Microstructural and tectonic applications of texturally-controlled Sm/Nd garnet geochronology
Stewart, Emily Mavis
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High precision 147Sm-143Nd geochronology of garnet is performed in two localities to solve problems in tectonics. In Chapter 1, the age of the basal amphibolite unit of the Ballantrae Ophiolite complex in Scotland is dated at 477.6 ± 1.9 million years old. This age constrains the duration of Grampian orogenesis to 12.6 ± 3.1 million years and allows us to conclude that classic metamorphism by overthickening of continental crust cannot account for the very short-lived event in this region. In Chapter 2, we report ages from a Variscan relict (318 ± 130 Ma) to a range of Cenozoic ages from 35.5 ± 2.1 Ma to 9 ± 10 Ma in the Betic Cordillera of southern Spain. This alone indicates prolonged orogenesis in the region. These ages are linked directly to a microstructure known as a Foliation Intersection Axis (FIA). Results are inconclusive, but they generally indicate that there may be a relationship between broad scale plate motion and FIA orientations at a regional scale.