Archean Mafic-Ultramafic Ikauna Layered Intrusion, Bundelkhand Craton, India: Petrography and Geochemistry

Figure 1:Geological map of Madawara-Girar area and Ikauna dunite-pyroxenite-gabbro layered complex (intrusion) location [12,14].

Bundelkhand craton is a protocontinent situated in the center of Indian shield, covers about 29000 km2 areas and constitute acid granitoid complex with lesser amount of metasedimentary, meta basics, with low grade metamorphics of the older crust and quartz veins. The Bundelkhand craton is mostly preserved 3.5-2.5Ga granitoids and granite–greenstone terrane [1-7]. The trough/graben and surrounding basins of Bundelkhand craton were filled by thick pile of Bijawar and Vindhyan sediments during Proterozoic times. The craton is seldom studied and its stabilization period was at the end of Archean eon with voluminous granitic magmatism at around 2.5Ga in the Earth’s evolutionary history. Singh and Slabunov [5,8] reported two greenstone complexes in the Bundelkhand craton. First is the Central Bundelkhand greenstone complex (CBGC), consisting of Babina and Mauranipur greenstone belts, with exposed rocks of TTG and granitoids, mafic–ultramafic, felsic volcanics, minor metasedimentary, and high-K granites [5,6,9]. The second is the Southern Bundelkhand schist complex comprising Girar and Berwar belt. It is occurring small isolated outcrops of quartzite, BIFs, ultramafic rocks. The less studied layered igneous intrusions occurring in southern Bundelkhand craton around Madawara to Ikauna [10-14]. Slabunov et al. [15] indicate that the craton is significance by last endogenic activity at Paleoproterozoic (1.9-1.8Ga) create quartz veins, generally display along NE-SW trend. The major lithounits of the Bijawar region are divided in to Mehroni and Mandawra group and detail stratigraphy is given in the Table 1 [16]. The present paper consists to Ikauna Layered Igneous Intrusive complex which form a part of the Southern portion of the Bundelkhand craton. It is located around Madawara to Ikauna regions of Lalitpur district, Uttar Pradesh (Figure 1).

The general geology of southern Bundelkhand craton has been discussed in detail by Singh and Slabunov [13]. In the southern Bundelkhand craton lies a large (15 by 6km) poorly studied intrusion, presumably a lopolith (Figure 1), known as the Ikauna Complex. The Madawara-Ikauna terrain comprises peridotite, harzburgite, serpentinite, pyroxenites and associated diorite and gabbro. Disseminated lensoidal exposures of these rocks are occurring around the Madawara areas for more than 400sq. km in the Southern part of the craton [10-14]. Figure 2 show the different kind of rock exposures of serpentinite, metagabbro, gabbro-pegmatite and Neoarchean pink granite intrusion in gabbroic rocks exposed around Ikauna area. This mafic-ultramafic rocks lie among Archean rocks of Bundelkhand granitoids, Rajaula Formation and apparently cut them, which determine the lower levels of their age. There are indirect, the demanding checks, data that rocks of Ikauna Complex cut by Neoarchean pink granite (Figure 2) and Paleoproterozoic doleritic dykes, that defines upper levels of their age. Thus, the geological ages of this mafic-ultramafic complex are Archean.

Figure 2:Photos of Ikauna dunite-pyroxenite-gabbro layered complex rocks in outcrops:

a) Serpentinite (Metadunite) with relict of panautomorphic texture in Madawara (scale on compass-in cm);

b) Metagabbro in canal near Ikauna (scale on compass-in cm).

c) Gabbro-pegmatite veins in gabbro (compass-10 cm).

Table 1:Stratigraphy of Madawara Block, Lalitpur Disrtict, Uttar Pradesh [12,16].

Table 2:Major (wt.%) and trace (ppm) element analytical data of Ikauna complex, Bundelkhand craton, India.

