Mineralogical and chemical characteristics of newer dolerite dyke around Keonjhar, Orissa: Implication for hydrothermal activity in subduction zone setting
TL;DR: The newer dolerite dykes around Keonjhar within the Singbhum Granite occur in NE-SW, NW-SE and NNE-SSW trends as mentioned in this paper.
Abstract: The newer dolerite dykes around Keonjhar within the Singbhum Granite occur in NE–SW, NW–SE and NNE–SSW trends. The mafic dykes of the present study exhibit several mineralogical changes like clouding of plagioclase feldspars, bastitisation of orthopyroxene, and development of fibrous amphibole (tremolite–actinolite) from clinopyroxene, which are all considered products of hydrothermal alterations. This alteration involves addition and subtraction of certain elements. Graphical analyses with Alteration index and elemental abundances show that elements like Rb, Ba, Th, La and K have been added during the alteration process, whereas elements like Sc, Cr, Co, Ni, Si, Al, Fe, Mg and Ca have been removed. It is observed that in spite of such chemical alteration, correlation between major and trace elements, characteristic of petrogenetic process, is still preserved. This might reflect systematic Alteration (addition or subtraction) of elements without disturbing the original element to element correlation. It has also been established by earlier workers that the evolution of newer dolerite had occurred in an arc-back arc setting which may also be true for newer dolerites of the present study. This is evident from plots of pyroxene composition and whole rock composition of newer dolerite samples in different tectonic discrimination diagrams using immobile elements. The newer dolerite dykes of the Keonjhar area may thus be considered to represent an example of hydrothermal activity on mafic rocks in an arc setting.
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TL;DR: In this article, the authors reported eight new Pb-Pb baddeleyite ages and paleomagnetic results on a series of hitherto unknown NNE-SSW trending mafic dyke swarms intruding the Paleoarchean basement rocks in the Singhbhum craton, eastern India.
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TL;DR: In this article, the authors reported the first key paleopole as a result of paleomagnetic study on a precisely dated 1765, which was used in this study to propose the paleogeographic reconstruction of India with Baltica Craton and North China Craton.
35 citations
TL;DR: The Bangriposi Granite Gneiss as discussed by the authors is composed of quartz, alkali feldspar, ferroan biotite (Fe/Fe+Mg: 0.7-0.9), titanite, illmenite, hastingsite, apatite, and numerous U-ThREE bearing accessory phases.
27 citations
TL;DR: The Singhbhum Craton in eastern India is host to at least seven sets of mafic dyke swarms and the dykes range in composition from basalt to andesite and have transitional tholeiitic to calc-alkaline affinities as discussed by the authors.
14 citations
TL;DR: In this article, the authors investigated the petrography and geochemistry of 19 NNE-SSW to NE-SW trending dolerite dykes in two sectors in the northern and southwestern part of Bahalda town, Odisha, India.
Abstract: The mafic dyke swarm, newer dolerite dykes (NDDs) intrudes the Archaean Singbhum granite of the Singhbhum craton, eastern India. The present investigation focuses on the petrography and geochemistry of 19 NNE–SSW to NE–SW trending NDDs in two sectors in the northern and south-western part of Bahalda town, Odisha, Singhbhum. Chondrite normalised rare earth element (REE) patterns show light REE (LREE) enrichment among majority of the 13 dykes while the remaining six dykes show a flat REE pattern. Critical analyses of some important trace element ratios like Ba/La, La/Sm, Nb/Y, Ba/Y, Sm/La, Th/La, La/Sm, Nb/Zr, Th/Zr, Hf/Sm, Ta/La and Gd/Yb indicate that the dolerite dykes originated from a heterogeneous spinel peridotite mantle source which was modified by fluids and melts in an arc/back arc setting. REE modelling of these dolerite dykes were attempted on LREE-enriched representative of NDD which shows that these dykes might have been generated by 5–25% partial melting of a modified spinel peridotite source which subsequently suffered around 30% fractional crystallisation of olivine, orthopyroxene and clinopyroxene. The reported age of ~2.75–2.8 Ma seems to be applicable for these dykes and this magmatism appears to be contemporaneous with major scale anorogenic granitic activity in the Singhbhum craton marking a major event of magmatic activity in eastern India.
