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Raza, M.
- Nature and Magma Type of Jagannathpur Volcanics, Singhbhum, Eastern India
Authors
1 Department of Geology, Aligarh Muslim University, Aligarh 202002, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 38, No 5 (1991), Pagination: 524-531Abstract
Jagannathpur volcanics which occur as faulted outliers within the Noa· mundi-Koira sequence of banded iron formation (BIF) of Singhbhum are analysed for major and selected trace elements. Chemical data indicate that the volcanics are calc-alkaline basalts. High MgO, Ni, Cr along with intermediate Si02, low CaO/Al203 ; Ti/Zr and high Zr/Y ratios in majority of the samples match well with modern boni- nites. It would, therefore, appear that Jagannathpur volcanics represent ao early phase of arc volcanism.Keywords
Basaltic Volcanism, Boninite, Subduction zone, Jagannathpur Volcanics, Singhbhum, Bihar.- Geodynamic Evolution of Indian Shield During Proterozoic: Geochemical Evidence from Mafic Volcanic Rocks
Authors
1 Department of Geology, Aligarh Muslim University, Aligarh-202002, IN
2 National Geophysical Research Institute, Uppal Road, Hyderabad - 500007, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 41, No 5 (1993), Pagination: 455-469Abstract
Geochemical data on Proterozoic volcanic rocks of Indian shield overwhelmingly suggest that tlhey were generated in two different tectonic settings. The mafic volcanic suites of Aravalli (Aravalli craton) and Bijawar (Rundelkhand craton) belts and those of lesser Himalayan region appear to be lift related continentat type. On the other hand Delhi volcanics (Aravalli craton), Dongargarh volcanics (Bhandara craton) and Dbanjori-Jagannathpur volcanics (Singhbhum craton) exliibit the characteristic signature of subduction zone magmatism implying the destruction of oceanic lithosphere by processes akin to those of modern plate tectonics. Geochemical and geological evidences suggest the occurrence of a nearly Proterozoic ocean in Central India located between Dharwar-Singbhum-Malwar rotocontinent in the south and Bundelkhand protocontinent in the north. During middle Proterozoic, the oceanic lithosphere subducted towards south along the northern margin of southern protocontinent. The lack of complete calc-alkaline series in the subduction - generated volcanic suites suggests that are volcanism along this margin could not acquire maturity and that the period of subduction was short lived. The collision of the two protocontinents led to the closure of ocean and induced the Satpura - Delhi orogeny at about 1500 m.y. ago-The ophiolitic seqeunce of Phulad (Delhi belt), Dalma (Singhbhum belt) and probably Tal (Bijawar belt) are the possible evidences of closure.Keywords
Geodynamics, Indian Shield, Proterozoic Volcanism, Crustal Evolulion.- Basal Aravalli Volcanism : Evidence for an Abortive Attempt to form Proterozoic Ensialic Greenstone Belt in Northwestern Part of Indian Shield
Authors
1 Department of Geology, Aligarh Muslim University, Aligarh 202 002, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 42, No 5 (1993), Pagination: 493-512Abstract
Early Proterozoic mafic volcanic rocks, occurring at the base of Aravalli Supergroup of northwestern Indian shield, have komatiitic, tholeiitic compositions. In discrimination diagrams based on immobile minor and trace elements they show a close affinity with MORB, However, the immobile incompatible element patterns and element ratios resemble those of enriched continental tholeiites which erupt at the time of initial rifting. Geochemical and geological evidences suggest a transitional nature of basal Aravalli sequence between Archaean greenstone belts and younger continental suites. It appears that the basal Aravalli volcanism was an attempt to form a Proterozoic greenstone belt on the stable continental crust through lithospheric rifting and lava eruption. The attempt failed with cessation of volcanism, probably due to falling geothermal gradient and basin subsidence by sediment loading. The occurrence of similar rock associations in other shields of the world indicates the existence of particular tectonic-thermal regimes during the early Proterozoic.Keywords
Volcanic Rocks, Proterozoic Tectonics, Aravallis, Geochemistry, Rajasthan.- Geochemistry of Early Proterozoic Mafic and Ultramafic Rocks of Jharol Group, Rajasthan, Northwestern India
Authors
1 Deptt. of Geology, Aligarh Muslim University, Aligarh-202002, IN
2 Wadia Insitute of Himalayan Geology, 33, Gen. Mahadeo Singh Road, Dehra Dun-248001, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 44, No 2 (1994), Pagination: 141-156Abstract
The deep water Jharol sediments of Aravalli Supergroup host sporadic bodies of mafic-ultramafic. rocks. Field evidence suggests that at least some of these rocks are extrusive in nature. Low to medium grade metamorphism and intense deformation has obliterated the original mineralogy and texture of these rocks. The ultramafic rocks are relatively more altered (serpentinized) with highly disturbed geochemical composition which cannot be used for petrogenetic interpretations. On the other hand, the mafic rocks are relatively less altered with some relict plagioclase feldpars. Geochemically, these mafic volcanics are Mgand Fe- rich tholeiites.
