Investigation of tectonic lineaments by using magnetic data in Poshtbadam area, Yazd province

Magnetic method is an important passive surface geophysical method which uses the Earth’s natural magnetic fields to investigate the susceptibility structure of the subsurface material. The geomagnetic field measurements can be used to determine the structure of the earth، because the rocks often contain magnetic minerals. The interpretation of data of this nature، in some cases، will determine geological characteristics that would help contribute to the success of mining or oil exploration. In this study، for the review of more details and achieving an idea about accurate location، dip، depth and mineralization spread، geomagnetic surveys were applied and then data processing method were used. Preparing a suitable map which contains the informative data without interference from noise is the main purpose of the data processing. To reach this aim، the acquired data should be corrected for different non-geological effects. These are: 1. Diurnal correction to remove time varying parts of the magnetic field. 2. IGRF correction to remove the field of earth core and upper mantle response. Many interpreting methods، that estimate the depth، location and the shape of a potential source، are based on using the gradients of potential fields. Derivatives are high pass filters. They intrinsically amplify any noise and shallow anomalies present in the data. Therefore، using high order derivatives would be less common. Tilt angle has many interesting properties. For example، due to the nature of arctan trigonometric function، all tilt amplitude are restricted to values between -90° and +90° (Salem et al. 2007). Another property of tilt angle is that the value of tilt angle above the edges of the contacts is 0°، and it is equal to 45° when h = zc and -45° when h = zc. This suggests that contours of magnetic tilt angle can identify the locations of contact-like structures. The studied area is located in Yazd province and it is part of micro continent Iran central. The intrusive rock in this area is genais and the sedimentary rock is schist and thehost rock of studied area is limestone. Igneous units of the trust are located on limestone. Also outcrop of hematite has been observed in this area. Designing the field operation grid were carried out based on geology and primary studies of region and therefore 2400 points were along 60 profiles. After diurnal correction، total magnetic intensity has been corrected by using IGRF 2000 so that components of Earth''s magnetic fields have been eliminated. Also reduction to pole operation was done. In this paper، first derivative، second derivative، analytical signal tilt angle and Euler deconvolution methods were used to study fractured structures. The edges of these faults were detected by using analytical signal، first derivatives، second derivatives and the tilt angle method. Then، we use the standard Euler deconvolution method. Reid et al (1990) used this method as Grade analysis. Simple geometric models for magnetic field source (Balkely، 1995) and determination of structural index with earlier data are disadvantages of the Euler method. However، Thompson (1982) and Reid et al (1990) determined the optimum structural index for different structures; nevertheless the Euler method estimated quite well the location and depth of magnetic sources (Aboud et al.، 2005) The results of the first vertical derivative showed three major faults in this area strikes of which were east-west in north، northeastern-southwestern in middle and northwesternsoutheastern in south of the area and the other interpretation methods have an acceptable degree of reliability. The faults specified by using these methods that are offsprings of mineralization have good compatibility with geological information. Also، the depths of the faults in the area were estimated by the Euler method. The estimated depths of the top of major faults in the area were similar at 5 m and 15 m.