Analysis of deep geological structures by variety of Curie point Depth in Birjand area, east of IRAN MOHAMMAD MAHDI KHATIB, HESAM YAZDANPENAH AND MOHAMAD HOSSEIN ZARRINKOUB Department of geology University of Birjand Po. Box :79 IRAN [email protected], [email protected]Abstract: - We examined the geology structures of the crust across complex deformation zones in Birjand (E Iran, 32°27′N to 33°28′N and 58°30′E to 59°30′E, ca. 600 km2) using the Curie Point Depth (CPD) estimates of the tectonic state of the crust with the seismic activity to provide insights for spatial limits of brittle failure in this region. The CPD estimates of Birjand area from 10.3 to 16 km below the surface. Birjand has one regions of shallow CPD. The shallow CPD region in the Bagheran Mountain in southern part of the study area is caused by upper crustal thinning and swallowing of high conductivity lower crust. In this area where hydrothermal reservoirs are located, CPD significantly shallows. Key-Words: - Birjand, Curie Point Depth (CPD), thermal structure, aeromagnetic data 1 Introduction From an analysis of the crustal magnetic field it is possible to make an estimate of the depth below which no magnetic sources exist. This depth extent of magnetic sources has become synonymous with the depth to the Curie temperature though sometimes it may represent a petrologic boundary [1]. Where the Curie depth correlates with an inferred velocity or density boundary, it is likely to reflect the change in composition; however, where it does not coincide with a velocity or density boundary, it may be interpreted as the Curie temperature isotherm [2]. As magnetite with a Curie temperature of 580 °C is believed to be the dominant magnetic mineral in the deep crust within the continental region [3], one can assume that this Curie temperature represents the temperature of 580 °C. Estimating depth to Curie temperature on a regional scale from long wavelength magnetic anomalies requires that large areas of survey data be used for the calculations. There is still no consensus on the minimum survey area required to arrive at a reliable estimate of the Curie isotherm depth [4]. Estimates of depth to the Curie temperature can provide valuable insights in the assessment of geothermal energy, calculation of thermal conductivity and tectonic/geodynamic evolution. The depth to the top of magnetic layer is often named as magnetic basement which does not necessarily correspond to geological basement where we have crystalline rocks. Sometimes magnetic basement simply is related to volcanic rocks. All sedimentary rocks are considered nun- magnetic. Therefore, the depth to magnetic basement can give us an estimate of the volume of the sedimentary basins in Birjand area. In this paper we utilize the aeromagnetic data over Birjand (E Iran) to calculate the Curie isotherm depths. The aeromagnetic data of Iran was surveyed by Aero-service Company (Houston, Texas) under the auspices of the Geological Survey of Iran during 1974-1977. The data was collected along flight lines with average line spacing of 7.5 km. the survey was done mostly for constant barometric flight heights. This data by 1 and 1 km grid of aeromagnetic map of Birjand was produced using a bidirectional interpolation scheme and filtering all wavelengths smaller than 15 km (fig. 1). Recent Researches in Environmental and Geological Sciences ISBN: 978-1-61804-110-4 475
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Analysis of deep geological structures by variety of Curie ...Abstract: - We examined the geology structures of the crust across complex deformation zones in Birjand (E Iran, 32°27′N
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Analysis of deep geological structures by variety of Curie point Depth in
Birjand area, east of IRAN
MOHAMMAD MAHDI KHATIB, HESAM YAZDANPENAH AND MOHAMAD HOSSEIN