The KoheSiah Volcanoes are located in the North of Qorveh city in the west of Iran. The KoheSiah volcanoes include several craters bearing domes located in the Kordestan Province, between latitudes 35 °23'13.54” to 35 °21'26.63”N and longitudes 47 °54'38.26”E to 47 °56'01.42”E. Based on the petrographic and geochemical analysis, the volcanic rocks in the KoheSiah area are classified as basalt, Alkali basalt, trachy-andesites and mugearite. The studied samples are alkaline with sodic to potasic feature based on Na 2O/K 2O ratios and belonging to Shoshonite series. Most of the alkaline volcanic rocks in the study area fall in the field of within in plate basalts (WPB) and represent of a mantle metasomatism trend associated with variable degrees in the partial melting of an enriched mantle source.
The study area is located in the Northern part of Qorveh city among the by lowland and flat area. The volcanic domes cluster gives a special morphology to the study area. These volcanoes are generally called Siahkoh volcanoes on the Qorveh 1:100,000 quadrangle map (
complex has surrounded among the several alkaline basalt volcanoes. These alkaline volcanoes include: 1) KoheQarineh with two main conduits in the south eastern sector of cone, 2) QarehBolagh volcanic cone in the Norhern part of KoheSiah area, 3) Saraijogh volcanic cone in the Noth east and Dirkolovolcano. The KoheSiah volcanic complex is key area for studying of tertiary volcanism in the Sanandaj-Sirjanzone. This provides a unique opportunity to study of Andean type arc magmatism that took place at the Neo-Tethyan subduction margins. Notwithstanding, despite the significance of KoheSiah volcanic rocks to understanding of arc magmatism along the Neo-Tethyan margin, due to limited field and geochemical data, tectonic evolution, this unit is relatively poorly constrained and there are many unknown about their tectonic setting. Our study presents major and trace element data for a number of volcanic rocks from KoheSiah volcanic domes, with the aim to study and evaluate the geochemical features and tectonic setting of KoheSiah volcanic rocks.
In this research detailed field studies include preparation of new geological map were combined with systematic and random sampling to aim multidisciplinary approach of this research. The twenty one sample after petrographical studies were selected for geochemical analysis. Forty Trace and Minor element for selected samples were analyzed using inductively coupled plasma mass spectrometry (ICP-MS) methods.
The Qorveh area is geologically, divided in two northern and southern sector. The northern and southern have main different magmatic and structural evolution history. The volcanic centers in the northern sector are part of NW-SE trending Takab-Qorveh volcanic belt with acidic, intermediate and basic lavas. The acidic and intermediate volcanoes are distributed as Domes, dyke and ignimbrite sheets. The basic volcanoes the basic volcanoes as low altitude scoria cones (50 m) and their lavas due to law gravity extent several kilometer above Qorve plain. The main volcanic center in the Takab-Qorveh region as follows [
1) Takhte Soleyman (Nosrat Abad) peripheral volcanic centers with high K andesite and dacite;
2) Ayob Ansar volcano with dacite composition;
3) Qare Tore volcano with basalt composition;
4) Nadri volcano with basalt composition;
5) Tahmorath volcano with basalt composition;
6) Jorovandi volcano with basalt in the basal part and trachy basalt in the upper part;
7) Ahmad Abad volcano with basalt composition and granitoids enclaves;
8) Gozel ghayeh-GhareBolagh volcano with basanite composition;
9) GhareBolagh volcano with dacite composition;
10) Ghizilja Kand volcano with basalt-andesite composition and several granitoids enclave;
11) Sheyda-Yakhi kamal volcanoes with dacite and andesite composition;
12) Kani Derij peripheral volcanoes with high K dacite composition.
In the southern sector of Qoeveh area, stratigraphical sequences from base to top include the Triassic, Triass-Jurassic and Jurassic metamorphic rocks and Eocene none metamorphed rocks. The Triassic and Jurassic units are lack of fossil and their ages is determinate by field relation and stratigraphic position.
