What is the reason for the high Bouguer gravity anomaly at Çumra, Konya (Central Anatolia)?

Authors: NEDİM GÖKHAN AYDIN, TURGAY İŞSEVEN

Abstract: The Bouguer gravity anomaly map of Turkey shows relatively high values around the Çumra region, Konya. This area has a flat topography and a thick cover of sediments despite being seated on a suture zone formed between Anatolide and Tauride Platforms after the Neo-Tethys Ocean closed. High Bouguer gravity anomalies indicate an anomalous mass excess buried under the flat topography. In the present study, the gravity anomaly is studied using several analysis and processing methods in order to understand and infer its possible sources. Spectral analysis of the anomaly showed that the mass should be buried at a depth of about 4.8 km. The geometry of the mass is forward modelled using the vertical prisms method, which assumes that the mass is a homogeneous layer, represented by separate identical prisms. The observed anomaly and the calculated anomaly retrieved from the modelled geometry are compared mathematically and the mass geometry is updated depending on the differences between them. After a total of 10 iterations, the RMS error decreases below 1% and thus the calculated model is considered accurate. Then the achieved model is used for mass estimations, which showed that if the density difference between the medium and the target mass is set as 0.25 g/cm³, about 67 Gt of extra mass is needed to produce such a gravity anomaly. Correlation with geological maps and aeromagnetic anomalies of the region points out that this excess mass may be due to a remnant ophiolitic rock from the Neo-Tethys Ocean.

Keywords: Gravity, Konya, Bouguer, spectral analysis, vertical prisms modelling, Tethys, obduction

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