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

Abstract

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.

Subduction-related origin of eclogite xenoliths from the Wajrakarur kimberlite field, Eastern Dharwar craton, Southern India: Constraints from petrology and geochemistry

“…Models put forward range between uniformitarian plate tectonic amalgamation by subduction in the Neoarchean (Chadwick et al, , 2007Moyen et al, 2001;Ram Mohan et al, 2013) and other models supporting formation by mantle plumes (Jayananda et al, 2000), sagduction (Choukroune et al, 1995;Chardon et al, 1998) or a combination of subduction and plume-related processes (Naqvi et al, 2002(Naqvi et al, , 2006Manikyamba and Kerrich, 2012). Geochemical evidence for a convergent margin setting for the Dharwar craton is becoming increasingly favored in the literature: felsic volcanics and granitoids in the northern EDC greenstone belts have adakitic characteristics including Sr/Y (>40) and La/Yb (>20) ratios indicative of slab melting (Naqvi et al, 2006(Naqvi et al, , 2008Prabhakar et al, 2009). Boninites are found in the Archean Gadwal greenstone belt of EDC (Manikyamba et al, 2005) and negative HFSE anomalies in the Mesoproterozoic Siddanpalli kimberlites have been interpreted to imply a subducted component in their mantle Fig.…”

Geochemistry and Petrogenesis of Diabase Dykes in the Northern Part of EDC, Karnataka, India: Implication for Sulfide Metal Exploration

“…Based on these grounds, and crystallization/differentiation trend as visualised through various petrochemical diagrams, it can be concluded that the abundant quartz diabases were available in greater bulk after the differentiation of the parent tholeiite magma and the depth of parent magma formation was probably greater and the silica saturated fractionates were derived at a depth lesser than 60 km, since silica saturated tholeiite cannot exist below that depth [31]. Subsequently, they intruded as mafic sweats into the granitoid rocks which in turn formed in a subducting geodynamic setting [34].…”

Tonalite–Trondhjemite and Leucogranodiorite–Granite Suites From the Rio Maria Domain, Carajás Province, Brazil: Implications For Discrimination and Origin of the Archean Na-Granitoids

“…Over the past few decades, rocks with strong geochemical similarities to the leucogranodioritegranite suite have been described from the central Pilbara and Yilgarn cratons (Transitional TTG;Champion & Smithies 2001, 2003, Wyoming province (GG suite of Frost et al 2006), Tanzania craton (Neoarchean granitoids; Opiyo-Akech et al 1999), Dharwar craton (Arsikere-Banavara and Chitradurga-Jampalnaikankote-Hosdurga suites, Jayananda et al 2006, and granitoids of the Hutti-Gurgunta area, Prabhakar et al 2009), and Karelia terrane (Transitional TTG; Mikkola et al 2011). These works have contributed to identifying this new group of Archean granitoids and to estimating the true volume of each plutonic component in the gray gneiss complexes (Moyen & Martin 2012).…”