11 citations
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Journal Article•
TL;DR: The results of diabase alteration experiments at elevatd temperatures and pressures have been combined with theoretical calculations to define the metasomatic processes reflected by the chemistry of hot-spring fluids and the chemistry and mineralogy of metabasalts dredged from midocean ridges and observed in ophiolite outcrops on land as discussed by the authors.
Abstract: Results of diabase alteration experiments at elevatd temperatures and pressures have been combined with theoretical calculations to define the metasomatic processes reflected by the chemistry of hot-spring fluids and the chemistry and mineralogy of metabasalts dredged from midocean ridges and observed in ophiolite outcrops on land. These data demonstrate that Mg-, Caand Na-fixation reactions are affected differently by different alteration conditions, and thus it is likely that each dominates a specific region within the submarine geothermal system. Mg fixation characterizes the downwelling limbs ofsubseafloor convection cells, whereas Ca and Na fixation are related more fundamentally to hydrothermal upflow zones, Ca at depth and Na nearer the surface. Ca removal from solution and attendant H * production are enhanced greatly by decompression effects, which contribute as well to oxidation and stabilization of epidote relative to other calcic alteration phases. Epidote-rich rocks (epidosites) observed at the base of sheeted intrusive complexes of numerous ophiolites likely represent he effects of Ca fixation, decompression, and oxidation within deep-seated, permeable upflow zones. The local, integrated, fluid/rock mass ratio of epidosite reaction zones may be as high as 1000. Experimental models of ridge-crest hydrothermal processes suggest hat epidote and plagioclase solid solutions control the chemistry and pH of hot-spring fluids. Temperatures and pressures of approximately 385-400oC and 300-4@ bars characterize the reaction zone of fluids discharging from black-smoker vents at 2l oN, East Pacific Rise. Reaction-zone conditions (?iP) can be estimated for virtually all hot-spring fluids provided that salinity effects and retrograde processes caused by conductive cooling and/or subseafloor mixing are unambiguously accounted for.
135 citations
TL;DR: The Ascot Formation of southeastern Quebec consists of greenschist facies metamorphosed silicic to mafic pyroclastic rocks and lava flows and associated metasediments as discussed by the authors.
Abstract: The middle Ordovician Ascot Formation of southeastern Quebec consists of greenschist facies metamorphosed silicic to mafic pyroclastic rocks and lava flows and associated metasediments. Chemical analyses of lavas reveal a preponderance of metarhyolites and metabasalts, together with some porphyritic rocks with intermediate SiO2 contents. The metabasalts exhibit wide ranges in concentrations of TiO2 (0.25–2.0 wt.°), Y (9–46 ppm), and Zr (5–135 ppm). The extent of the ranges, and unusual interelement ratios, suggest that the concentrations of these normally immobile elements have been affected by secondary processes. There is a strong correlation between trace-element concentrations and the degree of carbonatization of the metabasalts. Low carbonate rocks are severely depleted in Ti, Y, and Zr whereas high carbonate rocks are depleted in Y and Zr and enriched in Ti. The differing movement of Ti can be explained in terms of variable chemical potential due to the various carbonatization reactions affecting titaniferous phases. Overall mobility of these generally “immobile/rd elements is attributed to high CO2 levels in the fluid phase during metamorphism. Extrapolation of the two alteration trends to a common origin enables one to infer primary concentrations of the trace-elements. Primary inter-element ratios arrived at in this way are compatible with an island-arc origin for the Ascot Formation although TiO2 concentrations are a little high (1.5 wt/%).
