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| Titel |
Geochemistry and petrogenesis of Paleo-Proterozoic granitoids from Mahakoshal Supracrustal Belt (MSB), CITZ |
| VerfasserIn |
Bhupendra Yadav, Talat Ahmad, Tatiana Kaulina, Tamara Bayanova |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250105714
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| Publikation (Nr.) |
 EGU/EGU2015-5256.pdf |
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| Zusammenfassung |
| Voluminous granitic magmatism of Proterozoic age occupies a vast expanse at the
southern margin of Mahakoshal Supracrustal Belt (MSB), CITZ. The present study
focuses on eastern part of this belt and discusses possible crustal evolution processes
based on the geochemical, geochronological and Sm-Nd isotopic constraints on
these rocks. The rocks present are predominantly granites and gneisses viz. grey to
pink granite gneiss and leuco- to mesocratic granites. In general these rocks are
medium to coarse grained and microscopically show typical granitic assemblages with
apatite, titanite, zircon and allanite as accessories. Mineralogically these rocks are
grouped into three categories viz. Hbl-Bt granite gneiss, Bt- granite gneiss and
Bt-granite.
Major oxide characteristics show that the Hbl-Bt granite Gneiss are metaluminous
(ASI~0.98), whereas Bt- granite gneiss (ASI=1.05-1.22) and Bt- granite (ASI=1.03-1.21) are
weakly peraluminous to strongly peraluminous. In terms of Fe* number and alkali-lime index
these rocks belong to magnesian and calc-alkalic series respectively. Overall these rocks
range from 59.43 to 72.01 wt.% SiO2 and have low Na2O content (average ~2.60 wt.%) with
average ~4.02 wt.% K2O and high K2O/Na2O ratio. On Harker variation diagrams, all rock
types show negative correlation for TiO2, P2O5, CaO, MnO, MgO, Fe2O3T and Al2O3
against SiO2 suggesting fractionation of Pl-Hbl-Ttn-Mag-Ap during evolution of these
rocks. On chondrite-normalized Rare Earth Element (REE) plot, the Bt-granite is
enriched in LREE ((La/Sm)N ~10.21) and show negative Eu anomaly (Eu/Eu*=0.39)
with depleted HREE ((Gd/Yb)N ~4.38). The Hbl-Bt granite gneiss shows LREE
((La/Sm)N ~6.68) depletion and enriched HREE ((Gd/Yb)N ~2.05) patterns compared to
Bt-granite, with negative Eu anomaly (Eu/Eu*=0.44). Whereas Bt-gneiss is moderate
in comparison with LREE enrichment ((La/Sm)N ~9.17) and HREE depletion
((Gd/Yb)N ~3.02) with weak negative Eu anomaly (Eu/Eu*=0.60). Multi-elemental
plot shown for all rocks have positive U, Th and Pb anomalies and negative Nb
and Ti anomalies, commonly interpreted as continental crust involvement in their
genesis.
Sm-Nd analysis on two samples of Hbl-Bt granite gneiss show143Nd/144Nd ratio ranges
from 0.511384-0.511394 with a corresponding 147Sm/144Nd ratio of 0.118109–0.118762.
The analyzed samples yield TDM model ages of 2807-2804 Ma with present day ÉNd values
being negative, whereas the initial ÉNd values (calculated at TDM ages) are positive. The
positive initial epsilon values indicate its derivation from depleted mantle source but this
magma must have incorporated crustal material during their ascent and probably
had a longer crustal residence time to have the observed evolved ÉNdlower values.
However 143Nd/144Nd ratios when compared with present day enriched mantle
values of EM-I ( |
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