These tholeiites have nearly flat to slightly enriched REE patterns (about 30 to 40x % chondrite La and 20 to 25x % Chondrite Yb), with (LalYb)N ratio ranging between 1.29 and 1.54 and (GdIYb)N ratio ranging between 0.97 and 1.07. All samples show slight to strong positive Eu anomaly. Immobile incompatible-element geochemical patterns and other binary plots suggest that these tholeiites have enriched chemistry and that grobably they have been derived from enriched source(s) and resemble closely with within plate and initial rift tholeiites.
Trace elements, including REE based petrogenetic modelling indicate that (a) the source had about 3x% chondoritic REE abundances with nearly flat to slightly depleted pattern and (b) that these rocks were generated by about 8 to 12% partial melting of the modelled source followed by some olivine and clinopyroxene fractionation. Field as well as trace element characteristics indicate rift related (lithospheric extension) generation of these basalts with some influence of asthenosphere (deep mantle) on the lithospheric source(s) as indicated by positive Nb and Sr anomalies.
Keywords
Geochemistry, Jharol Mafics, Aravalli Supergroup, Proterozoic Volcanism, Rajasthan.- Geochemistry and Tectonic Significance of Ongarbira Volcanics, Singhbhum Craton, Eastern India
Authors
1 Department of Geology, Aligarh Muslim University, Aligarh-202 002, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 45, No 6 (1995), Pagination: 643-652Abstract
The Ongarbira volcanics of middle Proterozoic age occur with the Sahedba sedimentaries in the south of Singhbhum shear zone. The volcanics are of tholeiitic composition with high content of MgO (> 8%) and high MgO/Al2O3, ratio (> 0.6). In terms of REE data these rocks show LREE depleted patterns which resemble those of basaltic rocks from Dalma volcanic belt and basaltic komatiite of Kolar schist belt. MORB- normalized incompatible element patterns of these rocks display distinct enrichment of LILE including Th and depletion of HFSE and marked trough at Nb and Ta. These features suggest a subduction zone component in the source of Ongarbira volcanics. Nb-normalized ratio spidergrams and incompatible element ratio plots Ce/Yb- Ta/Yb-, Th/Yb- Ta/Yb and Th- Hf- Ta are consistent with their eruption in a subduction related environment. REE modelling spggests that they were generated through 14 to 18 percent partial melting of a LREE depleted source. The source was probably selectively enriched in LILE by materials derived from the subducting slab.
Geochemical-Geological evidences indicate that Ongarbira volcanics were probably erupted on a thin continental crust or even on oceanic crust as a result of a southward plate convergence below the Singhbhum craton.
