Dating Illitic Fault Rocks, and Applications to Cordilleran Normal Faults

伊利石断层岩的年代测定及其在科迪勒拉正断层中的应用

• 批准号: 0738435
• 负责人: Ben van der Pluijm
• 金额: --
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-01-15 至 2012-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0738435&HistoricalAwards=false
• 关键词: Dating; Illitic; Fault; Rocks; Applications

Radiometric dating of K-rich minerals in shallow fault rocks offers a unique opportunity to resolve long-standing controversies about upper crustal fault movements and related deformation. Clay-bearing fault rocks are common in exhumed fault zones, which typically preserve both primary (detrital) and newly-grown (authigenic) phyllosilicates. Analysis of these fault rocks, therefore, reflects a mixture of the roles of both mineral populations. Using X-ray characterization of grain size populations in the clay fraction, and sample encapsulation for irradiation and dating by the Ar/Ar method, a reliable approach to dating authigenic growth of illite- and illite-smectite-rich materials to track the timing of faulting has been developed. This project uses phylosilicate polytype characterization and quantification, and applies the dating method to test existing hypotheses in well-known normal fault settings in the western US Cordillera. The method will be applied to core complex faulting problems, with a view toward solving long standing problems in this field of structural geology. Questions such as regional timing of deformation, concurrent displacement on steep and shallow brittle faults and time gap between brittle and plastic deformation can be answered if the approach is successful. A protocol for sampling of K-rich fault zone materials will be created, including the full characterization and dating of clay gouge, an exciting new area of research that is virtually unexplored.The public in the US understands that there are many faults that wind their way across the landscape, one of the most famous being the San Andreas Fault in California. The importance of such Earth features to the public increases if the faults are actively moving due to the potential damage they might cause. The faults can be serious hazards if they cross urban or suburban areas. There are few ways to probe the history of activity on faults, yet the work outlined in this proposal promises to do just that: Measure the history of some test case faults in the western US. The approach is in principle simple. Minerals that have growth during fault movements are collected and purified, and then their radiometric age is measured. The measured age of the bulk material is that of the collective history of fault movement, and the different mineral subtypes within the sample may contain additional chemical clues that help to further decipher that collective history.

浅层断裂岩中富钾矿物的放射性测年为解决有关上地壳断裂运动和相关变形的长期争议提供了一个独特的机会。含粘土的断层岩在折返的断裂带中很常见，通常保存有原生(碎屑)和新生长(自生)的层状硅酸盐。因此，对这些断层岩的分析反映了这两种矿物群体的混合作用。利用粘土组分中颗粒大小群体的X射线表征，以及样品的辐照和Ar/Ar法测年，发展了一种可靠的方法来测定伊利石和伊利石蒙脱石物质的自生生长年龄，以追踪断裂的时间。该项目使用层状硅酸盐多型表征和定量化，并应用测年方法在美国西部科迪勒拉著名的正断层环境中检验现有假说。该方法将应用于岩心复杂断裂问题，以期解决这一构造地质领域长期存在的问题。如果方法成功，则可以回答变形的区域时序、陡脆断层和浅脆断层上的同步位移以及脆性和塑性变形之间的时间差距等问题。将制定一项富含K的断裂带材料采样协议，包括对粘土泥的全面表征和测年，这是一个令人兴奋的新研究领域，几乎没有被开发。美国公众知道，有许多断层蜿蜒穿过这片土地，其中最著名的是加利福尼亚州的圣安德烈亚斯断层。如果断层由于可能造成的潜在损害而活跃地移动，那么这样的地球特征对公众的重要性就会增加。如果这些断层穿过城市或郊区，可能会造成严重的危险。探索断层活动历史的方法很少，但这项提案中概述的工作有望做到这一点：测量美国西部一些测试用例错误的历史。这种方法原则上很简单。在断层运动期间生长的矿物被收集和提纯，然后测量它们的辐射年龄。测量到的大量物质的年龄是断层运动的集体历史的年龄，样品中不同的矿物亚型可能包含有助于进一步破译集体历史的额外化学线索。