The study area (KoheSiah volcanic complex) is located in the north east of Qorve city within the Sanandaj-Sirjan structural zone. This area is part of volcanic center between Takab and QaraAghaj cities which refereed as Takab-Qorveh volcanic belt within the northern part of Sandaj-Sirjan structural zone. The KoheSiah volcanic complex situated 25.6 Km of NE ofQorveh city between KoheQarineh in the NW and QareBolagh in the SW (
Several rock classification diagrams are used for classification and nomenclature of volcanic rocks of rocks of KoheSiah area. They are including:
The Kohesiah volcanic rocks were classified using the total alkalis (K2O + Na2O wt.%) vs. SiO2 diagram of Cox et al. (1979) (
This compositional variation of Siah Koh volcanic rocks is investigated by using the millication proportions of their major oxides according to the rock classification of De La Roche, et al. (1980) (
In The Zr/TiO2*0.0001 vs. Nb/Y (
One of the main objects in the petrological studies is determination of magmatic series. According to Kuno (1968) [
In the SiO2 versus K2O diagram (peccerillo and Taylor., 1976) [
In order to evaluation of the tectonic setting of KoheSiah volcanic rocks several tectonic discriminate diagram have been used they are include:
The KoheSiah volcanic rocks lie in the field of within plate basalts in the Zr/Y versus Zr discriminate diagram (Pearce and Norry., 1979) [
In the Ti/100-Zr-Y*3 ternary discriminate diagram (Pearce and Cann., 1973) [
The siah Koh volcanic rocks lie in the field of within plate alkaline basalts (Al) in the Nb*2-Zr/4-Y ternarydiscriminate diagram (Meschede., 1989) [
The spider diagrams are used for identification of the petrogenic processes and
inferring of different tectonic setting. Therefore, abundance of rare earth elements in the studied samples are normalized to the average abundance of these elements in the different tectonic settings, and interpreted magmatic processes such as fractionational crystallization, partial melting and magmatic contaminations by the diagram patterns such as their trends and positive and negative anomalies in the some elements (Rollinson., 1993) [
Thampson et al. (1984) [
However, negative anomaly of Ti could be related to the titanomagnetite fractionation, remaining of Ti bearing of amphibole, iron oxide, titan and clinopyroxene in the source region, or high degree of partial melting of source or crustal contamination (Fodor., 1987; Wilson, 1989) [
Wood et al. (1979) [
Sun and Mc Donough (1989) [
The rare earth element of KoheSiah Normalized to most accepted rare earth elements values of chondrite composition from Boynton (1984) [
The volcanic rocks of KoheSiah volcanic complex include basalt, Alkali basalt,
trachy-andesite and mugearite. The studied samples are alkaline with sodic to potasic feature based on Na2O/K2O ratios and belonging to Shoshonite series. Most of the alkaline volcanic rocks in the study area fall in the field of within in plate basalts (WPB) and represent of a mantle metasomatism trend associated with variable degrees in the partial melting of an enriched mantle source. In the incompatible trace, element patterns for all volcanic rocks from the KoheSiah volcanic rocks represent negative anomalies in the Ti and Nb elements. However, negative anomaly of Ti could be related to the titanomagnetite fractionation, remaining of Ti bearing of amphibole, iron oxide, titan and clinopyroxene in the source rgion, or high degree of partial melting of source or crustal contamination. Negative anomaly of Ta is consistent with crustal contamination. The study of incompatibles trace and rare earth element and comparison of them with high alkaline and basic rocks of study area indicate they are in related to the within plate continental rifting magmatism. The high slope of LREE/HREE in the most of samples is consistent with presence of residual garnet in the mantle source. The La/Yb(Cn) ratios range between 14.95 to 11.75 (averaging 13.1) for FR-10 and FR-13 samples, respectively. This could be in related to the heterogeneity of mantle source or changes in the partial melting degrees of different mantle sources.
Koohbanani, S.K., Sheikhzakariee, S.J., Emami, M.H. and Dabiri, R. (2018) Geochemistry and Tectonic Setting of Kohe Siahvolcanoes, North Qorveh, Sanandaj, Iran. Open Journal of Geology, 8, 474-488. https://doi.org/10.4236/ojg.2018.85028