Keywords
Geochemistry, Tectonics, Proterozoic Voicanics, Singhbhurn Craton.- Proterozoic Mafic Volcanism in the Aravalli-Delhi Orogen, North-western India: Geochemistry and Tectonic Framework
Authors
1 Department of Geology, University of Delhi, Delhi - 110 007, IN
2 Department of Geology, University of Leicester, Leicester LE1 7RH, GB
3 Department of Geology, Aligarh Muslim University, Aligarh - 202 001, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 72, No Spl Iss 1 (2008), Pagination: 93-111Abstract
The Aravalli-Delhi orogen in Rajasthan and northern Gujarat, NW India, hosts extensive bodies of mafic metavolcanic rocks within the Archaean Banded Gneissic Complex (BGC) basement and in the Proterozoic supracrustal belts of Bhilwara, Aravalli, Jharol and Delhi. There is no significant occurrence of mafic dykes in these terrains. All metavolcanic rocks within the supracrustal belts show typical tholeiitic compositions except for the samples from the Basantgarh area of the Delhi belt, which show calc-alkaline nature. The Bhilwara belt and Aravalli belt samples show light rare earth elements (LREE) enrichment, the Jharol belt samples are predominantly LREE depleted, whereas the Delhi belt samples show wide variations from slightly depleted through flat to highly fractionated REE patterns. Multi-element patterns are consistent with the REE patterns in terms of enrichment or depletion for the large ion lithophile elements (LILE) and with respect to high field strength elements (HFSE). The incompatible trace elements ratios (e.g. Nb/Zr, Y/Zr, Ce/Nd, etc.) are similar for the metavolcanic rocks of the Bhilwara and Aravalli belts. Samples from the Jharol and Delhi belts differ amongst themselves as well as with those from the Bhilwara and Aravalli belts. The Delhi belt samples show large variations in incompatible trace element ratios. Comparison of multi-element patterns for the volcanic rocks from the Aravalli-Delhi orogen with those from various modern tectonic settings, potentially allows constraining their tectonic setting of eruption. The tholeiitic metavolcanic rocks of the Bhilwara belt erupted along the incipient divergent eastern margin of the Archaean BGC continent and the basal Aravalli and Jharol metavolcanic rocks along its rifted western margin. The Delhi belt metavolcanic rocks indicate the evolution of the Delhi island arc through eastward subduction and emplacement of the Basantgarh-Ajari and Ranakpur-Desuri metavolcanic rocks close to the Phulad-Jetgarh suture zone on the western fringe of the arc and those of the Ambaji-Deri region along back arc spreading zones to the east, where protracted rifting led to the emplacement of gabbro-syenite plutons.Keywords
Geochemistry, Mafic Volcanism, Tectonics, Proterozoic, Delhi-Aravalli Orogen.- Bombolai Continental Pillow Lavas (Neoproterozoic) from Trans-Aravalli Region, Pali District, Rajasthan and their Tectonic Significance
Authors
1 Government College, Sirohi- 307 00 1 (Rajasthan), IN
2 Dept. of Geology, Aligarh Muslim University, Aligarh - 202 003, IN
3 Department of Earth Sciences, Kurukshetra University, Kurukshetra - 136 1 19, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 66, No 3 (2005), Pagination: 376-379Abstract
No Abstract.- Bombolai Continental Pillow Lavas (Neoproterozoic) from Trans-Aravalli Region, Pali District, Rajasthan and their Tectonic Significance
Authors
1 Department of Geology, Aligarh Muslim University, Aligarh 202 002, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 64, No 6 (2004), Pagination: 803-812Abstract
Neoproterozoic Bombolai volcanics of Trans - Aravalli terrain of western Rajasthan, consist of three distinct flows separated by metasediments including bedded chert, phyllite and quartzite In terms of their major oxides and trace and rare earth element abundances, all these flows are compositionall identical and evolved (Mg No 0 397-0 474, Ni - 61-92 ppm and Cr - 172-234 ppm) Major and trace element contents permi one to classify them as subalkaine basalts having enriched LREE abundances However, MORB and PM- nomalised spidergrams characterize them as within plate tholeites On the basis of their TiO2, content (1 84-2 43), Ti/Y ratio (294-347) and Zr/Y ratio (2 9-3 7), the Bombolai volcanics are classified as low Ti-continental tholentes The general geology geochemistry and associated lithologies indicate that the Bombolai volcanics were erupted in a reactivated nit environment (Pali lineament) which probably occurred as a precursor event to a large magmatic activity ie Malani volcanism in Trans-Aravalli region.Keywords
