No abstract

No abstract

In this investigation, we reconstruct the latest Palaeoproterozoic to Early Mesoproterozoic orogenic events along the southern margin of the Central Indian Tectonic Zone (CITZ), using sensitive high resolution ion microprobe (SHRIMP) U-Pb zircon dating and Lu-Hf isotope analyses of zircon and Th-U-Pb chemical dating of monazite from samples of the Tirodi biotite gneiss (TBG) unit in the Sausar Mobile Belt (SMB), the latter constituting the southernmost litho-tectonic component of the CITZ. U-Pb zircon dating of one migmatitic gneiss sample from the type locality of the Tirodi biotite gneiss in the northern domain of the SMB has yielded an age of 1618 AE 8 Ma, which is considered to be the time of magmatic crystallization of its protolith. Combined U-Pb zircon and monazite chemical dating of two granite gneiss samples from the southern domain of the SMB broadly constrain magmatic crystallization between 1603 AE 23 Ma and 1584 AE 17 Ma and an overprinting metamorphic recrystallization event at 1572 AE 7 Ma. Monazites from the granite gneiss samples also record a terminal metamorphic event at 1415 AE 23 Ma. Lu-Hf isotopic analyses of zircons reveal fundamentally different source rock reservoirs for the protoliths of these magmatic rocks across the SMB. While the type TBG from the northern domain was derived from an Early Palaeoproterozoic source T DM c (Hf) from 2093 to 2523 Ma, with a mean value at 2379 Ma) of essentially juvenile material with minor crustal components (eHf(t) from À3.3 to þ 3.7), the granite from the southern domain had a mature crustal source (eHf(t) from À12.5 to À21.9) of Palaeoarchaean age T DM c (Hf) from 3051 to 3630 Ma, with a mean value at 3218 Ma). When integrated with metamorphic information previously obtained from the 1.6 Ga ultra-high temperature granulite facies metamorphic event in the SMB, the discrete magmatic and metamorphic events between 1.62/1.60 Ga and 1.42 Ga can be correlated with the formation of an Early Mesoproterozoic accretionary orogen in the CITZ.

In this study, we present precise pressure-temperature (P-T) and age constraints of ultrahigh-temperature (UHT) metamorphism of the Bhandara-Balaghat granulite (BBG) domain at the southern margin of the Central Indian Tectonic Zone (CITZ). Supracrustal and metaigneous granulites of this domain, which lie as detached pods and lenses of various sizes within felsic gneiss-migmatite association record protracted high-T crustal anatexis events, broadly synchronous with and/or punctuated with felsic and mafic plutonism. Magnesian metagreywacke protolith of the supracrustal suite records extensive biotite melting and subsequent melt extractions at deep crustal, UHT metamorphic conditions (T ! $9008C at P$8 kbar), producing restitic mineral assemblages of garnet þ rutile, garnet þ cordierite and garnet þ aluminous orthopyroxene. The diversity of the mineral assemblages is related to the domainal-scale variation of the bulk rock composition. In situ chemical age dating of five monazite grains, which occur in the different textural settings of the garnet þ cordierite þ orthopyroxene þ rutile-bearing granulite reveals two age domains: (1) Pervasive $1.6 Ga domain, which is recorded in monazites occurring as inclusions in garnet and in the leucosome matrix is correlated with the timing of the UHT metamorphism. (2) $1.47 Ga domain reflects a fluid-mediated recrystallization event leading to dissolution and re-precipitation of older monazite. The $1.6 Ga monazite chemical ages provide robust constraints on the timing of the earliest stage of tectonothermal processes in the CITZ (defined here as the 'Central Indian Orogeny'). The significance of the $1.6 Ga hot orogenesis in interorogen correlation is discussed.

No abstract