Zircon Geochronology (U-Pb), Petrography, Geochemistry and Radioisotopes of Bornaward Metarhyolites (Central Taknar Zone-Northwest of Bardaskan)

Document Type : Research Article

Authors

1 Ferdowsi university of Mashhad

2 Ferdowsi University of Mashhad

3 Colorado

4 Aveiro

Abstract

Introduction
The Bornaward area is located in the Northeastern Iran (in the Khorasan Razavi province) 28 km northwest of the city of Bardaskan at 57˚ 46΄ to 57˚ 52΄ N latitude and 35˚ 21΄ to 35˚ 24΄E longitude. The Taknar structural zone, situated in the North central Iranian micro continent, is part of the Lut block (Forster, 1978). The Taknar zone is an allochthonous block bounded by the Darouneh and Taknar major faults. Much of this zone consists of metarhyolite-rhyodacite volcanic rocks, and rhyolitic tuff with interlayers of sandstone and dolomite (Taknar Formation).

Analytical Results
ICP-MS analysis of REE and minor elements of samples of the Bornaward metarhyolites was carried out at the ACME Laboratory in Vancouver, Canada. U-Pb dating of the metarhyolites was performed on isolated zircons in Crohn's Laser Lab, in Arizona (Gehrels et al., 2008). Measurement of Rb, Sr, Sm and Nd isotopes and (143Nd/144Nd)i and (87Sr/86Sr)i ratios took place in the radioisotope laboratory of the University of Aveiro in Portugal.
Petrography
The volcanic rocks are porphyritic, commonly containing phenocrysts of orthoclase and rarely sanidine, quartz and intermediate plagioclase in a groundmass of fine-grained quartz and feldspar. An alteration has produced oriented needles of sericite and clay minerals, clusters of fine-grained green biotite and clots of epidote and chlorite.
Geochemistry
The compositions of the volcanic rocks are calc alkaline and high K- calc alkaline. The obtained Shand index (Al2O3/( CaO+Na2O+K2O) is above 1.1, in the peraluminous S-type granite field (Chappell and White, 2001). Plotted on the TAS diagram (Middlemost, 1994), all the metarhyolite-rhyodacite samples are located in the sub-alkaline field and the majority fall into the rhyolite group. The metarhyolite-rhyodacites show enrichment of LREE with a moderately ascending pattern ((La/Yb)N=2.51-10.11 and La=46.45-145.48). Europium shows a negative anomaly (Eu/Eu*=0.23-0.71).
U-Pb zircon geochronology
Measurement of U-Pb isotopes of the Bornaward metarhyolite zircons of sample BKCh-103, indicates an age of 552.23+4.73,-6.62 Ma (Upper Precambrian).
Sr-Nd isotopes
The Sr ratios of the metarhyolites (87Sr/86Sr) were found to fall in the range of 0.688949 to 0.723435 and the Nd ratios (143Nd/144Nd)i were in the range of 0.511701 to 0.511855. These values indicate that the metarhyolites of samples BKCh-12, BKCh-103 and BKCh-177 were affected by hydrothermal alteration since their (87Sr/86Sr)I ratios are high. The Sr ratios suggest that the more negative Nd anomaly and the more negative ɛNd(552) of the samples BKCh-12, BKCh-103 and BKCh-177 indicate that these lavas originated in an enriched upper mantle source and/or lower continental crust. In contrast, two recent examples (Xua et al., 2005) can be related to sialic continental crust with significant contamination.
Petrogenesis
The Bornaward metarhyolite- rhyodacites show an enriched pattern for Rb, Th, U, K, Pb, Nd and Y relative to the primitive mantle, while Ba, P, Ti, Sr, Zr and Nb show a reduction as a result of fractional crystallization. Based on isotopic correlations of207Pb/204Pb vs 206Pb/204Pb, the primitive source of the Bornaward metarhyolite- rhyodacites is the lower continental crust. This part of the continental crust is only slightly depleted in Pb. Consequently, it has a low 87Sr/86Sr ratio (Samples BKCh-138 and BKCh-198). In contrast, the samples of BKCh-12, BKCh-103 and BKCh-177 have high 87Sr/86Sr ratios that could be the result of significant contamination to parts of the continental crust with very high 87Sr/86Sr (Karimpour et al., 2011).

