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.

Surface geochemical data evaluation and integration with geophysical observations for hydrocarbon prospecting,Tapti graben,Deccan Syneclise,India

The Deccan Syneclise is considered to have significant hydrocarbon potential. However, significant hydrocarbon discoveries, particularly for Mesozoic sequences, have not been established through conventional exploration due to the thick basalt cover over Mesozoic sedimentary rocks. In this study, near-surface geochemical data are used to understand the petroleum system and also investigate type of source for hydrocarbons generation of the study area. Soil samples were collected from favorable areas identified by integrated geophysical studies. The compositional and isotopic signatures of adsorbed gaseous hydrocarbons （methane through butane） were used as surface indicators of pe- troleum micro-seepages. An analysis of 75 near-surface soil-gas samples was carried out for light hydrocarbons （C_1-C_4） and their carbon isotopes from the western part of Tapti graben, Deccan Syneclise, India. The geochemical results reveal sites or clusters of sites containing anomalously high concentrations of light hydrocarbon gases. High concentrations of adsorbed thermogenic methane （C1 518 ppb） and ethane plus higher hydrocarbons （∑C2＋ = 977 ppb） were observed. Statistical analysis shows that samples from 13% of the samples contain anomalously high concentrations of light hydrocarbons in the soil-gas constituents. This seepage suggests largest magnitude of soil gas anomalies might be generated/source from Mesozoic sedimentary rocks, beneath Deccan Traps. The carbon isotopic composition of methane, ethane and propane ranges are from 22.5‰to -30.2‰ PDB, -18.0‰ to 27.1‰,, PDB and 16.9‰-32.1‰ PDB respectively, which are in thermogenic source. Surface soil sample represents the intersection of a migration conduit from the deep subsurface to the surface connected to sub-trappean Mesozoic sedimentary rocks. Prominent hydrocarbon concentra- tions were associated with dykes, lineaments and presented on thinner basaltic cover in the study area, which probably acts as channel for the micro-seepage of hydrocarbons.

Seismic Imaging of the Upper Mantle under the Erebus Hotspot in Antarctica

P-wave velocity images are determined under the Mount Erebus hotspot,Antarctica by using teleseismic tomography.Our results show a prominent low-velocity(low-v)anomaly of nearly circular symmetry(about 250-300 km in diameter)to about 200 km depth under the Mount Erebus volcanic region,which further extends down to～400 km as a narrow tilted column.The observed low-v anomaly beneath the Mount Erebus volcano can be an expression of a thermal anomaly of deep origin.

Optimization of Groundwater Pumping on Coral Islands Through the Application of Artificial Neural Network

The development and growing population has resulted in the increasing demand for potable water in tiny atolls of Lakshadweep group,off the western coast of India.In recent years,the groundwater quality,in such atolls,has been deteriorated due to indiscriminate exploitation of groundwater to meet the demand.Thus arranging a sustainable supply of groundwater has become the most challenging task on these tiny atolls for the survival of human life. Groundwater floats in the form of thin lens,which

Formation and Evolution of Dharwar Craton in South India-Synthesis from Broadband Seismological Experiment

Understanding the structure,composition and survival of Archaean cratons over geological times is critical to model the process of crustal evolution.The South India Broadband Seismic Imaging Experiment was organized to answer fundamental questions of craton formation,with the principal objective of characterizing physico-chemical nature of the crust and mantle of Dharwar craton and adjoining terrains.

Significance of Precipitation Chemistry for Delineating Polluted Parts of Maheshwaram Aquifer System,Andhra Pradesh

The chemistry of subsurface water bodies is difficult to understand unless precipitation chemistry and atmospheric processes are taken into consideration. Limited pioneer work has been carried out on considering precipitation chemistry.Polluted zone delineation is very much significant before the planning for any of the remedial measures.The dual contamination is a common problem noticed

Fluoride Hydro-geochemistry Studies:A Case Study from Granitic Aquifer System of Maheshwaram,Hyderabad,India

The impact of population pressure has been observed on several systems,groundwater resource is one among them.Mismanagement and over-exploitation has not only caused the decline of groundwater levels but also causes deterioration in water quality. Fluoride is one of such parameters where impact of over exploitation has been observed.Fluoride is

Co-Integration Models for Koyna and Warna Reservoirs, India

Koyna region, a seismically active region, has many time series observations such as seismicity, reservoir water levels, and many bore well water levels. One of these series is used to predict others since these parameters are interlinked. If these series were stationary, we used correlation analysis. However, it is seen that maximum of these time series are nonstationary. In this case, co-integration method is used that is extracted from econometrics and forecast is possible. We have applied this methodology to study time series of reservoir water levels of this region and we find them to be co-integrated. Therefore, forecast of water levels for one of the reservoir is done from the other as these will never drift apart too much. The outcomes demonstrate that a joint modelling of both data sets based on underlying physics resolves to be sparingly useful for understanding predictability issues in reservoir induced seismicity.