Document Type : Original Research Paper

Authors

1 Assistant Professor, Department of Geology, Faculty of Sciences, University of Zanjan, Zanjan, Iran

2 M. Sc., Department of Geology, Faculty of Sciences, University of Zanjan, Zanjan, Iran

Abstract

The Aqkand area is located at 48 km north of Zanjan and is a part of the Tarom subzone within the Western Alborz-Azerbaijan structural zone. Acidic rocks exposed in this area consist of Oligocene rhyolite-rhyodacite, perlite, pitchstone and ignimbrite. Rhyolites and rhyodacites are exposed as domes and lava flows. Perlites are located at the lower parts of the rhyolitic-rhyodacitic domes. Geochemical investigations indicate calc-alkaline nature along with magmatic arc affinity for the studied rocks. These rocks are characterized by LREE-rich patterns with high LREE/HREE ratio and distinctive negative Eu anomaly. Positive anomalies of Rb, Pb and Th on the spider diagrams suggest continental crust involvement in the genesis and evolution of the parental magma. Based on tectonic setting discrimination diagrams, Aqkand acidic rocks are plotted in the post-collision tectonic setting. In overall petrographic, petrologic and geochemical evidence demonstrate that during the final stages of the continental collision, the thickened sub-continental lithosphere in the Alborz was delaminated and replaced by hot asthenospheric mantle. Rapid upwelling of hot asthenosphere gave rise to the partial melting of sub-continental lithosphere which produced the Oligocene basaltic rocks of the study area. Emplacement of basaltic magma in the upper part of the continental crust led to the partial melting of the crust and generation of the acidic magmas. Rapid cooling of acidic lavas led to the generation of glassy rocks such as obsidian which are changed to perlite in contact with meteoric and warm waters.

