U-Pb Ages of Zircon and Sphene for Two Gneiss Terranes Adjacent to the Kolar Schist Belt, South India: Evidence for Separate Crustal Evolution Histories

Krogstad, E. J.; Hanson, Gilbert N.; Rajamani, V.

doi:10.1086/629553

Cited by 120 publications

(69 citation statements)

References 20 publications

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“…They are formed on the base of migmatites, granite gneiss and granites ranging in composition from granodiorite to tonalite and intruded younger dolerites. These abundant granitoid rocks are of calc-alkaline nature (Balakrishnan et al 1990;1999;Krogstad et al 1991). Sanukitioids, a high Mg, high Ni granitoids are also present and monoclinic series of amphiboles tremolite, actinolite comprising Ca, Mg and halogens (F, Cl) occur as intrusive with the PGCs.…”

Section: Geology and Hydrogeologymentioning

confidence: 99%

Influence of geochemical processes on hydrochemistry and irrigation suitability of groundwater in part of semi-arid Deccan Plateau, India

et al. 2017

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Major ion geochemistry was used to characterise the chemical composition of groundwater in part of semiarid Deccan plateau region to understand the geochemical evolution and to evaluate the groundwater quality for irrigation. The study area comprises peninsular gneissic complex of Archean age, younger granites and basaltic alluvium. Forty-nine georeferenced groundwater samples were collected and analysed for major ions. The ionic sequence based on relative proportions was Na. High Na ? , Mg 2? and Ca 2? were generally associated with basaltic alluvial formation, whereas pH, electrical conductivity (EC) and total dissolved salts (TDS) were found to be higher in granitic formations. High standard deviation for EC, TDS, Na ? , Ca 2? and Mg 2? indicated the dispersion of ionic concentration throughout the study area. Four major hydrochemical facies identified were Na-Mg-HCO 3 type; Mg-Na-HCO 3 type; Na-Mg-Ca-SO 4 and Mg-Na-Ca-SO 4 type. The graphical plots indicated that the groundwater chemistry was influenced by rock-water interaction, silicate weathering and reverse ion exchange. Sodium-dominated waters might have impeded the hydraulic properties of soils as a result of long-term irrigation.

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Section: Geology and Hydrogeologymentioning

confidence: 99%

Influence of geochemical processes on hydrochemistry and irrigation suitability of groundwater in part of semi-arid Deccan Plateau, India

et al. 2017

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“…The U-Pb titanite and zircon ages determined on the granitoid rocks of the Kolar belt by Krogstad et al (1989Krogstad et al ( , 1991 and in the Ramagiri areas by Balakrishnan et al (1999), are shown in table 1. In the Kolar area, the Patna granitoid has yielded identical titanite and zircon U-Pb ages of 2552 ± 1 and 2551 ± 2.5 Ma respectively, whereas, in the Dod gneiss the zircon age of 2631 ± 6.5 Ma is about 80 million years older than the titanite U-Pb age of 2551 ± 2 Ma.…”

Section: Kolar Schist Beltmentioning

confidence: 99%

“…Thus Sm-Nd isotope study on titanites, hornblende or biotite crystallized at the same time along with the whole rock can provide meaningful age information. Two samples, a granodiorite and a quartz monzodiorite surrounding Kolar and Ramagiri schist belts respectively, whose ages were precisely determined by U-Pb titanite and zircon geochronology (Krogstad et al 1991;Balakrishnan et al 1999), were chosen for this exercise.…”

Section: Introductionmentioning

confidence: 99%

Geochemical and Sm–Nd isotopic study of titanite from granitoid rocks of the eastern Dharwar craton, southern India

Anand

Balakrishnan

2011

J Earth Syst Sci

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Titanite occurs as an accessory phase in a variety of igneous rocks, and is known to concentrate geologically important elements such as U, Th, rare earth element (REE), Y and Nb. The differences in the abundances of the REEs contained in titanite from granitoid rocks could reflect its response to changes in petrogenetic variables such as temperature of crystallization, pressure, composition, etc. Widespread migmatization in the granodiorite gneisses occurring to the east of Kolar and Ramagiri schist belts of the eastern Dharwar craton resulted in the enrichment of the REEs in titanite relative to their respective host rocks. A compositional influence on the partitioning of REEs between titanite and the host rock/magma is also noticed. The relative enrichment of REEs in titanite from quartz monzodiorite is lower than that found in the granodioritic gneiss. Depletion of REE and HFSE (high field-strength elements) abundances in granitic magmas that have equilibrated with titanite during fractional crystallization or partial melting has been modelled. As little as 1% of titanite present in residual phases during partial melting or in residual melts during fractional crystallization can significantly lower the abundances of trace elements such as Nb, Y, Zr and REE which implies the significance of this accessory mineral as a controlling factor in trace element distribution in granitoid rocks. Sm-Nd isotope studies on titanite, hornblende and whole rock yield isochron ages comparable to the precise U-Pb titanite ages, invoking the usefulness of Sm-Nd isochron ages involving minerals like titanite.

