جستجوی مقالات مرتبط با کلیدواژه « تالش » در نشریات گروه « زمین شناسی »

The Shafarud Metamorphic Complex is located in the northwestern part of Iran in the Alborz-Talesh Mountain range. Paleozoic metamorphism (Carboniferous-Permian) are the oldest rocks of this region. The eclogites of the Shafarud Metamorphic Complex are exposed as lenses of several meters in size along with serpentinite masses in the basal parts. The mineral assemblage of the eclogites includes garnet, pyroxene, amphibole, white mica, epidote, plagioclase, chlorite, quartz and sphene. SEM images and the results of electron probe micro-analyzer (EPMA) show the growth chemical zoning in garnet porphyroblasts. According to the calculation of the temperature-pressure pattern, using Jacobian transformation, the core and the rim of garnets have been formed respectively at temperature-pressure 600 ºC -18.2 Kbar (eclogite facies, ~60 Km) and 550 ºC- 7.5 Kbar (green schist facies, ~25 Km). According to the results of this study, the structural pattern of the eclogites of the Shafarud Metamorphic Complex is similar to the alpine type, during which the process of uplift and pressure reduction occurred in almost isothermal conditions due to a rapid uplift.

Talesh alkali basalts (TAB), accompanied by Upper Cretaceous sedimentary units, are exposed in the western Alborz (North of Iran). Clinopyroxene, plagioclase, ± alkali feldspar are the main minerals in these rocks. The geochemical characters such as high contents of TiO2 (1.68-2.96 wt.%), K2O+Na2O (3.09-9.06 wt.%), and high ratios of (La/Yb)N (9.3-23.4), and Nb/Y>1(1.51-3.9), are consistent with their alkaline composition. In the primitive mantle-normalized multi-elements diagram, these rocks show enrichment of all incompatible elements that are similar to intraplate basalts or oceanic island basalts (OIB). The trace element ratios such as Zr/Y (5.52-10.80), Ta/Yb (1.12-2.65), Th/Yb (1.80-5.81), and Ti/Y (418-753) plot within the range of the alkali within plate basalt. Therefore, the Talesh area in the western Alborz recorded an intra-continental volcanic activity during the Late Cretaceous. This magmatism was generated by lower partial melting (3-7%) of an EMII-enriched asthenospheric mantle source of garnet lherzolite facies. The presence of the high-Ti alkali basalts in Talesh and other parts of western and central Alborz (such as southern Lahijan and Marzanabad basalts) to Georgia could be interpreted by forming a rift system on the southern margin of Eurasia from the Lesser Caucasus to the central Alborz during the Late Cretaceous.

In the Talesh area (western Alborz), a thick sedimentary- volcanic association formed in a littoral- deltaic environment during the Late Cretaceous. The extrusives comprise volcanoclastics (tuffs), lava flows (pillow and massive) and basic dykes. The lava flows are dominated by basalts. Basalts are petrographically diverse including clinopyroxene- and plagioclase- phyric suites. Clinopyroxene is chemically in the ranges of augite to diopside and plagioclase is labradorite to bytownite. Here, using clinopyroxene chemistry, we performed thermobarometry and hygrometry calculations. Thermometric results of different samples are in the ranges of 1000 to 1200 °C. Moreover, barometric calculations show pressure ranges of <2.5 and 2.5 to 6 kbar correlating with crystallization depth of upper to middle continental crust (<10 to 22 km). Regarding parental melt chemistry and the magmatic series, the clinopyroxene and whole rock chemistry suggest two alkaline and subalkaline series. Hygrometric calculations provide H2O contents of 2.7- 2.97 and 2.97- 3.53 wt.% for alkaline and subalkaline basalts, respectively. Tectonically, the alkaline basalts could be related to extensional tectonic regime, asthenosphere upwelling or mantle plume/hot spots, while the subalkaline basalts resulted from subduction- related magmatism probably related to northward subduction of an oceanic basin beneath western Alborz or a Neo-Tethyan branch below southern margin of the  Eurasia.

The study area is located in 9 km south of Germi city and 52 km north of Ardabil Province. From Structurally point of view this area is a part of south Talesh Zone. The volcanic rocks are mostly basaltic in composition with prismatic structure. Minerals of olivine, plagioclase, clinopyroxene and minor minerals such as titanomagnetite are formed the rocks. By the way calcite, sericite and chlorite with a lesser amount of idengsite are secondary minerals. Investigates show that phenocrysts of feldspar are mostly labradorite in composition and clinopyroxenes in studied rocks located in augite domain. Clinopyroxenes and olivines are originated from alkaline magma that belong to back-arc- basin magmatism. Thermobarometry of clinopiroxenes show that these minerals are crystallized from magma at ~5 Kbar pressure and 1000 C. Chlorite as a secondary mineral in these rocks generally are located in diabanit domain.and from geochemically point of view and zonation including two alteration stages that indicator of variety of factors in produce of secondary minerals.