Timing and span of the continental crustal growth in SE Pakistan: Evidence from LA-ICP-MS U-Pb zircon ages from granites of the Nagar Parkar Igneous Complex

We present a detailed LA-ICP-MS U-Pb age data of zircons from the Nagar Parkar Igneous Complex in order to evaluate the duration of the Late Proterozoic magmatism in the Indian Shield. Igneous zircons from gray and pink granites in the complex have been investigated texturally, morphologically, and finally measured for Pb-207/Pb-206, Pb-207/U-235, Pb-206/Pb-238, and Pb-208/Th-232 isotope ratios. Most of the zircons are euhederal, oscillatory zoned, and contain common inclusions of needle-like apatite and less common monazite, xenotime, and K-feldspar. Selected grains in six samples from gray and pink granites were analyzed for U-Pb dating and the results plotting on or near the concordia were used for interpretation. Zircons from four samples of gray granites yielded U-Pb mean ages of 751 +/- 9 Ma (MSWD = 0.29) with concordia intercepting at 750 +/- 9 Ma (MSWD = 0.29) for sample NGP62a, 726 +/- 13 Ma (MSWD = 1.6) with concordia intercepting at 731 +/- 15 Ma (MSWD = 1.7) for sample NGP62b, 662 +/- 13 Ma (MSWD = 2.7) with concordia intercepting at 711 +/- 27 Ma (MSWD = 0.98) for sample NP12, and 740 +/- 9 Ma (MSWD = 1.3) with concordia intercepting at 736 +/- 12 Ma (MSWD = 1.3) for sample NP62. One sample (NP01) from grayish white granite gave U-Pb mean age of 699 +/- 26 Ma (MSWD = 10.4) with concordia intercepting at 62 and 950 Ma (MSWD = 2.8). Similarly, zircons from one sample from pink granite (sample NP10) yielded U-Pb mean age of 713 +/- 32 Ma (MSWD = 1.5) with concordia intercepts at 726 +/- 41 Ma (MSWD = 1.9). The combined U-Pb zircon age data from the analyzed samples show a continuous crustal growth, from 775 Ma until 640 Ma, indicating a magmatic span of >100 million years. The magmatism in the Nagar Parkar Igneous complex, a part of the Indian Shield, could be associated with an earlier Andean-type tectonic setting in the Rodinia supercontinent followed by rift-related extensional tectonic setting during the Neoproterozoic Era. Our comprehensive age data thus define a precise time span of crustal growth in the Indian Shield between 640 and similar to 775 Ma and refine the previously reported ages spanning between 1.1 Ga and 0.75 Ga. (C) 2018 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.