Timing and conditions of brittle faulting on the Silltal-Brenner Fault Zone, Eastern Alps (Austria)

摘要: The Silltal Fault is the northern brittle continuation of Brenner Zone, marked by a narrow zone cataclasis and, in three locations, clay-rich fault gouges. clay mineral composition these gouges dominated higher temperature 2M1 polytype illite/muscovite, with no 1M/1Md illite or mixed layer illite/smectite detected. Smectite limited to samples from Stephansbrucke location, whereas chlorite present all samples. K–Ar ages different sample size fractions (<0.1, <0.4, <2, 2–6, 6–10 μm, “whole rock gouge”) show wide spread, ca. 115 12 Ma, consistently decreasing grain size. Although ranges overlap, are generally older (115–36 Ma) than those south near Matrei (55–12 Ma), possibly reflecting increasing regional metamorphic temperatures south. well-defined linear relationship between apparent age and hydrogen stable isotope (δD) values establishes direct correlation rejuvenation system increased interaction meteoric water introduced focussed within zone. dependence both δD on also indicates that radiogenic exchange was controlled size, new growth, mechanical grinding protolith muscovite during cataclastic faulting, both. results demonstrate advantages combining analysis interpretation combined approach necessary establish crucial influence influx its clay-size-fraction grains.