22 research outputs found
Major, Trace, and Rare-Earth Element Geochemistry of Nb-V Rich Andradite-Schorlomite-Morimotoite Garnet from Ambadungar-Saidivasan Alkaline Carbonatite Complex, India: Implication for the Role of Hydrothermal Fluid-Induced Metasomatism
In situ major, trace and rare-earth element composition of Ti-rich garnets from Ambadungar-Saidivasan alkaline carbonatite complex (ASACC) are presented to constrain its likely genesis. The garnets are characterized by high andradite (42.7ā57.3), schorolomite (22.0ā31.0), and morimotoite (15.6ā26.5) end members. No distinct chemical zonation is noticed except for minor variations in Ti content. The garnets are enriched in LREE (average 731 ppm) and relatively depleted in HREE (average 186 ppm) and show an M-type first tetrad that leads to a convex upward pattern between Ce and Gd. Mildly positive to no Eu anomalies are observed (Eu/Eu* = 1.06ā1.17). The REE patterns (LaN/YbN = 1.11ā2.11) are similar to those of garnets from skarn deposits. The presence of tetrad effect in the LREE pattern suggests an active role of metasomatic processes involving hydrothermal fluids during the growth of the garnets. These garnets also contain high Nb (282ā2283 ppm) and V (1083ā2155 ppm) concentrations, which stand out against the composition of the host rock. Therefore, late-stage metasomatic reactions of earlier formed minerals with hydrothermal fluid enriched in Fe, Si, LREE, Nb, V, and Ti led to the formation of garnet. The primary source for these elements could be magnetite, ilmenite, and pyrochlore present in different varieties of carbonatites in the ASACC, with the required elements being released during their interaction with the hydrothermal fluid. The hydrothermal fluid was likely to be moderately acidic, and having fluoride and sulfate as the primary ligands
Geochemical characteristics and petrogenesis of four Palaeoproterozoic mafic dike swarms and associated large igneous provinces from the eastern Dharwar craton, India
<div><p>Palaeoproterozoic mafic dike swarms of different ages are well exposed in the eastern Dharwar craton of India. Available U-Pb mineral ages on these dikes indicate four discrete episodes, viz. (1) ~2.37Ā Ga Bangalore swarm, (2) ~2.21Ā Ga Kunigal swarm, (3) ~2.18Ā Ga Mahbubnagar swarm, and (4) ~1.89Ā Ga Bastar-Dharwar swarm. These are mostly sub-alkaline tholeiitic suites, with ~1.89Ā Ga samples having a slightly higher concentration of high-field strength elements than other swarms with a similar MgO contents. Mg number (Mg#) in the four swarms suggest that the two older swarms were derived from primary mantle melts, whereas the two younger swarms were derived from slightly evolved mantle melt. Trace element petrogenetic models suggest that magmas of the ~2.37Ā Ga swarm were generated within the spinel stability field by ~15ā20% melting of a depleted mantle source, whereas magmas of the other three swarms may have been generated within the garnet stability field with percentage of melting lowering from the ~2.21Ā Ga swarm (~25%), ~2.18Ā Ga swarm (~15ā20%), to ~1.89Ā Ga swarm (~10ā12%). These observations indicate that the melting depth increased with time for mafic dike magmas. Large igneous province (LIP) records of the eastern Dharwar craton are compared to those of similar mafic events observed from other shield areas. The Dharwar and the North Atlantic cratons were probably together at ~2.37Ā Ga, although such an episode is not found in any other craton. The ~2.21Ā Ga mafic magmatic event is reported from the Dharwar, Superior, North Atlantic, and Slave cratons, suggesting the presence of a supercontinent, āSuperiaā. It is difficult to find any match for the ~2.18Ā Ga mafic dikes of the eastern Dharwar craton, except in the Superior Province. The ~1.88ā1.90Ā Ga mafic magmatic event is reported from many different blocks, and therefore may not be very useful for supercontinent reconstructions.</p></div
Mapping the Dyke Swarms Emplaced within the Different Archean Cratons of the Indian Shield Using Googleā¢ Earth Images and ArcGISā¢ Techniques
Geochemical studies and petrogenesis of ~2.21ā2.22 Ga Kunigal mafic dyke swarm (trending N-S to NNW-SSE) from eastern Dharwar craton, India: implications for Paleoproterozoic large igneous provinces and supercraton superia
