PRECAMBRIAN INHERITED ZIRCONS WITHIN THE EARLY PERMIAN SILICIC PANJAL TRAPS: EVIDENCE OF ISOTOPIC RE-FERTILIZATION OF THE ARAVALLI-BUNDELKHAND CRATON

The Panjal Traps of the western Himalaya are composed of basalt with subordinate silicic volcanic rocks. In situ zircon U-Pb dating of the rhyolites yielded similar Early Permian ²⁰⁶Pb/²³⁸U weighted-mean emplacement ages (286.1 ± 1.7 Ma; 287.2 ± 2.5 Ma; 287.3 ± 2.8 Ma; 283.6 ± 2.8 Ma) and contained a minor amount of Late Carboniferous (305-330 Ma) inherited zircons. The Carboniferous zircons may be derived from the Agglomeratic Slate, the earliest magmatic unit of the Panjal Traps. All zircons have enriched ε_Hf(t) isotopic values (ε_Hf(t) = -10.4 to -4.2) indicating the parental magmas were derived from the continental crust. In contrast, the lone dacite sample did not yield a weighted-mean age. Although two Early Permian (~280 Ma) zircons were identified from the dacite, the majority of zircons are inherited/xenocrystic and have Neoarchean (2.6-2.5 Ga), Paleoproterozoic (2.4-1.8 Ga), Mesoproterozoic (1.4-1.0 Ga), Neoproterozoic (0.9-0.6 Ga), and Early Paleozoic (0.58-0.42 Ga) ages with secularly variable ε_Hf(t) values (-23.1 to +5.4). Two distinct isotopic trends are identified within the Precambrian inherited zircons and correspond to crustal evolution age curves at 3000 Ma and 2000 Ma. The Early Permian zircons from the silicic Panjal Traps fall along the 2000 Ma curve and are less isotopically enriched compared to the zircons that fall along the 3000 Ma curve. Furthermore, the Precambrian inherited zircon groupings match the detrital zircon age populations from the Indus River system, Indus Group sedimentary rocks, and major tectonomagmatic periods identified in the Aravalli-Bundelkhand Craton of Northern Peninsular India. The results indicate that the Aravalli-Bundelkhand Craton was: 1) the basement to the Early Permian Panjal rift, 2) isotopically re-fertilized during the Early Neoproterozoic, and 3) the leading edge of western cratonic India prior to the Himalayan Orogeny.