Major and trace element geochemistry and 3.0 Ga Sm–Nd age for the gabbro–norite–anorthosite cumulates of the Mayurbhanj Complex (eastern India): petrogenesis and implications for sulfide and Fe–Ti oxide mineralization

The Archean Mayurbhanj Mafic Complex of the Singhbhum Craton in eastern India consists of a suite of gabbro–norite–anorthositic rocks with magnetitite ore bodies in the upper part. Petrography and whole-rock loss on ignition (LOI) values of 0.12–1.78 wt% indicate negligible to minor local-scale secondary alteration of the rock suite. Petrology and the bulk-rock geochemistry of the rocks indicate pyroxene and plagioclase-controlled fractionation of the Fe–Ti-rich basaltic parental magma. The rocks show elevated rare earth element (REE) contents (light REE (LREE) = 10–70× chondrite, heavy REE (HREE) = 10–30× chondrite) with LREE enrichment. The enrichment of large-ion lithophile elements (LILE), small negative Nb, Ta and Ti anomalies, weak positive Zr and Hf anomalies, and co-variations of various incompatible elements suggest minor incorporation of crustal components. The upper gabbro–anorthositic rock suite yields a bulk-rock Sm–Nd isochron age of 3022 ± 180 Ma, with an initial 143 Nd/ 144 Nd ratio of 0.50849 ± 0.00017, corresponding to an ε Nd(T) value of −4.4 ± 3.3. This value and the trace element geochemistry may indicate a metasomatized mantle source for the parental basaltic magma. Our study suggests that the parental basaltic magma might have originated from a metasomatized lithospheric mantle wedge in an active continental margin setting. The parental magma was emplaced within the early Archean tonalite–trondhjemite–granodiorite (TTG)-dominated continental crust of the Singhbhum Craton. The contemporaneous Mesoarchean granitic plutons were formed by reworking of this older TTG-rich crust. The Mayurbhanj Mafic Complex and other time-equivalent Mesoarchean–Late Archean ultramafic–mafic intrusive and extrusive rocks in the Singhbhum and Dharwar Cratons in the Indian Shield represent a large-scale magmatic event likely related to the amalgamation of the supercontinent ‘Ur’. Rocks of similar age in different parts of this hypothetical supercontinent in the world have significant resource endowments of chromite, platinum group elements, Ti–V–Fe oxides and Ni–Cu sulfides, thus enhancing the exploration potential of the Mayurbhanj and equivalent mafic rock suites within the Indian cratons.