The Archean eastern Dharwar craton is transacted by at least four major Proterozoic mafic dyke swarms. We present geochemical data for the ~2.21ā2.22 Ga N-S to NNW-SSE trending Kunigal mafic dyke swarm of the eastern Dharwar craton to address its petrogenesis and formation of large igneous province as well as spatial link to supercontinent history. It has a strike span of about 200 km; one dyke of this swarm runs ~300 km along the western margin of the Closepet granite. Texture and mineral compositions classify them as dolerite and olivine dolerite. They show compositions of high-iron tholeiites, high-magnesian tholeiites or picrites. Geochemical characteristics of the sampled dykes suggest their co-genetic nature and show variation from primitive (Mg#; as high as ~76) to evolved (differentiated) nature. Although geochemical characteristics indicate possibility of minor crustal contamination, they show their derivation from an uncontaminated mantle melt. These mafic dykes are probably evolved from a sub-alkaline basaltic magma generated by ~20 % batch melting of a depleted lherzolite mantle source and about 15ā30 % olivine fractionation. Paleoproterozoic (~2.21ā2.22 Ga) mafic magmatism is recognized globally as dyke swarms or gabbroic sill complexes in the Superior, Slave, North Atlantic, Fennoscandian and Pilbara cratons. Possible Paleoproterozoic DharwarāSuperiorāNorth-AtlanticāSlave correlations are constrained with implications for the configuration of supercraton Superia
Spatial and temporal distribution of Large Igneous Provinces in the Indian Shield - Highlights of recent investigations
This report highlights investigations since 2016 on the Large Igneous Provinces (LIPs), particularly based on their mafic dyke swarms (MDSs) and continental flood basalts (CFBs), from the Indian Shield. Recent research, particularly geochemistry, geochronology and paleomagnetism, allow identification and characterization of distinct generations of LIPs in space and time in the Indian Shield. This could be the basis for critical new tests of paleogeographic reconstructions of supercontinents and paleocontinents of the Earth's history and the position of India in different ancient supercontinent/supercratons. The high-quality data generated in recent years also helped significantly to understand the nature, composition and evolution of the sub-continental lithospheric mantle beneath the Indian Shield, which aims at resolving important geological aspects, such as the role of plume tectonics, ancient subduction events, extent of the LIPs paleo-supercontinent reconstructions, etc., and has received considerable national and international attention
Precambrian mafic dyke swarms in the Singhbhum craton (eastern India) and their links with dyke swarms of the eastern Dharwar craton (southern India) ā Reply
Based on trend, cross-cutting relationships and U-Pb dating, Precambrian mafic dykes in the Singhbhum craton, earlier collectively identified as āNewer Dolerite Swarmā, have been separated into seven distinct swarms, which are thought to be the plumbing systems for Large Igneous Provinces (LIPs). These Singhbhum swarms range in age fromā¼2.80 Ga toā¼1.76 Ga, and include theā¼2.80 Ga NE-SW trending Keshargaria swarm,ā¼2.75ā2.76 Ga NNE-SSW to NE-SW trending Ghatgaon swarm, the ā¼2.26 Ga NE-SW to ENE-WSW trending Kaptipada swarm (based on a new U-Pb ID-TIMS age 2256 Ā± 6 Ma), the ā¼1.77 Ga WNW-ESE trending Pipilia swarm, the early- Paleoproterozoic E-W to ENE-WSW trending Keonjhar swarm, the middle-Paleoproterozoic NW-SE to NNW-SSE trending Bhagamunda swarm, and the late-Paleoproterozoic N-S to NNE-SSW trending Barigaon swarm. Two of the Singhbhum swarms, the ā¼2.26 Ga Kaptipada and ā¼1.77 Ga Pipilia, are closely matched with the ā¼2.26ā2.25 Ga Ippaguda-Dhiburahalli and ā¼1.79 Ga Pebbair swarms, respectively, of the eastern Dharwar craton. The correlations suggest that the Singhbhum and Dharwar cratons were close enough at these times to share two reconstructed LIPs, a 2.26ā2.25 Ga Kaptipadaā Ippaguda-Dhiburahalli LIP and a 1.79ā1.77 Ga Pipilia- Pebbair LIP, and if so, both swarms must be present in the intervening Bastar craton (candidates are proposed). Also, the 2.76ā2.75 Ga Ghatgaon swarm of the Singhbhum craton can be provisionally correlated with ā¼2.7 Ga Keshkal swarm of the Bastar craton. The 2.26ā2.25 Ga KaptipadaāIppaguda-Dhiburahalli LIP of the Singhbhum- Bastar-Dharwar reconstruction has age matches in the Vestfold Hills of Antarctica (ā¼2.24 Ga dykes), the Kaapvaal craton (the ā¼2.25ā2.23 Ga Hekpoort lavas) and perhaps the Zimbabwe craton (2.26 Ga Chimbadzi troctolite intrusions). The 1.76ā1.79 Ga Pipilia-Pebbair LIP of the Singhbhum-Bastar-Dharwar reconstruction has age matches in the North China, Australian Shield, Amazonian, Rio de Plata and Sarmatia cratons. The relevance of these matches for reconstructions will require future testing using paleomagnetic studies. While there are ā¼2.7ā2.8 Ga LIP-type greenstone belts in many crustal blocks, there are no precise matches with the 2.76ā2.75 Ga Ghatgaon swarm of the Singhbhum craton. However, the 2.80 Ga Keshargaria swarm can be potentially linked with units in the Pilbara and Yilgarn cratons
