We present regional variations of whole-rock Sr/Y and (La/Yb) ratios of magmatic rocks along the Cenozoic Urumieh-Dokhtar and Alborz magmatic belts, Iran. Both the magmatic belts are located at the north of the main Zagros Neo-Tethyan suture. The Urumieh-Dokhtar magmatic belt (UDMB), which trends NW-SE for 1000 km across Iran, was characterized by the intensive volcanism and plutonism, and defined the magmatic front (MF) of the Zagros orogenic belt. The Alborz magmatic belt (AMB) is situated to the north, and characterized by less intense magmatic activity. The Alborz magmatic belt was formed behind it in the rear-arc (RA) domain. A striking feature of the both magmatic belts is the transition from normal calc-alkaline arc magmatism during the Eocene–Oligocene to adakite-like calc-alkaline magmatism during the Middle to Late Miocene–Pliocene. The late-Cenozoic magmatism of the UDMB and AMB shows higher Sr/Y and (La/Yb). However, it should be noted that crustal thickening event is intensive in the UDMB than AMB during Late Cenozoic. Using the composition of the Lale-Zar zircons from the SE UDMB we determined the oxygen fugacity (O) during zircon crystallization to be between FMQ (fayalite–magnetite–quartz buffer) -0.69 to +2.41, whereas those of the Hashroud-Teckmdash-Gormolla zircons from NW AMB range from −1.22 to +5.99. The O estimates suggest relatively more oxidized conditions for the Late Cenozoic igneous rocks of the AMB. Compiled data from the UDMB and AMB intrusions show an increase in average zircon crystallization temperatures with decreasing age. These outcomes have been interpreted in terms of variation of the crustal thickness, from 30 to 35 km during Eocene-Oligocene to 40–55 km during the middle-late Miocene. We propose the increase in crustal thickness is associated with the collision between the Arabian plate and Iran and subsequent convergence during the middle-late Miocene.

中文翻译：

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伊朗乌鲁米耶-多赫塔尔和厄尔布尔士岩浆带地壳厚度新生代时间变化

我们展示了伊朗新生代乌鲁米耶-多赫塔尔和厄尔布尔士岩浆带沿线岩浆岩全岩 Sr/Y 和 (La/Yb) 比率的区域变化。两条岩浆带均位于扎格罗斯新特提斯缝合带的北部。乌鲁米耶-多赫塔尔岩浆带（UDMB）沿西北-东南走向横贯伊朗1000公里，以强烈的火山活动和深成作用为特征，定义了扎格罗斯造山带的岩浆前缘（MF）。厄尔布尔士岩浆带（AMB）位于北部，岩浆活动较弱。厄尔布尔士岩浆带形成于其后方的弧后（RA）区域。这两个岩浆带的一个显着特征是从始新世-渐新世的正常钙碱性岩浆作用过渡到中新世-上新世中晚期的类埃达克岩岩浆作用。UDMB和AMB的晚新生代岩浆活动显示出较高的Sr/Y和(La/Yb)。但值得注意的是，晚新生代UDMB地壳增厚事件比AMB更强烈。利用来自 SE UDMB 的 Lale-Zar 锆石的成分，我们确定了锆石结晶过程中的氧逸度 (O) 在 FMQ（铁橄榄石-磁铁矿-石英缓冲液）-0.69 至 +2.41 之间，而 Hashroud-Teckmdash 的氧逸度 (O) 介于 FMQ（铁橄榄石-磁铁矿-石英缓冲液）-0.69 至 +2.41 之间。 NW AMB 的 Gormolla 锆石的范围为 -1.22 至 +5.99。O 估计表明 AMB 晚新生代火成岩的氧化条件相对较高。UDMB 和 AMB 岩体的汇编数据显示，随着年龄的降低，平均锆石结晶温度会升高。这些结果被解释为地壳厚度的变化，从始新世-渐新世期间的30至35公里到中新世中晚期的40至55公里。我们认为地壳厚度的增加与阿拉伯板块和伊朗之间的碰撞以及随后中新世中晚期的汇聚有关。