TITLE:
Comparative Geochemical and Petrographic Studies of the Various Granitoids between Central and Western Arm, in the Central Part of Ramagiri Schist Belt and Their Petrogenetic Histories
AUTHORS:
Eirin Kar, Prasun Ghosh, Shibani Mishra
KEYWORDS:
Ramagiri Schist Belt, Granodiorites, Monzogranites, Volcanic Arc
JOURNAL NAME:
International Journal of Geosciences,
Vol.13 No.5,
May
31,
2022
ABSTRACT: Granitoids between the central and western arm of Ramagiri schist belt in
its central part, are broadly classified into the migmatite gneiss, grey granodiorite
and pink monzogranite, based on field characteristics and petrographic features.
These granitoids belong to the Tonalite-Granodiorite-Monzogranite (TGM) suite of
PGC-II. All the samples are fresh as per the CIA values, PC1-PC2 binary plot and
MFW ternary plot. The granodiorites occupy the expected field in the normative IUGS,
TAS, and R1-R2 classification diagrams, but the monzogranites
occupy the monzogranite field in the normative IUGS classification diagram and granite
to alkali granite field in the rest. The granodiorites exhibit both ferroan to magnesian,
alkali-calcic nature with metaluminous I type features and falls in the calc-alkaline
to high K calc-alkaline series. They have high ΣREE (an average 327.905 ppm) content,
and show LREE enrichment ((La/Sm)N = 3.1 - 6.8) with enriched but relatively flat HREE ((Gd/Yb)N = 1.75 - 5.26) patterns and weak negative to positive Eu anomaly (Eu/Eu* = 0.62 - 1.18). The
monzogranites, on the other hand, are peraluminous, alkalic, ferroan, high K calc-alkaline,
S-type granites, exhibiting relatively low ΣREE (an average 118.693 ppm) contents,
strongly fractionated REE patterns with highly enriched LREE ((La/Sm)N =1.74 - 9.76), depleted HREE ((Gd/Yb)N = 0.43 - 2.21) patterns having concave upward shape, and strong negative Eu anomaly
(Eu/Eu* = 0.23 - 0.89). Geothermobarometry revealed the average emplacement temperature and
pressure of the granodiorites and monzogranites as 812.5℃, 8.14 ± 0.6 kbar and
775℃, 3.14 kbar, respectively. Based, on the observations, it can be concluded
that the granodiorites have formed in volcanic arc setting by partial melting of
the lower crust and S-type monzogranites have been produced at a relatively shallower
depth in the crust, by continental crust recycling due to hydrothermal influx.