جستجوی مقالات مرتبط با کلیدواژه "کال کافی" در نشریات گروه "زمین شناسی"

The Kal-e-Kafi area is located at 65th km of northeast of the Anarak city (Isfahan province). Metaperidotites of this area and associated Anarak Paleozoic metasediments are in contact with the Kal-e-Kafi Eocene intrusive body. Metaperidotites of Paleozoic age are remnants of the Paleo-Tethys oceanic crust. Petrography study shows that these rocks are consist of metamorphic minerals of olivine (forsterite-chrysolite) (CaO According to the results from the field study, petrography evidences, mineral chemistry and thermobarometry calculations, it can be concluded that peridotites of the Kal-e-Kafi area and Anarak sediments, have suffered a regional metamorphism in P-T condition of green schist facies in the Paleozoic, then in the Eocene the intrusive phases of the Kal-e-Kafi, caused to a progressive contact metamorphism in 680 to 770 °C and at pressure 0.5 kbar. This T-P conditions of metamorphism points to the metamorphism in pyroxene hornfels facies. Partial serpentinization of some metamorphic olivines and orthopyroxenes, and formation of late-stage chlorite around of some of tremolites, indicate occurrence of the retrograde metamorphism.

IntroductionLamprophyres are mesocratic to melanocratic igneous rocks, usually hypabyssal, with a panidiomorphic texture and abundant mafic phenocrysts of dark mica or amphibole (or both) with or without pyroxene, with or without olivine, set in a matrix of the same minerals, and with alkali-feldspar restricted to the groundmass (Woolley et al., 1996). Lamprophyres are frequently associated with orogenic settings and a mantle modified by dehydration of subducted slab (Gibson et al., 1995).
Small outcrops of lamprophyres with Paleozoic to Oligocene age are reported from the central parts of Iran (Torabi 2009 and 2010). The primary magmas of these lamprophyres were derived from decompression melting of the mantle induced by a tensional regime of continental crust (Torabi, 2010). Bayat and Torabi (2011) called the western part of the CEIM (Central-East Iranian Microcontinent) (Anarak to Bayazeh) a “Paleozoic lamprophyric province” and suggested that the lamprophyre magmas were formed by subduction of Paleo-Tethys oceanic crust from the Early to late Paleozoic which resulted in the mantle metasomatism and enrichment.
Lamprophyric dykes and stocks of the Kal-e-kafi area (Central Iran, Northern part of Yazd Block) cross-cut the Eocene volcanic rocks and other older rock units such as Cretaceous limestone. These lamprophyres are mainly composed of hornblende (magnesio-hastingsite), clinopyroxene (diopside) and plagioclase (labradorite to bytownite) as phenocryst, in a matrix of fine to medium grained of the same minerals and orthoclase, apatite, magnetite, chlorite and epidote.
In this paper that is a report on the first study on the calc-alkaline lamprophyres of Central Iran, the petrography and mineral chemistry of calc-alkaline lamprophyric dykes of the Kal-e-kafi area are discussed.
Materials and methodsChemical composition of minerals were conducted at Kanazawa University (Kanazawa, Japan) using the wavelength-dispersive electron probe microanalyzer (EPMA) (JEOL JXA-8800R), with 20kV accelerating potential, 20 nA beam current and a counting time of 40 seconds. Natural minerals and synthetic materials were used as standards. The ZAF program was used for data correction. The Fe3 content of minerals was estimated by stoichiometry. The Mg# and Fe# were calculated as [Mg/(Mgᗭ)], and [Fe2(Fe2)] atomic ratio of minerals, respectively.
Trace element values of phenocrystic clinopyroxene, amphibole and plagioclase were analyzed by LA-ICP-MS (laser ablation-inductively coupled plasma-mass spectrometry) using an ArF 193 nm Excimer Laser coupled to an Agilent 7500S at the Earth Science Department of the Kanazawa University (Japan). The diameter of the analyzed points was 60 micrometers for clinopyroxene and 120 micrometers for amphibole and plagioclase.
Mineral abbreviations are adopted from Whitney and Evans (2010).
Results and DiscussionLamprophyres of the Kal-e-kafi area (Central Iran, West of Yazd Block) are exposed as dykes and stocks which cross-cut the Eocene volcanic rocks and other older rock units such as Cretaceous limestone. Field studies indicate that calc-alkaline lamprophyric dykes of the Kal-e-kafi (east of Anarak) are younger than the other igneous rocks.
According to the results of petrography and mineral chemistry, the mesocratic lamprophyres of Kal-e-kafi area are calc-alkaline spessartite.
Unique values of Al2O3 and TiO2 associated with oscillatory zoning of clinopyroxenes reveal the crystallization of clinopyroxenes during ascending of magma.
Plagioclase phenocrysts are labradorite to bytownite in composition and the plagioclases of matrix are labradorite. Chemical composition diversity of plagioclase indicates the fractional crystallization of these lamprophyres.
Amphibole thermometry estimate average temperature of 860°C and barometry by Anderson and Smith (1995) shows 1.5 to 3 kbars pressure. Clinopyroxene thermobarometry calculate 1150 °C temperature and pressure between 2 to 5 kbars.
The geochemical features and thermobarometry of the Kal-e-kafi spessartite minerals suggest that the primary lamprophyric magma was derived from partial melting of a lithospheric mantle spinel lherzolite. Changes in values of pressure, water content, and Oxygen fugacity during magma ascending lead to oscillatory zoning minerals.
Based on the mineral chemistry, it can be concluded that the Kal-e-kafi lamprophyres were formed in a subduction-related environment by a calc-alkaline magmatism.

