Petrogenetic source and tectonic evolution of the Neoproterozoic Nagar Parkar Igneous Complex granitoids: Evidence from zircon Hf isotope and trace element geochemistry

Abstract

We investigated zircons from the Nagar Parkar Igneous Complex (NPIC) Gray and Pink granites for hafnium isotope and trace elements geochemistry to elucidate their petrogenetic source and tectonic setting. The studied zircons are characterized by oscillatory zoning, contain micro-inclusions of apatite, monazite, xenotime, and plagioclase. Rare-earth elements of the Neoproterozoic (ca. 750 Ma) zircons are characterized by a positive slope from La to Lu, exhibit distinct positive Ce- and negative Eu-anomalies that suggest their crystallization in magma that was fractionating plagioclase. The relatively smaller but variable Ce/Ce*N ratios (2–62), smaller Eu/Eu*N (0.01 to 0.45), and comparatively higher Th/U ratios (>0.30, reaching up to 3.20) affirm their derivation mainly from the continental crustal type magmas. The εHf(t) values of zircons in Gray and Pink granites range from +5.7 to +14.4 and +1.9 to +10.7, respectively, indicate their derivation from a juvenile crust and the absence of negative εHf(t) values point towards non-involvement of the older or reworked material during the crustal growth. The TDM model ages, calculated from the Hf isotope values of zircons, spread between 1119 and 736 Ma for Gray and 1013 and 900 Ma in Pink granites, further opine their derivation from a comparatively young and juvenile crust. Crystallization temperatures, estimated from the titanium content in zircon and zircon-saturation in whole-rock, range from 631 to 905 °C and 784 to 918 °C, respectively, show consistent results for the crystallization conditions of most granitic melts. Whole-rock major and trace element data, combined with zircon Hf isotope and trace elements geochemistry suggest within-plate A-type granitic magma that likely generated in a rift-related tectonic setting that persisted along the western margin of Rodinia during the Neoproterozoic era.