Results and Conclusions
The calc-alkaline compositions of samples BKCh-12, BKCh-103 and BKCh-177, the high K- calc alkaline of samples BKCh-138 and BKCh-198 of the Bornaward metarhyolites and the higher temperature overgrowth of plagioclase on lower temperature microcline phenocrysts can be a reason for entrance lavas with different generations. The distinct isotopic characteristics of the two groups of rhyolitic samples are the reasons for two different sources for the production of these lavas: 1) partial melting of an enriched mantle reservoir or lower continental crust, and 2) sialic continental crust with high contamination. With respect to the Bornaward metarhyolite- rhyodacites with (143Nd/144Nd)i ratios from 0.511701 to 0.511855, geochemical characteristics and the high volume of volcanic rocks in the area, their formation can be attributed to a continental rift environment. This rift system can be formed by initiation of a plume in the upper mantle beneath East Iran during Neoproterozoic time.

References
Chappell, B.W. and White, A.J.R., 2001. Two contrasting granite types. Australian Journal of Earth Sciences, 48(4): 489-499.
Forster, H., 1978. Mesozoic – cenozoic metallogenesis in Iran. Journal of the Geological Society, 135(4): 443-455.
Gehrels, G.E., Valencia, V.A. and Ruiz, J., 2008. Enhanced precision, accuracy, efficiency, and spatial resolution of U–Pb ages by laser ablation–multicollector–inductively coupled plasma-mass spectrometry. Geochemistry, Geophysics, Geosystems, 9(3): 1-13.
Karimpour, M.H., Farmer, G.L., Stern, C.R. and Salati, E., 2011. U-Pb zircon geochronology and Sr-Nd isotopic characteristic of Late Neoproterozoic Bornaward granitoids (Taknar zone exotic block), Iran. Iranian Society of Crystallography and Mineralogy, 19(1): 1-18.
Middlemost, E.A.K., 1994.Naming materials in the magma igneous rock system. Earth Science Reviews, 37(3- 4): 215-224.
Xua, B., Jianb, P., Zhenga, H., Zouc, H., Zhanga, L. and Liub, D., 2005. U–Pb zircon geochronology and geochemistry of Neoproterozoic volcanic rocks in the Tarim Block of northwest China: implications for the breakup of Rodinia supercontinent and Neoproterozoic glaciations. Precambrian Research, 136(2): 107–123.