Keywords

Alavi, M., 1991- Sedimentary and Structural characteristics of the Paleo-Tethys remnants in northeastern Iran. Geological Society of America Bulletin, 103: 983-992.
Aldanmaz, E., Pearce, J. A., Thirlwall, M. F. and Mitchell, J. G., 2000- Petrogenetic evolution of Late Cenozoic, post-collision volcanism in western Anatolia, Turkey. Journal of Volcanology and Geothermal Research, 102: 67-95.
Allen, M. B., Ghassemi, M. R., Shahrabi, M. and Qorashi, M., 2003- Accommodation of late Cenozoic oblique shortening in the Alborz range, northern Iran. Journal of Structural Geology, 25(5): 659-672.
Asiabanha, A. and Foden, J., 2012- Post-collisional transition from an extensional volcano-Sedimentary basin to a continental arc in the Alborz Ranges, N-Iran. Lithos, 148: 98-111.
Barnes, S. J., Acterberg, E., Makovicky, E. and Li, C., 2001- Proton probe results for partitioning of platinum group elements between mono-sulphide solid solution and sulphide liquid. South African Journal of Geology, 104: 337-351.
Chesterman, C. W., 1954- Genesis of perlite. Geological Society of America Bulletin, 65(12): 1336.
Cox, K. G., Bell, J. D. and Pankhurst, R. J., 1979- The interpretation of igneous rocks. London, Unwin Hyman, 450 p.
Dehghani, G. A. and Makris, J., 1984- The gravity field and crustal structure of Iran. Neues Jahrbuch Fur Geologie Und Palaontolgie Abhandlungen, 168: 215-229.
Dostal, J., Church, B. N., Reynolds, P. H. and Hopkinson, L., 2001- Eocene volcanism in the Buck Creek basin, central British Columbia (Canada): transition from arc to extensional volcanism. Journal of Volcanology and Geothermal Research, 170(1-3): 149-170.
Edwards, C. M. H., Menzies, M. A., Thirlwall, M. F., Morrid, J. D., Leman, W. P. and Harmon, R. S., 1994- The transition to potassic alkaline volcanism in island arcs: the Ringgit-Beser complex, east Indonesia. Journal of Petrology, 35: 1557-1595.
Esmaeli, M., Lotfi, M. and Nezafati, N., 2015- Fluid inclusion and stable isotope study of the Khalyfehlou copper deposit, southeast Zanjan, Iran. Arabian Journal of Geosciences, 8(11): 9625-9633.
Fan, W. M., Guo, F., Wang, Y. J. and Lin, G., 2003- Late Mesozoic calc-alkaline volcanism of post-orogenic extension in the northern Da Hinggan Mountains, northeastern China. Journal of Volcanology and Geothermal Research, 121(1): 115-135.
Flink, J. H., 1983- Structure and emplacement of rhyolitic obsidian flow, Little Glass Mountain, Medicine Lake Highland, Northern California. Geological Society of America Bulletin, 94: 262-280.
Friedman, L., Smite, R. L. and Long, W. D., 1966- Hydration of natural glass and formation of perlite. Geological Society of America Bulletin, 77: 323-328
Gill, J. B., 1981- Orogenic Andesite and plate tectonic. Springer, New York, 390 p.
Guest, B., Guest, A. and Axen, G., 2007- Late Tertiary tectonic evolution of northern Iran: a case for simple crustal folding. Global and Planetary Change, 58: 435-453.
Harris, C., 1986- The petrology of lavas and associated plutonic characteristics of collision zone magmatism. In: Cowards, M. P. and Reis, A. C. (Eds), Collision tectonics. Special Publication, Geological Society of London, 19: 67-81.
Hirayama, K., Samimi, M., Zahedi, M. and Hushmand-Zadeh, A., 1966- Geology of the Tarom District, Western Part (Zanjan area northwest Iran), Geological Survey of Iran, Report 8, 31 p.
Hofmann, A. W., 1986- Nb in Hawaiian magmas: constraints on source composition and evolution. Chemical Geology, 7: 17-30.
Hongyan, G., Sun, M., Yuan, C., Xiao, W., Zhao, G., Zhang, L., Wong, K. and Fuyuan, W., 2009- geochemical, Sr–Nd and Zircon U–Pb–Hf isotopic studies of Late-Subduction. Chemical Geology, 266: 364-398.
Houseman, G. A., Mckenzie, D. P. and Molnar, P., 1981- Convective instability of a thickened boundary layer and its relevance for thermal evolution of convergent belts. Journal of Geophysical Research, 86: 6115-6132.
Irvine, T. N. and Baragar, W. R. A., 1971- A guide to the chemical classification of the common volcanic rocks. Canadian Journal of Earth Sciences, 8: 523-548.
Jesek, P. A. and Noble, D. C., 1978- Natural hydration and ion exchange of obsidian, an electron microprobe study. American Mineralogist, 63: 266-273.
Kamber, B. S., Ewart, A., Collerson, K. D., Bruce, M. C. and McDonald, G. D., 2002- Fluid-mobile trace element constraints on the role of slab melting and implication for Archean crustal growth models. Contributions to Mineralogy and Petrology, 144: 38-56.
Kuster, D. and Harms, U., 1998- Post-collisional potassic granitoids form the southern and northwestern parts of the late Neoproterozoic East African Orogen: a review. Lithos, 45: 177-195.
Lehmann, W. P. and Sisson, V. B., 1996- Geochemistry of boron and its implication for crustal and mantle processes. Reviews in Mineralogy and Geochemistry, 33: 645-707.
