Scientific Quarterly Journal of Geosciences

Scientific Quarterly Journal of Geosciences

Geology of Precambrian in Central Iran; on the Context of Stratigraphy, magmatism and metamorphism

Document Type : Original Research Paper

Authors
Bahram Samani 1
Chen Zhuyi 2
Guo Xuetao 2
Tao Chuan 2
1 Atomic Energy Organization of Iran, Iran
2 Beijing Research Institute of Uranium Geology, Beijing, China
Abstract
From the remote sensing (TM, MSS), and geophysical data interpretation, isotopic geology and field surveying in Central Iran it is proved that the formerly named Tashk formation, Chapedony and Boneh Shurow complexes originally were a unique miogeosynclinal- type clastic sequence. This rock unit is named Natk formation which is 874- 750 m.y. old (Sm- Nd isotopic age calculated from REE depleted- type basalt model).
The oldest sialic crust (continental margin- type) is 1300- 1000 m.y. in Iran, where the Natk formation with continental slope facies deposited over it.
The geological evolution of Upper Precambrian is defined as the following:
a)- The Natk formation was formed on Upper Precambrian (> 874- 750 m.y.). This unit is a mature clastic rock that metamorphosed in greenschist facies grade. K- type granites were intruded to this formation. The measured isotopic ages (Zircon, Uraninite) are 850- 800 m.y. which is characteristics of a mature sialic crust consolidation. Granodioritic magmatism occurred in 749± 97 m.y. (Pb 207/Pb 206) and followed by 624 ±5 m.y. (isochrons of Pb 207/U 235 and Pb 206/U 238) granitization.
b)- Development of Saghand formation with riftogenic facies, consists of five lithologic members. This rock Unit is unconformably underlained by Natk formation. This formation has peculiarities and features of intracontinental rift, where Fe/U/ Th, REE, and apatite deposits were formed. This major rifting started not later than 750 m.y. but ended by 583 m.y. It is characterized by enriched- mantle magmatism, extensive linear metasomatism, and related ore formation.
c)- Alkaline metasomatism, and granitization interrupted after 583 m.y. by uplifting and development of erosional surface. The subsidiary rifting caused high K-volcanism (561± 73 m.y.) which was derived from an enriched- mantle, grading into normal- type. This stage of rifting is characterized by volcanics, evaporites, shales, clastics, and carbonates with Vendian- early Cambrian age. This sequence is named Desu Series and Soltanieh Dolomite after stratigraphic correlation.
d)- The only recorded metamorphism of Upper Precambrian age is older than Saghand formation. The main components of conglomeratic beds at the base of Saghand formation show the greenschist facies metamorphism, like the Natk formation.
e)- The Natk, Saghand and Desu rock Units were metamorphosed on the western part of Bafq- posht-e- Badam Block on Mesozoic and early Cenozoic time. The former one is high pressure- type and could be related to the detachment faulting of late Triassic- Early Jurassic time. The later dynamothermal high grade metamorphism occurred at 52 m.y. (K/Ar, Zircon minerals, Rb/Sr), as a result of Neotethys oceanic crust subduction beneath the central continental crust. Granitization, migmatization and high-grade metamorphism of Khoshumi, Neibaz and Chapedony is related to this stage of deformation. Finally, it is concluded that, two types of uppermost Precambrian rock units crop out in the region: 1) riftogenic series, and, 2) platform- type cover namely Saghand formation and Desu Series for first type and Barut- Soltanieh Formations as platform cover.
Subjects
Adamia S. A., Lordkipanidze M. B., and Zakariadze G. S., 1977: Evolution of an active continental margin as exemplified by the Alpine history of Caucasus, Tectonophysics 40; pp. 183-199.
