Petrology
Morteza Delavari; Khadijeh Ghorbani; Amir Ali Tabbakh Shabani
Abstract
The Urmieh- Dokhtar magmatic belt (UDMB) lying parallel to the Zagros suture zone is resulted from the subduction of Neotethyan oceanic lithosphere beneath the southern margin of Eurasia. The studied volcanic rocks of the Razan- Avaj area are part of UDMB magmatism. These rocks are composed of olivine-basalts, ...
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The Urmieh- Dokhtar magmatic belt (UDMB) lying parallel to the Zagros suture zone is resulted from the subduction of Neotethyan oceanic lithosphere beneath the southern margin of Eurasia. The studied volcanic rocks of the Razan- Avaj area are part of UDMB magmatism. These rocks are composed of olivine-basalts, basalts and occasional trachyandesites with alkaline nature. The interlayered stratigraphic relationships of volcanic horizons with sediments of Qom Formation implies Oligo-Miocene age. Major and trace element contents of volcanics and chemical modeling are indicative of significant role of olivine + clinopyroxene + plagioclase fractional crystallization (35-45%) in melt compositional trend. Bulk rock chemistry of theses rocks displays LREE/HREE enrichment and lack of HFSE negative anomaly similar to oceanic island basalts (OIB). It seems that after Eocene magmatic flare-up with obvious magmatic arc signatures in UDMB, during the Oligo-Miocene the origin of magmas has shifted to a deeper asthenospheric mantle. Probably, after the initial stages of the Arabian-Eurasian plate collision in the Late Eocene-Early Oligocene and the slab roll-back, an upwelling asthenospheric mantle is injected into the mantle wedge and is weakly affected by the subduction material, which is the source of Oligo-Miocene melts.
Petrology
Maryam Kouchi; Malihe Nakhaei
Abstract
In northeast of Sarbisheh city, southern Khorasan, outcrops of lava rocks are exist that from view of geological subdivisions, located in eastern part of Lut block. Lithologic composition of studied collections consist of andesite (pyroxene andesite, andesite, trachy andesite), dacite and rhyolite. The ...
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In northeast of Sarbisheh city, southern Khorasan, outcrops of lava rocks are exist that from view of geological subdivisions, located in eastern part of Lut block. Lithologic composition of studied collections consist of andesite (pyroxene andesite, andesite, trachy andesite), dacite and rhyolite. The main texture of these rocks are porphyry with microlitic-glass groundmass, glomeroporphyritic, poikilitic and vesicular. The mineral constituents of andesitic rocks are plagioclase, pyroxene and amphibole with small quantities of biotite and sanidine and in rhyolite and dacite include of quartz, sanidine, plagioclase, amphibole and biotite. Disequilibrium textures such as chemical zoning, sieve texture, rounded and gulf shape margins in phenocrysts of these rocks are observed. Geochemical study results show that these lavas belong to high to medium-K calc alkaline series. Enrichment in LREE and LILE, depletion in HREE and HFSE with negative anomaly of Ti, Nb and P in these rocks indicated active continental margin volcanic arc magmatism. Based on tectonic discrimination diagrams, also support the relation of Zoolesk area lavas with subduction zone and active continental margin. Low ratio of Dy/Yb(<2) in studied lavas, indicated spinel lherzolite mantle source for magma.
S. M. Tabatabaei Manesh; F. Javadi; F. S Zohouri2
Abstract
The Nabar skarn is located about 35 km southwest of Kashan and within the Urumieh- Dokhtar magmatic belt and is formed along the contact between limestone of Qom formation with a probably middle to upper Miocene intermediate and basic intrusion body. The main minerals forming this skarn are garnet, ...
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The Nabar skarn is located about 35 km southwest of Kashan and within the Urumieh- Dokhtar magmatic belt and is formed along the contact between limestone of Qom formation with a probably middle to upper Miocene intermediate and basic intrusion body. The main minerals forming this skarn are garnet, clinopyroxene, epidote and accessory minerals are vesuvianite, chlorite, tremolite- actinolite, sphene, quartz and calcite. Ore minerals are pyrrhotite, pyrite with smaller amounts of chalcopyrite, sphalerite and magnetite. According to the presence of magnesium minerals like diopside and calcium minerals such as garnet, vasuvianite and epidote the type of host rock is probably calcite-dolomite. Skarn formation and mineralization in this region was occurred during three development stages. Presence of high temperature anhydrous minerals such as grossular and diopside specifies the formation of the first Stage in these rocks. Stage 2 is associated with the formation of andradite and sphene. Stage 3 is specified by replacement of anhydrous minerals at temperatures below 470 ° C by hydrous minerals such as tremolite-actinolite, epidote, chlorite and vesuvianite.
