The use of carbonate precipitates in neotectonic research:
A case study from SW Turkey
Griet Verhaert1,2, Philippe Muchez1, Manuel Sintubin2, Dominique Similox-Tohon2,1 & Marc Waelkens3
1 Fysico-chemische Geologie, K.U.Leuven, Celestijnenlaan 200C, 3001 Leuven, Belgium
2
Structural Geology & Tectonics Group, K.U.Leuven, Redingenstraat 16, 3000 Leuven, Belgium3
Department of Archaeology, K.U.Leuven, Blijde Inkomststraat 21, 3000 Leuven, Belgiumgriet.verhaert@geo.kuleuven.ac.be
During tectonic activity, large amounts of fluids may be expelled at the surface. These fluids could result in the cementation of pores, fractures and faults. The aim of this study is to investigate the possibility to combine a structural, mineralogical and geochemical approach of calcite precipitates to determine neotectonic activity in a seismic active region. This includes on the one hand the reconstruction of the geodynamic framework of the calcite precipitates and on the other hand the determination of the origin of the responsible fluids. The area selected is located in the western part of the Isparta Angle (SW Turkey), where during the last century a number of large earthquakes (Ms > 6.0) occurred, and where a number of seismogenic faults are identified (Burdur, Dinar and Baklan faults). In this area, the ancient Roman site of Sagalassos is situated. The archaeological relics of Sagalassos show clear evidence that the area was struck by earthquakes during the first, third, sixth and seventh century AD.
Joints, faults and screes, postdating the Miocene emplacement of the Lycian nappe, are cemented by several calcite generations. A preliminary palaeostress analysis revealed two important extension phases, i.e. a NW-SE and a ENE-WSW oriented extension. The NW-SE extension represents the most recent event, affecting Late Tertiary and Quaternary scree deposits. This stress field may still be present, as corroborated by the focal mechanism of the 1971 Burdur earthquake. The ENE-WSW extension coincides rather well with the Late Pliocene – Early Quaternary stress regime active in the Isparta Angle region. Fault activity on NW-SE trending normal faults, such as the Dinar fault, seemingly coincides with fault activity on NE-SW trending normal faults, such as the Burdur fault. This suggests a biaxial extension of the region with both NE-SW and NW-SE components of extension.
The oxygen isotopic composition of the calcites (d 18O = -9.2 to -4.5 ‰ VPDB) cementing the screes and the joints are similar to the values reported for local, Holocene travertine deposits and reflect precipitation from meteoric water. The influence of soil-gas CO2 in the formation of the calcites is clearly indicated by the low d 13C values (-9.5 to -1.9 ‰ VPDB). In contrast, the d 18O (-12.6 to -2.2 ‰ VPDB) and d 13C (+1.1 to +2.7 VPDB) values of calcites in a fault zone indicate a deeper origin of the fluid. The high carbon isotopic values are due to isotopic buffering by the carbonate host rock. The high d18O values could also reflect an intense water-rock interaction and the lower d 18O values indicate a higher precipitation temperature. The calcites related with faults precipitated from tectonically expelled fluids during fault activity. The joints and scree cavities were passively filled with calcites precipitating from infiltrating meteoric water. Therefore, it is currently fair to assume that major fluid flow during seismic activity was restricted to the fault zones.