AEOT & BRIUG, 1992: Regional Evaluation and Target Area selection in Central Iran (unpub. Rep.), AEOI, Tehran, 326p.
Aghanabati, 1986: Geological Map of the Middle East, GSI, Tehran, Iran
Berberian, M. and G. C. King, 1981: Towards a paleogeography and tectonic evolution of Iran, Can. J. Earth sci. vol. 18, PP. 210- 265.
Bozhko, N. A. 1986: The evolution of the mobile zones of Gondwana and Laurasia in the Late precambrian, Tectonophysics 126, PP. 125- 135.
Hurely, P. M. 1974: Pangeaic orogenic system Geology 2, PP. 373-376.
Gass, I. G. 1979: Evolutionary model for the pan- African Crystalline Basement. In Evolution and Mineralization of the Arabian- Nubian Shield "I. A. G. Bulletin No. 3, Vol 1, PP. 11- 20, Pergamon press.
Grant, N. K. 1969: The Late precambrian to Early paleozoic pan- African orogeny in Ghana, Togo, Dahomey and Nigeria, Geol. Soc. Am. Bull., 80 PP. 45- 56.
Haghipour, A., 1978: Etude geologique de la region de Biabanak- Bafq (Iran Central), Petrologie et tectonique du socle precambrian et de sa couverture, GSI, Rep. No 34.
Haghipour, A., Valeh, N., pelissier, G., and M. Davoudzadeh, 1977: Explanatory text of the Ardekan quadrangle map, 1:250,000 GSI, H8, 114p.
Hushaokang, 1988: The main characteristics of Archean basement rock evolution and their relationship to uranium mineralization in the Northern China platrorm, BRIUG, China, Unpublished, 19P.
Huckriede, R., M. Kursten and H. venzlaff, 1962: Zur Geologic des Gebietes zwischen Kerman und Saghand (Iran), Beih Geol. JB vol. 51, 197 p.
Kennedy, W. Q.,1964: The structural differentiation of Africa in the Pan-African (500 m.y) tectonic episode, 8 Ann. Rep. Res. Inst. Afr. Geol., University of Leads, PP. 48-49
Kroner A., 1979: Pan- African mobile belts as evidence for a transitional tectonic regime from intraplate orogeny to paleo marginorogeny, in "Evolution and mineralization of the Arabian- Nubian shield" I. A. G. Bulltin No. 3, PP. 21- 38. pergamon press.
Romanko, E. (Editor), 1984: Outline of metallogeny of Anarak Area (Central Iran), V/O Technoexport TE/NO. 21 Geological Survey of Iran, Tehran, 138p.
Sahandi, M., Baumgartner, and Schmidt K., 1983: Contribution of stratigraphy and tectonics of the Zeber- Kuh Range (East of Iran) in Geodynamic project (Geotraverse) in Iran, Rep No. 51, GSI, PP. 185- 203
Salop J. Lazarus, 1983: Geological Evolution of the Earth During the Precambrian, 495p., Springer-Verlag.
Samani, Bahram, 1988 a: Recognition of Uraniferous provinces from the precambrian of Iran, KRYSTALINIKUM, 19, PP. 147-165.
Samani Bahram, 1988 b: Metallogeny of precambrian in Iran, precambrian Research, vol. 39. No. 1-2, PP. 85- 106.
Stoeser, D. B. and Elliott, J. E., 1980: post- Orogenic peralkaline granites and associated mineralization of the Arabian Shield, Kingdom of Saudi Arabia in "Evolution and mineralization of the Arabian- Nubian shield", I. A. G. Bulletin No. 3. Vol. 4, PP. 1- 24, Pergamon press.
Stocklin, J., 1968: Structural history and tectonics of Iran, a review, AAPG, vol. 59, PP. 1229- 1258.
Stocklin, J., 1972: Iran central, septentrional et oriental, in lexique stratigraphique International, III, Fasc. Qb CNRS, Paris PP. 1-283
Stocklin, J., 1974: Possible ancient continental margins in Iran, in the Geology of continental margins, edited by C. A. Burk and C. L. Drake, New-York, Springer PP. 873-887.
Weber Diefenbach, K., Hushmandzadeh, A., & Davoudzadeh, M., 1992: Geology and Geochemistry of the volcanic rocks from the Saghand Area, Central Iran, (Unpublished).
Scientific Quarterly Journal of Geosciences
Volume 3, Issue 10
Winter 1994, Vol. 3, No. 10
Winter 1994
Pages 40-63