Cenozoic curst magmatic activities, related to the skarn deposit in the Arasbaran –Ahar magmatic zone, NW of Iran: Evidence from the geochemistry and Sr-Nd isotopic characteristic

Iranian Journal of Earth Sciences

مقالات آماده انتشار، پذیرفته شده، انتشار آنلاین از تاریخ 18 تیر 1401

نوع مقاله: Review Articles

شناسه دیجیتال (DOI): 10.30495/ijes.2022.692669

نویسندگان

Habib Mollail¹؛ Rahim Dabiri¹؛ Georgia Pe-Piper²؛ José Francisco Santos³؛ Abdollah Yazdi⁴

¹Department of Geology, Mashhad Branch, Islamic Azad University, Mashhad, Iran

²Department of Geology, Saint Mary's University, Halifax, N.S., B3H 3C3, Canada

³Department of Geosciences, Geobiotec Research Unit, University of Aveiro, Portugal

⁴Department of Geology, Kahnooj Branch, Islamic Azad University, Kahnooj, Iran

چکیده

 Numerous skarn deposits formed in the contact between Upper Cretaceous impure carbonate rocks and Oligocene–Miocene plutonic rocks in the Varzeghan region East Azarbaijan. The skarns were classified into exoskarn, endoskarn and ore skarn. Andraditic garnet is the main skarn mineral; the pyroxene belongs to the Diopside- hedenbergite series. Garnets from this deposit range from Adr90 Grs30 to almost pure andradite (Adr>99). Fe-rich garnets (Adr>90) are isotropic and anisotropic, garnets deviate from cubic symmetry and are anisotropic, often showing sectorial dodecahedral twinning and zoning. The history of skarn formation starts with the pluton emplacement and assimilation of limestone by the magma. The first stage involved prograde metasomatism and the formation of anhydrous minerals like garnet and pyroxene, followed by retrograde stages along with hydrous minerals and mineralization. The considerable variation of chemical and isotopic composition depends upon mineral proportions, assemblages and chemistry. Isotopically, three end-members can be identified within the granulite: (i) lowest ⁸⁷Sr/⁸⁶Sr (0.702870) with low ¹⁴³Nd/¹⁴⁴Nd (0.511541, ϵNd-21.4); (ii) high 87Sr/86Sr (0.711069) with the lowest ¹⁴³Nd/¹⁴⁴Nd (0.511434, ϵNd-23.5); (iii) highest ⁸⁷Sr/⁸⁶Sr (0.715306) with low 143Nd/144Nd (0.511793, ϵNd-16.5). Two important age ranges deduced from the isotopic data probably relate to episodes of crustal-growth beneath the SFVF (1.88 ± 0.33 Ga and Cenozoic) for related igneous rocks. Fe, Si and Mg, substantial amounts of Cu, along with volatile components such as H₂S and CO₂ were added to the skarn system. SiO₂ with average 57.58%, the average Al₂O₃ is 15.66, Iron 7.65, CaO with average of 5.70.and 3.72 and 2.58 % for Na₂O and K₂O respectively.  This study presents new field observations of skarns in the Arasbaran –Ahar Magmatic Zone (AAMZ) north- west of Iran, and is based on geochemistry of igneous rocks, mineralogy of the important skarn deposits and isotope analysis of Sr and Nd. These data are used to interpret the metasomatism during sequential skarn formation and the geotectonic setting of the skarn deposit.  Skarn mineralogy and geochemistry of igneous rocks and Isotope studied indicate that the extensive I type calc-alkaline and alkaline magmatic activity and related skarn deposits in the northwest of Iran and especially in the Varzeghan, Ahar, and other region are due to Cenozoic Curst Magmatic Activities and tectonic processes of island arc or subduction-related origin of the Fe-Cu skarn deposit in northwest Iran.