|Title:||U‐Pb geochronology and geochemistry of Bibi‐Maryam pluton, eastern Iran: Implication for the late stage of the tectonic evolution of the Sistan ocean|
|Authors:||M. Delavari, S. Amini, A. K. Schmitt, K. D. McKeegan, and T. M. Harrison|
|Publication:||Lithos, v. 200, p. 197‐211.|
The Bibi‐Maryam pluton crops out in the Sistan suture zone, eastern Iran. This pluton is a 1.5 \times 2 km stock composed of leucocratic tonalite, granodiorite and granite. U‐Pb zircon geochronology of a leucogranite indicates an emplacement age of 58.6 ± 2.1 Ma (95% confidence). The Bibi−Maryam rock suite is sodic with elevated Na2O/K2O (2.9 to 5.5), Sr/Y (15.6‐62.2), La/Yb (13.3‐22.2), and low MgO (0.86‐1.81) abundances. It lacks significant Eu anomalies. Because of these geochemical characteristics, Bibi‐Maryam rocks are similar to high‐SiO2 adakites. Trace element modeling indicates that the Bibi‐Maryam adakitic rocks could be produced by 5‐8% non−modal batch partial melting from a source with composition of 95% N−MORB + 5% sediment in the presence of 35−40% amphibole + 5−10% garnet + 55−60% clinopyroxene + 1% apatite + 1% rutile. This source mineralogy is similar to hornblende eclogite or garnet amphibolites. Collectively, these data provide new constraints for the evolution of the Sistan suture zone and suggest that the Bibi‐Maryam pluton formed via slab melting in an oceanic arc and pre‐plate collision tectonic setting. This implies that the closure of the Sistan Ocean and Lut‐Afghan continental blocks collision happened after the Bibi‐Maryam emplacement at 58.6 ± 2.1 Ma.