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1.
The Proterozoic basins of India adjoining the Eastern Ghats Granulite Belt (EGGB) in eastern and southern India contain both Mesproterozoic and Neoproterozoic successions. The intracratonic set-up and contractional deformation fo the Neoproterozoc successions in the Paland sub-basin in the northeastern part of Cuddapah basin and similar crustal shortening in contemporaneous successions lying west of the EGGB and Nellore Schist Belt (NSB) are considered in relation to the proposed geodynamic evolution of the the Rodinia and Gondwana supercontinents. Tectonic shortening in the Palnad sub-basin (northeast Cuddapah), partitioned into top-to-westnorthwest thrust shear, flexural folds and cleavage development under overall E-W contraction, suggests foreland style continental shortening within an intracratonic set-up. A thrust sheet containing the Nallamalai rocks and overlying the Kurnool rocks in the northeastern part of Palnad sub-basin exhibits early tight to isoclinal folds and slaty (phylllitic) cleavage, which can be correlated with early Mesoproterozoic deformation structures in the nothern Nallamalai Fold Belt (NFB). NNE-SSW trending folds and cleavage affect the Kurnool Group and overprint earlier structures in the thrust sheet. Thrusting of the Nallamalai rocks and the later structures may have been related to convergence of the Eastern Ghats terrane and the East-Dharwar-Bastar craton during Early Neoproterozoic (Greenvillian) and/or later rejuvenation related to Pan-African amalgamation of East and West Gondwana.  相似文献   

2.
The Siddanpalli kimberlites constitute a newly discovered cluster (SKC) of Mesoproterozoic (1090 Ma) dykes occurring in the granite-greenstone terrain of the Gadwal area in the Eastern Dharwar Craton (EDC), Southern India. They belong to coherent facies and contain serpentinized olivines (two generations), phlogopite, spinel, perovskite, ilmenite, apatite, carbonate and garnet xenocrysts. A peculiar feature of these kimberlites is the abundance of carbonate and limestone xenoliths of the eroded platformal Proterozoic (Purana) sedimentary cover of Kurnool/Bhima age. Chemically, the Siddanpalli dykes are the most magnesium-rich (up to 35 wt.% MgO) and silica-undersaturated (SiO2?<?35 wt.%) of all kimberlites described so far from the Eastern Dharwar Craton. The La/Yb ratio in the Siddanpalli kimberlites (64–105) is considerably lower than that in the other EDC kimberlites (108–145), primarily owing to their much higher HREE abundances. Since there is no evidence of any crustal contamination by granitic rocks we infer this to be a specific character of the magmatic source. A comparison of the REE geochemistry of the Siddanpalli kimberlites with petrogenetic models for southern African kimberlites suggests that they display involvement of a wide range in the degree of melting in their genesis. The different geochemical signatures of the SKC compared to the other known kimberlites in the EDC can be explained by a combination of factors involving: (i) higher degrees of partial melting; (ii) relatively shallower depths of derivation; (iii) possible involvement of subducted component in their mantle source region; and (iv) previous extraction of boninitic magmas from their geological domain.  相似文献   