Keywords


Aghanabati, S.A., 2004. Geology of Iran. Geological Survey of Iran, Tehran, 586 pp (in Persian).
Allegre, C.J., Lewin, E. and Dupre, B., 1988. A coherent crust- mantle model for the uranium- thorium- lead isotopic system. Chemical Geology, 70(3): 211-234.
Babakhani, A., Mehrpartow, M., Radfar, J. and Majidi, J., 1999. Geology and exploration studies of Taknar polymetal deposit, correction and complete of geological maps 1:5000 and completion of geological maps 1:1000 of Taknar I and III and preparation of geological maps of Taknar IV. Ministry of Mines and Metals, Tehran, Report, 104 pp (in Persian).
Barrie, C.T., Ludden, J.N. and Green, T.H., 1993. Geochemistry of volcanic rocks associated with Cu-Zn and Ni-Cu deposits in the Abitibi subprovince. Economic Geology, 88(6): 1341-1358.
Boynton, W.V., 1984. Cosmochemistry of the rare earth elements: meteorite studies. Elsevier, Amsterdam, 522 pp.
Chappell, B.W. and White, A.J.R., 2001. Two contrasting granite types. Australian Journal of Earth Sciences, 48(4): 489-499.
DePaolo, D.J. and Wasserburg, G.J., 1979. Petrogenetic mixing models and Nd-Sr isotopic patterns. Gheochimica et Cosmochimica Acta, 43(4): 615-627.
Eftekhar-Nezhad, J., Eghanabati, A., Hamzehpour, B. and Baroyant, V., 1976. Geological map of Kashmar, Scale 1:250000. Geological Survey of Iran.
Forster, H., 1978. Mesozoic – cenozoic metallogenesis in Iran. Journal of the Geological Society, 135(4): 443-455.
Gaboury, D. and Pearson, V., 2008. Rhyolite Geochemistry Signatures and Association with Volcanogenic Massive Sulfide Deposits: Eamples from the Abitibi Belt, Canada. Economic Geology, 103(7): 1531- 1562.
Gehrels, G.E., Valencia, V.A. and Ruiz, J., 2008. Enhanced precision, accuracy, efficiency, and spatial resolution of U–Pb ages by laser ablation–multicollector–inductively coupled plasma-mass spectrometry. Geochemistry, Geophysics, Geosystems, 9(3): 1-13.
Hart, T.R., Gibson, H.L. and Lesher, C.M., 2004. Trace element geochemistry and petrogenesis of felsic volcanic rocks associated with volcanogenic massive Cu-Zn-Pb sulfide deposits. Economic Geology, 99(5): 1003-1013.
Homam, S.M., 1992. Petrology of metamorphic and volcanic rocks of Taknar-Sarborg area, Northwest Kashmar. M.Sc. Thesis, Esfahan University, Esfahan, Iran, 126 pp (in Persian).
Hoskin, P.W., Kinny, P.D., Wyborn, D. and Chappell, B.W., 2000. Identifying accessory mineral saturation dueing differentiation in granitoid magmas: an integrated approach. Journal of Petrology, 9(41): 1356-1396.
Hu, A.Q., Jahn, B.M., Zhang, G.X., Chen, Y.B. and Zhang, Q.F., 2000. Crustal evolution and Phanerozoic crustal growth in northern Xinjiang: Nd isotopic evidence. Part I. Isotopic characterization of basement rocks. Tectonophysics, 328(1-2): 15–51.
Humphris, S.E. and Thompston, G., 1978. Hydrothermal alteration of oceanic basalts by seawater. Geochimicaet Cosmochimica Acta, 42(1): 107–125.
Huppert, H.E. and Sparks, R.S.J., 1988. The generation of granitic magmas by intrusion of basalt into continental crust. Journal of Petrology, 29(3): 599–624.
Jiangxi, Co., 1995. Explanatory Text of Geochemical Map of Bardaskan (7560), Stream Sediment Survey, scale 1:100000. Geological Survey of Iran, Tehran, Report 18, 40 pp.
Kampunzu, A.B., Tombale, A.R., Zhai, M., Bagai, Z., Majaule, T. and Modisi, M.P., 2003. Major and trace element geochemistry of plutonic rocks from Francistown, NEBotswana: evidence for a Neoarchaean continental active margin in the Zimbabwe craton. Lithos, 71(2-4): 431-460.
Karimpour, M.H., Farmer, G.L., Stern, C.R. and Salati, E., 2011. U-Pb zircon geochronology and Sr-Nd isotopic characteristic of Late Neoproterozoic Bornaward granitoids (Taknar zone exotic block), Iran. Iranian Society of Crystallography and Mineralogy, 19(1): 1-18.
Karimpour, M.H. and Malekzadeh Shafaroudi, A., 2005. Taknar Polymetal (Cu-Zn-Au-Ag-Pb) Deposit. A New Type Magnetite-Rich VMS Deposit, Northeast of Iran. Journal of Sciences, Islamic Repoblic of Iran, 16(3): 239-254.
Karimpour, M.H., Saadat, S. and Malekzadeh Shafaroudi, A., 2002. Knowledge and introduction of Fe- Oxides Cu-Au mineralization and magnetite related to volcanic-plutonic belt of Khaf- Kashmar- Bardaskan. 21th Geosciences Congress. Geological and Mining Explorarion Survey of Iran, Tehran, Iran (in Persian).
Krauskopf, K.B. and Bird, D.K., 1995. Introduction to Geochemistry. McGraw-Hill, New York, 647 pp.
Li, X., Li, Z., Zhou, H., Liu, Y. and Kinny, P.D., 2002. U–Pb zircon geochronology, geochemistry and Nd isotopic study of Neoproterozoic bimodal volcanic rocks in the Kangdian Rift of South China: implications for the initial rifting of Rodinia. Precambrian Research, 113(1-2): 135–154.
Lindenberg, H.G. and Jacobshagen, V., 1983. Post-Paleozoic geology of the Taknar zone and adjacent areas (NE Iran, Khorasan). Geological Survey of Iran, Tehran, Report 51, 145-163.