Kalkafi area is located about 76 km northeast of Anarak (Isfahan Province), in Central Iran structural zone. Based on field observations, petrographical and XRD examinations, three major alteration zones were identified in the studied area including potassic, phyllic-argillic, and silicic zones. Potassic alteration is characterized by orthoclase + biotite + quartz ± sericite assemblage. Phyllic alteration is composed of sericite + quartz + pyrite associated with clay minerals ± calcite, and argillic alteration is characterized by kaolinite + dikite + sericite + quartz + hematite + limonite + goethite. Two major ore mineralization were identified in the studied area: (1) Cu-Mo mineralization and (2) Au-Pb-Zn polymetallic mineralization. Cu-Mo mineralization is mainly related to porphyry quartz monzonites and granites. Chondrite normalized REE patterns of unaltered intrusive bodies (quartz monzonites) indicate a‎ strong LREE and a weak HREE differentiations. Lower content of total REEs in‎ the altered samples of the studied area indicates their mobility in hydrothermal environment. Microthermometric analysis of fluid inclusions of the studied samples indicates that salinity of mineralizing fluid ranges from 1.74 to 21.11 NaCl equivalent wt%. Collected homogenization temperatures confirm the existence of at least two generations of fluid inclusions or mineralizing fluids in this area.

Kal-e Kafi granitoid complex is a part of Central Iranian structural zone called Yazd block. This complex is composed of a wide spectrum of plutonic rocks ranging from gabbro to alkalike granite with age range of Upper Eocene-Lower Oligocene. Potassic granitoid shows geochemical and mineralogical characteristics distinct from other plutonic rocks in the complex. The potassic granitoids are peralkaline and ferroan while other plutonic rocks in the complex are alkaline to calc-alkaline and magnesian. With respect to REE abundances and patterns, the potassic rocks of the complex are different from other Kal-e Kafi granitoids. Low REE abundances of the potassic granitoids indicate that the rocks could not be related to other plutonic bodies through magmatic differentiation. This would probably demonstrate that different petrogenetic processes were involved in petrogenesis of the potassic granitoids. The potassic granitoids are likely to be the consequence of crustal partial melting.