3.
The Peninsular India hosts extensive record of Mesoproterozoic, and Neoproterozoic successions in several mobile belts, and cratonic basins. The successions provide excellent opportunities for chronostratigraphic classification, in tune with the chronometric classification adopted by IUGS for inter-regional correlation on a global scale. Major tectono-thermal events at 1000–950 Ma in the mobile belts, correlatable with the Grenville orogeny may be considered as the datum for Meso-Neoproterozoic classification in India. Principles of chronostratigraphic classification, however, can not be applied yet to the cratonic successions of India because of inadequate radiometric data, paucity of biostratigraphic studies, and lack of regionally correlatable stratigraphic or palaeoclimatic datum. The kimberlite magmatism which affected the Peninsular India on a continental scale at about 1100 Ma, holds the key to the identification of Neoproterozoic successions of the cratonic basins. Thus, the stratigraphically confined diamond-bearing conglomerates and/or the tuffs associated with kimberlites, may be considered as the datum to define the base of the Neoproterozoic, fixed at about 1000 Ma. Accordingly, the Rewa, and Bhander Groups in the Vindhyan basin, the Kurnool Group in the Cuddapah basin, the Jagdalpur Formation in the Indravati basin, and the Sullavai Group in the Pranhita-Godavari basin are taken to represent the Neoproterozoic successions in the Peninsular India. The Chattisgarh Group in the central India, the lower part of the Marwar Supergroup in western Rajasthan, the Badami Group in the Kaladgi basin, and the Bhima Group are the other “possible Neoproterozoics” in the Peninsula.The closing phase of the Mesoproterozoic in all these basins are characterised by stable shelf lithologic associations attesting to high crustal stability. The Neoproterozoic basins, by contrast, mark a new phase of rifting, and extension, and the basin fills exhibit signatures of initial instability which evolved with time into a more stable platformal condition. A major episode of sea level rise has been recorded in most of the basins. The riftogenic origin, and evolution of the basins are comparable with the history of Neoproterozoic basins of Australia though there is no unequivocal record of glaciation in the Indian formations.  相似文献   

4.
Cuddapah basin is known for hosting unconformity proximal uranium deposits viz., Lambapur, Peddagattu, Chitirial and Koppunuru along the northern margin of the basin. It is well known that these deposits are mostly associated with basement granitoids in Srisailam Sub-basin, and with cover sediments in Palnad subbasin where basement topography and fault/fracture system influence the fluid flow causing basement alteration and ore deposition. Geological setup, surface manifestation of uranium anomalies and association of the hydro-uranium anomalies near Durgi area in southern part of the Palnad sub-basin, have prompted detail investigation by geophysical methods to probe greater depths. Controlled Source Audio Magneto Telluric (CSAMT) survey conducted over five decades of frequency (0.1-9600 Hz) delineated the various lithounits of Kurnool and Nallamalai Groups along with their thicknesses as there exist an appreciable resistivity contrast. Interpretation of CSAMT sounding data are constrained by resistivity logs and litholog data obtained from the boreholes drilled within the basin indicated three to four layered structure. Sub-surface 2-D and 3-D geo-electrical models are simulated by stitching 1-D layered inverted resistivity earth models. Stitched 1-D inverted resistivity sections revealed the unconformity between the Kurnool Group and Nallamalai Group along with basement undulations. The faults/fractures delineated from the CSAMT data corroborated well with the results of gravity data acquired over the same area. Simulated 3-D voxel resistivity model helped in visualising the faults/fractures, their depth extent, thickness of the Banganapalle quartzite and basement configuration. Integrated interpretation of CSAMT, gravity and borehole data facilitated in delineating the unconformity and the structural features favourable for uranium mineralisation in deeper parts of the Palnad sub-basin.  相似文献   

5.
Structural trends in the upper Proterozoic Cuddapah basin, at the basement level and at the Moho level have been discussed based on Deep Seismic Sounding (DSS) studies. Results of DSS studies along the Alampur-Koniki profile (profile 2 of Fig. 1) crossing the northern part of the Cuddapah basin have been discussed in detail. These results, combined with the results of the Kavali-Paranpalle section of the Kavali-Udipi DSS profile (profile 1 of Fig. 1, Kaila et al., 1979) crossing the basin on its southern flank, along with geological data and earthquake epicentral locations, are used to explain the structural trends of the area. It has been shown that the Cuddapah basin was first created in its western part by downfaulting of the crustal block between faults 7 and 14 towards the west and fault 6 in the east (Fig. 1). Subsequently, the eastern part was downfaulted against fault 6 before the commencement of upper Cuddapah sedimentation. Further downfaulting towards the north along fault 5 created the Srisailam block. Minor-scale downfaulting between faults 7 and 13 in the west and fault 6 in the east and fault 8 in the north gave rise to the Kurnool sub-basin at a later stage. Similar downfaulting east of fault 9 and north of fault 5 gave rise to the Palnad sub-basin. Both these sub-basins received Kurnool sediments.After the close of Kurnool sedimentation, the blocks between faults 4 and 6 along profile II and between 11 and 6 along profile I were uplifted at the basement level, thus giving rise to the Nallamalai hills and Iswarakuppam dome (Fig. 1). The low-angle thrust fault 3 on the eastern margin of the Cuddapah basin might be a post-Cuddapah phenomenon. The low-angle thrust fault 2 probably occurred in the post-Dharwar period. Faults 1, 17 and 10 near the east coast of India seem to be comparatively younger probably of Mesozoic time, along which the coastal block is downfaulted giving rise to the sedimentary basins.  相似文献   

