RARE-EARTH ELEMENT CHARACTERISTICS AND K-AR AGES OF THE BAND ZIARAT OPHIOLITE COMPLEX, SOUTHEASTERN IRAN

The Band Ziarat complex of southeastern Iran is located on the western boundary of the Jaz Murian depression and is bounded by two major fau lt systems. The principal rock units of this complex are a gabbro sequ ence that includes low- and high-level cumulate gabbros, a late intrus ive sequence that consists of diorite and plagiogranite, and a volcani c sequence that includes diabase dikes and a lesser amount of basaltic lava. Mantle rocks are virtually absent because of the presence of th e two bounding fault systems, but we consider the complex to be an oph iolite in nature. Rare earth element (REE) whole-rock data clearly dif ferentiate the classic ophiolitic lithologies for the crustal rocks in this complex. Based on the REE data, there are two distinct types of basalt present at Band Ziarat: (i) those that formed from an initial b asaltic melt with a light rare earth element (LREE) enriched signature (similar to intraplate basalts), and (ii) those that have LREE-deplet ed patterns (similar to normal mid-ocean-ridge basalts). The data also suggest (i) that the gabbros are adcumulates and were derived from a source slightly enriched in LREE, with fractionation controlled by rem oval of clinopyroxene or hornblende and plagioclase, and (ii) that the late intrusive rocks as well as a majority of the diabase dikes are c ogenetic and were derived from the same LREE-enriched source. K-Ar age s ranging from 134 +/- 4 to 146 +/- 5 Ma for low-level gabbros and fro m 121 +/- 4 to 130 +/- 4 Ma for high-level gabbros were measured on fi ve hornblende and two whole-rock samples, which suggests that these ro cks may have formed early in the Cretaceous period.