Malekzadeh Shafaroudi, A., 2003. Geology, mineralogy and geochemistry of Taknar deposits (Tak I and II) and presented as a magnetite-rich polymetal type (Cu-Zn-Au-Ag-Pb) massive sulfide deposit. M.Sc. Thesis, Ferdowsi University of Mashhad, Mashhad, Iran, 287 pp (in Persian with English abstract).
Middlemost, E.A.K., 1994.Naming materials in the magma igneous rock system. Earth Science Reviews, 37(3- 4): 215-224.
Monazzami Bagherzadeh, R., Karimpour, M.H., Farmer, G.L., Stern, C.R., Santos, J.F., Rahimi, B. and Heidarian Shahri, M.R., 2014. U–Pb zircon geochronology, petrochemical and Sr–Nd isotopic characteristic of Late Neoproterozoic granitoids of the Bornaward complex (Bardaskan-NE Iran).32thNational and 1th International Geosciences congress. Geological and mining exploration society, Mashhad, Iran (in Persian).
Moradi, M., 2007. Geochemistry exploration in western Taknar zone. M.Sc. Thesis, Ferdowsi University of Mashhad, Mashhad, Iran, 200 pp (in Persian with English abstract).
Muller, R. and Walter, R., 1983. Geology of the Precambrian-Paleozoic Taknar Inlier northwest of Kashmar, Khorasan province (NE Iran). Geological Survey of Iran, Tehran. Report 51, 165-183.
Patin˜o Douce, A.E., 1997. Generation of metaluminous A type granites by low-pressure melting of calc-alkaline granitoids. Geology, 25(8): 743–746.
Pearce, J.A., 1975. Basalt geochemistry used to investigate past tectonic environments on Cyprus. Tectonophysics, 25(1-2): 41– 67.
Peccerillo, A. and Taylor, S.R., 1976. Geochemistry ofEocene calc-alkaline volcanic rocks from the Kastamonu area, Northern Turkey. Contributions to Mineralogy and Petrology, 58(1): 63-81.
Rollinson, H., (translated by Karimzadeh Somarin, A.R.) , 2002. Using Geochemical Data: Evaluation, Presentation & Interpretation. Tabriz University Press, Tabriz, 557 pp.
Salati, E., 2007. Geology and ground magnetic geophysical exploration in Tak I and IV of Taknar mine. M.Sc. Thesis, Ferdowsi University of Mashhad, Mashhad, Iran, 298 pp (in Persian with English abstract).
Sepahi Gherow, A.A., 1993. Granitoids petrology of Taknar area-Sarborg (East North Kashmar). M.Sc. Thesis, Esfahan University, Esfahan, Iran, 201 pp (in Persian with English abstract).
Sylvester, P.J., 1998. Post-Collisional Strongly Peraluminous Granites. Lithos, 45(1-4): 29-44.
Tankut, A., Wilson, M. and Yihunie, T., 1998. Geochemistry and tectonic setting of Tertiary volcanism in the Guvem area, Anatolia, Turkey. Journal of Volcanology and Geothermal Research, 85(1-4): 285–301.
Taylor, S.R. and McLennan, S.M., 1995. The geochemical evolution of the continental crust. Reviews in Geophysics, 33(2): 241-265.
Tepper, J.H., Nelson, B.K., Bergantz, G.W. and Irving, A.J., 1993. Petrology of the Chilliwack batholith, North Cascades, Washington: generation of calc-alkalinegranitoids by melting of mafic lower crust with variable water fugacity. Contributions to Mineralogy and Petrology, 113(3): 333-351.
Thuy, N.T.B., Satir, M., Siebel, W., Vennemann, T and Long, T.V., 2004. Geochemical and isotopic constrains on the petrogenesis of granitoids from the Dalat zone, southern Vietnam. Journal of Asian Earth Sciences, 23(4): 467-482.
Trua, T., Deniel, C. and Mazzuoli, R., 1999. Crustal control in the genesis of Plio-Quaternary bimodal magmatism of the Main Ethiopian Rift (MER): geochemical and isotopic (Sr, Nd, Pb) evidence. ChemicalGeology, 155(3): 201–231.
Yousefi, E. and Friedberg, J. L., 1977. Aeromagnetic map of Iran,scale 1:100000 Qayen. Geological Survey of Iran.
Wilson, M., 1989. Igneous Petrogenesis. Unwin Hyman, London, 466 pp.
Wood, D.A., Joron, J.L. and Treuil, M., 1979. A re-appraisal of the use of trace elements to classify and discriminate between magma series erupted in different tectonic settings. Earth Planetary Science Letters, 45(2): 326–336.
Wu, F.Y., Jahn, B.M., Wilde, S.A., Lo, C.H., Yui, T.F., Lin, Q., Ge, W.C. and Sun, D.Y., 2003. Highly fractionated I-type granites in NE Chine, I: geochronology and petrogenesis. Lithos, 66(3-4): 241-273.
Xua, B., Jianb, P., Zhenga, H., Zouc, H., Zhanga, L. and Liub, D., 2005. U–Pb zircon geochronology and geochemistry of Neoproterozoic volcanic rocks in the Tarim Block of northwest China: implications for the breakup of Rodinia supercontinent and Neoproterozoic glaciations. Precambrian Research, 136(2): 107–123.
Zindler, A. and Hart, S.R., 1986. Chemical geodynamics.Annual Review of Earth and PlanetarySciences, 14: 493-571.
Zirjanizadeh, S., 2007. Petrology and fluid inclusion micro-thermometry of Taknar Massive sulfide deposit. M.Sc. Thesis, Ferdowsi University of Mashhad, Mashhad, Iran, 186 pp (in Persian with English abstract).
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