Collaborative Research: Metamorphic Fluid Evolution and Rock Rheology

相关领域、实验和分析研究正在记录碳酸盐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之间存在相关性。然而，目前人们对碳酸盐流体如何影响变形机制以及地壳深处的流变学知之甚少，而地壳深处的韧性通常是可以预期的。该项目(1)描述了碳酸盐和水混合流体的变质释放与天然富石英岩石中形成的变形微结构之间的关系，以及(2)利用变形实验来探索控制这些关系的潜在机制。其目的是确定变质过程中C-O-H流体成分的递进变化是否会导致岩石流变学的递进变化？在许多造山带，碳酸盐流体是在变质过程中产生的。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不同而变化很大。混合C-O-H流体是在石墨质片岩和含碳酸盐片岩变质过程中自然产生的。石墨和片状硅酸盐在晶体结构上的相似之处表明，高度石墨化岩石中的应变调节机制应该与云母片岩中的相似。然而，从阿尔卑斯山的石墨片岩中观察到，相对于只含水的层间非石墨片岩，与含二氧化碳流体平衡的石墨片岩中大量的拉伸裂缝优先脆化和发展。初始变形实验记录了在二氧化碳-水-氯化钠-氯化钙混合流体中变形的石英岩较冷的变形组织，而在相同条件下在无二氧化碳盐水中变形的石英岩的较热的微结构。因此，二氧化碳的存在似乎对富含石英的岩石的流变行为产生了根本的控制作用，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体制，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关于脆性构造和韧性构造中流体成分的直接信息，以及这些构造活动的深度和温度。岩石变形实验是在野外研究和分析研究的基础上设计的，目的是研究碳酸盐流体引起脆化的机制。

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.