Scientific Quarterly Journal of Geosciences

Scientific Quarterly Journal of Geosciences

Geological identity of Soghan ultramafic-mafic complex south-east Iran

Document Type : Original Research Paper

Authors
Hamid Ahmadipour 1
Mosayeb Sabzehei 2
Huber Whitechurch 3
Thiery Juteau 4
1 ,Tarbiat Modarres University, Tehran, Iran
2 Research Institute for Earth Sciences, Geological Survey of Iran, Tehran, Iran
3 University of Louis Pasteur (strasborg), France
4 University of Bretagne Occidentale (Brest), France
Abstract
Soghan ultramafic- mafic complex is situated in Esfandagheh, south-east Iran. It is composed of three main bodies, (1): The oldest body is composed of ultramafic- mafic rocks with metamorphic fabrics. This body is composed of three units: A: Lower dunite- harzburgites and related chromitite, B: Transition zone, being composed of lherzolite- websterite-dunite-wherlite, C: Upper layered gabbros: Paleozoic marbles, amphibolites, skarns and micaschists of Sanandaj- Sirjan Zone are lying directly on the top of unit "C". (2) Isotropic gabbro body which cuts "1" and metamorphic rocks of Sannandaj- Sirjan Zone. This gabbro is formed between Upper Triassic and Lower Jurassic. (3): Diabasic dykes of Late Cretaceous age which cut "1" and "2" bodies. In the lower part of metamorphic rocks of Sannandaj- Sirjan, differentiated ultramafic lavas and sills have been formed.
All the constituents of "1" have metamorphic fabrics, which were formed in high pressure- high temperature condition- Existence of a pervasive foliation and less dominant lineation in dunite- harzburgite, as well as kink bands in olivines of "C" unit, all indicate a solid-state deformation. Invasion of basaltic magma into the "1" body, which is materialized by isotropic gabbro, has initiated a metasomatic exchange between basaltic magma and all the constituents of body "1", as well as it's pervasive recrystallization. The existence of :(1) Non-deformed orthopyroxenes forming at the expense of olivine, (2) crystallization of chrome spinels with a different composition in comparison to the original spinels of dunites- harzburgites, (3) Formation of websteritic dykes in lherzolite which cut the foliation of host lherzolite, (4) recrystallization of layered gabbros and rocks of unit "B" all indicate the passage of a basaltic melt through the "1" body. The invasion of this basaltic magma into metamorphic rocks of Sanandaj-Sirjan, produced skarns at the expense of marble and it has imposed a partial anatexis of the amphibolites. Sodic plagiogranitic mobilizate forming by this process, cuts the layered gabbro of "1" body and causes a severe metasomatic effect on it.
From all these studies, it has been concluded that (1): Soghan Complex is a polygenetic association of ultramafic-mafic rocks. Every part of this complex is formed particular period of time, (2): This complex can not be called an ophiolite senso stricto. (3) In spite of existence of many textural similarities between mantellic ultramafics and ultramafic rocks in lower part of the body "1" a petrological continuity of deterrent constituent of the body "1" from bottom to top indicate that the latter may have been formed from the differentiation of an ultramafic magma in the lower Paleozoic.
Keywords
Ultramafic complex, Soghan

Subjects

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Scientific Quarterly Journal of Geosciences
Volume 7, 27-28
Spring & Summer 1999, vol. 7, No. 27-28
Summer 1999
Pages 38-53