alireza ravankhah

The study area, Tarom, is situated in northwestern Iran, within the Zanjan province. Geologically, it falls within the western Alborz zone, a volcanic-plutonic belt, oriented northwest-southeast. This region, extending from Qazvin (west of Taleghan) to the north-northwest of Miane and north of the Manjil embayment, is bounded by the Abhar-Zanjan-Miane axis to the south (Ghorbani, 2009). Within this mountain range, numerous intrusive masses, primarily granodiorite, have intruded into the Eocene volcanic rocks. These masses, including the Bakhtar Takhestan, Khorasanlu, Zaker, and Chal masses, follow a northwest-southeast trend, aligning with the overall orientation of the Tarom mountains. They are arranged in two parallel rows, cutting through the older volcanic formations.

Geology of the area:

The most important rock units in the Tarom Mountains consist of Eocene pyroclastic rocks, including andesite, rhyolite, basalt, andesite basalt, and rhyodacite, as well as shear tuff and andesite tuff. The region's main elevations are composed of Eocene volcanic and volcano-clastic rocks, along with Oligocene intrusive masses, which form the bulk of the mountain unit. Oligocene trachytic deposits, which are deposited on the Eocene units at an angle of approximately 23 degrees, are exposed in the northern part of the Kabbarik syenitic porphyroid stock. The syenitic porphyroid stock has intruded into the Eocene volcanic and volcano-clastic rocks.This study is grounded in field surveys, sampling of the slightly intrusive mass, and the examination of thin sections. Additionally, chemical analyses were conducted on ten samples from Zarazma Company to determine major, minor, and trace elements using inductively coupled plasma mass spectrometry (ICP-MS). Two samples were also analyzed using electron microscopy. To analyze the mineral composition of Kabbarik rocks for major elements, a JEOL JXA-8100 Superprobe electron microprobe (EMP) equipped with an Oxford Instruments INCA EDS system was employed at the Institute of Geology and Geophysics, Chinese Academy of Science. A 5-micron spot size, a 20 nA beam current, and a 15 keV accelerating voltage were utilized during these analyses.

Petrography:

The intrusive Kabbarik stock exhibits a porphyritic texture, characterized by euhedral to subhedral phenocrysts of alkali feldspar. Its primary mineral composition includes alkali feldspar (Orthoclase) constituting 65-70 Vol.%, followed by 10-15 Vol.% clinopyroxene (diopside), 5-7 Vol.% anorthoclase, and 3-5 Vol.% secondary minerals such as olivine, altered to iddingsite. Minor amounts of apatite, zircon, and dark minerals are also present. Orthoclase phenocrysts often display Carlsbad and polysynthetic twinning. Megacrysts of Orthoclase may contain tiny inclusions of olivine and clinopyroxene, exhibiting a poikilitic texture. Some crystals exhibit a sieve texture, and in certain cases, overgrowth on plagioclase results in a Rapakivi texture. Clinopyroxene (diopside) crystals are generally euhedral to subhedral, with some containing small dark mineral inclusions distributed along their edges and conforming to their shape. Subhedral crystals of iddingsitized olivine are scattered throughout the rock matrix in small quantities. The overall texture of the microlithic rock remains porphyritic.

Mineral Chemistry:

The chemical composition of clinopyroxene and alkali feldspar minerals from the syenitic stock was analyzed using a JEOL JXA-8200 electron microscope at the Department of Geology and Geophysics, Chinese Academy of Sciences.Based on relevant diagrams, the clinopyroxenes were classified as diopside-type (Eby et al., 1998; Morimoto, 1988). The chemical composition of the pyroxenes indicates a sub-alkaline, volcanic arc magmatic setting. EPMA analysis of the alkali feldspars revealed an anorthoclase composition (Deer et al., 1991).

