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An integrated interpretation of multi-channel seismic reflection, gravity and magnetic datasets belonging to northern most part of the 85 degrees E Ridge in the Mahanadi offshore is carried out to study the crustal structure and mode of its emplacement. The basement structure map of the ridge reveals that it is 130-150 km wide and is composed of an eastern high which appears as a continuous, broad and smooth topography- and the western high characterized by several steep isolated highs. The seismic velocities reported for the first time over the ridge indicate several sedimentary sequences ranging in velocities between 1.6 and 4.0 km/s above the acoustic basement top. The salient aspects of the sedimentary velocities are; a low velocity layer (2.6-3.2 km/s) within the Cretaceous sequence in the intervening depressions encompassing the flank region, and a regionally widespread higher velocity layer (3.5-3.8 km/s) belonging to the Eocene-Oligocene section overlying the ridge. A layer having a velocity of 4.2-4.7 km/s probably made of volcanoclastic rocks is observed immediately below the acoustic basement. The sediment isopach maps presented here for three major horizons are used to compute the 3-D sediment gravity effect to obtain a crustal Bouguer anomaly map of the region. Detailed analysis of the gravity and magnetic anomaly maps clearly demonstrates the continuity of ridge up to the Mahanadi coast at Chilka Lake. Seismically constrained gravity and magnetic models indicate that the ridge is composed of volcanic material that was emplaced on continental crust in the shelf-slope areas and over the oceanic crust in the deep offshore areas. The modeled crustal structure below the ridge further indicates volcanic emplacement of the ridge on a relatively younger lithosphere. We propose two alternative models for the emplacement of the ridge. (C) 2014 Elsevier Ltd. All rights reserved.

WOS: 000308679200003, In this paper, a new method estimating the ratio of magnetic intensity to density contrast of a body that creates magnetic and gravity anomalies is presented. Although magnetic intensity and density of an anomalous body can be measured in the laboratory from the surface samples, the proposed new method is developed to determine the magnetic intensity and density contrast from the magnetic and gravity anomalies when the surface samples are not available. In this method, density contrast diagrams of a synthetic model are produced and these diagrams are prepared as graphics where the magnetic intensity W is given in the vertical axis and Psg (pseudogravity)/Grv (gravity) values in horizontal axis. The density contrast diagrams can be prepared as three sub-diagrams to show the low, middle and high ranges allowing obtain density contrast of body. The proposed method is successfully tested on the synthetic models with and without error. In order to verify the results of the method, an alternative method known as root-mean-square (RMS) is also applied onto the same models to determine the density contrast. In this manner, maximum correlation between the observed gravity and calculated gravity anomalies is searched and confirmation of the results is supported with the RMS method. In order to check the reliability of the new method on the field data, the proposed method is applied to the Tetbury (England) and Hanobasi (Central Turkey) magnetic and gravity anomalies. Field models are correlated with available geological, seismic and borehole data. The results are found consistent and reliable for estimating the magnetic intensity and density contrast of the causative bodies. (C) 2012 Elsevier B.V. All rights reserved., TUBITAK [YDAB-CAG-118], Authors would like to thank the Mineral Exploration and Research Institute of Turkey for the use of gravity and aeromagnetic data that were provided for a TUBITAK Project (Project No: YDAB-CAG-118). Our appreciations are also extended to the General Directory of Petroleum Affairs (GDPA) for provision of seismic sections. We are the grateful to Dr. Kumar Hemant Singh and other anonymous reviewer for their constructive suggestions. Many thanks are extended to Dr. Kei Hirose for his delicate management of editorial process.