Erdinc Oksum

The Tectonic History of the Niğde-Kırşehir Massif and the Taurides since the Late Mesozoic: Paleomagnetic Evidence for Two-Phase Orogenic Curvature in Central Anatolia†

The Nigde-Kirsehir Massif, known also as the Central Anatolian Block, is bordered by the sutures of the NeoTethys Ocean. The Massif suffered several deformation phases during and after the consumption of the surrounding oceans and the post-collisional events of the continental pieces of Anatolia in latest Cretaceous to Miocene. Previous paleomagnetic studies on the Nigde-Kirsehir Massif and its surroundings displayed either insufficient data or have claimed large rotations and/or remagnetization. In order to understand the tectonic history of the Nigde-Kirsehir Massif and its adjacent blocks we have sampled 147 different sites in the age range of Upper Jurassic to Miocene from the Nigde-Kirsehir Massif throughout its W/SW and E/SE boundaries and the Central- Southeastern Taurides. The results display that except the limestones in Central Taurides, all rocks examined carry a primary magnetization. Among these an important finding is that rotations between the Massif and the Central-Eastern Taurides indicate an oroclinal bending with counterclockwise rotation of R=41.1°±7.6° in the SE and clockwise rotation of R=45.9°±9.3° in the Central Taurides from Upper Cretaceous rocks with respect to the African reference direction. Paleomagnetic rotations in the SE Taurides are compatible with the vergent direction of the thrusts generated from consumption of the Intra-Tauride ocean prior to post collisional convergence between Taurides and the Massif. In the Central Taurides it has been shown that the clockwise rotation of 45.9±9.3 started in Middle Eocene, because of a remagnetization in Upper Creataceous limestones. The deformation was linked to the final closure of the southern Neotethys and the collision between the African and Eurasian plates. In the Nigde-Kirsehir Massif counterclockwise rotation up to 25.5°±7.3° is recognised during Middle Eocene and interpreted in terms of block rotation together with the Taurides. After the Miocene a counterclockwise rotation of 16.8°±3.9° along the Eastern Taurides shows that this area was mostly affected by the westward movement of Anatolia despite the Nigde-Kirsehir Massif and its SW/W area-the Central Taurides, which is recognised as stable with counterclockwise rotation less than 10°.

Exponential approach to estimate the Curie-temperature depth

To utilize the power density spectra of magnetic anomaly is a classical routine in the estimation of the Curie-temperature depth. Many applications of this technique are encountered in the geophysical literature in spite of the difficulty arising from the selection of the points for the slope of the straight line on the power density graph. In this study, a different approach for the estimation of the Curie-temperature depth from magnetic data was introduced. It is based on the analytical solution of the exponential equations obtained from the Fourier transformation of the magnetic data. The proposed approach has been tested on the synthetic magnetic anomalies originated by single prism and multi-prisms. According to encouraging test results, this technique was also treated on the field data which were studied to estimate the top and bottom depths by using power spectra and optimization solutions.

Evidence of Late Cretaceous oroclinal bending in north-central Anatolia: palaeomagnetic results from Mesozoic and Cenozoic rocks along the İzmir–Ankara–Erzincan Suture Zone