Whole Rock Geochemistry:

The chemical analysis of significant, rare, and rare earth elements (ICP-MS) reveals a calc-alkaline composition for the intrusive mass of the syenite zone and its parent magma. Normalized spider diagrams compared to chondrite demonstrate a clear enrichment of light rare earth elements (LREE) and incompatible elements relative to heavy rare earth elements (HREE) in the examined rocks. Based on tectonic environment diagrams, the studied samples are classified as post-collisional.

The predominant rock formations in the Tarom Mountains consist of Eocene volcanic and volcaniclastic rocks, which constitute the bulk of the mountain range. The investigated syenitic stock, intruding into the overlying rocks, dates back to the Oligocene epoch. Based on spider diagrams, the absence of significant heavy rare earth element (HREE) depletion suggests a mantle that has been metasomatized by subduction-related fluids. Studies indicate that the analyzed samples originated in a setting associated with an arc and a post-collisional environment.

According to the outcrops of volcanic and intrusive rocks with different compositions and ages in the northwest of Iran, the magmatism of the northwest of Iran has been introduced under the titles of Talash and Arsbaran tectonomagmatic zone (Berberian, 1981; Aghazadeh et al, 2010, 2011; Castro et al, 2013). The Talash zone in the east of the Western Alborz-Azerbaijan zone, like the rest of Azerbaijan and Urmia-Dakhtar magmatism, has experienced the peak of magmatism in the Eocene to Oligomiocene (Vincent et al, 2005; Shafaii Moghadam and Shahbazi Shiran, 2010). Volcanic rocks in the northeast of Lahrud are andesitic, basaltic eruptive outcrops and plutonic internal alkaline, calc-alkaline and Shoshonitic masses (Vincent et al, 2005), which continue to spread significantly beyond the borders of the country. Eocene volcanic rocks are seen in the 1:100,000 maps of Lahrud with a northwest-southeast trend. In this research, the lithological, geochemical and petrogenesis characteristics of volcanic rocks in the north of Lahrood in the Khanali Daresi section have been evaluated.
Volcanic rock outcrops in the study area were first evaluated in the field and 45 samples were taken from different parts and then 20 thin sections were prepared from the samples for petrographically studies by using an Olympus type polarizing microscope. Then 11 fresh samples were sent to MS Analytical Laboratory in Canada by Zaminriz Kavan company for chemical analysis and determining the main oxides of whole rock.
Eocene- trachy-andesite and trachy andesy basaltic rocks in northwestern Iran, north of Lahroud (Ardabil province), Extruded with northwest-southeast trend. These rocks have hyalomicrolith porphyritic textures and have plagioclase as major minerals with minor amphibole, pyroxene, biotite and opaque minerals and alkali feldspar minerals. The productive magmas of these rocks are of potassic and shoshonitic nature of Roman type. The parent magma of these volcanic rocks is affected by the fractional crystallization process and Eu / Eu * ≤ values (0.83 to 1.08) indicate plagioclase separation in the magmatic reservoir. Negative anomaly of Ta Ti, Nb in the spider diagrams and enrichment of the LILE and LREE index indicate the effect of subduction environments component in generation of g these rocks. Ba / Nb ratios of 45 to 131, La / Sm ratios of N above 2 and Th / Ce ratios of 0.13 to 0.2 indicate enrichment correlations with melting of subducted sediments during subduction. Also, low Ba / Rb ratios from 0.10 to 15.2 and Rb / Sr ratios from 0.07 to 0.1 indicate melting of phlogopitic bearing source with shoshonitic nature in genesis of these rocks. primary magmas of these rocks form from partial melting of less than 10% matosomatized phlegopolite bearing spinel- lherzolite source and melting of magmatic subduction sediments during subduction in the post-Collisional setting.
 
The geochemical characteristics of the studied samples indicate their enrichment and formation in connection with the subduction environment. This indicates a continental volcanic arc in the experimental diagrams of determining the tectonic environment. The primary magma of volcanic rocks consists of the melting of less than 10% of spinel-phlogopite mantle and metasomatized with subduction factors and associated sediments.