6.
A lirst report on tuff beds from the Owk Shale in the Proterozoic Kurnool sub-basin in southern India is presented.The rhvolitic lo ihodacitic tuffs,overlying shclfal limestones formed at depths below storm wave base,have rheomorphic features indicative of viscoplaslic flow.and geochemical signatures of rhvolitic to rhyodacitic unwekled to welded tuffs,similar to those described from other Proterozoic intracratonie basins like Vindhvan and Chhattisgarh basins in India.Fragmentary naiure of altered glass with perlitic cracks and local admixture with intrabasinal sediments suggest phreatomagmatic reactions.The widespread and repealed occurrences of felsic luffs in these basins.possibly derived from low degree melting of continental crust.suggest intermittent(ectonothermal instability which likely intluenced hasinal topography and cyclic development of the carbonate platforms.  相似文献   

7.
New geochemical data of the crater-facies Tokapal kimberlite system sandwiched between the lower and upper stratigraphic horizons of the Mesoproterozoic lndravati Basin a::e presented. The kimberlite has been subjected to extensive and pervasive low-temperature alteration. Spinel is the only primary phase identifiable, while olivine macrocrysts and juvenile lapilli are largely pseudomorphed (talc-serpentine- carbonate alteration). However, with the exception of the alkalies, major element oxides display systematic fractionation trends; likewise, HFSE patterns are well correlated and allow petrogenetic interpretation. Various crustal contamination indices such as (SiO2 + AI::O3 ~ Na20)](MgO ~ K20) and Si] Mg are close to those of uncontaminated kimberlites. Similar La]Yb ('79-109) of the Tokapal samples with those from the kimberlites of Wajrakarur (73-145) and Narayanpet (72-156), Eastern Dharwar craton, southern India implies a similarity in their genesis. In the discriminant plots involving HFSE the Tokapal samples display strong affinities to Group 1I kimberlites from southern Africa and central India as well as to 'transitional kimberlites' from the Eastern Dharwar craton, southern India, and those from the Prieska and Kuruman provinces of southern Africa. There is a striking ~;imilarity in the depleted-mantle (TOM) Nd model ages of the Tokapal kimberlite system, Bastar craton, th~ kimberlites from NKF and WKE Eastern Dharwar craton, and the Majhgawan diatreme, Bundelkhand craton, with the emplacement age of some of the lamproites from within and around the Palaeo~Mesoproterozoic Cuddapah basin, southern India. These similar ages imply a major tectonomagmatic event, possibly related to the break- up of the supercontinent of Columbia, at 1.3-1.5 Ga across the l:hree cratons. The 'transitional' geochemical features displayed by many of the Mesoproterozoic po~:assic-ultrapotassic rocks, across these Indian cratons are inferred to be memories of the metasomatisi  相似文献   