116 citations
"Mineralogical and chemical characte..." refers background in this paper
...It has been observed that mobile elements like Ba, Rb, Th, etc., and even some immobile elements as Nb and Zr can be affected under specific conditions (Hellman et al. 1979; Hynes 1980)....
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Journal Article•
TL;DR: A critical review of present available geological and radiometric age data suggests that Chotanagpur Gneissic Complex was evolved from a supracrustal precursor, some of them were formed at least before -2 3 Ga.
Abstract: The Precambrian granite-Greenstone terrain of eastern Indian shield includes Singhbhum-Orissa craton, Singhbhum Mobile Belt supracrustals (Singhbhum Group) along its northern, eastern and western margins, and Chotanagpur Gneissic Complex towards further north. Recent isotopic ages along with other geological considerations show that these three crustal units perhaps constitute a single cratonic block, which grew in sequence from -3 55 to 1 00 Ga. The center of crustal growth gradually migrated with younging from the present south to north. Prior to the onset of this crustal growth, there was a still older crust in this region at -3 60 Ga, the remnants of which are preserved only as detrital zircons at present. However, the Singhbhum-Orissa craton represented the nucleus of the presently existing cratonic block, which had formed between -3 55 and 3 12 Ga through two successive supracrustal-granite cycles, well separated by an erosional unconformity. The first cycle included Older Metamorphic Group supracrustals, Older Metamorphic Tonalite Gneiss and Singhbhum Granite, phase-I, Singhbhum Granite, phases II, Chakradharpur Granite Gneiss and Nilgiri Granite that grew in sequence from -3 55 to 3 30 Ga. The second cycle included Iron Ore Group supracrustals followed by emplacement of Bonai Granite and Singhbhum Granite, phase III, and had an evolutionary history ranging from -3 30 to 3 16 Ga or up to -3 12 Ga. The supracrustal-Granite cycles began with formation of supracrustal sequences in anorogenic setting, followed successively by major folding during following orogeny and final emplacement of orogenic granites into these deformed supracrustals. The emplacement of anorogenic Mayurbhanj Granite pluton with Mayurbhanj Gabbro along the northeastern margin of the craton at -3 09 Ga marked the stabilization of Singhbhum-Orissa craton. Emplacement of Singhbhum Granite, phase II, Singhbhum Granite, phase III and Mayurbhanj Gabbro recorded metamorphism on the older rock units of Singhbhum-Orissa craton. In the late Meso- to Neoarchaean period Singhbhum-Orissa craton grew along its northern, western and eastern margins by formation of a supracrustal sequence of syn-Rift nature including mostly clastic sediments and minor basic and acid volcanics, which followed upward by major basic volcanisms. These supracrustals included Singhbhum Group, which unconformably overlay the Singhbhum Granite, phase-III and equivalent granite basements and was subjected to two major phases of folding, before being overlain by undeformed. Simlipal volcano-Sedimentary basin occurring at the eastern part of the craton. The evolution of Singhbhum Group and Simlipal basin took place between -3 12 and 3 09 Ga, before being intruded by anorogenic Mayurbhanj Granite( -3 09 Ga) and was followed by the formation of overlying riftogenic Dalma Group and adjacent Dhanjori Group of basic volcanics and some minor acid plutonics at the marginal part of the craton at -2 80 Ga and their subsequent major metamorphism at -2 50 Ga. A critical review of present available geological and radiometric age data suggests that Chotanagpur Gneissic Complex was evolved from a supracrustal precursor, some of them were formed at least before -2 3 Ga. The Singhbhum Group supracrustals and adjacent Chotanagpur Gneissic Complex perhaps had evolved from a common sedimentary precursor along with volcanics, which were deposited in a marine basin that existed at the present north of Singhbhum-Orissa craton during late Mesoarchaean period. The syn-rift sedimentary assemblage of the Singhbhum