Abstract The Sakarya Zone and the Kırşehir Block of northern Turkey are separated by the İzmir–Ankara–Erzincan Suture (IAES) Zone which is the remnant of the northern branch of the Neotethys Ocean. During the closure of the IAES in the Late Cretaceous, northwards drift of the Kırşehir Block and its eventual indentation into the Sakarya Zone produced crustal deformation defined by thrusts and reverse faults, mainly between the indenting Kırşehir Block and the Sakarya Zone. Previous palaeomagnetic studies in the eastern part of the Pontides and the Sakarya Zone showed that palaeomagnetic declinations could record the deformation that resulted in the curvature of the IAES. In order to define the tectonic deformation of the northern part of the Kırşehir Block, we present new palaeomagnetic data from 57 different sites that include Mesozoic–Cenozoic sedimentary and volcanic rocks. The results from Late Cretaceous rocks (40 sites) indicate that large clockwise rotations of c. 140–165° occurred in the eastern limb of the bend, while anticlockwise rotations progressively decreased from c. 80° to 55° from SW to NW in the western limb of the bend. In contrast, small clockwise and anticlockwise rotations are observed in the flat-lying segment of the suture zone. These rotation patterns are consistent with the geometrical trends of the IAES in northern Turkey. Declinations of seven different Middle Eocene sites within the Kırşehir Block are rotated anticlockwise by c. 30–10°. This indicates that the deformation in the Sakarya Zone and the Kırşehir Block continued in the Middle Eocene.

MATLAB code for estimating magnetic basement depth using prisms

There is a need, within both geophysical exploration and deep geophysical research, to estimate magnetic basement depth. Forward and inverse modeling studies to map the basement depth are commonly used within petroleum geophysics. To obtain the basement topography, modeling studies are made of the 2D profile data or 3D map data. In this study, a different algorithm was introduced to estimate the magnetic basement depth from map data. The algorithm is based on the analytical solution of exponential equations obtained from Fourier transformation of magnetic data. This algorithm has been tested on synthetic magnetic anomalies originated from multi-prisms. Following encouraging test results, the proposed algorithm was also tested on field data. The depths obtained from the proposed approach were satisfactory in comparison with the depths obtained from seismic survey cross-sections and boreholes. Basic MATLAB code is included in the Appendix.

Geophysical applications for Fe-rich emery exploration in the Elmacik area on the Menderes Massif (Turkey)

Abstract To determine the continuity of known Fe-rich emery horizons and to explore new deposits in the Elmacik area (Yatagan, Turkey), a geophysical survey was carried out using magnetic and electrical methods. Magnetic measurements were taken in the target area of 5 km2 and a vertical electrical sounding technique was applied at 15 locations in the alluvial/eluvial (A/E) part of the area in order to explore possible placer emery horizons, and to investigate the thickness of the A/E assembly and any probable faults. Significant magnetic anomalies occur in the vicinity of old and abandoned emery pits in the marbles of Mt Ismail. The anomalies in the marbles were caused by Fe-rich emery bodies, which did not crop out and were not more than 10 m deep. The magnetic anomalies in the A/E part of the area were weak in amplitude and may suggest small new placer emery deposits. The result of the vertical electrical soundings indicated two fault zones, one in a N–S direction, and the other approximately in an E–W direction. The thickness of the A/E assembly varies from 2–3 m to 60–100 m. A low resistivity zone, which is located in the mid-east of the A/E part of the study area, correlates well with the long-wavelength magnetic anomaly. According to the survey results, further exploration activities should take place around abandoned emery pits.

GCH_gravinv: A MATLAB-based program for inverting gravity anomalies over sedimentary basins

Abstract This paper presents a Matlab-based program GCH_gravinv including an easy-to-use graphical user interface (GUI) for determining the depth to the basement of a sedimentary basin derived from inverting its gravity anomalies by an iterative procedure. The developed code uses an advanced iterative rapid algorithm based on the combination of the FFT-based algorithm of Granser and the space domain technique of Cordell and Henderson. As an advantage, this combination performs a fast computation with high precision and the inversion scheme does not require a mean depth or low-pass filtering. Given the required density contrast varying exponentially with depth and a pre-assigned criterion for the termination of the iterative procedure, the GUI allows the user an instant view of the convergence between the observed and inverted anomalies. The feasibility of the proposed algorithm is demonstrated on synthetic data from a 3D model where the obtained results coincide well with the actual depths. The inversion of a real gravity anomaly over Chintalapudi subbasin (India) is presented to compute the basement depths as a practical example. The obtained results from the real data application are in agreement with published information available for the study area.