ABSTRACT

Granitoid intrusions of Zagros orogenic and metallogenic belt were mainly emplaced during the Jurassic-Cretaceous and Upper Eocene – Pliocene along the Sanandaj-Sirjan Zone (SaSZ) and Urumieh-Dokhtar magmatic Arc (UDMA), respectively. The present work tried to answer the question of whether or not there are fundamental differences in magmatic systems of Mesozoic versus Cenozoic intrusions of Zagros orogen resulting in the lack of porphyry mineralization in SaSZ compared with the widespread occurrence of porphyry-bearing intrusions in the UDMA. Characterizing the geochemical features of six major granitoid intrusions in the SaSZ (Alvand, Almogholagh, Aligoodarz, Boroujerd, Dehno, and Kolah-Ghazi) show they mostly represent low to high-K calc-alkaline and peraluminous magmatic suite, which is analogous to those reported previously for the UDMA porphyry Cu intrusions. However, the SaSZ intrusions are characterized by extremely low Sr/Y contents, distinct negative Eu anomalies, and less fractioned HREE patterns with OIB signature in the less fractionated samples indicating a source dominated by melting of subcontinental lithosphere mantle. This study proposed that the inception of Cenozoic flat slab subduction followed by dehydration melting of ~ 29 Ma of metasomatized subcontinental lithospheric mantle (SCLM) during the continuous stages of continental-continental collision has a decisive role in magmatic change to a more hydrous and oxidized nature. These processes provided unique conditions for increasing metal fertility of these Miocene intrusions compared to those of older Mesozoic igneous activities in the Zagros orogenic and associated metallogenic belt.

摘要

Zagros造山带和成矿带的花岗岩侵入体主要在侏罗纪-白垩纪和上始新世-上新世沿Sanandaj-Sirjan带（SaSZ）和Urumieh-Dokhtar岩浆弧（UDMA）分别侵位。目前的工作试图回答Zagros造山带的中生代和新生代侵入体的岩浆系统是否存在根本差异导致SaSZ缺乏斑岩矿化的问题，与UDMA中广泛出现的含斑岩侵入体相比。对 SaSZ 中六个主要花岗岩侵入体（Alvand、Almogholagh、Aligoodarz、Boroujerd、Dehno 和 Kolah-Ghazi）的地球化学特征表明，它们主要代表低至高 K 钙碱性和过铝质岩浆组，这类似于先前报道的 UDMA 斑岩铜侵入。然而，SaSZ 侵入体的特点是 Sr/Y 含量极低、明显的负 Eu 异常，以及在较少分馏的样品中具有 OIB 特征的分馏较少的 HREE 模式，表明以次大陆岩石圈地幔熔融为主的来源。本研究提出，在大陆-大陆碰撞的连续阶段，新生代平板俯冲开始，随后约 29 Ma 的交代次大陆岩石圈地幔 (SCLM) 脱水熔融，这对岩浆转变为更加含水和氧化的性质具有决定性作用。 .