Group was deposited along the margin of Singhbhum Orissa craton, whereas the post-rift stable shelf sedimentary precursor of the Chotanagpur Gneissic Complex was deposited towards further north. In the Neoarchaean period between - >3 09 Ga and -2 5 Ga the nature of deformation along the marginal part of Singhbhum-Orissa craton was extensional type. In the following Palaeo- to Mesoproterozoic period, the protolith of Chotanagpur Gneissic Complex grew in sequence between - > 2 3 and 1 0 Ga through two time-Separated supracrustal granite cycles where the first and second cycles ended at -1 60 and 1 00 Ga respectively. Radiometric ages suggest that Chotanagpur Gneissic Complex along with Singhbhum Group experienced major magmato-metamorphic activities during Palaeo- and Mesoproterozoic periods at -2 5 or >2 3 Ga, 1 6 Ga, 1 0 Ga and 0 9 Ga. During this period Singhbhum-Orissa craton recorded basic volcanism (Jagannathpur and possibly Malangtoli Volcanics) at -2.25 Ga, followed by deposition of clastic sediments (Kolhan Group) and finally emplacement of mafic dykes and sills (Newer Dolerite) in three successive sequences at -2.0 Ga, 1.6 Ga and 1.0 Ga, where all these phenomena took place under anorogenic setting. The Singhbhum Shear Zone, which marked a tectonic boundary between Singhbhum-Orissa craton and Singhbhum Mobile Belt to north, was reactivated several times during geological past, the oldest being at -3.09 Ga, followed by emplacement of Soda Granite pluton along this shear zone at -2.22 Ga, copper mineralization at -1.77 Ga, shearing at - 1.67-1.63 Ga, uranium mineralisation at -1.58- 1.48 Ga and the final phase of shearing at - 1.0 Ga.
107 citations
"Mineralogical and chemical characte..." refers background in this paper
...The chronostratigraphic succession of rocks of Singhbhum craton (Misra 2006) indicate that the newer dolerite dykes are the youngest mafic magmatic unit....
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TL;DR: The isotopic data provide evidence that parts of the earth's mantle were already differentiated with respect to the chondritic samarium-neodymium ratio 3800 x l0(6) years ago.
Abstract: Samarium-neodymium data for nine granitic and tonalite gneisses occurring as remnants within the Singhbhum granite batholith in eastern India define an isochron of age 3775 ± 89 x 10 6 years with an initial 143 Nd /144 Nd ratio of 0.50798 ± 0.00007. This age contrasts with the rubidium-strontium age of 3200 x 10 6 years for the same suite of rocks. On the basis of the new samarium-neodynium data, field data, and petrologic data, a scheme of evolution is proposed for the Archean crust in eastern India. The isotopic data provide evidence that parts of the earth's mantle were already differentiated with respect to the chondritic samarium-neodymium ratio 3800 x l0 6 years ago .
86 citations
TL;DR: In this article, the authors describe the lithology, structure, and field relations of selected Arabian shield ophiolites and illustrate the outcrop characteristics and degrees of dismemberment and structural complexity.
Abstract: Publisher Summary This chapter describes the lithology, structure, and field relations of selected Arabian shield ophiolites, thereby providing examples of Neoproterozoic ophiolites and illustrating the outcrop characteristics and degrees of dismemberment and structural complexity that may be expected of Neoproterozoic ophiolites elsewhere. Peridotite is mainly exposed on the southern slope of Jabal Ess in the central part of the ophiolite. Dunite contains bastatized pyroxene ghosts and local disseminated chromite and podiform chromite lenses 20 cm across. Enstatite banding and trains of ovoid, stretched chromian spinel define a metamorphic foliation and lineation, which are suggestive of high-temperature subsolidus deformation possibly as a result of plastic mantle flow beneath a spreading ridge. The complex is steeply dipping, and the exposures are effectively a cross-section through the ophiolite. The gross distribution of rock types suggests an ophiolite succession younging from south to north but the succession is disrupted by deformation.
81 citations