Relative contributions of crust and mantle to the origin of the Bijli Rhyolite in a palaeoproterozoic bimodal volcanic sequence (Dongargarh Group), central India
TL;DR: The Bijli rhyolite is a poorly sorted pyroclastic deposit, and comprises of phenocrystic K-feldspar + albite ± anorthoclase set in fine-grained micro-fragmental matrix of quartz-feld-spar-sericite-chlorite-ironoxide ± calcite as discussed by the authors.
Abstract: New mineralogical, bulk chemical and oxygen isotope data on the Palaeoproterozoic Bijli Rhyolite, the basal unit of a bimodal volcanic sequence (Dongargarh Group) in central India, and one of the most voluminous silicic volcanic expressions in the Indian Shield, are presented. The Bijli Rhyolite can be recognized as a poorly sorted pyroclastic deposit, and comprises of phenocrystic K-feldspar + albite ± anorthoclase set in fine-grained micro-fragmental matrix of quartz-feldspar-sericite-chlorite-iron-oxide ± calcite. The rocks are largely metaluminous with high SiO2, Na2O + K2O, Fe/Mg, Ga/Al, Zr, Ta, Sn, Y, REE and low CaO, Ba, Sr contents; the composition points to an ‘A-type granite’ melt. The rocks show negative Cs-, Sr-, Eu- and Ti- anomalies with incompatible element concentrations 2–3 times more than the upper continental crust (UCC). LREE is high (La/Yb ∼ 20) and HREE 20–30 times chondritic. δ18Owhole-rock varies between 4.4 and 7.8‰ (mean 5.87±1.26‰). The Bijli melt is neither formed by fractionation of a basaltic magma, nor does it represent a fractionated crustal melt. It is shown that the mantle-derived high temperature basaltic komatiitic melts/high Mg basalts triggered crustal melting, and interacted predominantly with deep crust compositionally similar to the Average Archaean Granulite (AAG), and a shallower crustal component with low CaO and Al2O3 to give rise to the hybrid Bijli melts. Geochemical mass balance suggests that ∼ 30% partial melting of AAG under anhydrous condition, instead of the upper continental crust (UCC) including the Amgaon granitoid gneiss reported from the area, better matches the trace element concentrations in the rocks. The similar Ta/Th of the rhyolites (0.060) and average granulite (0.065) vs. UCC (0.13) also support a deep crustal protolith. Variable contributions of crust and mantle, and action of hydrothermal fluid are attributed for the spread in δ18Owhole-rock values. The fast eruption of high temperature (∼ 900°C) rhyolitic melts suggests a rapid drop in pressure of melting related to decompression in an extensional setting.
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TL;DR: In this paper, the authors presented five new discriminant function diagrams based on an extensive database representative of basic and ultrabasic rocks from four tectonic settings of island arc, continental rift, ocean island, and mid-ocean ridge.
Abstract: We present five new discriminant function diagrams based on an extensive database representative of basic and ultrabasic rocks from four tectonic settings of island arc, continental rift, ocean-island, and mid-ocean ridge. These diagrams were obtained after loge-transformation of concentration ratios of major-elements — a technique recommended for a correct statistical treatment of compositional data. Higher % success rates (overall values from ∼ 83 to 97%) were obtained for proposing these new diagrams as compared to those (∼82 to 94%) obtained from the discriminant analysis of the raw major-element concentration data (i.e., without the loge-transformation and without taking ratios of the compositional data, but using exactly the same database to provide an unbiased comparison), suggesting that such a data transformation constitutes a statistically correct and recommended technique. The new diagrams also resulted in less mis-classification of basic and ultrabasic rocks from known tectonic settings than the diagrams obtained from the raw data. The use of these highly successful new discriminant function diagrams is illustrated using Miocene to Recent basic and ultrabasic rocks from three areas of Mexico with complex or controversial tectonic settings (Mexican Volcanic Belt, Los Tuxtlas volcanic field, and Eastern Alkaline Province), as well as older rocks from three areas (Deccan, Malani, and Bastar) of India. Additionally, the major-element data from two ‘known’ continental arc settings are used to show that they are similar to those from the island arc setting. Continental rift setting is inferred for all Mexican cases and for one cratonic area of India (Malani) and an IAB setting for the Bastar craton. The Deccan flood basalt province of India is used to warn against an indiscriminate use of those discrimination diagrams that do not explicitly include the likely setting of the area under evaluation. An Excel template is also provided for an easy application of these new diagrams for discriminating the four settings considered in this work.
126 citations
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...This recommendation is also valid for other workers such as: Sensarma et al (2004) on Bijli Rhyolite of central India; Alam et al (2004) on Barren Island lavas and dykes; and Duraiswami et al (2004) on Daund lava flow....