Miyashiro, A., 1977- Nature of alkalic volcanic series. Contributions to Mineralogy and   Petrology, 66: 91-110.
Murrell, S. A. F., 1986- Mechanics of tectogenesis in plate collision zone. In: Cowards, M. P. and Reis, A. C. (Eds), Collision tectonics. Special Publication, Geological Society of London, 19: 95-111.
Nabatian, Gh., Ghaderi, M., Neubauer, F., Honarmand, M., Xiaoming, L., Dong, Y, Jiang, Sh, Quadt, A., Bernroider, M., 2014- Petrogenesis of Tarom high-potassic granitoids in the Alborz–Azarbaijan belt, Iran: Geochemical, U–Pb zircon and Sr–Nd–Pb isotopic constraints. Lithos, 184-187: 324-345. 
Nagudi, N. O., Koberl, C. H. and Kurat, G., 2003- Petrography and geochemistry of the Sing granite, Uganda, and implication for its origin. Journal of African Earth Sciences, 35: 51-59.
Nakamura, N., 1974- Determination of REE, Ba, Fe, Mg, Na and K in carbonaceous and ordinary Chondrites. Geochimica et Cosmochimica Acta, 38: 755-773.
Pearce, J. A., 1983- Role of sub-continental lithosphere in magma genesis at active continental margins. In: Howkesworth, C. J. and Norry, M. J., (Eds), Continental basalt and mantle xenoliths. Shiva, Nanwich, p. 230-249.
Pearce, J. A., Harris, N. B. and Tindel, G. A., 1984- Tarace element discrimination diagrams for the tectonic interpretation of granitoid rocks. Journal of Petrology, 25: 956-983.
Richards, J. P., 2011- High Sr/Y arc magmas and porphyry Cu±Mo±Au deposits: Just add water. Economic Geology, 106: 1075-1081.
Rickwood, P. C., 1989- Boundary lines within petrologic diagrams which use oxides of major and minor elements. Lithos, 22: 247-263.
Rodgers, A. J., Ni, J. F. and Heam, T. M., 1997- Propagation characteristics of short-period Sn and Lg in the Middle East. Bulletin of the Seismological Society of America, 87(2): 396-413.
Rollinson, H. R., 1993- Using geochemical data: evolution, presentation, interpretation. London, UK, 652 p.
Ross, C. S. and Smith, R. L, 1955- Water and other volatiles in volcanic glasses. American Mineralogists, 40(11-12): 1076-1089.
Schandle, E. S. and Gorton, M. P., 2002- Application of high strength elements to discriminate tectonic setting in VMS environments. Economic Geology, 97: 629-642.
Seber, D., Vallve, M., Sandvol, E., Steer, D. and Barazangi, M., 1997- Middle East tectonics: application of geographic information system (GIS). GSI Today, 7(2): 1-5.
Shang, G. K., Satir, M., Sieble, W., Nasifa, E. N., Taubuld, H., Liegeoise, J. P. and Tchoua, F. M., 2004- Geochemistry, Rb–Sr and Sm–Nd systematic: case of the Sangmelima region, Ntem complex, southern Cameroon. Journal of African Earth Sciences, 40(1-2): 61-79.
Shelley, D., 1993- Igneous and metamorphic rocks under the microscope: classification, textures, microstructures and mineral preferred-orientations. Chapman and hall, London, 445 p.
Srivastava, R. K., Singh, R. K., 2004- Trace element geochemistry and genesis of Precambrian sub-alkaline mafic dikes from the central Indian craton evidence for mantle metasomatism. Journal of Asian Earth Sciences, 23: 373-389.
Sun, S. S. and McDonough, W. F., 1989- Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. In: Saunders, A. D. and Norry, M. J., (Eds), Magmatism in the Ocean Basins. Special Publication (42), Geological Society of London, p. 313-345.
Sylvestre, P. J., 1989- Post Collisional alkaline granites. Journal of Geology, 97: 261-280.
Thompson, A. B., 1982- Dehydration melting of pelitic rocks and the generation of H2O under-saturated granitic liquids. Journal of Science, 282: 1567-1595.
Ulmer, P., 2001- Partial melting in the mantle wedge–the role of H2O in the genesis of mantle-derived ‘arc-related’ magmas. Physics of the Earth and Planetary Interiors, 127: 215-232.
Verdle, C., 2009- Cenozoic geology of Iran: an integrated study of extensional tectonics and related volcanism. Ph.D. Thesis, California Institute of Technology, Pasadena, California.
Wilson, M., 1989- Igneous Petrogenesis: a global tectonic approach. Unwin Hyman Ltd, London, 466 p.
Winchester, J. A., and Floyd, P. A., 1977- Geochemical discrimination of different magma series and their differentiation products using immobile elements. Chemical Geology, 16: 325-343.
Winter, J. D., 2001- An introduction to igneous and metamorphic petrology. Prentice Hall, 697 p.
Wu, F., Jahnb, B., Wildec, S. A., Lod, C. H., Yuie, T. F., Lina, Q., Gea, W. and Suna, D., 2003- Highly fractionated I-type granites in NE China (II): isotopic geochemistry and implications for crustal growth in the Phanerozoic. Lithos, 67(3-4): 191-204.
Zhou, L., Mab, C., and She, Z., 2012- An Early Cretaceous garnet-bearing metaluminous A-type granite intrusion in the East Qinling Orogen, Central China: Petrological, mineralogical and geochemical constraints. Geoscience Frontiers3(5): 635-646.