T Salehi; M Ghaderi; N Rashidnejad-Omran
Abstract
Gomish-Tappeh Zn-Pb-Cu (Ag) deposit is located in northwestern part of Urumieh-Dokhtar volcano-plutonic zone, 90 km southwest of Zanjan. Exposed rocks at the area include Oligo-Miocene volcano-sedimentary and sedimentary sequences as well as Pliocene dacitic subvolcanic dome, rhyodacitic volcanics and ...
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Gomish-Tappeh Zn-Pb-Cu (Ag) deposit is located in northwestern part of Urumieh-Dokhtar volcano-plutonic zone, 90 km southwest of Zanjan. Exposed rocks at the area include Oligo-Miocene volcano-sedimentary and sedimentary sequences as well as Pliocene dacitic subvolcanic dome, rhyodacitic volcanics and andesite porphyry dykes. The main mineralization at Gomish-Tappeh deposit has occurred in a steeply deeping normal fault and fracture system defined by NE-SW trend in three stages including hydrothermal breccias, silicic-sulfidic, silicic-sulfidic-carbonate veins and veinlets and late banded veins (rich in silica and specularite). Host rocks to mineralization include dacitic crystal lithic tuff, dacitic subvolcanic dome, and specifically acidic tuff. Paragenetic minerals at the deposit consist of pyrite, arsenopyrite, chalcopyrite, bornite, galena, low-Fe sphalerite, tetrahedrite, tennantite and specularite. The main alteration types at the area are silicic, silicic-sulfidic, sericitic, carbonate, argillic and propylitic. Based on element distribution and frequency patterns in the ore samples, among base metals, Zn, Pb, Cu and Ag show the highest concentrations. Average grades in the ore veins at Gomish-Tappeh deposit are: 6% Zn, 4% Pb, 2% Cu, 88 ppm Ag and 44 ppb Au. Fluid inclusion microthermometric studies on quartz crystals of the first and second stages of mineralization indicate homogenization temperatures of 260-367 °C, salinities of 9.1-16.9 wt% NaCl equiv., and approximate mineralization depth of 956 m below the paleowater table. Considering high salinity fluids and base metal contents, it is likely that base metals and silver were transported by chloride complexes. Fluid inclusion studies, hydrothermal breccias, banded-colloform-crustiform textures and amorphous silica indicate that boiling is the main factor for instability of the complexes and eventually, ore deposition.
H Ghasemi; M Rostami Hossuri; M Sadeghian; F Kadkhodaye Arab
Abstract
Subduction of the Neo–Tethyan oceanic lithosphere beneath the southern edge of the Central Iran caused development of extensional back-arc basins behind the Urumieh–Dokhtar magmatic belt during Mesozoic and Cenozoic. Some researchers have noted formation of the oceanic back-arc basins in ...
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Subduction of the Neo–Tethyan oceanic lithosphere beneath the southern edge of the Central Iran caused development of extensional back-arc basins behind the Urumieh–Dokhtar magmatic belt during Mesozoic and Cenozoic. Some researchers have noted formation of the oceanic back-arc basins in Nain, Sabzevar and Sistan in Central Iran during Mesozoic, but little is known about generation of such basins in Cenozoic. The depressed extensional back-arc basin of Central Iran contains sedimentary successions of intracontinental extensional environments associated with alkaline basic magmatic rocks. These magmatic rocks are outcropped in the Oligo-Miocene gypsiferous red marls (red formations), as both intrusive (gabbro) and extrusive (basalt) forms. The present study has focused on the basaltic lava flows in the Oligo-Miocene siliciclastic-evaporitic sedimentary succession extending for about 300 kilometers from Sabzevar to Shahroud along the northern edge of Central Iran. These lava flows are observed as interbedded with the Oligo-Miocene sedimentary units. In the Kalate-Sadat area, located SW of Sabzevar, there are at least five intermittent basaltic lava flows in the red marls. These basaltic rocks (with a composition of olivine-basalt to basalt) show porphyritic, glomeroporphyritic and trachytic textures and are composed of olivine, clinopyroxene and plagioclase phenocrysts in a glassy to microlitic ground mass. On the basis of geochemical data, the parent magma of these rocks had a sodic-alkaline affinity, enriched in LILEs and LREEs and depleted in HREEs, without negative anomalies in HFSEs. The basalts show the geochemical characteristics of the basaltic magmas originated from partial melting of adjusted enriched garnet lherzolite mantle source beneath the continental areas of extensional back-arc basins.
