Behaviour of argon during high pressure metamorphic fluid-rock interaction

~（40）Ar/~（39）Ar质谱是确定地球过程绝对年龄和速率的最有力工具之一。此外，Ar作为一种流体活动的微量元素，可以用来量化流体通量和流体-岩石相互作用，如果Ar的传输参数在变质作用。我们的初步工作已经确定，在来自西阿尔卑斯山的天然高压岩石中，流体渗透导致矿物组合的三种不同的改性类型：（1）粒内溶解-再沉淀，（2）体积扩散和（3）在反应位点和在现有颗粒上过度生长形成的含钾和无钾相的新固结。矿物颗粒的部分叠印允许确定残留物中的Ar的同位素组成和丰度，以及多晶白色云母和角闪石的改性部分。此外，流体敏感元素，如Li，Be，B和大离子亲石元素（LILE）的浓度将在现场确定。这些数据，连同热力学和微量元素的正演模型将被用来约束的速度和流体流入，再结晶机制和晶内微量元素和同位素再平衡的大小之间的关系。结合已知的微量元素的信息，新获得的原位Ar数据将使我们能够建立变质作用期间Ar的分配、运输和扩散行为：这些数据非常缺乏。

40Ar/39Ar mass spectrometry is one of the most powerful tools to determine absolute ages and rates of geo-processes. Furthermore, Ar as a fluid-mobile trace element can be used to quantify fluid fluxes and fluid-rock interaction, if Ar transport parameters during metamorphism are known. Our preliminary work has identified, in natural high-pressure rocks from the Western Alps, that fluid infiltration has led to three different modification types of the mineral assemblage: (1) intra-grain solution-reprecipitation, (2) volume diffusion and (3) neocrystallisation of K-bearing and K-free phases that form in reaction sites and in overgrowth on existing grains. Partial overprinting of mineral grains allows to determine the isotopic composition and abundances of Ar in relict as well as modified parts of phengitic white mica and amphiboles. Additionally, concentrations of fluid-sensitive elements, such as Li, Be, B and large ion lithophile elements (LILE) will be determined in situ. These data, together with thermodynamic and trace element forward models will be used to constrain the relationship between rates and magnitudes of fluid influx, recrystallisation mechanisms and intracrystalline trace element and isotopic re-equilibration. Combined with the information from the well-known trace elements, the newly won in situ Ar data will allow us to establish the partitioning, transport and diffusive behaviour of Ar during metamorphism: data that are sorely lacking.