Geochemistry, Continental Flood Basalts, Neoproterozoic, Tans-Aravallis, Pali District Rajasthan.- Geochemistry of Mesoproterozoic Mafic Volcanics of Bayana Basin, North Delhi Fold Belt: Constraints on Mantle Source and Magmatic Evolution
Authors
1 Department of Geology, Aligarh Muslim University, Aligarh -202002, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 57, No 6 (2001), Pagination: 507-518Abstract
Mesoproterozoic volcanism in Bayana basin in the northeastern part of Aravalli-Delhi fold belt consists of mafic lava flows with quartzite-conglomerate intercalations. The volcanics are tholeiites, characterized by enrichment of large ion lithophile elements (LILE) and light rare earth elements (LREE) and depletion of Nb, P and Sr. The values of TiO2 (1.06 to 2.31 %), Zr (50 to 182 ppm), Ti/Y (286 to 521), and Zr/Y (2.63 to 5.70) are low, which illustrate their close similarity with low-Ti continental flood basalts. The Bayana volcanics may have been derived from an enriched mantle source with no significant crustal contamination. The parental magma appears to have been derived from a subcontinental lithospheric mantle source with Fe/Mg ratio exceeding that of model pyrolite. It is suggested that the mantle source of these volcanics was enriched through metasomatism by progressive transport of mantle fluids and/or melts from deeper mantle. Olivine and clinopyroxene dominated the fractional crystallization and played a major role in the evolution of magma, following its derivation from shallow mantle source(s) where clinopyroxene occurred as a residual phase.Keywords
Geochemistry, Mafic Volcanism, Bayana Basin, Delhi Fold Belt, Proterozoic, Rajasthan.- Accretionary Lapilli from the Basal Vindhyan Volcanic Sequence, South of Chittaurgarh, Rajasthan and their Implication
Authors
1 Department of Geology, Aligarh Muslim University, Aligarh - 202002, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 57, No 1 (2001), Pagination: 77-82Abstract
Well-preserved accretionary lapilli of different types are reported from the basal volcanic sequence (Khairmalia basalts) of Lower Vindhyan occurring to the south of Chittaurgarh. Four types of lapilli are identified on the basis of the nature of their core, surrounding rim zone and physical appearance. The first two types comprise cores of volcanic glass and welded tuff surrounded by rims similar to the coated accretionary lapilli or type-B of Reimer. The third type is a typical armoured lapilli, and the fourth type is a core type lapilli or type - A of Reimer. The internal structure and characteristics of the lapilli suggest their formation from ash-charged volcanic cloud produced by repeated volcanic explosions. Their excellent preservation, lack of fragmentation, presence of large size vesicles and absence of sedimentary structures in the matrix suggest little post-depositional transport. The initial explosive volcanic events and resultant basic flows and volcaniclastics, succeeded by deposition of interlayered fine clastics and conglomeratic coarse cross-bedded sandstone in the adjoining down warped (? half graben) basin (s) has heralded the onset of Vindhyan sedimentation in a fluctuating shore zone environment in southeastern Rajasthan.Keywords
Volcanism, Mesoproterozoic pyroclastics, Accretionary Lapilli, Tectono-Magmatic Event, Vindhyan Basin, Chittaurgarh, Rajasthan.- Barrier Inlet and Associated Facies of Shore Zone: An Example from Khardeola Formation of Lower Vindhyan Sequence in Chittaurgarh, Rajasthan
Authors
1 Department of Geology, Aligarh Muslim University, Aligarh - 202 002, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 58, No 2 (2001), Pagination: 97-111Abstract
Khardeola Formation (∼200 m), representing the lowermost clastic assemblage of Vindhyan Supergroup in southeast Rajasthan, consists of a fine clastic sequence in the lower part and a gritty, coarse to medium grained sandstone in the upper part. The formation crops out as discontinuous linear patches close to the western boundary of the basin. The Khardeola assemblage is investigated in this study for sedimentary facies, palaeocurrents, depositional environments and palaeogeography at the onset of Vindhyan sedimentation.