8.
A singular outcrop of a lamproite dyke is located ~1.5 km south-west of Chintalapalle village at the NW margin of the Cuddapah basin, eastern Dharwar craton, southern India.. The dyke trends E-W and is emplaced within the granitic rocks belonging to the peninsular gneissic complex. The lamproite dyke has a porphyritic to weakly porphyritic texture comprising microphenocrysts of sanidine, and potassic richterite set in a groundmass rich in carbonate, and chlorite with rutile and titanate as accessory phases. This new occurrence of lamproite is located mid-way between the well-known Narayanpet kimberlite field towards the west and the Ramadugu and Vattikod lamproite fields in east. The Chintalapalle lamproite dyke, together with those from Vattikod, Ramadugu, Krishna and Cuddapah basin lamproite fields, constitute a wide spectrum of ultrapotassic magmatism emplaced in and around the Palaeo-Mesoproterozoic Cuddapah basin in southern India.  相似文献   

9.
The peninsular shield of India is characterized by a number of intra-cratonic sedimentary basins of which the Cuddapah and Vindhyan Basins are conspicuous.The crescent-shaped Cuddapah Basin (~1400 m.y.) covering roughly 35,000 square kilometers in the southern peninsula and enclosing the Cuddapah formations (Precambrian) includes shallow marine shales, limestones, sandstones and quartzites. These sediments are overlain by the younger Kurnool formations of Vindhyan (Upper Precambrian) age in the western and northern marginal portions of the basin and are intruded by basaltic sils and dykes. The eastern margin of the basin is characterized by an overthrust with steeply folded beds, while in the remaining parts, the formations show a gentle eastward dip. Evidence for Recent epeirogenic movements is provided by geomorphic features and current seismicity.The Great Vindhyan Basin of north-central India covering more than 100,000 square kilometers encloses Vindhyan sediments including some marine shales and limestones in the lower parts and shallow-water deposits of red sandstones and shales in the upper parts. The beds are generally horizontal, but are strongly disturbed along the southern margin. There are intrusions of basaltic dykes and kimberlite pipes.The Gondwana basins (Upper Carboniferous to Jurassic) are relatively smaller cratonic units in Archaean faulted troughs.Gravity and magnetic investigations, both regional and detailed, supplemented by deep seismic sounding profiles in the Cuddapah Basin have brought out the deep structural features of the basin, including the Moho, indicating a total thickness of generally 5–8 km with a maximum thickness of sediments of nearly 12 km in the eastern part. The beds show both a layered structure in the horizontal and block structure in the vertical, disturbed by a low-angle thrust fault on the eastern margin. In the Vindhyan Basin, the gravity and magnetic data indicate about 5000 m of sediments in the central portions, with major, roughly faults over the western and southern margins.The deep structural features of these intra-cratonic basins, as indicated by the geophysical results, are discussed in relation to the geological theories proposed for their genesis and development.  相似文献   

10.
Paleostress orientations from mechanically twinned calcite in carbonate rocks and veins in the neighborhood of large faults were investigated to comment on the nature of weak upper crustal stresses affecting sedimentary successions within the Proterozoic Cuddapah basin, India. Application of Turner's P–B–T method and Spang's Numerical dynamic analysis on Cuddapah samples provided paleostress orientations comparable to those derived from fault-slip inversion. Results from the neighborhood of E–W faults cutting through the Paleoproterozoic Papaghni and Chitravati groups and the Neoproterozoic Kurnool Group in the western Cuddapah basin, reveal existence of multiple deformation events − (1) NE–SW σ3 in strike-slip to extensional regime along with an additional event having NW–SE σ3, for lower Cuddapah samples; (2) compressional/transpressional event with ESE–WNW or NNE–SSW σ1 mainly from younger Kurnool samples.Integrating results from calcite twin data inversion, fault-slip analysis and regional geology we propose that late Mesoproterozoic crustal extension led to initial opening of the Kurnool sub-basin, subsequently influenced by weak compressional deformation. The dynamic analysis of calcite twins thus constrains the stress regimes influencing basin initiation in the southern Indian cratonic interior and subsequent basin inversion in relation to craton margin mobile belts and plausible global tectonic events in the Proterozoic.  相似文献   

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