Abdolnaser Fazlnia; Amir Pahnaei
Abstract
The Gharuchah-Sofla intrusion from south Mahabad (southeast of West Azerbaijan) consist mostly of granodiorite and tonalite, interspersed with small bodies of quartz diorite, monzogranite, ...
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The Gharuchah-Sofla intrusion from south Mahabad (southeast of West Azerbaijan) consist mostly of granodiorite and tonalite, interspersed with small bodies of quartz diorite, monzogranite, syenogranite, and alkali feldspar granite. Microgranular mafic enclaves, which are mainly gabbroic diorite, diorite, and quartz diorite in composition, occur as elliptical or circular throughout the intrusion. Samples with gabbroic diorite, diorite, and quartz diorite, in composition consist primarily of plagioclase, clinopyroxene, hornblende, biotite, opaque minerals, and small amount of quartz. Similar mineralogy with the occurrence of K-feldspar and only small amount of clinopyroxene, are found in tonalites, granodiorites and monzogranites. The enclaves are also characterized by the presence of clinopyroxene, biotite, opaque minerals, and small amount of quartz and alkali-feldspar. There are minor minerals such as prismatic apatite and titanite in several samples. The samples show I-type, metaluminus and calc-alkaline characteristics. The Gharuchah-Sofla dioritic gabbro-granitic intrusions are poor in high field strength elements (HFSE) such as Nb, Ta, Hf, and Zr along with P and rich in Sr, K, Rb, and somewhat Ba. Based on the element ratios of (La/Yb)n and (La/Sm)n, levels of light rare Earth elements in the samples from the main mass are more than those of the enclaves; a demonstration of the enrichment of these elements in the main mass. The intrusions resulted from the partial melting of a metasomatized mantle wedge of supra subduction zone typical of subduction-related magmas. These rocks were evolved in an active continental volcanic arc with respect to the Laramide orogeny and the Neotethys subduction under the Sanandaj-Sirjan zone at the post Cretaceous. Magmatic ages of the intrusions are post Cretaceous during the Laramide orogeny. Deep subduction-related faults and fractional crystallization in the crustal chambers helped to petrological evolve the intrusions.
