Petrology
M. Sadeghian; S. H. Hosseini; A. Hemmati; S. Shekari
Abstract
Granitoid plutons of SW Mayamey (60 Km east of Shahrood), located at the most northern margin of the central Iran structural zone, have granite composition (in general) and calk alkaline and peralouminous nature. In spite of coverage of these granitoids by Late Triassic – Early Jurassic sedimentary ...
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Granitoid plutons of SW Mayamey (60 Km east of Shahrood), located at the most northern margin of the central Iran structural zone, have granite composition (in general) and calk alkaline and peralouminous nature. In spite of coverage of these granitoids by Late Triassic – Early Jurassic sedimentary rocks, Late Neoproterozoic host gneiss are exposed in limited areas. These granitoids invaded by two series of the Late Neoproterozoic and middle Jurassic diabasic dikes. Although post – Liass, Pre- Dogger, younger than Jurassic and older than Cretaceous ages are considered for these granitoids, but for the first time U–Pb age dating on separated zircons indicates Late Neoproterozoic age (Late Ediacaran) (545±10 Ma) for them and they are a part of very ancient basement rocks of Iran. The studied rocks are similar Band -e-Hezar Chah, Sefid Sang, Delbar, Shotor Kuh, Reza Abad and Do Chah granitoids in age. Mayamey granitoids are resulted from partial melting of metapelites and metagraywackes, and they belong to S-type granioids. SW Mayamey granitoids were generated in a collisional tectonic setting in the Late Neoproterozoic, in relation to closing of intracontinental back arc basin and then metamorphism of the associated rocks from greenschist facies to amphibolite and rarely granulite facies, which finally companied with s-type granitization
F Kozekoulani; M Rahgoshay; H Shafaii Moghadam
Abstract
Intrusive rocks from SW Salmas include mafic-intermediate and acidic rocks, which occur in the border of Sanandaj-Sirjan and Urmia-Dokhtar zones in Northwest of Iran. The mafic-intermediate rocks comprise metadiorite and metagabbros that are the oldest rocks in the region. The acidic rocks include metagranite ...
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Intrusive rocks from SW Salmas include mafic-intermediate and acidic rocks, which occur in the border of Sanandaj-Sirjan and Urmia-Dokhtar zones in Northwest of Iran. The mafic-intermediate rocks comprise metadiorite and metagabbros that are the oldest rocks in the region. The acidic rocks include metagranite and metagranodiorite. These rocks have intruded into the Precambrian metamorphosed volcanic-sedimentary rocks. U-Pb zircon dating of the Salmas metagranite and metagranodiric rocks yielded age ranges of 565±2/7 Ma to 567±2/4 Ma (Ediacaran-Early Cambrian). Zircons have inherited cores. Zircon Hf isotope data (and Hf model ages) indicate that these rocks are not juvenile mantle melt derived but instead are products of juvenile melts interaction with old Mesoproterozoic continental crust. Furthermore, zircon δ18O values suggest contribution of continental crustal rocks during generation of the Salmas rocks. The Salmas Cadomian rocks are coeval with other similar-aged metagranites and gneisses from Central Iran, Sanandaj-Sirjan zone and Alborz Mountains. All these dispersed basement rocks are suggested to be fragments of the Neoproterozoic-early Cambrian magmatism of northern margin of Gondwana.
N Etemad-Saeed; M. H Adabi; A. Sadeghi; M. Hosseini- Barzi
Abstract
This work is focused on tectonic provenance of the Late Neoproterozoic Kahar Formation in the northern Iran. KaharMountain (type locality) provides valuable information on tectonic events during this time. The Kahar Formation in this area is a well preserved sedimentary sequence and consists of about ...
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This work is focused on tectonic provenance of the Late Neoproterozoic Kahar Formation in the northern Iran. KaharMountain (type locality) provides valuable information on tectonic events during this time. The Kahar Formation in this area is a well preserved sedimentary sequence and consists of about 1000 meters of predominantly fine grained siliciclastic rocks and minor sandstones, conglomerates and dolomitized stromatolites. Kahar lithic arkose sandstones with low compositional and textural maturity, contain abundant feldspar (plagioclase and K feldspar), quartz, and volcanic lithic fragments and have an average composition of Q38F40L22, Qt39F40L21, Qm32F40Lt28,Qp27Lvm60Lsm13 and Qm44P33K23 suggesting a proximal source and a dissected arc setting. The type of lithic fragments in the sandstones show andesitic and felsic volcanic rock sources. Heavy mineral analysis (abundant metastable and unstable minerals such as biotite, and pyroxenes) indicate that Kahar sandstones were derived from unroofing of arc-type magmatic rocks. The low diversity of heavy mineral assemblages in the Kahar sandstones indicates that the source rocks were uniform and localized. Considering the two common tectonic views regarding the Late Neoproterozoic condition of Iran (rift-passive margin and magmatic arc-subduction zone), the results of this study which confirm the magmatic arc tectonic setting of Alborz-Iran at that time seems critical.