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01 Jan 2007
TL;DR: Foulger et al. as mentioned in this paper proposed a plate tectonic model for the genesis of melting anomalies, which is supported by the observation that most present-day "hotspots" erupt either on or near spreading ridges or in continental rift zones and intraplate regions observed or predicted to be extending.
Abstract: The plate tectonic processes, or “plate,” model for the genesis of melting anomalies (“hotspots”) attributes them to shallow-sourced phenomena related to plate tectonics. It postulates that volcanism occurs where the lithosphere is in extension, and that the volume of melt produced is related primarily to the fertility of the source material tapped. This model is supported in general by the observation that most present-day “hotspots” erupt either on or near spreading ridges or in continental rift zones and intraplate regions observed or predicted to be extending. Ocean island basalt-like geochemistry is evidence for source fertility at productive melting anomalies. Plate tectonics involves a rich diversity of processes, and as a result, the plate model is in harmony with many characteristics of the global melting-anomaly constellation that have tended to be underemphasized. The melting anomalies that have been classified as “hotspots” and “hotspot tracks” exhibit extreme variability. This variability suggests that a “one size fits all” model to explain them, such as the classical plume model, is inappropriate, and that local context is important. Associated vertical motion may comprise pre-, peri-, or post-emplacement uplift or subsidence. The total volume erupted ranges from trivial in the case of minor seamount chains to ~108 km3 for the proposed composite Ontong Java–Manihiki–Hikurangi plateau. Time progressions along chains may be extremely regular or absent. Several avenues of testing of the hypothesis are being explored and are stimulating an unprecedented and healthy degree of critical debate regarding the results. Determining seismologically the physical conditions beneath melting anomalies is challenging because of problems of resolution and interpretation of velocity anomalies in terms of medium properties. Petrological approaches to determining source temperature and composition are controversial and still under development. Modeling the heat budget in large igneous provinces requires knowledge of the volume and time scale of emplacement, which is often poorly known. Although ocean island basalt–type geochemistry is generally agreed to be derived from recycled near-surface materials, the specifics are still disputed. Examples are discussed from the Atlantic and Pacific oceans, which show much commonality. Each ocean hosts a single, currently forming, major tholeiitic province (Iceland and Hawaii). Both of these comprise large igneous provinces that are forming late in the sequences of associated volcanism rather than at their beginnings. Each ocean contains several melting anomalies on or near spreading ridges, both timeand non-timeprogressive linear volcanic chains of various lengths, and regions of scattered volcanism several hundred kilometers broad. Many continental large igneous provinces lie on the edges of continents and clearly formed in association with continental breakup. Other volcanism is associated with extension in rift valleys, back-arc regions, or above sites 1 *E-mails: g.r.foulger@durham.ac.uk, gfoulger@usgs.gov. Foulger, G.R., 2007, The “plate” model for the genesis of melting anomalies, in Foulger, G.R., and Jurdy, D.M., eds., Plates, plumes, and planetary processes: Geological Society of America Special Paper 430, p. 1–28, doi: 10.1130/2007.2430(01). For permission to copy, contact editing@geosociety.org. ©2007 The Geological Society of America. All rights reserved.
116 citations
TL;DR: In this article, the authors proposed a hierarchical classification of LIPs that is independent of composition, tectonic setting, or emplacement mechanism, and suggested that the term LIP is used in its broadest sense and that it should designate igneous provinces with outcrop areas ≥ 50,000 km 2.
90 citations
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...While this category of LVP is relatively unusual and uncommon as compared to LBPs, examples include the Tertiary Snake River Plain–Oregon High Lava Plains province in the western U.S.A. (e.g., Jordan, 2005), and the Palaeoproterozoic (2.5–2.2 Ga) Dongargarh province in central India (Sensarma et al., 2004; Sensarma, 2007)....
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...The Archaean and Proterozoic charnockite (hypersthene–granite) massifs of southern India (Rajesh and Santosh, 2004) would be included in the LGP category....
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...2 Ga) Dongargarh province in central India (Sensarma et al., 2004; Sensarma, 2007)....
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...Besides the Whitsunday and the Sierra Madre Occidental provinces, the Neoproterozoic Malani province of northwestern India (Sharma, 2004, 2005) is a good example....
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...The Deccan Traps, for example, cover 0.5 million km2 of western-central India today and have an estimated original extent of 1.5 million km2 (Wadia, 1975)....
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TL;DR: In this article, the felsic volcanic rocks of Neoarchaean Shimoga greenstone terrane of western Dharwar Craton in India are dominantly represented by rhyolites occurring at stratigraphically upper horizons.