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“…The absence of mafic end-member (that could be the result of magma fractionation hidden at depth) within the TTGs of the study area thus indicates the possibility of fractional crystallization . Thus, to constrain the potential sources of the parent magma of TTGs, different petrogenetic models have been reviewed for both global occurrence (Condie, 1981;Martin,1986;Smithies, 2000;Martin and Moyen, 2002;Smithies et al 2003; as well as for EDC (Balakrishnan and Rajamani, 1987;Krogstad et al 1991Krogstad et al , 1995Jayananda et al 2000Jayananda et al , 2006Moyen et al 2003b). Different possibilities such as (1) reworking of older crust to direct melting of mantle and slab melting at different depths in subduction setting have been tried for the TTGs of the present study.…”

Section: Ttgsmentioning

confidence: 99%

“…Older basement gneisses are present as huge enclaves (within younger TTG gneisses) in the southeastern part of the EDC (Jayananda et al 2000(Jayananda et al , 2003Chardon et al 2002), whereas the younger TTG gneisses occupy vast areas, especially in the northern parts and are accreted during 2.7 -2.55 Ga (Krogstad et al 1991;Peucat et al1993;Jayananda et al 2000Jayananda et al , 2003Chardon et al 2002). The juvenile continental accretion during 2.55-2.51 Ga has led to emplacement of large magmatic bodies like Closepet granite and other related granite intrusions during a tectono-metamorphic event that affected the craton at the close of the Archaean (Peucat et al 1993;Krogstad et al 1991;Jayananda et al 1995Jayananda et al , 2000Chardon et al 2002;Moyen et al 2003a, b). This accretion event was immediately followed by reworking of newly formed crust and granulite event close to 2.51 Ga (Peucat et al 1993;Mahabaleswar et al 1995) that affected the entire Archaean continental crust of the Dharwar craton.…”

Section: Introductionmentioning

confidence: 99%

Petrology and geochemistry of late archaean granitoids in the northern part of Eastern Dharwar Craton, Southern India: Implications for transitional geodynamic setting

et al. 2009

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Abstract:The results of field, petrographic and geochemical work of the granitoids of Hutti-Gurgunta area in the northern part of Eastern Dharwar Craton (EDC) is presented in this paper. This crustal section comprises polyphase banded to foliated TTG gneisses, middle amphibolite facies Gurgunta schist belt and upper greenschist facies Hutti schist belt and abundant granite plutons. The focus of the present study is mainly on basement TTG gneisses and a granite pluton (~ 240 sq km areal extent), to discuss crustal accretion processes including changing petrogenetic mechanism and geodynamic setting. The TTGs contain quartz, plagioclase, lesser K-feldspar and hornblende with minor biotite while the granite contain quartz, plagioclase, K-feldspar and hornblende. Late stage alteration (chloritisation, sericitisation and epidotisation) is wide spread in the entire area. A huge synplutonic mafic body which is dioritic to meladioritic in composition injects the granite and displays all stages of progressive mixing and hybridization. The studied TTGs and granite show distinct major and trace element patterns. The TTGs are characterized by higher SiO 2 , high Al 2 O 3 , and Na 2 O, low TiO 2 , Mg#, CaO, K 2 O and LILE, and HFS elements compared to granite. TTGs define strong trondhjemite trend whilst granite shows calc-alkaline trend. However, both TTGs and granite show characteristics of Phanerozoic high-silica adakites. The granite also shows characteristics of transitional TTGs in its high LILE, and progressive increase in K 2 O with differentiation. Both TTGs and granite define linear to sub-linear trends on variation diagrams. The TTGs show moderate total REE contents with fractionated REE patterns (La/Yb N =17.73-61.73) and slight positive or without any significant Eu anomaly implying little amount of amphibole or plagioclase in residual liquid. On the other hand, the granite displays poor to moderate fractionation of REE patterns (La/Yb N = 9.06-67.21) without any significant Eu anomaly. The TTGs have been interpreted to be produced by low-K basaltic slab melting at shallow depth, whereas the granite pluton has been formed by slab melting at depth and these melts interacted with peridotite mantle wedge. Such changing petrogenetic mechanisms and geodynamic conditions explain increase in the contents of MgO, CaO, Ni and Cr from 2700 Ma to 2500 Ma granitoids in the EDC.

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U-Pb Ages of Zircon and Sphene for Two Gneiss Terranes Adjacent to the Kolar Schist Belt, South India: Evidence for Separate Crustal Evolution Histories

Cited by 120 publications

References 20 publications

Influence of geochemical processes on hydrochemistry and irrigation suitability of groundwater in part of semi-arid Deccan Plateau, India

Influence of geochemical processes on hydrochemistry and irrigation suitability of groundwater in part of semi-arid Deccan Plateau, India

Geochemical and Sm–Nd isotopic study of titanite from granitoid rocks of the eastern Dharwar craton, southern India

Petrology and geochemistry of late archaean granitoids in the northern part of Eastern Dharwar Craton, Southern India: Implications for transitional geodynamic setting

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