Seismic Properties of Shear Zones in the Lower Continental Crust

下陆壳剪切带的地震特性

• 批准号: 8720703
• 负责人: David Fountain
• 金额: $ 10.35万
• 依托单位: University of Wyoming
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1988
• 资助国家: 美国
• 起止时间: 1988-07-01 至 1990-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=8720703&HistoricalAwards=false
• 关键词: Seismic; Properties; Shear; Zones; Lower

Mylonite zones exposed within the granulite facies terrains of the Ivrea-Verbano zone, northern Italy, and the Bergen Arc, western Norway, provide examples of fault zones in the lower continental crust of extensional and compressional regimes, respectively. Within the Ivrea zone, the shear zones occur as mylonites of the Pogallo fault zone and as high temperature shear zones in the granulite domain of Valle d'Ossola. Deformed ultramafic rocks are also important constituents of deep structural levels of the Ivrea zone. Mylonites in the Bergen Arc are superimposed on an anorthositic complex and are characterized by an eclogite facies mineralogy. The research investigated the seismic properties of rocks from the these zones in order to evaluate the hypothesis that mylonite zones cause deep crustal reflections. The main phases of the work are 1) a sampling program in both regions; 2) investigation of preferred mineral orientations in the mylonitic rocks; 3) thin section and geochemical study of the composition of samples; 4) determination of the elastic constant tensor by measurement of P- and S-wave velocities at confining pressures up to 600 MPa; 4) construction of hypothetical velocity profiles through deformed and undeformed sequences.

出露在意大利北部伊夫雷亚-韦尔巴诺带麻粒岩相地体中的糜棱岩带和挪威西部卑尔根弧中的糜棱岩带，分别提供了伸展和挤压体制下大陆地壳中的断裂带的例子。在伊夫雷亚带内，剪切带以波加洛断裂带的糜棱岩和奥索拉谷麻粒岩域的高温剪切带的形式出现。变形超镁铁质岩也是伊夫雷亚带深部构造层次的重要组成部分。卑尔根弧中的糜棱岩叠加在斜长杂岩上，具有榴辉岩相矿物学特征。这项研究调查了这些地区岩石的地震性质，以验证糜棱岩带引起地壳深反射的假说。这项工作的主要阶段是：1)两个地区的取样程序；2)糜棱岩中优选矿物方向的调查；3)样品成分的薄片和地球化学研究；4)通过测量围压达600 Mpa的P波和S波的速度来确定弹性常数张量；4)利用变形和未变形的层序构造假想速度剖面。