Presently it is believed that the EGB is a collage of several provinces/domains having distinctive geological histories [13] . The provinces/domains are said to be separated by structural discontinuities (Figure 1(a)) as represented by crustal scale shear zones [14] [15] . These shear zones were described as inter-domainal shear zones. However, a recent work [16] convincingly demonstrated the Mahanadi Shear Zone (part of North Boundary Shear Zone) as an outcome of intra-terranne transpression in response to far field stress generated by collision of EGB with the Singhbhum Craton (SC) and thereby challenged the efficacy of the domainal classification [15] .

The EGB comprises three broad lithological groups, namely metapelitic granulites, charnockite-enderbite gneisses and associated mafic granulites and migmatitic gneisses. NE-SW regional tectonic trend represented by S₁ gneissosity [17] [18] [19] , a steep axial planar foliation, and common structural repetitions, are akin to a convergent orogen that evolved under a regional NW-SE

compression [18] . Oblique collisional juxtaposition of the EGB against the Singhbhum and Bastar Cratons have also been described [20] [21] and was interpreted as a syntaxial bend during oblique collision of an indenter [22] . Complex tectonothermal records include ultra-high-temperature metamorphism, mostly represented by metapelitic migmatites [8] [9] [10] [23] [24] ; dehydration melting in different crustal protoliths [10] [25] [26] [27] [28] , and complex, possibly distinct P-T paths in different sectors [9] [11] [29] [30] [31] . Recent isotopic data, particularly, Ndmapping has confirmed that different crustal domains or provinces with unrelated pre-metamorphic history are present in the EGB [14] [15] [18] .

The present study area around Paikmal, at the northwestern margin of the EGB, belongs to the Western Khondalite Zone (WKZ) of [32] and EGP of [14] . The area exposes dominantly metapelitic granulites (khondalites), with minor bands of mafic granulites of the EGP and granite gneisses of the BC with some mafic enclaves [21] . The pervasive gneissosity in the metapelitic granulites and axial traces of F₂ folds describe a bend from E-W in the northeast to NNE-SSW in the southwest (Figure 1(b)). Besides the quartzite mylonites, mylonitic fabrics are also observed in metapelitic granulites in the boundary shear zone. The granitoids of the BC have a crude gneissosity, which is at a high angle to the boundary. [6] described microstructures and quartz C-axis fabrics, attesting to a high-temperature shear zone separating the craton from EGB. Also, the rocks of BC are affected by the shear deformation.

The electron microprobe analyses (EPMA) were undertaken at the Geological Survey of India, Kolkata using CAMECA SX 100 machine. Operating conditions for the electron microprobe were 15 KV accelerating voltage, 0.2 nA sample current and 2 µm beam diameter.

EPMA analytical data is given in Table 1. Pressure-temperature estimates for these equilibrations were derived using multi-equilibrium calculations [33] . P-T estimate for the mafic granulite outside the shear zone was reported as 9 Kbar,

850˚C [6] . In the shear zone khondalite, using garnet-sillimanite-ilmenite-rutile barometer, pressure was estimated at ~4.7 kbar, at 600˚C; and in the mafic granulite using the garnet-orthopyroxene-plagioclase-quartz barometer, the estimated pressure is ~5.1 kbar at 600˚C. Hence, a minimum of 4 kbar exhumation (from 9 to 5 kbar) could be assigned to the shearing event. This comes out to around 15 km of exhumation.

U-Pb isotopic data for zircon and monazite in Khondalite (Table 2) by TIMS (Thermal Ionisation Mass Spectrometer) provide the following constraints on the time relation between granulite metamorphism and shear zone development, in this boundary shear zone. The three zircon fractions dated 948, 1036 & 1056 Ma could be interpreted as a long-lived thermal (granulite-formation) event, as reported by [24] from the different areas in the EGP. The two older populations, 1244 and 1355 Ma could represent partially modified detrital zircons [37] . Two monazite fractions dated 918 & 1096 Ma would further corroborate the long-lived thermal event. Monazite fraction dated 865 Ma on the other hand, could signify the beginning of the Rodinia break-up [38] . Monazite fraction dated 541 Ma, could represent the late Neoproterozoic thermal event in East Gondwana, which is believed to have been completely assembled by around 600 Ma [39] . It is important to note that though no extensive areas or rock suites of this age are recorded in the EGP, this Pan-African imprint only sporadically appears in several areas in the EGP [40] , as also in this presentation and has no significance in the context of an orogenic event.

Zircon U-Pb isotopic analysis by LAICPMS is presented in Table 3 and Figure 3. Here also, two zircon populations could easily be identified. Concordant zircon population of the Grenvillian orogeny ranges between 1040 & 920 Ma and

consistent with the long-lived UHT event in the EGP [24] . The Neoproterozoic population, however, could be further sub-divided into two age groups, namely, between 815 & 700 Ma and between 600 & 530 Ma respectively and this is consistent with 541 Ma monazite fraction, as recorded by TIMS analysis.

The whole rock Rb-Sr and Sm-Nd isotopic data for granulites and granites of this boundary region is presented in Table 4. It is interesting to note that some mafic granulites (4MG) are observed interbanded with the khondalites (4KH), away from the shear zone, similar to that recorded from Sunki area (cf. Figure 4(a) in [41] ). Rb-Sr data in the Khondalite (4KH) indicated ~1.6 Ga Sr-model date. The Sr model date for khondalites in the EGP (including 4 KH) provide some constraints on the age of sedimentation [42] . Sm-Nd isotopic data for the interbanded mafic granulite (4MG), indicated mafic crust formation around 1.6 Ga.

As for the Paleoproterozoic provenance of the precursor khondalite sediments, the Nd-model date of the khondalite, 2.5 Ga and the dominantly granitic, but including some mafic rocks of the BC, as reported by [42] , are also recorded from granite in this boundary region.

Secondary amphibole, aligned in the direction of extension (Figure 2(c)) provides 580 Ma cooling age (Table 4).