Collaborative Research: Metamorphic Fluid Evolution and Rock Rheology

合作研究：变质流体演化与岩石流变学

• 批准号: 0509937
• 负责人: Jane Selverstone
• 金额: --
• 依托单位: University of New Mexico
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-06-01 至 2009-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0509937&HistoricalAwards=false
• 关键词: Collaborative; Research; Metamorphic; Fluid; Evolution

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.

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，CO2超压的产生与地震活动之间存在相关性。然而，目前很少有人知道碳流体如何影响变形机制，因此流变学，在地壳深处的韧性行为通常会被预期。本项目的主要目的是（1）描述天然富石英岩石中碳质和水相混合流体的变质释放与变形显微结构之间的关系，（2）利用变形实验探索控制这些关系的潜在机制。其目的是确定在变质作用过程中，C-O-H流体成分的渐进变化是否会引起岩石流变学的渐进变化？在许多造山带中，变质作用产生了碳质流体。这些流体的成分可以根据深度、温度、当地矿物组合和岩石的渗透性结构而变化很大。混合C-O-H流体是含石墨和碳酸盐片岩在变质作用过程中自然生成的。石墨和片状硅酸盐之间的晶体结构的相似性表明，在高度石墨化的岩石应变调节机制应该是类似的云母片岩。然而，观察石墨片岩从阿尔卑斯山显示优先脆化和丰富的拉伸裂纹的石墨片岩，平衡与含二氧化碳的流体相对于夹层nongraphitic片岩只含有含水流体的发展。初始变形实验记录了在混合二氧化碳-水-氯化钠-氯化钙流体的存在下变形的石英岩中的较冷变形微观结构，而在相同条件下在无二氧化碳盐水的存在下变形的石英岩中的较热微观结构。因此，二氧化碳的存在似乎对富含石英的岩石的流变行为产生了根本性的控制，但造成这种影响的具体机制尚不清楚。在本项目中，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与韧性结构中流体成分的直接信息，以及关于结构活跃时的深度和温度的信息。岩石变形实验，通知现场和分析研究，旨在研究机制，使碳流体诱发脆化。