U-Pb zircon dating, Sr-Nd isotope and petrogenesis of Sarduiyeh granitoid in SE of the UDMA, Iran: implication for the source origin and magmatic evolution

The Sarduiyeh granitoid (SG) is intruded in the southeastern part of the Dehaj-Sarduiyeh volcano-sedimentary belt in the southeastern end of the Urumieh-Dokhtar Magmatic Arc (UDMA) in Iran. The medium-to-coarse-grained granitoid unit, with granular texture consists mainly of diorite, tonalite, granodiorite and monzogranitic rocks. Mineralogically, these rocks consist mainly of plagioclase, K-feldspar, quartz, biotite and hornblende. The whole rock geochemical analyses indicates that the SG is calc-alkaline, I-type, metaluminous, enriched in large ion lithophile elements (LILE; such as K, Cs, Pb) and depleted in high field strength elements (HFSE; such as Ti, Nb, Ta, Zr). Chondrite normalized plot of SG rare earth elements (REE) show light rare earth element enrichments with (LaN/YbN = 2.44–8.68) and flat heavy rare earth element patterns with (GdN/YbN = 1.02–1.36). The rather high Y (av. 19.35 ppm), low Sr content (av. 293.76 ppm) and low Cr and Ni contents (av. 20.1 and 4.69 ppm, respectively) of the SG demonstrate its normal calc-alkaline and non-adakitic nature, the features of Jebal Barez-type granitoids. The geochemical characteristics and isotopic composition, low ISr (0.7046–0.7049) and positive ɛtNd (+3.4 to +4.03) values, of the SG suggest that its parental magma formed as a result of partial melting from metabasic rocks of lower crust in a subduction-related arc setting. Fractionation of an assemblage dominated by plagioclase, K-feldspar, amphibole and magnetite may have been responsible for the evolution of the SG magma. U-Pb zircon geochronology gives an age of 27.95 ± 0.27 Ma for the SG, suggesting that the final collision between the Arabian plate and Central Iranian microcontinent may have happened in the Late Oligocene.

萨杜伊埃花岗质侵入岩（Sarduiyeh granitoid，SG）侵入于伊朗乌鲁米耶-多赫塔尔岩浆弧（Urumieh-Dokhtar Magmatic Arc，UDMA）东南端的德哈杰-萨杜伊埃火山沉积带东南部。该中粗粒花岗质侵入岩单元具粒状结构，主要由闪长岩、英云闪长岩、花岗闪长岩和二长花岗岩类岩石组成。矿物学上，此类岩石主要由斜长石、钾长石、石英、黑云母和角闪石构成。全岩地球化学分析显示，该侵入岩属于钙碱性、I型、准铝质岩石，富集大离子亲石元素（large ion lithophile elements，LILE；如K、Cs、Pb），亏损高场强元素（high field strength elements，HFSE；如Ti、Nb、Ta、Zr）。萨杜伊埃花岗质侵入岩的稀土元素（rare earth elements，REE）球粒陨石标准化图解显示，其轻稀土元素富集（LaN/YbN=2.44~8.68），重稀土元素配分模式平缓（GdN/YbN=1.02~1.36）。该侵入岩具有较高的Y含量（平均19.35 ppm）、较低的Sr含量（平均293.76 ppm）以及较低的Cr和Ni含量（分别平均20.1 ppm和4.69 ppm），表明其属于正常钙碱性非埃达克质岩石，具备杰巴尔巴雷斯型花岗质侵入岩（Jebal Barez-type granitoids）的特征。该侵入岩的地球化学特征与同位素组成（低初始Sr同位素比值ISr=0.7046~0.7049，正εNd(t)值+3.4~+4.03）表明，其母岩浆形成于俯冲相关弧环境下的下地壳变基性岩部分熔融过程。以斜长石、钾长石、角闪石和磁铁矿为主的矿物组合分离结晶，可能是该侵入岩岩浆演化的主控因素。锆石U-Pb年代学测得该侵入岩的形成年龄为27.95±0.27 Ma，表明阿拉伯板块与伊朗中部微大陆的最终碰撞事件可能发生于渐新世晚期。