Structural and temporal evolution of a reactivated brittle-ductile fault - Part II: Timing of fault initiation and reactivation by K-Ar dating of synkinematic illite/muscovite
Present-day exposures of ancient faults represent only the end result of the faults' often protracted and heterogeneous histories. Here we apply K-Ar dating of synkinematic illite/muscovite to constrain the timing of the complete temporal evolution of a complex, multiply-reactivated brittle-duc...
Published in: | Earth and Planetary Science Letters |
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Main Authors: | , , , |
Other Authors: | |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
2014
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Subjects: | |
Online Access: | http://hdl.handle.net/11585/569750 https://doi.org/10.1016/j.epsl.2014.09.031 http://www.sciencedirect.com/science/journal/0012821X/321-322 |
Summary: | Present-day exposures of ancient faults represent only the end result of the faults' often protracted and heterogeneous histories. Here we apply K-Ar dating of synkinematic illite/muscovite to constrain the timing of the complete temporal evolution of a complex, multiply-reactivated brittle-ductile fault, the Kvenklubben Fault in northern Norway. All obtained ages vary as a function of grain size. Geologically significant events are identified principally on the basis of detailed structural analysis presented in a companion paper (Torgersen and Viola, 2014). Faulting initiated at 531±11Ma, but most strain was accommodated during Caledonian compression at 445±9Ma. The fault was reactivated extensionally at 121±5Ma. C and O isotopic composition of carbonates and silicates in the fault rocks demonstrates that mineral authigenesis was linked to wall-rock disintegration through dolomite decarbonation and metabasalt carbonation. We suggest that the commonly observed case of age decreasing with grain size in K-Ar and 40Ar/39Ar dating of brittle fault rocks can be interpreted as a consequence of mixing between two end-member illite/muscovite generations: an authigenic and a protolithic, in which the finest authigenic grains constrain the timing of the last faulting increment. Integrating detailed structural analysis with age dating is the key towards a better understanding of fault architecture development and the temporal evolution of strain localization and deformation mechanisms. |
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