Normalized edge detection, and the horizontal extent and depth of geophysical anomalies

Edge detection is an image processing technique for finding the boundaries of objects within images. It is typically used to interpret gravity and magnetic data, and find the horizontal boundaries of geological bodies. Large deviations between model and true edges are common because of the interference of depth and errors in computing the derivatives; thus, edge detection methods cannot provide information about the depth of the source. To simultaneously obtain the horizontal extent and depth of geophysical anomalies, we use normalized edge detection filters, which normalize the edge detection function at different depths, and the maxima that correspond to the location of the source. The errors between model and actual edges are minimized as the depth of the source decreases and the normalized edge detection method recognizes the extent of the source based on the maxima, allowing for reliable model results. We demonstrate the applicability of the normalized edge detection filters in defining the horizontal extent and depth using synthetic and actual aeromagnetic data.

Geochemical and Geophysical Data Processing Aided by“Multifractal-Spectrum”Filters for GIS-Based Mineral Exploration

A recently developed method, on the bases of “multifractal spectrum” filters for mineral exploration, is introduced in this paper. The “multifractal spectrum” filters, a group of irregularly shaped filters that are constructed on each processed datum, can be used to separate various types of geochemical and geophysical anomalies. The basic model, with an emphasis on the GIS based implementation and the application to the geochemical and geophysical data processing for mineral exploration in southern Nova Scotia, Canada, indicates its advantage in the separation of multiple anomalies from the background.

Proterozoic orogenic belts and rifting of Indian cratons: Geophysical constraints

The Aravalli-Delhi and Satpura Mobile Belts （ADMB and SMB） and the Eastern Ghat Mobile Belt （EGMB） in India form major Proterozoic mobile belts with adjoining cratons and contemporary basins. The most convincing features of the ADMB and the SMB have been the crustal layers dipping from both sides in opposite directions, crustal thickening （ -45 km） and high density and high conductivity rocks in upper/ lower crust associated with faults/thrusts. These observations indicate convergence while domal type re- flectors in the lower crust suggest an extensional rifting phase. In case of the SMB, even the remnant of the subducting slab characterized by high conductive and low density slab in lithospheric mantle up to - 120 km across the Purna-Godavari river faults has been traced which may be caused by fluids due to metamorphism. Subduction related intrusives of the SMB south of it and the ADMB west of it suggest N-S and E-W directed convergence and subduction during Meso-Neoproterozoic convergence. The simultaneous E-W conver- gence between the Bundelkhand craton and Marwar craton （Western Rajasthan） across the ADMB and the N-S convergence between the Bundelkhand craton and the Bhaodara and Dharwar cratons across the SMB suggest that the forces of convergence might have been in a NE SW direction with E-W and N-S compo- nents in the two cases, respectively. This explains the arcuate shaped collision zone of the ADMB and the SMB which are connected in their western part. The Eastern Ghat Mobile Belt （EGMB） also shows signatures orE -W directed Meso Neoproterozoic convergence with East Antarctica similar to ADMB in north India. Foreland basins such as Vindhyan （ADMB-SMB）, and Kurnool （EGMB） Supergroups of rocks were formed during this convergence. Older rocks such as Aravalli （ADMB）, Mahakoshal-Bijawar （SMB）, and Cuddapah （EGMB） Supergroups of rocks with several basic/ultrabasic intrusives along these mobile belts, plausibly formed during an earlier episode of rifting during Paleo-Mesoproterozoic period. They are highly disturbed and deformed due to subsequent Meso-Neoproterozoic convergence. As these Paleoproterozoic basins are characterized by large scale basic/ultrabasic intrusives that are considerably wide spread, it is suggested that a plume/superplume might have existed under the Indian cratons at that time which was responsible for the breakup of these cratons. Further, the presence of older intrusives in these mobile belts suggests that there might have been some form of convergence also during Paleoproterozoic period.

Subsurface geological model of sedimentary and metasedimentary wedge from Mansehra to Battal based on gravity data,Hazara area,Pakistan

This study is aimed to delineate the subsurface structural elements using geophysical techniques in the Haraza area of Pakistan.We investigated the Oghi and Battal thrust faults,sedimentary and metasedimentary wedge,and the absolute crustal thickness based on terrestrial gravity data.Unlike seismic survey relying on wave propagation,magnetic survey is based on both attraction and repulsion,and electrical and electromagnetics on induction.The attractive gravity field produces relatively simpler patterns of anomalies,like a series of highs and lows over regions with undulating basements and buried structures.A qualitative interpretation of gravity data reveals a good deal of information.During the collision of Indian and Eurasian Plates,compressional structures were developed in the Lesser Himalayas or northwest of the Hazara Kashmir Syntaxis.The study mainly focuses on the western limb of the Hazara Kashmir Syntaxis.The regional and local Bouguer anomalies were incorporated to delineate the regional structural units.The gravity model is computed through geophysical technique along with profile A-A'from Mansehra to the Battal area that demarcates the blind Oghi Thrust and emergent Battal Thrust.Tanol Formation of Precambrian age demarcates the Oghi Thrust near Kotli Pine while the Battal Thrust is demarcated within the Mansehra Granite of Cambrian to Ordovician age near Battal.Along with the Battal Thrust,fault gouge and breccias have been observed during the field studies.The total thickness of the sedimentary/metasedimentary wedge in the Mansehra and Battal areas was estimated to be 13.6 km and 14.2 km.In comparison,the total thickness of crust in the Mansehra and Battal areas was 51.6 km and 52.2 km,respectively.

Mineralogical and Geochemical Evidence of Fluid-rock Interaction at the Shallow Crustal Level in Koyna Seismogenic Region, Maharashtra, India: Impact and Implications

The Koyna region of Maharashtra located in the western part of the~65 Myr old Deccan traps province,overlying the Neoarchean cratonic granitoid basement of peninsular India,has been experiencing recurring seismicity since 1962 after the impoundment of the Shivajisagar Reservoir behind the Koyna Dam.