喷作业。在金伯利岩角砾岩中发现的上地幔岩石碎片记录了化石地热（温度剖面），其压力-温度轨迹在约50kbar的压力下发生了弯曲（变化）。最深的样品记录的压力为60千巴。在这些石榴石橄榄岩碎片和金伯利岩中发现的钻石表明，压力稍高。地温的变化表明主要的过程发生在这个压力范围内。在50-70 kbar压力范围内，研究挥发物与矿物和岩浆的相互作用所提出的问题是：*哪些H2O储层矿物是稳定的，它们是否含有钾等必需成分？*二氧化碳对岩浆成分的影响是什么？*压力对岩浆中铁/亚铁比率的影响是什么？H2O-CO2-oxygen与原始岩浆组成的关系是什么？一种新开发的装置，一种常规工作范围为70千巴的主动环式活塞缸，将用于探索这些问题。

Small quantities of the volatile molecules H2O and CO2 are found magmas and rocks from the Earth's upper mantle. These volatiles can have important effects on such problems as the origin of magmas, the melting temperature of the mantle as a function of depth, the existence of melts along geotherms in the primitive mantle, and the chemical differentiation of the mantle. Experimental research completed in the past 30 years has focused on answering these questions at pressures up to 35 kbar, reaching only into the uppermost mantle. The upper pressure was largely determined by apparatus limitations. In the last three years, a burst of activity focusing on the 70-250 kbar pressure range has occurred due to the advent of the multiple anvil high pressure device. Fragments of upper mantle rocks found in kimberlite breccias record fossil geotherms (temperature profiles) with an inflection (change) in their pressure-temperature trajectories at pressure of about 50 kbar. The deepest samples record pressures of 60 kbar. Diamonds found in these garnet peridotite fragments and in the kimberlites suggest somewhat higher pressures. The inflection in the geotherm suggests that major processes occur in this pressure range. The proposed problems that will investigate the interaction of volatiles with minerals and magmas at a 50-70 kbar pressure range are: *Which H2O reservoir minerals are stable, and do they have a required constituent such as potassium? *What is the effect of CO2 on magma compositions? *What is the effect of pressure on the ferric/ferrous iron ratio in magmas? *What is the relationship between H2O-CO2-oxygen and primary magma composition? A newly developed apparatus, an active girdle piston-cylinder with a routine operating range to 70 kbar, will be used to explore these questions.