Dikes in the north of Saveh are located in a region with an area of approximately 200 square kilometers, in
a distance of approximately 100 kilometers south of Tehran. Dikes mentioned in terms of petrological composition, are divided into two categories: alkaline and intermediate to acidic. Alkaline dikes include: andesitic basalt and andesite and intermediate to acidic dikes include: trachyte
and trachyandesite. In terms of geochemical, dikes in the north of Saveh have a dual nature of alkaline and calc-alkaline. Both groups are derived from more enrichment source than primitive mantle. Despite similarity of pattern of both groups, varieties of alkaline having less silica, in the elements Sr, Ti, Nb and Ta show more enrichment and in the elements Hf, Rb, Th, K show less enrichment than varieties of calc-alkaline.
Swarm Dikes Alkaline and Calc-Alkaline Saveh Iran1. Introduction
The studied area with an area of approximately 200 square kilometers, in the north of Saveh city, is located between 55˚15' to 55˚50' East and 35˚00' to 35˚15' North. In this area, more than 250 dikes with an approximate thickness of 0.4 to 12 m and a length of approximately 50 to 3000 meters have been intruded in an area of approximately 200 square kilometers and with a combination of andesitic basalt, andesite and trachyte in Eocene volcanic rocks (Figure 1). Studied swarm dikes, are alike type IV swarm dikes of Ernst [1] which are due to creation of the regional stress fields [4] . According to the studies of Hou [2] and [3] , dikes in this area can be considered similar to dikes parallel to the linear pattern which have created in a relatively wide area and influenced by regional tensions caused by a phenomenon such as subduction [4] .
Dikes in the north of Saveh on the geological map of the studied area [<xref ref-type="bibr" rid="scirp.64339-ref4">4</xref>]
Previous studies in this area have been carried out by different people and Geological Survey of Iran, in the form of preparing geological mapping at a scale of 1:100,000 and 1:250,000. Based on the studies, the mentioned dikes are acidic and alkaline dikes [5] and have the feeder role of Eocene volcanic rocks of the region [4] . In this article it is tried to introduce a variety of petrology, geochemical characteristics and tectonomagmatic environment of dikes in the north of Saveh. In this regard, after doing field studies and detailed petrography, 15 samples of dikes have been subjected to chemical analysis by XRF ICP_MAS and methods in laboratories of the University of Tarbiat Modarres and Zarazma Company for major, minor and trace elements (Table 1), then on two selected samples, 44 point microprobe analyses were carried out by electron microprobe machine type GEOL8200 in the laboratory of the University of Lisbon in Portugal to determine the mineral types (Table 2 and Table 3).
2. Geology of the Area
In the division of geological units, the studied area is a part of the volcanic zone of Orumieh-Dokhtar. The most ancient rocks in this area is dependent on the Middle Eocene. In general, structures in this area have a trend of the West-North West, East-South East. The most important structural elements in this area are original fractures and folding. Due to governing movement pattern of the area (shear-compressional) in most cases, regional faults zone have both horizontal and vertical displacement components [6] . Swarm dikes investigated in this study, are cut Tertiary volcanic rocks (Figure 2).
3. Petrography
Dikes in the studied area are generally divided into two categories: alkaline and intermediate to acidic.
3.1. Alkaline Dikes
These dikes in terms of petrology include andesitic basalt, basaltic andesite and andesite. Their texture is Porphyritic, Hyalo porphyritic with microlitic pulp and sometimes glomeroporphyritic. Plagioclase Phenocrysts with a combination of Andesine (An% = 42.59) to labradorite (An% = 50.73) semi-shaped to self-shaped make their coarsely crystals (Figure 3(a) and Figure 3(b)). Some of them are quite normal and have zoning (An% = 47.77 - 50.5) (Figure 3(c)) with inclusions of biotite. Plagioclase strongly altered and changed to sericite.
Pyroxenes are in the form of semi-shaped Phenocrysts of augite type with chemical changes of En43.45 Fs15.37Wo41.43 to En40.06Fs23.51Wo36.43 (Figure 4) which partly are altered to chlorite and amphibole. In glomeroporphyritic sectors, pyroxene phenocrysts are often as integrated crystals with each other and completely altered so that only their shape remains and their empty space is filled with calcite and quartz and opaque minerals. Just in a few spots small parts of them remain.
Another mafic mineral in these rocks, is olivine in very low quantity which is completely altered and their vacancies are filled by epidote and calcite and remain only spherical forms of them in size about one millimeter. These minerals are often in a basis of composed plagioclase microlites and fine opaque minerals and scattered and a little glass with an eligible spherical cavities in the size of mm and are filled by radial calcite and iron oxides.
3.2. Intermediate to Acidic Dikes
Intermediate to acidic dikes are included Trachyte and trachyandesite. Trachytic dikes of the area show trachytic, microlitic and glomeroporphyritic texture. Phenocrysts in some trachytic cases are very rare. These phenocrysts are types of self-shaped sanidine and have 500 microns dimension. Other phenocrysts samples are pyroxene and plagioclase (Figure 5). Almost all phenocrysts completely altered and only original form of these phenocrysts is remaining. Background of these rocks entirely consists of oriented microlites of feldspar which along with them secondary fine crystal biotites are seen. These biotites are result of recrystallization of primary biotites. Fine- grained opaque and amorphous minerals are scattered in the total amount of rocks and their quantity is less than 5%. Sericites are scattered and can be seen in the context as fine crystals. Calcite and hematite are scattered in the whole context of stone and in pores sized in mm also calcite and hematite is formed with opaque minerals.
4. Geochemistry
In the diagram Na2O + K2O-SiO2 [7] the composition of dikes samples are in two sub-alkaline and alkaline
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