Hydrogen and ⁴⁰Ar/³⁹Ar isotope evidence for multiple and protracted paleofluid flow events within the long‐lived North Anatolian Keirogen (Turkey)

Abstract

We present a new approach to identifying the source and age of paleofluids associated with low-temperature deformation in the brittle crust, using hydrogen isotopic compositions (dD) and 40 Ar/ 39 Ar geochronology of authigenic illite in clay gouge-bearing fault zones. The procedure involves grain-size separation, polytype modeling, and isotopic analysis, creating a mixing line that is used to extrapolate to dD and age of pure authigenic and detrital material. We use this method on samples collected along the surface trace of today's North Anatolian Fault (NAF). dD values of the authigenic illite population, obtained by extrapolation, are 289 6 3&, 290 6 2&, and 297 6 2& (VSMOW) for samples KSL, RES4-1, and G1G2, respectively. These correspond to dD fluid values of 262& to 285& for the temperature range of 1258C 6 258, indistinguishable from present-day precipitation values. dD values of the detrital illite population are 245 6 13&, 260 6 6&, and 264 6 6& for samples KSL, G1G2, and RES4-1, respectively. Corresponding dD fluid values at 3008C are 226& to 245& and match values from adjacent metamorphic terranes. Corresponding clay gouge ages are 41.4 6 3.4 Ma (authigenic) and 95.8 6 7.7 Ma (detrital) for sample G2 and 24.6 6 1.6 Ma (authigenic) and 96.5 6 3.8 Ma (detrital) for sample RES4-1, demonstrating a long history of meteoric fluid infiltration in the area. We conclude that today's NAF incorporated preexisting, weak clay-rich rocks that represent earlier mineralizing fluid events. The samples preserve at least three fluid flow pulses since the Eocene and indicate that meteoric fluid has been circulating in the upper crust in the North Anatolian Keirogen since that time.

Evolution of an early Eocene pull‐apart basin in the Central Pontides (Northern Turkey): New insights into the origin of the North Anatolian Shear Zone

“…The radiometric data on fault gouges that document the onset of significant strike‐slip faulting along the NASZ in the Eocene (ca 57 Ma, Uysal et al., ; ca 40 Ma, Boles et al., ) can be reconsidered in the proposed geodynamic scenario.…”

Meteoric fluid infiltration in crustal-scale normal fault systems as indicated by δ18O and δ2H geochemistry and40Ar/39Ar dating of neoformed clays in brittle fault rocks

“…By contrast, data from deeply rooted strike systems suggest fluid sources are more variable in these systems. Data from the crustalscale North Anatolian fault zone indicate fluid infiltration at various times by fluids of metamorphic or magmatic origin (Tonguç Uysal et al, 2006) and meteoric origin (Boles et al, 2015). Data from the subparallel but shallower-rooted Savcili strike-slip fault zone (Isik et al, 2014) suggest a deep basinal origin for circulating fluids.…”

Timing and conditions of clay fault gouge formation on the Naxos detachment (Cyclades, Greece)

“…δD illite/smectite values of −89 to −95‰ are rather low when compared to δD values of illite/smectite that formed in the presence of fluids with basinal or metamorphic origin. Similar δD illite/smectite values have been also observed in fault‐related settings in the Eastern Mediterranean, including the Menderes metamorphic core complex [ Hetzel et al ., ] and the North Anatolian Fault [ Boles et al ., ]. Such low δD illite/smectite values are indicative of meteoric (surface‐derived) fluid interaction during crystallization and growth of the fault gouge clay material.…”

“…This discovery is important because the gouge contains illite, and this K‐bearing clay mineral can be dated to directly establish the time of detachment activity [e.g., Van der Pluijm et al ., ; Zwingmann and Mancktelow , ; Zwingmann et al ., ; Hetzel et al ., ; Boles et al ., ]. The clay mineralogy and crystallography can also establish the approximate temperature of gouge formation, and hydrogen isotope analysis can characterize the source of fluids involved during faulting and clay formation [e.g., Mulch et al ., ; Campani et al ., ; Hetzel et al ., ; Boles et al ., ; Mancktelow et al ., ].…”