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Srinivas, S.
- Petrology of Basic Granulites from Maruturu Near Anakapalle in the Eastern Ghats Granulite Belt
Authors
1 Department of Geology, Andhra University, Visakhapatnam - 530 003, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 54, No 3 (1999), Pagination: 279-289Abstract
Basic granulites frequently occur in garnetiferous quartzo-feldspathic gneisses and rarely in garnetiferous sillimanite gneisses, calc-silicate rocks and quartzites in the entire Eastern Ghats Granulite Belt (EGGB). Commonly these basic layers are parallel to the foliation and are occasionally boudinaged. These share a common tectonic and metamorphic history with those of the associated litho-units. There are also unusual basic granulite dykes which crosscut the foliation in quartzo-feldspathic gneisses, folded calc-silicate rocks and basic granulites at Maruturu near Anakapalle in the EGGB. The two generations of basic granulites are even grained with a polygonal annealed mosaic and characterised by the mineral assemblage: coexisting pyroxenes and plagioclase. The mineral composition data of coexisting pyroxenes indicate large scale equilibrium at granulite facies conditions. Both types of basic granulites have almost similar bulk composition and have tholeiitic affinity. The basic granulite dykes have low contents of REE with a smooth distribution pattern and a general decrease from LREE to HREE. The revival of basic magmatism during post D1 and D2 at Maruturu reveals that extensional set-up recurs in the EGGB. The basic granulites of Maruturu are correlated with Proterozoic metabasic dykes in East Antarctica and Western Australia. The 1300 Ma basic granulites reported in Maruturu and Rayagada in the vicinity of Maruturu indicate that these intrusive basic bodies are coeval with the dyking events in Eastern Albany Mobile Belt in Western Australia and Vestfold Hill Block in Prydz Bay region in East Anatarctica.Keywords
Petrology, Geochemistry, Basic Granulite, Mineral Compositions, Eastern Ghats Granulite Belt, Andhra Pradesh.
- Basinal and Structural Appraisal of Magnetic Data of Chattisgarh Region, Central India
Authors
1 Plot No 12, Vtkaspuu, S R Nagat (Post), Hyderabad 500 038, IN
2 Department of Geophysics, Banaias Hindu University Varanasi 221005, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 63, No 3 (2004), Pagination: 323-335Abstract
The Chattisgarh Basin ot the Ccntial Indian Piecambnan Shield is one of the Puiana basins of Meso to Neopioteiozoic age which has not been geophysically investigated in good detail so far Under the Deep Continental Studies Pioject, two regional magnetic piofiies over a stietch of 382 and 403 km acioss the Chattisgaih legion weie can led out fot the fust time in ncai east west and noith south dnections respectivelyThe Chattisgaih Basin lecoided a bioad magnetic high compared to Sakoh Belt and Dongargaih Supergioup in the west and Sonakhan Greenstone Belt in the east which were reflected as lows on either side of the basin Two dimensional modelling of the data reveals a maximum thickness ot 3000 m toi the Chattisgaih sediments The acidic and basic volcanic locks associated with Sakohs Dongargarh, Sonakhan Greenstone belt and Kondagaon Granuhte belt weie demaicated and their geometiy decipheied The Indravati sediments along north south piofile indicate a maximum thickness of 2500 m Besides this, modelling of magnetic data also leveals the presence of possible inti usives into the Chattisgaih and Indravati sediments / basement
Based on the model lesults and available geological information an attempt is made to study the natuie of the uppei ciust beneath die Chattisgarh basin It appeals that the detritus to the basin sediments is derived fiom the basic locks in the centie, aiound Raipur while the peripheries are of gtanitic / acidic natuie indicating a ring type stiuctuie.
Keywords
Geophysics Magnetic Modelling, Ciustal Structuie, Pioterozoic Chattisgarh Region.- Insitu Rock Conductivity Measurement - EM Approach
Authors
1 Centre of Exploration Geophysics, Osmania University, Hyderabad - 500 007, IN
2 BHP Pvt LTd, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 61, No 6 (2003), Pagination: 685-692Abstract
Insitu electrical conductivity measurements were made over Deccan Traps using EM38 ground conductivity meter The equipment is a light weight dipole - dipole system wIth a coil separation of 1 m utilizing a frequency of 146KHz The measurements were made over chosen lava flow Units viz, compact basalt, amygdaloidal basalt and redbole The statistical analysis shows that (1) the mean resistivity of amygdaloldal basalt is 38 Ωm (range 25-42 Ωm), (2) the mean resistivity of the compact basalt under whIch a thm redbole is present is 113 Ωm, (range 105 - 131 Ωm), (3) the mean resistivity of red bole which is present under the compact basalt is 11 Ωm (range 10-13 Ωm) and (4) all the lnsitu resistivities show lognormal dIstnbution.The EM approach conductivity values (converted to resistivity values) compare well with the earher reported mwu resistivity values usmg DC resistivity measurements (Sathyamurthy, 1985) However, the values of the resistivity obtamed on bulk samples In the laboratory show markedly higher values Synthetic MT/CSAMT data generated using the insitu resistivity values obtamed via EM approach is utilized to estimate the errors In the Inverted geoelectnc parameters of resistivity and thickness.