سن سنجی زیرکون U-Pb و ژئوشیمی رادیو ایزوتوپ ها Sr-Nd گرانیتوئیدهای اواخر نئوپروتروزوئیک بورناورد

The study area (Bornaward granite) is located in northeast of Iran (Khorasan Razavi province), about 280 km southwest of Mashhad city. Taknar zone is an exotic block, bordered by two major faults, Great Kavir fault (Drouneh) to the south and Rivash fault in the north. A complex of granite, granodiorite, monzonite and diorite crop out at the center of Taknar zone. They are named as “Bornaward granite”. Published data using Rb–Sr whole-rock and biotite isotopic methods on granitoid rocks (Bornaward granite) gave ages of 154 to 111 Ma. The results of U-Pb zircon dating of granodiorite is 552.69 ± 10.89 Ma and granite is 538.22 – 1.82, + 4.28 Ma (Late Neoproterozoic time). Both granite and granodiorite are classified as belonging to the ilmenite-series of reduced S-type granitoids. Chemically, they are per-aluminous, high-K calc-alkaline with relatively enriched in LILE, Rb, K and depleted in Sr, Ba, Nb, Ti, Ta, Y and Yb. Chondrite-normalized Rare Earth Element (REE) plots indicate minor enrichments of light REE in composition with heavy REE, with (La/Yb)N between 3.5-5.6 and high total REE (193-252) with strong negative anomaly of Eu. They have a initial 87Sr/86Sr and 143Nd/144Nd ranging from 0.713566 to 0.716888 and 0.511791 to 0.511842, respectively, when recalculated to an age of 553 and 538 Ma, consistent with the new radiometric results. Initial εNd isotope values for granite and granodiorite range from -2.62 to -2.01. Granite and granodiorite of Bornaward yields a TDM age of 1.4-1.41 Ga. This indicates that the granites and granodiorite being derived from partial melting of distinct basement source regions with very high initial 87Sr/86Sr.