ABSTRACT

The Marivan granitoid body of the northern Sanandaj–Sirjan Zone (N-SaSZ) of northwest Iran was emplaced into Cretaceous sediments, and is associated with minor amounts of iron skarn-type mineralization along the contact between the intrusion and surrounding country rocks. The granitoids within the intrusion include (hornblende-rich) diorite, granodiorite, and granite phases, and zircon U–Pb dating of four samples from this intrusion indicate they were emplaced during the late Eocene (Bartonian; 37.7 ± 1.0 Ma). These plutonic rocks can be classified into two main types, granitic and dioritic rocks, according to petrography and whole-rock major element geochemistry. Both the granitic and dioritic rocks are high-K, and some of the granitic rocks have an I-type affinity and peraluminous to metaluminous compositions. Both the granitic and dioritic rocks have ε_Nd(t) values that cluster around zero (–3.3 to +3.0) and low ⁸⁷Sr/⁸⁶Sr_(i) values (0.7040–0.7076), suggesting derivation from a mafic juvenile crustal or depleted mantle source, which was possibly mafic calc-alkaline rocks or amphibolites within the lower crust. The new zircon U–Pb ages and petrological and geochemical data presented in this study suggest that the Palaeocene–early Eocene collision of the Arabian and Iranian plates caused the ascent and emplacement of hot mafic magma through a slab window into the crust. This increased the geothermal gradient within the root zone of the developing magmatic system at the base of the continental crust, causing the partial melting of lower crust in this region. This generated mafic to intermediate magmas that were either directly emplaced into the upper crust or mixed with varying amounts of upper crustal material prior to emplacement, which formed the diorite to leucogranite range of compositions within the Marivan granitoid intrusion.

摘要

伊朗西北部 Sanandaj-Sirjan 带 (N-SaSZ) 北部的 Marivan 花岗岩体就位在白垩纪沉积物中，并伴随着少量的铁矽卡岩型矿化，沿着侵入体和周围的围岩之间的接触。侵入体内的花岗岩包括（富含角闪石）闪长岩、花岗闪长岩和花岗岩相，该侵入体的四个样品的锆石 U-Pb 测年表明它们在始新世晚期（巴顿纪；37.7 ± 1.0 Ma）就位。根据岩石学和全岩主量元素地球化学，这些深成岩可分为花岗岩和闪长岩两大类。花岗岩和闪长岩均为高钾，部分花岗岩具有 I 型亲和性，对金属铝成分具有过铝质。_Nd (t) 值聚集在零（–3.3 至 +3.0）和低⁸⁷ Sr/ ⁸⁶ Sr _(i)附近值（0.7040-0.7076），表明源自镁铁质幼年地壳或贫化地幔源，可能是下地壳内的镁铁质钙碱性岩石或角闪岩。本研究中提供的新锆石 U-Pb 年龄以及岩石学和地球化学数据表明，阿拉伯和伊朗板块的古新世 - 早始新世碰撞导致热镁铁质岩浆通过板片窗口上升和进入地壳。这增加了大陆地壳底部发育中的岩浆系统根区的地温梯度，导致该地区下地壳部分熔融。这产生了镁铁质到中间岩浆，这些岩浆要么直接进入上地壳，要么在就位前与不同数量的上地壳物质混合，