Abstract
Brittle deformation can saturate the Earth's crust with faults and fractures in an apparently chaotic fashion. The details of brittle deformational histories and implications on, for example, seismotectonics and landscape, can thus be difficult to untangle. Fortunately, brittle faults archive subtle details of the stress and physical/chemical conditions at the time of initial strain localization and eventual subsequent slip(s). Hence, reading those archives offers the possibility to deconvolute protracted brittle deformation. Here we report K-Ar isotopic dating of synkinematic/authigenic illite coupled with structural analysis to illustrate an innovative approach to the high-resolution deconvolution of brittle faulting and fluid-driven alteration of a reactivated fault in western Norway. Permian extension preceded coaxial reactivation in the Jurassic and Early Cretaceous fluid-related alteration with pervasive clay authigenesis. This approach represents important progress towards time-constrained structural models, where illite characterization and K-Ar analysis are a fundamental tool to date faulting and alteration in crystalline rocks.
Highlights
Brittle deformation can saturate the Earth’s crust with faults and fractures in an apparently chaotic fashion
It is generally acknowledged that careful, multiscalar structural analysis can produce reliable geometric and kinematic/dynamic models of brittle deformation histories spanning over several hundreds of millions years, even in geologically complex and multiply-deformed terrains[2,3,4,5,6]
Most dating studies tend to overlook the structural complexity of the dated faults to focus instead on advancing the geochronological component of the research and, as a result, it is generally difficult to link the obtained ages to the subtle details of the structural evolution recorded by the fault
Summary
In the case of geologically old faults, continued reactivation may lead to the almost complete obliteration of the early strain increments, which hampers efforts aiming at an efficient use of a fault’s archive Despite these difficulties, it is generally acknowledged that careful, multiscalar structural analysis can produce reliable geometric and kinematic/dynamic models of brittle deformation histories spanning over several hundreds of millions years, even in geologically complex and multiply-deformed terrains[2,3,4,5,6]. We demonstrate an innovative methodological approach to untangle deformational histories, which would otherwise remain hidden within the commonly complex, if not chaotic, architecture of brittle faults and fault rocks This is in turn crucial to regional tectonic reconstructions and/or better understanding of the processes that steer fault localization and growth as a function of the delicate and time-dependent interplay between hardening and weakening mechanisms
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