The mafic-ultramafic Ikauna intrusion is a well-differentiated complex and its petrographic characteristics show essential minerals of serpentine, amphiboles, plagioclase, tremolite–actinolite and chlorite which comprising dunite (serpentinite) (Figure 3(a-b)), pyroxenite, gabbro (Figure 3(c-d)) and gabbro-pegmatite. Ikauna intrusive rocks vary considerably in composition (Table 2). The dunite contains high MgO (39.14-41.02wt.%), Cr (2619-7093ppm), Ni (1991-2507ppm) and low SiO2 (43.17-43.56wt.%), Al2O3 (3.46-4.57wt.%), CaO (0.24-0.57wt%) and alkali concentrations (Na2O+K2O=0.02 to 0.03wt.%). The gabbro and gabbro-pegmatite have lower MgO (8.26-9.86wt.%), Cr (799ppm) and Ni (252ppm) and higher SiO2 (50.18 wt.% in gabbro and 51.02wt.% in gabbro- pegmatite), Al2O3 (15.51-17.55wt.%), CaO (10.89-12.28wt.%) and alkali concentrations (Na2O+K2O=3.0 to 3.59wt.%) than Ikauna intrusion dunites. The position of the points of compositions of Ikauna intrusive rocks on the TAS (SiO2-Na2O+K2O) classification diagram (Figure 4a) [17] for plutonic rocks and in the AFM diagram (Figure 4b) [18] allow to define them as ultrabasic and basic rocks mainly tholeiitic series. Same fields on these diagrams are characteristic for typical mafic-ultramafic Paleoproterozoic layered intrusions of the Karelian craton (Figure 5). Ni and Cr increases with increasing MgO, consistent with the accumulation of olivine and chromite.

SiO2, Al2O3 and CaO increase with decreasing MgO, consistent with the accumulation of clinopyroxene and plagioclase in gabbro (Figure 5). Similar rock composition variations trends are characteristic of the Paleoproterozoic layered intrusions of the Karelian craton, e.g. the Kivakka massif [19]. Ikauna intrusion rocks are characterized by a slight enrichment in LREE ((La/Sm)n=1.8-3.3) and largely unfractionated or a slight depletion in HREE ((Gd/Yb) n=1.1-2). In addition, samples from the metagabbro display a positive Eu anomaly (Figure 6) [20]. The REE patterns of different types of rocks in the Ikauna intrusion have sub-parallel trends, suggesting that the different rock types are related to each other by differentiation of the same primary magma. The trace element abundanc es and patterns for the different types of rocks in the intrusion are variable. The metagabbro samples are characterized by Rb and Ba enrichment and positive Sr and Eu anomalies, as would be expected for the presence of cumulus plagioclase. The metad unites and metapyroxenites are marked by lower trace element abundances than the metagabbros and negative Sr anomalies, which might be related to fractional crystallization of plagioclase. The compositional characteristics of the Ikauna intrusive rocks discussed and suggest that they are comparable with the layered intrusions of the peridotite-gabbronorite complex characteristic of the Karelian craton [13,14].

Figure 3:Petrography of Ikauna dunite-pyroxenite-gabbro layered complex rocks:

Figure 3(a-b): Photomicrographs of Metadunite (serpentinite).

Figure 3(c-d): Gabbro (polarized light (a, c) and cross nicol (b, d)).

Figure 4:Classification diagram

Figure 4a: TAS (SiO2 - Na2O + K2O) [17].

Figure 4b: AFM diagram [18] for Ikauna intrusion (Bundelkhand craton, India) and Kivakka (Karelian craton, Russia) layered intrusion.

Figure 5:Variations in major element vs MgO in Ikauna (Bundelkhand craton) and Kivakka (Karelian craton) layered complexes.

Figure 6:Chondrite-normalized REE [20] patterns in Ikauna layered complex.

We are highly thanks for RFBR (17-55-45005 IND) and DST (INT/RUS/RFBR/P-279) grants for financial support. This work is supported under MOU between Bundelkhand University, Jhansi, India and Institute of Geology, Karelian Research Centre, RAS, Petrozavodsk, Russia.

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