Precambrian mafic dyke swarms in the Singhbhum craton (eastern India) and their links with dyke swarms of the eastern Dharwar craton (southern India)
Based on trend, cross-cutting relationships and U-Pb dating, Precambrian mafic dykes in the Singhbhum craton, earlier collectively identified as āNewer Dolerite Swarmā have been separated into seven distinct swarms, which are thought to be the plumbing systems for Large Igneous Provinces (LIPs). These Singhbhum swarms range in age from ā¼2.80 Ga to ā¼1.76 Ga, and include the ā¼2.80 Ga NE-SW trending Keshargaria swarm, ā¼2.75ā2.76 Ga NNE-SSW to NE-SW trending Ghatgaon swarm, the ā¼2.26 Ga NE-SW to ENE-WSW trending Kaptipada swarm (based on a new U-Pb ID-TIMS age 2256 Ā± 6 Ma), the ā¼1.77 Ga WNW-ESE trending Pipilia swarm, the early-Paleoproterozoic E-W to ENE-WSW trending Keonjhar swarm, the middle-Paleoproterozoic NW-SE to NNW-SSE trending Bhagamunda swarm, and the late-Paleoproterozoic N-S to NNE-SSW trending Barigaon swarm. Two of the Singhbhum swarms, the ā¼2.26 Ga Kaptipada and ā¼1.77 Ga Pipilia, are closely matched with the ā¼2.26ā2.25 Ga Ippaguda-Dhiburahalli and ā¼1.79 Ga Pebbair swarms, respectively, of the eastern Dharwar craton. The correlations suggest that the Singhbhum and Dharwar cratons were close enough at these times to share two reconstructed LIPs, a 2.26ā2.25 Ga Kaptipadaā Ippaguda-Dhiburahalli LIP and a 1.79ā1.77 Ga Pipilia-Pebbair LIP, and if so, both swarms must be present in the intervening Bastar craton (candidates are proposed). Also, the 2.76ā2.75 Ga Ghatgaon swarm of the Singhbhum craton can be provisionally correlated with ā¼2.7 Ga Keshkal swarm of the Bastar craton. The 2.26ā2.25 Ga KaptipadaāIppaguda-Dhiburahalli LIP of the Singhbhum-Bastar-Dharwar reconstruction has age matches in the Vestfold Hills of Antarctica (ā¼2.24 Ga dykes), the Kaapvaal craton (the ā¼2.25ā2.23 Ga Hekpoort lavas) and perhaps the Zimbabwe craton (2.26 Ga Chimbadzi troctolite intrusions). The 1.76ā1.79 Ga Pipilia-Pebbair LIP of the Singhbhum-Bastar-Dharwar reconstruction has age matches in the North China, Australian Shield, Amazonian, Rio de Plata and Sarmatia cratons. The relevance of these matches for reconstructions will require future testing using paleomagnetic studies. While there are ā¼2.7ā2.8 Ga LIP-type greenstone belts in many crustal blocks, there are no precise matches with the 2.76ā2.75 Ga Ghatgaon swarm of the Singhbhum craton. However, the 2.80 Ga Keshargaria swarm can be potentially linked with units in the Pilbara and Yilgarn cratons
Neoarchaean-Palaeoproterozoic Mafic Dyke Swarms from the Singhbhum Granite Complex, Singhbhum Craton, Eastern India : Implications for Identification of Large Igneous Provinces and Their Possible Continuation on Other Formerly Adjacent Crustal Blocks
Geochemistry of an ENEāWSW to NEāSW trending ā¼2.37 Ga mafic dyke swarm of the eastern Dharwar craton, India: does it represent a single magmatic event?
A vast tract of ENEāWSW to NEāSW trending mafic dyke swarm transects Archaean basement rocks within the eastern Dharwar craton. Petrographic data reveal their dolerite/olivine dolerite or gabbro/olivine gabbro composition. Geochemical characteristics, particularly HFSEs, indicate that not all these dykes are co-genetic but are probably derived from more than one magma batch and different crystallization trends. In most samples the LaN/LuN ratio is at ā¼2, whereas others have a LaN/LuN ratio >2 and show higher concentrations of high-field strength elements (HFSEs) than the former group. As a consequence, we assume that the ENEāWSW to NEāSE trending mafic dykes of the eastern Dharwar craton do not represent one single magmatic event but were emplaced in two different episodes; one of them dated at about 2.37 Ga and another probably at about 1.89 Ga. Trace element modelling also supports this inference: older mafic dykes are derived from a melt generated through ā¼25% melting of a depleted mantle, whereas the younger set of dykes shows its derivation through a lower degree of melting (ā¼15%) of a comparatively enriched mantle source