52 citations
TL;DR: In this paper, the authors illustrate and discuss the morphology and emplacement of the modern and active lava flows of Kilauea volcano in Hawaii, and based on them, interpret the compound pahoehoe lavas of the Deccan Traps.
Abstract: There is a growing interest in deciphering the emplacement and environmental impact of flood basalt provinces such as the Deccan, India. Observations of active volcanism lead to meaningful interpretations of now-extinct volcanic systems. Here, I illustrate and discuss the morphology and emplacement of the modern and active lava flows of Kilauea volcano in Hawaii, and based on them, interpret the compound pahoehoe lavas of the Deccan Traps. The latter are vastly larger (areally extensive and voluminous) than Kilauea flows, and yet, their internal architecture is the same as that of Kilauea flows, and even the sizes of individual flow units often identical. Many or most compound flows of the Deccan Traps were emplaced in a gentle, effusive, Kilauea-like fashion. Bulk eruption rates for the Deccan province are unknown, and were probably high, but the local eruption rates of the compound flows were no larger than Kilauea’s. Large (≥ 1000 km3) individual compound pahoehoe flows in the Deccan could have been emplaced at Kilauea-like local eruption rates (1 m3/sec per metre length of fissure) in a decade or less, given fissures of sufficient length (tens of kilometres), now exposed as dyke swarms in the province.
41 citations
Cites background from "Relative contributions of crust and..."
...…subcontinent (see references in Sheth and Pande 2004) e.g., the Malani province (Sharma 2004; Singh and Vallinayagam 2004), the Dongargarh sequence (Sensarma et al 2004), ophiolitic basalts in the Himalaya and the Andaman Islands (e.g., Srivastava et al 2004), as well as India’s active volcano…...
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References
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01 Jan 1985
TL;DR: In this paper, the authors describe the composition of the present upper crust and deal with possible compositions for the total crust and the inferred composition of lower crust, and the question of the uniformity of crustal composition throughout geological time is discussed.
Abstract: This book describes the composition of the present upper crust, and deals with possible compositions for the total crust and the inferred composition of the lower crust. The question of the uniformity of crustal composition throughout geological time is discussed. It describes the Archean crust and models for crustal evolution in Archean and Post-Archean time. The rate of growth of the crust through time is assessed, and the effects of the extraction of the crust on mantle compositions. The question of early pre-geological crusts on the Earth is discussed and comparisons are given with crusts on the Moon, Mercury, Mars, Venus and the Galilean Satellites.
12,457 citations
TL;DR: In this paper, the authors compared the relative abundances of the refractory elements in carbonaceous, ordinary, and enstatite chondritic meteorites and found that the most consistent composition of the Earth's core is derived from the seismic profile and its interpretation, compared with primitive meteorites, and chemical and petrological models of peridotite-basalt melting relationships.
10,830 citations
5,637 citations
TL;DR: A-type granites as mentioned in this paper were found to have high SiO2, Na2O+K2O, Fe/Mg, Ga/Al, Zr, Nb, Ga, Y and Ce, and low CaO and Sr.
Abstract: New analyses of 131 samples of A-type (alkaline or anorogenic) granites substantiate previously recognized chemical features, namely high SiO2, Na2O+K2O, Fe/Mg, Ga/Al, Zr, Nb, Ga, Y and Ce, and low CaO and Sr. Good discrimination can be obtained between A-type granites and most orogenic granites (M-, I and S-types) on plots employing Ga/Al, various major element ratios and Y, Ce, Nb and Zr. These discrimination diagrams are thought to be relatively insensitive to moderate degrees of alteration. A-type granites generally do not exhibit evidence of being strongly differentiated, and within individual suites can show a transition from strongly alkaline varieties toward subalkaline compositions. Highly fractionated, felsic I- and S-type granites can have Ga/Al ratios and some major and trace element values which overlap those of typical A-type granites. A-type granites probably result mainly from partial melting of F and/or Cl enriched dry, granulitic residue remaining in the lower crust after extraction of an orogenic granite. Such melts are only moderately and locally modified by metasomatism or crystal fractionation. A-type melts occurred world-wide throughout geological time in a variety of tectonic settings and do not necessarily indicate an anorogenic or rifting environment.
4,216 citations
TL;DR: In this article, the saturation behavior of zircon in crustal anatectic melts as a function of both temperature and composition has been studied and a model of Zr solubility given by: In D Zr Zircon/melt = −3.80−[0.85(M−1)]+12900/T where T is the absolute temperature, and M is the cation ratio (Na + K + 2Ca)/(Al · Si).
3,330 citations