Scientific Quarterly Journal of Geosciences

Scientific Quarterly Journal of Geosciences

The Source and Tectonic Characteristics of the Boroujerd Granitoid Mass (western Iran)

Document Type : Original Research Paper

Authors
Department of Geology, Faculty of Science, University of Tehran, Tehran, Iran
Abstract
Boroujerd granitoid mass belongs to Sanandaj – Sirjan zone (SSZ). It consists of granodiorites, quartz diorites and monzogranites. The country rocks into which the Boroujerd granitoid was emplaced consist of greenschist rocks of the regional metamorphism.
The statistical technique of discriminant analysis, using major element differences alone, shows that this mass has characteristics of orogenic granitoids (R>0). The Boroujerd granitoid has geochemical characteristics typical of arc intrusives e.g. I-type, high-K calc-alkaline series, metaluminous to weakly peraluminous, a greater enrichment in LILEs (Cs, K, Rb, U, Th) compared to HFSEs (Nb, Ta), depletion in Sr, Ba, P and Ti relative to other trace elements. High Th/Yb (>5) ratios correlated to high values (>10, up to ca. 100) for La/Yb and plot as volcanic arc granites on various discriminant diagrams. This granitoid is a typical representative of a volcanic arc environment, spatially related to an active continental margin. Crustal contamination processes provide a further complication in the interpretation of the Boroujerd rocks. The rarity of primitive magma compositions in arcs, particularly continental margin arcs, points to the important and consistent role of such processes. Probably, Boroujerd granitoid is the result of the subduction of Neo- Tethyan oceanic plate below the Iranian microcontinent.
Keywords

Subjects


Agrawal, S., 1995- Discrimination between late-orogenic, post-orogenic and anorgenic granites by major element compositions. The journal of geology, 103, 529 – 537.
Ashworth, J.R., 1985- Migmatitites: Blackie, New York.
Batchelor, R.A. and Bowden, P., 1985- Petrogenetic interpretation of granitoid rock series using multicationic parameters. Chem. Geol. 48, pp. 43–55.
Berberian, M.,1983- Generalized tectonic map of Iran. In: Berberian, M., (Ed.), Continental Deformation in the Iranian Plateau, Geological Survey of Iran, Report No. 52.
Berberian, M. and King G.C.P., 1981- To wards a paleogeography and tectonic evolution of Iran. Canadian journal of Earth sciences.vol.18, No.2.pp.210-265.
Berberian, M., 1977- Three phases of metamorphism in Haji-Abad quadrangle (southern extremity of the Sanandaj–Sirjan structural Zone): a palaeotectonic discussion. In: M. Berberian, Editor, Geological Survey of Iran, Report 40, Tehran, Iran Geological Survey of Iran, Report 40, Tehran, Iran ,pp. 239–263.
Berberian, M. and Nogol, M.,1974- Preliminary explanatory text of the geology of Deh Sard and Khabr maps with some remarks on the metamorphic complexes and the tectonics of the area (two geological maps 1:100000, from the Hadjiabad quadrangle map). G.S. of Iran, internal report, 60 p.
Berberian, M., 1972- A brief note on early Kimmerian orogeny and high grade metamorphism in Sanandaj-Sirjan belt, Iran. Geological Survey of Iran, internal report.
Berthier,F; Billiaul, H.P; Halbroronn, B and Marizot, p.,1974- Etude Stratigraphique, petrologique et structural de La region de khorramabad (zagros, Iran) - These De 3e cycle,Grenoble,282.p.
Chappell, B.W., White, A.J.R., 1974- Two contrasting granite types. Pacific Geology 8, 173–174.
Condie, K.C., 1989- Geochemical changes in basalts and andesites across the Archean–Proterozoic boundary: identification and significance. Lithos 23, pp. 1–18.
Floyd, P.A. and Winchester, J.A., 1975- Magma type and tectonic setting discrimination using immobile elements. Earth and Planetary Science Letters 27, pp. 211–218.
Froster,H.J., Tischendorf, G. and Trumbull, R.B., 1997- An evaluation of the Rb vs. (Y+Nb) discrimination diagram to infer tectonic setting of silicic igneous rocks. Lithos 40, pp. 261–293.
Gill, J.B., 1981- Orogenic Andesite and Plate Tectonics, Springer Verlag, New York , p. 390.
Gorton, M. P., and Schandl, E. S., 2000- From continental to island arc: A geochemical index of tectonic setting for arc-related and witin plate felsic to intermediate volcanic rocks. Canadian Mineralogist, Vol. 38, pp. 1065-1073.
Harris, N.B.W., Pearce, J.A., Tindle, A.G., 1986- Geochemical characteristics of collision-zone magmatism. In: Coward, M.P., Ries, A.C. (Eds.), Collision Tectonics. Geological Society London, Special Publication 19, pp. 67–81.
Irvine, T.N. and Baragar, W.R.A., 1971- A guide to the chemical classification of the common volcanic rocks. Can. J. Earth Sci., 8,523-484.
Masoudi, F., 1997- Contact metamorphism and pegmatite development in the region SW of Arak, Iran, Unpublished PhD Thesis, Leeds University, UK.
Mohajjel, M., Fergusson, C.L., Sahandi, M.R., 2003- Cretaceous–Tertiary convergence and continental collision, Sanandaj-Sirjan zone, Western Iran. Journal of Asian earth Sciences 21, 397–412.
Pearce, J.A., Harris, N.B.W. and Tindle, A.G., 1984- Trace element discrimination diagrams for the tectonic interpretation of grantitic rocks. Juornal of petrology, 25, 956 – 983.
Pitcher,W.S.,1987- Granites and yet more granites forty years on: Geologische Rundschau, v.76,p.51-79.
Roberts M.P. and Clemens, J.D., 1993- Origin of high-potassium, calc-alkaline, I-type granitoids. Geology 21, pp. 825–828.
Rogers, G. and Hawkesworth, C.J., 1989- A geochemical traverse across the North Chilean Andes: evidence for crust generation from the mantle wedge. Earth and Planetary Science Letters 91, pp. 271–285.
Sajona, F.G., Maury, R.C., Bellon, H., Cotton, J. and Defant, M., 1996- High field strength elements of Pliocene-Pleistocene island-arc basalts Zamboanga Peninsula, Western Mindanao (Philippines), Journal of Petrology 37, pp. 693–726.
Schandl, E. S., and Gorton, M. P., 2002- Appplication of high field strength elements to discriminate tectonic setting in VMS environments. Economic Geology, Vol. 97, pp. 629–642.
Shahabpour, J., 2005- Tectonic evolution of the orogenic belt in the region located between Kerman and Neyriz. Journal of Asian Earth Sciences 24, 405-417.
Thompson, A.B., 1982- Magmatism of the Bristish Terciary volcanic Province, Scott. J. Geol. 18, pp. 50–107.
Wilson, M., 1989- Igneous petrogenesis, Unwin Hyman London., 466 p.