U-Th dating of striated fault planes
Résumé
Direct dating of brittle fault activity is of fundamental impor- tance to tectonic reconstructions and paleoseismic studies. One way to address this issue is by constraining the timing of fault striations, but this requires a better understanding of the striation formation mechanism and associated mineralization. We present results from a microstructural, geochemical, and geochronological study of cal- cite precipitates associated with striated fault planes from the Dead Sea fault zone in northern Israel. We recognize four types of coexist- ing calcite precipitates, including calcite cement in dilation breccia, calcite in striated groove morphology, calcite gouge associated with hydraulic fracturing and pressure solution, and calcite coating of the fault surface. Carbon-oxygen isotopes, 87Sr/86Sr ratios, and rare earth element and yttrium (REY) patterns indicate various precipi- tation mechanisms associated with formation of syntectonic (calcite cement and striations), coseismic (calcite gouge), and interseismic (calcite coating) precipitates in the fault zone. Using U-Th dating of samples from three adjacent fault planes, we delineate four well- defined deformation ages in the period from 220 to 60 ka. We con- clude that these ages constrain the timing of activity along the Dead Sea fault zone in northern Israel, and argue that a similar meth- odological approach could potentially shed light on the timing of deformation in other brittle fault zones.