Rb–Sr and Sm–Nd study of granite–charnockite association in the Pudukkottai region and the link between metamorphism and magmatism in the Madurai Block

Abstract

Pudukkottai region in the northeastern part of the Madurai Block exposes the garnetiferous pink granite that intruded the biotite gneiss. Charnockite patches are associated with both the rock types. Rb-Sr biotite and Sm-Nd whole-rock isochron ages indicate a regional uplift and cooling at ∼550 Ma. The initial Nd isotope ratios (ε t Nd = −20 to −22) and Nd depleted-mantle model ages (T DM = 2.25 to 2.79 Ga) indicate a common crustal source for the pink-granite and associated charnockite, while the biotite gneiss and the charnockite within it represent an older crustal source (ε t Nd = −29 and T DM = >3.2 Ga). The Rb-Sr whole-rock data and initial Sr-Nd isotope ratios also help demonstrate the partial but systematic equilibration of Sr isotope and Rb/Sr ratios during metamorphic mineral-reactions resulting in an 'apparent whole-rock isochron'. The available geochronological results from the Madurai Block indicate four major periods of magmatism and metamorphism: Neoarchaean-Paleoproterozoic, Mesoproterozoic, mid-Neoproterozoic and late-Neoproterozoic. We suggest that the high-grade and ultrahigh-temperature metamorphism was preceded by magmatism which 'prepared' the residual crust to sustain the high P -T conditions. There also appears to be cyclicity in the tectono-magmatic events and an evolutionary model for the Madurai Block should account for the cyclicity in the preserved records.

Proterozoic felsic and mafic magmatism in India: Implications for crustal evolution through crust-mantle interactions

“…Origin of charnockites in the SGT and the Dharwar craton has been a matter of debate since Pichamuthu discovered 'incipient charnockite' in a quarry in Kabbal village in Karnataka. Subsequently, similar charnockites were widely reported from Trivendrum block which lies south of the Achankovil shear zone and is characterized by paragneisses and S-type granites, and also from the other parts of the SGT (Ravindra Kumar et al 1985, Chandra Sekaran et al 2015, Touret et al, 2019 and the references therein). The charnockite patches within the granitic gneisses, are believed to be related to the dehydration caused by CO 2 influx whereas the charnockite massifs could be magmatic intrusions.…”

“…PCSZ has long been thought to be a Neoproterozoic suture, closing the Mozambique Ocean between the Dharwar craton and the MB during the pan-African orogeny. However, extensive geochronological studies (Ghosh et al 2004;Plavasa et al 2012;Brandt et al 2014;Chandra Sekaran et al 2015 and the references therein) suggest continuity of Neoarchean and Paleoproterozoic lithounits across the PCSZ till the KKPTSZ (Karur-Kambam-Painauv-Trissur Shear Zone). Brandt et al (2014) emphasized the petrological, geochemical and geochronological differences between the western and eastern parts of the MB to propose a new tectonomorphic model for the SGT.…”

“…The charnockite patches within the granitic gneisses, are believed to be related to the dehydration caused by CO 2 influx whereas the charnockite massifs could be magmatic intrusions. Chandra Sekaran et al (2015) reported two generations of charnockites from the northeastern part of the MB, the older associated with the biotite gneiss, and the younger one with the garnet-bearing metaluminous granite. The Sr-Nd isotopes revealed the older one to be of Neoarchean age, while the younger granite-charnockite originated from a common source in mid-Neoproterozoic.…”

Petrography and geochemistry of Neoproterozoic charnockite–granite association and metasedimentary rocks around Okpella, southwestern Nigeria

“…The association of charnockite-granite igneous rocks is widely recognized worldwide, commonly interpreted as the results of mantle-crust interaction during late orogenic stages (Hubbard 1968(Hubbard , 1988Whitley 1978, 1979;Thomas et al 1993;Rajesh 2004Rajesh , 2008McLelland and Selleck 2010;Harlov et al 2012;Sekaran et al 2016;Kumar et al 2020). In Nigeria, the close association of charnockites and granites with respect to field relations is well documented in different parts of the Basement Complex, especially around Ado-Ekiti-Ikerre-Akure, Idanre, Toro and Rahama (Hubbard 1968;Cooray 1972;Tubosun et al 1984;Olarewaju 1987;Dada et al 1989;Ocan 1990;Ferré et al 1997;Ademeso 2010).…”