Collaborative Research: Metamorphic Fluid Evolution and Rock Rheology

相关的现场、实验和分析研究正在记录碳流体对深部地壳岩石流变学的影响。最近的几项研究表明，二氧化碳超压的产生与地震活动性之间存在相关性。然而，目前对碳流体如何影响变形机制知之甚少，因此，流变学，在地壳深处，韧性行为通常是预期的。本项目(1)描述了碳水混合流体的变质释放与天然富石英岩中发育的变形微观结构之间的关系，(2)利用变形实验探索控制这些关系的潜在机制。目的是确定变质作用过程中碳氧氢流体成分的渐进变化是否会导致岩石流变学的渐进变化？在许多造山带中，碳流体是在变质作用中产生的。这些流体的组成随深度、温度、当地矿物组合和岩石渗透性结构的变化而变化很大。混合碳氧氢流体在含石墨片岩和含碳酸盐片岩变质过程中自然生成。石墨和硅酸片晶体结构的相似性表明，高石墨岩石中的应变调节机制与云母片岩中的应变调节机制相似。然而，对阿尔卑斯山脉的石墨片岩的观察表明，相对于仅含含水流体的层间非石墨片岩，含二氧化碳流体的石墨片岩更容易脆化，并且具有丰富的拉伸裂纹。初始变形实验记录了在二氧化碳-水-氯化钠-氯化钙混合流体存在下变形的石英岩的低温变形微观结构，以及在相同条件下无二氧化碳盐水存在下变形的石英岩的高温微观结构。因此，二氧化碳的存在似乎对富含石英的岩石的流变行为起着根本的控制作用，但造成这种影响的具体机制尚不清楚。在这个项目中，阿尔卑斯山的野外工作记录了脆化发生的空间尺度，有利于异常脆化的构造机制，以及脆化和非脆化岩石类型之间的关系。流体包裹体分析提供了脆性和韧性结构中流体组成的直接信息，以及结构活跃时的深度和温度。岩石变形实验，根据现场和分析研究的信息，旨在研究碳流体诱导脆性的机制。

Linked field, experimental, and analytical studies are documenting the effect of carbonic fluids on rheology of deep-seated crustal rocks. Several recent studies show a correlation between generation of CO2 overpressures and seismicity. However, little is currently known about how carbonic fluids affect deformation mechanisms, and hence rheology, at depths in the crust where ductile behavior would normally be expected. This project is (1) describing the relationships between metamorphic release of mixed carbonic and aqueous fluids and deformation microstructures developed in natural quartz-rich rocks, and (2) using deformation experiments to explore the underlying mechanisms that control these relationships. The intent is to determine if progressive changes in C-O-H fluid composition during metamorphism cause progressive changes in rock rheology?In many orogenic belts, carbonic fluids are produced during metamorphism. These fluids can vary widely in composition as a function of depth, temperature, local mineral assemblage, and permeability structure of the rocks. Mixed C-O-H fluids are generated naturally during metamorphism of both graphitic and carbonate-bearing schists. Similarities in crystal structure between graphite and sheet silicates suggest that strain accommodation mechanisms in highly graphitic rocks should be similar to those in mica schists. However, observations in graphitic schists from the Alps show preferential embrittlement and development of abundant tensile cracks in graphitic schists that equilibrated with carbon dioxide-bearing fluids relative to interlayered nongraphitic schists containing only aqueous fluids. Initial deformation experiments document colder deformation microstructures in quartzite deformed in the presence of mixed carbon dioxide-water-sodium chloride-calcium chloride fluid versus hotter microstructures in quartzite deformed at the same conditions in the presence of carbon dioxide-free brine. The presence of carbon dioxide thus appears to exert a fundamental control on the rheologic behavior of quartz-rich rocks, but the specific mechanism responsible for this effect is not yet known.In this project, fieldwork in the Alps is documenting the spatial scales over which embrittlement occurs, the tectonic regimes that favor anomalous embrittlement, and the relationships between embrittled and non-embrittled rock types. Fluid inclusion analysis is providing direct information on the composition of the fluids in brittle versus ductile structures, and also on the depths and temperatures at which the structures were active. Rock deformation experiments, informed by the field and analytical studies, are designed to investigate the mechanisms whereby carbonic fluids induce embrittlement.