Petrogenesis and tectonic setting of bimodal volcanism in the Sakoli Mobile Belt, Central Indian shield

Abstract

The Sakoli Mobile Belt comprises bimodal volcanic rocks that include metabasalt, rhyolite, tuffs, and epiclastic rocks with metapelites, quartzite, arkose, conglomerate, and banded iron formation (BIF). Mafic volcanic rocks are tholeiitic to quartz‐tholeiitic with normative quartz and hypersthene. SiO2 shows a large compositional gap between the basic and acidic volcanics, depicting their bimodal nature. Both the volcanics have distinct geochemical trends but display some similarity in terms of enriched light rare earth element–large ion lithophile element characteristics with positive anomalies for U, Pb, and Th and distinct negative anomalies for Nb, P, and Ti. These characteristics are typical of continental rift volcanism. Both the volcanic rocks show strong negative Sr and Eu anomalies indicating fractionation of plagioclases and K‐feldspars, respectively. The high Fe/Mg ratios for the basic rocks indicate their evolved nature. Whole rock Sm–Nd isochrons for the acidic volcanic rocks indicate an age of crystallization for these volcanic rocks at about 1675 ± 180 Ma (initial 143Nd/144Nd = 0.51017 ± 0.00017, mean square weighted deviate [MSWD] = 1.6). The εNdt (t = 2000 Ma) varies between −0.19 and +2.22 for the basic volcanic rock and between −2.85 and −4.29 for the acidic volcanic rocks. Depleted mantle model ages vary from 2000 to 2275 Ma for the basic and from 2426 to 2777 Ma for the acidic volcanic rocks, respectively. These model ages indicate that protoliths for the acidic volcanic rocks probably had a much longer crustal residence time. Predominantly basaltic magma erupted during the deposition of the Dhabetekri Formation and part of it pooled at crustal or shallower subcrustal levels that probably triggered partial melting to generate the acidic magma. The influence of basic magma on the genesis of acidic magma is indicated by the higher Ni and Cr abundance at the observed silica levels of the acidic magma. A subsequent pulse of basic magma, which became crustally contaminated, erupted as minor component along with the dominantly acidic volcanics during the deposition of the Bhiwapur Formation.

Geochemical characterization and petrogenesis of Proterozoic Khairagarh volcanics: implication for Precambrian crustal evolution

“…GEODYNAMIC IMPLICATIONS AND DISCUSSION Figure 9 shows epsilon Nd evolutionary lines for the Khairagarh samples with respect to depleted mantle and chondritic uniform reservoir (CHUR) evolutionary trends. These data indicate that the protolith for the acidic volcanics were extracted earlier and had longer crustal residence time than the Sakoli mafic volcanics (Ahmad et al, 2009). Therefore, the Khairagarh volcanics and the adjoining Sakoli volcanics in the Bastar Craton suggest mafic-felsic bimodal volcanism and their derivation from nearly similar sources and the time of extraction of their protolith.…”

“…For the Sakoli acidic volcanics, the depleted mantle model ages vary from 2426 to 2777 Ma and ε Nd ( t = 2000 Ma) vary from −2.85 to −4.29. These data indicate that the protolith for the acidic volcanics were extracted earlier and had longer crustal residence time than the Sakoli mafic volcanics (Ahmad et al ., ). Therefore, the Khairagarh volcanics and the adjoining Sakoli volcanics in the Bastar Craton suggest mafic–felsic bimodal volcanism and their derivation from nearly similar sources and the time of extraction of their protolith.…”

“…The adjoining Sakoli Group in the Bastar Craton is dated at ca. 1675 ± 180 Ma (Ahmad et al, 2009). The eruption age of the Dongargarh lavas of the Bastar Craton varies from ca.…”

“…The ENE-WSW trending Central Indian Tectonic Zone (CITZ) divides the Central Indian Shield into two crustal provinces, the Bundelkhand Craton in the north and the Radhakrishna, 1989), (b) geological map of part of the Central Indian Shield (modified after Chattopadhyay et al, 2001;Ahmad et al, 2009;Chattopadhyay and Khasdeo, 2011), (c) detailed geological map of the study area showing lithological units of the Khairagarh Group, Central Indian Shield (modified after Deshpande et al, 1990;Ghosh et al, 2006).…”

“…( a ) Outline map of India showing different cratons and mobile belts of the Indian Shield (modified after Radhakrishna, ), ( b ) geological map of part of the Central Indian Shield (modified after Chattopadhyay et al ., ; Ahmad et al ., ; Chattopadhyay and Khasdeo, ), ( c ) detailed geological map of the study area showing lithological units of the Khairagarh Group, Central Indian Shield (modified after Deshpande et al ., ; Ghosh et al ., ). This figure is available in colour online at wileyonlinelibrary.com/journal/gj…”