The lower fine clastic sequence (15-60 m thick) consists of interlaminated shale and siltstone, thinly bedded sandstone and mudstone,and red sandstone in a coarsening upward sequence, showing parallel to wavy lamination, ripple marks, desiccation cracks, bidirectional cross lamination, and gently inclined lamination. The facies assemblage, their characteristics, and occurrence alongside linear bodies of Khardeola sandstone, call for a protected depositional environment (back barrier lagoonal to tidal flat). The succeeding Khardeola sandstone, forming the upper part of the assemblage, represents 40-150 m thick sequence of moderately well sorted quartzarenite, subarkose and sublitharenite, and crops out as narrow linear ridges trending north-South. These sandstone units are divisible into four facies on the basis of fining upward texture, bedding types, and scale of sedimentary structures. Conglomeratic facies occurs in the basal part of sandstone with well defined scour base. The succeeding facies of lenticular sandstone with scour base comprises upward thinning sets of large, medium and small scale planar and trough cross bedding. The paleocurrent pattern reflects bipolar, bimodal to trimodal dispersal from the base of the sequence upward, directed broadly towards east and west, and occasionally towards north or south. Inasmuch as the source area providing quartzo feldspathic sediments was located mainly to the west of study area, the easterly paleocurrents were directed basinward (seaward). These deposits are interpreted as originating within laterally migrating tidal inlets (barrier inlets), in which easterly oriented ebb currents were dominant, with intermittent influx of flood oriented and north or south directed longshore currents. Plane bedded to gently inclined units of quartzarenite are interpreted as beach foreshore (spit) deposits that occur in places, capping the barrier inlet sequence. A combination of barrier inlet migration and shoreline transgression resulted in a truncated and modified barrier island sequence, dominated by inlet fill sandstone that merges with or oversteps westward (landward) the interlayered, fine grained clastic lagoonal/Tidal flat facies.
The Khardeola sedimentation was terminated with the decline in sediment supply, rise in sea level and landward migration of shoreline, followed by deposition of the overlying algae dominated Bhagwanpura Limestone in a quiet,open shelf of transgressive phase.
Keywords
Mesoproterozoic, Cratonic Basin, Sedimentary Facies, Paleocurrents, Beach, Barrier Island, Palaeogeography, Vindhyan, Rajasthan.- Geochemistry of Mesoproterozoic Lower Vindhyan Shales from Chittaurgarh, Southeastern Rajasthan and its Bearing on Source Rock Composition, Palaeoweathering Conditions and Tectono-Sedimentary Environments
Authors
1 Department of Geology, Aligarh Muslim University, Aligarh - 202 002, IN
Source
Journal of Geological Society of India (Online archive from Vol 1 to Vol 78), Vol 60, No 5 (2002), Pagination: 505-518Abstract
The western margin of the Vindhyan Basin of north Indian shield, is characterized by well developed Mesoproterozoic Lower Vindhyan succession. It contains thick units of shales and sandstonc with minor conglomcratc and limestone at different stratigraphic levels. Five shale units, namely Khardeola Shale (KHS), Palri Shale (PRS), Binota Shale (BNS), Bari Shale (BRS) and Suket Shale (SKS) occurring in chronological order, have been examined for their geochemistry to determine the composition of their source rocks, to understand the environments of weathering and sedimentation and the tectonic conditions at the time of their deposition.The Lower Vindhyan shales are characterized by high SiO2, low CaO and MgO, very low Na2O and very high K2O/Na2O ratio relative to average Proterozoic shales. All the shale units are severely depleted in Ca, Na and Sr and slightly enriched in some trace elements such as Co and Nb, relative to the early Proterozoic upper continental crust. It appears that the high field strength and transition elements remained immobile throughout the sedimentary processes and represent the source rock composition. Geochemically, the individual shale units do not show any significant variation with age, excepting the Khardeola Shale that is relatively more enriched in ferromagnesian and large ion lithophile elements.
Geochemical data suggest that sediments of Lower Vindhyan shales had their source in stable continental areas and deposited in intracratonic basin away from active plate boundaries. The immobile trace element data suggest that the source material of these shales have been derived from felsic and mafic components of Banded Gneissic Complex occurring to the west of the Great Boundary Fault in the proportion of about 4: 1. Severe but non-steady-state weathering conditions in the source region having humid, and tropical climate appcar to have prevailed throughout the sedimentation of Lower Vindhyan sequence. The sequence of events suggcsts passive type rifting environment during the Vindhyan Basin formation.