Mesoproterozoic Reworking of Palaeoproterozoic Ultrahigh-temperature Granulites in the Central Indian Tectonic Zone and its Implications

∼1.6 Ga ultrahigh‐temperature granulite metamorphism in the Central Indian Tectonic Zone: insights from metamorphic reaction history, geothermobarometry and monazite chemical ages

“…The UHT metamorphism produced sapphirine (X Mg ¼ 0.73) þ green spinel (X Mg ¼ 0.39-0.52) þ sillimanite þ mesoperthite (ternary feldspar composition of Or 47-51 Ab 44-47 An 06 ) assemblage in the aluminous granulite, ferroaugite (Wo ¼ 39; X Mg ¼ 0.49) in the BIF granulite and aluminous orthopyroxene (Al 2 O 3 ¼ 5.6 wt %) þ garnet (X Mg ¼ 0.37) in the felsic granulites. A counterclockwise P-T path of metamorphic evolution was previously proposed for the UHT granulites (Bhowmik et al, 2005;Bhowmik, 2006). Subsequent reworking of the UHT granulites led to the decomposition of porphyroblastic (BM 1 ) garnets in the BIF and felsic granulites to orthopyroxene þ plagioclase symplectites and renewed growth of garnet þ quartz AE clinopyroxene assemblage.…”

“…The BBG domain is a $190 km long and $4-20 km wide granulite-gneiss terrain, which occurs as a tectonic sheet in between the low-grade (greenschist facies) Sausar metasediments to the north and the South Indian Block (SIB) to the south ( Figure 1a; Bhowmik and Pal, 2000;Bhowmik and Roy, 2003;Bhowmik et al, 2005). An interlayered sequence of supracrustal and metaigneous granulites of the banded iron formation (BIF), quartzite, sapphirine-spinel-sillimanitegarnet-corundum-bearing aluminous granulite, garnet-cordierite granulite, orthopyroxene-garnet-bearing felsic granulite and metamorphosed noritic gabbro, norite and orthopyroxenite form $500-1000 m long and $50-200 m wide dismembered pods and lenses within an extremely tectonized felsic gneiss-migmatite association (Figure 1b).…”

“…The relative chronological order of evolution of different phases of metamorphism and mafic-ultramafic to felsic magmatism were presented in Basu Sarbadhikari and . The supracrustal granulites from the southern segment of the BBG domain record an early UHT metamorphism (BM 1P, T$950-10008C) at relatively deep crustal levels (P$9 kbar) and a subsequent post-peak, near isobaric cooling P-T history (BM 1R , P$9 kbar, T$700-7508C; Bhowmik et al, 2005;Bhowmik, 2006). The UHT metamorphism produced sapphirine (X Mg ¼ 0.73) þ green spinel (X Mg ¼ 0.39-0.52) þ sillimanite þ mesoperthite (ternary feldspar composition of Or 47-51 Ab 44-47 An 06 ) assemblage in the aluminous granulite, ferroaugite (Wo ¼ 39; X Mg ¼ 0.49) in the BIF granulite and aluminous orthopyroxene (Al 2 O 3 ¼ 5.6 wt %) þ garnet (X Mg ¼ 0.37) in the felsic granulites.…”

“…Although deep crustal UHT metamorphism (P$9 kbar, T$950-10008C) has been known for sometime now from the Bhandara-Balaghat granulite (BBG) domain (Figure 1a), at the southern margin of the Central Indian Tectonic Zone (CITZ; Bhowmik et al, 2005;Bhowmik, 2006), its exact significance to the growth of the Peninsular India through amalgamation of the North and the South Indian Blocks and its relation with the supercontinent cycle are poorly understood because of lack of precise age constraints. While monazite chemical age dating of the garnet þ orthopyroxene-bearing felsic granulite yielded a Palaeoproterozoic age ($2.0-2.1 Ga, Bhowmik et al, 2005), Sm-Nd garnet dating of the same rock, but from a different location produced an Archaean age ($2.67 Ga, Roy et al, 2006) for the UHT metamorphism (Figure 1b).…”

“…While monazite chemical age dating of the garnet þ orthopyroxene-bearing felsic granulite yielded a Palaeoproterozoic age ($2.0-2.1 Ga, Bhowmik et al, 2005), Sm-Nd garnet dating of the same rock, but from a different location produced an Archaean age ($2.67 Ga, Roy et al, 2006) for the UHT metamorphism (Figure 1b). In this work, we make an attempt to resolve this issue by undertaking an integrated petrological and geochronological investigation of garnet-cordierite-orthopyroxene-bearing granulite, from a new location of the BBG domain (Figure 1b).…”