火星内部水含量及其分布特征

The water content of the martian mantle is one of the most important factors for studying the evolution history of Mars, however, water content of the martian mantle is under debate (dry Vs wet) compared with Earth and is poorly constrained of spatial and temporal evolution history. Martian meteorites, the only samples from the red planet, are the windows to study the water content of the martian mantle. Based on the study on martian meteorite GRV 020090, we have found the martian mantle is depleted in water contents around 2 Ga ago and established the analytical method for determining the water contents and hydrogen isotopes. Meanwhile, the debate reasons were clarified. This program will use NanoSIMS 50L to establish the analytical method for determining the volatile elements (F, Cl, S) contents and Cl isotopes, supplying new constraints for the variations of the water contents and hydrogen isotopes and clarifying the effect of fractional crystallization, magma degassing, crustal assimilation, shock metamorphism and water-rock interaction. More martian meteorites will be chosen for studying the spatial distribution and temporal evolution history of the water contents in the martian mantle.

火星幔的水含量是制约其演化历史的最重要因素之一，但与地球相比，一直存在火星幔的“干”与“湿”之争，更缺少对火星幔水含量在时空上演化的认识。火星陨石作为目前唯一的火星样品，是研究火星内部水含量的重要窗口。基于火星陨石GRV 020090的研究，我们得到其幔源区约2亿年前贫水的证据，建立了火星水含量和H同位素分析的关键技术，找到了产生争议的主要原因。本项目在技术上拟新建立F、Cl、S等挥发份含量和Cl同位素的纳米离子探针分析方法，为水含量和H同位素的变化提供更多制约，厘清结晶分异、岩浆去气、壳源混染、冲击变质以及水岩作用的影响；在研究对象上，拟选用更多的火星陨石样品，从而揭示火星幔水含量的空间变化，其中不同年龄的样品还提供了时间轴的变化趋势。

本项目主要聚焦火星内部的挥发份含量研究。主要研发了锆石图像定年和微量元素联测技术、挥发份含量分析技术和磷灰石Cl同位素分析技术；对火星陨石NWA 7034，NWA 6162，NWA 8657，Y 980459，Y 002192，ALH 77005，Tissint，Y 000593，NWA 2737等火星陨石开展岩相学、矿物学和地球化学分析；对火星陨石得熔融包裹体、磷灰石、熔长石、冲击玻璃等组分开展了水含量、Cl、S、H和Cl同位素分析；发现了火星多期次水岩作用，且火星浅表流体具有富37Cl和富D的特征，制约了火星幔的水、Cl和S含量分别为0.1-3ppm、0.5-4ppm和0.5-15ppm，明显比地幔“干”；根据不同类型火星陨石的水含量和H同位素分析，提出了火星存在全球性地下冰川的模型；首次在火星陨石中发现柯石英。