Magnetic susceptibility mapping of felsic magmatic lithounits in the central part of Bundelkhand Massif, central India

Abstract

Late Archaean to Palaeoproterozoic felsic magmatic lithounits exposed in the central part of the Bundelkhand massif have been mapped and their redox series (magnetite vs ilmenite series) evaluated based on magnetic susceptibility (MS) data. The central part of Bundelkhand massif comprises of multiple felsic magmatic pulses (~2600-2200 Ma), commonly represented by coarse grained granite (CGG-grey granite, CPG-pink granite), medium grained pink granite (MPG), fine grained pink granite (FPG) , grey and pink rhyolites and granite porphyry (GP). However, the pink colour of these felsic rocks is the result of hydrothermal fluid-flushing leading to potassic alteration of grey granites. MS values of CGG vary from 0.058 to 14.75×10 -3 SI with an average of 6.35×10 -3 SI, which mostly represent oxidized type, magnetite series (73%) granites involving infracrustal (igneous) source materials. CPG (av. MS=3.95×10 -3 SI) is indeed a pink variety of CGG, the original oxidizing nature of which must have been similar to the bulk of CGG, but has been moderately to strongly reduced because of distinctly more porphyritic nature together with partial assimilation of metapelitic (supracrustal) materials, surmicaceous enclaves, carbonaceous material included in the source materials, and to some extent, induced by hydrothermal and later deformational processes. MPG (av. MS= 1.15×10 -3 SI) as lensoidal stock-like bodies intrudes the CPG and represent both magnetite series (18%) and ilmenite series (82%) granites, which are probably formed by heterogeneous (mixed) source rocks. GP (av. MS=6.26×10 -3 SI) occur as dykes (mostly trending NE-SW) intrudes the MPG, CPG and migmatites and bears the nature similar to oxidized type, magnetite series granite. FPG (av. MS= 0.666×10 -3 SI) trending NE-SW occur as lensoid bodies including a large outcrop, is intrusive into both CPG and MPG, and is moderately to very strongly reduced type, ilmenite series granites, which may be derived by the melting of metapelitic crustal sources. FPG hosting microgranular (mafic magmatic) enclaves commonly exhibit high MS values (7.31-10.22×10 -3 SI), which appear induced by the mixing and mingling of interacting felsic and mafic magmas prevailed in an open system. Grey (av. MS=10.30×10 -3 SI) and pink (av. MS=6.72×10 -3 SI) rhyolites represent oxidized type, magnetite series granites, which may have been derived from infracrustal (magmatic) protoliths. Granite series evaluation of felsic magmatic rocks of central part of Bundelkhand massif strongly suggests their varied redox conditions (differential oxygen fugacity) mostly intrinsic to magma source regions and partially modified by hydrothermal and tectonic processes acting upon them.

Radioelemental, petrological and geochemical characterization of the Bundelkhand craton, central India: implication in the Archaean geodynamic evolution

“…The NeoArchaean acidic magmatism was a part of major geological process when the granite production occurred on a large scale and subsequently the Bundelkhand craton acquired thermal equilibrium of the stable geotherm. The signature of this event is marked by the emplacement of different types of granitoids that are available throughout the craton in time and space (Basu 2010;Mondal et al 2002;Kumar et al 2010). The successive events of granitoid magmatism occurred within a very short span of time in this craton (~50 Ma, Mondal et al 2002).…”

“…The variation in the REE data is in agreement with the concentration of radiogenic elements in different varieties of rocks. The geochemical studies based on redox potentiality (Kumar et al 2010) suggest that grey granitoid is dominated by magnetite series (oxidizing environment), while most of the pink granitoid is related to ilmenite series (reducing environment). The low oxidation (strongly reducing conditions) estimates, high K 2 O and SiO 2 content and high radiogenic elemental abundances suggest the dominance of crustal source materials (pelitic) for fine-grained pink granite compared to that of mantle component for grey granitoid in their genesis.…”

“…A discordant field relationship between TTG gneisses and granitoids recorded from different areas (Singh 2012) points out that undeformed Neo-Archaean granitoids of Bundelkhand were emplaced subsequent to Bundelkhand gneisses. The geochronological data shows that the age for the TTG rocks associated with pelitic gneisses ranges between 3300 and 3100 Ma, whereas for the granitoids, it ranges between 2570 and 2525 Ma (Mondal et al 2002;Kumar et al 2010). These data suggest two different thermal events in the Bundelkhand craton.…”

Geochronological and geochemical signatures of the granitic rocks emplaced at the north‐eastern fringe of the Eastern Dharwar Craton, South India: Implications for late Archean crustal growth

“…2.56–2.51 Ga; Jayananda, Peucat, et al, ; Jayananda, Tsutsumi, et al, ). Widespread granitic magmatism in the adjoining Bundelkhand Craton and the Bastar Craton (Meert et al, ) occurred at a similar time frame producing the vast batholithic bodies of the Bundelkhand Granite and the Dongargarh‐Kanker‐Malanjkhand Granites, respectively (Kumar et al, ; Meert et al, ; Mondal, Goswami, Deomurari, & Sharma, ). Thus, the southern and central Indian crustal blocks characterized by amalgamated proto‐continents, mostly formed and stabilized by large‐scale granite magmatism in the end Neoarchaean (ca.…”

Chromian spinel compositions from Madawara ultramafics, Bundelkhand Craton: Implications on petrogenesis and tectonic evolution of the southern part of Bundelkhand Craton, Central India

“…All these lithologies are intruded by NE–SW trending quartz reefs and NW–SE trending dolerite dike swarms during the crustal‐scale shearing (Basu, ; Basu, ; Bhattacharya & Singh, ; Mondal et al, ; Singh, Singh, Srivastava, & Basu, ). Geochronological studies carried out by several workers in the Bundelkhand Craton (Joshi et al, ; Kaur, Zeh, Chaudhri, & Eliyas, ; Kumar, Raju, Pathak, & Pandey, ; Mondal et al, ; Mondal, Sharma, Rahman, & Goswami, ; Saha et al, ; Sarkar, ; Verma, Verma, Oliveira, Singh, & Moreno, ) suggest that accretion of tonalite‐trondhjemite‐granodiorite (TTG) occurred in three phases from 3,500 to 3,200 Ma (Kaur et al, ). Ultramafic–mafic and basalt‐andesite‐rhyolite‐dacite magmatism (plume‐arc type) in the Mauranipur–Babina greenstone belt accreted at approximately 2,700 to 2,545 Ma (Singh et al, ).…”