Writers : Fathi, Turaj;supervisor: Darvishzade, Ali; advisor:M. Valizadeh
Refference : Thesis _ Tehran university, Tehran
Publishing Year : 1377

Abstract :

The lower paleozioc volcanic rocks do have outcrop in several localities in northeast Iran. In this investigation three regions having typial section, i.e., Shahrud, Robat-e-Gharabil and south Bojnurci ، ،were studied. These sections, from structural and stratigraphic points of view in lower paleozoic of the region do have a similar geologic history but, in mesozoic and Cenozoic each had a different geological evolutior and history. But, at present time they are all having similar and history? But ,at present time they are all having similar structures which resemble each other.
The volcanic rocks of the investigated regions are accompained by
sedimentary rocks of shale and shalysand which the chemica compostion of sedimentery rocks and investigations carried out on theii sandstone reveals that these rocks were originated from continental margin settings.

The studied volcanic rocks of the region have been formed under? three main different stages. Most of these rocks have undergone an tolerated. Secondery processes by reacting with seawater and affected them to change into spilite. The first stage of volcanism which started al late combrian continued to lower ordovician times, and it is seen as remains of eruptions and sub-areial explotions, or it had happened in the near-water environment leaving volcanic ashes, lapilli tuffs. and agglomerates and these rocks make up the near water facies. In this stage of volcanism agglomerates are also seen as hydrovolcanic rocks The second stage of eruptions like the first one do contain basalt -
as well as pyroclastic rocks. The time of formation of these rocks were middle ordovician and contains basalts having olivine, clinopyroxene titaniferrous augite) and plagioclase. The alkaline nautre of these( rocks do show their distinct presense by investigations carried out or their major and minor elements. The first and second stages of eruptions warrant the conditions of their formation in sub-areial tc shallow environments along with formation of sandstones
The third eruption phase happened in the late ordovician tc - silurian age and includes basalts which have erupted as flowing lava which usally have pillow-lava structures. The environment of formation of these rocks are deeper with respect to the first two stages of eruption and accompany shales and sandstones. In addition to the stated basalts above, these rocks from mineralogical point of view, dc have clinopyroxene (subcalsic augite), plagioclase, and to lesser exteni containing olivine.
Investigation of major elements reveal that these rocks are of - olivine tholeiite type and are very distinctly different from the first two stages.
Geochemical investigations of major and trace elements in connection with the environment of formations of these rocks show that the concerned rocks are of continental type and have probably been formed in a rift environment of continental margin, and in the
early stages did have an alkaline nature and then changed to an
.type? transitional
From economic geology point of view and valuable resources the -
studies presented here are mostly on gems and gemstones. Numerous
. e. specimens from rocks semipreciaus and precious minerals (i
gemstones) were identified in the rocks.These include amatyst
hematite, quartz, opal, jasper, chert, epidote, and chlorite minerals.

Subject List : volcanism and volcanic rocks