Scientific Quarterly Journal of Geosciences

Scientific Quarterly Journal of Geosciences

Geological Character of Sikhoran Mafic - Ultramafic Complex, Southeast Iran

Document Type : Original Research Paper

Authors
Habibollah Ghasemi 1
Mosayeb Sabzehei 2
Thiery juteau 3
1 Tarbiat Modarres University, Tehran, Iran
2 Geological Survey of Iran, Tehran, Iran
3 Universit de Bretagne Occidentale, Brest, France
Abstract
Sikhoran Complex is a polygenetic, mafic- ultramafic complex composed of three main parts with different ages including a mafic-ultramafic part, a large isotropic gabbro intrusion and scattered diabasic dykes. Mafic- ultramafic part consists of an harzburgitic- dunitic unit with mantle character and an ultramafic and a mafic- ultramafic cumulate units with magmatic structures. The harzburgitic- dunitic- part consists of foliated porphyroclastic harzburgites with orthopyroxene lineations in the lower part and porphyroclastic dunites and stratiform chromitites in the upper part.
Ultramafic cumulates are a thick sequence of cumulative dunites, chromitites, wehrlites, olivine websterites and olivine clinopyroxenites. Mafic- ultramafic cumulates contain a thick sequence of feldspathic peridotites and layered gabbros including melagabbros, picrtic troctolites, olivine gabbroes, allivalites, noritic gabbroes and ferrgabbros intruded in the ultramafic and mafic cumulates and Paleozoic metamorphic rocks created an intense contact metamorphism. Scattered diabasic dykes cut all of them.
Paleozoic metamorphic rocks including amphibolites, marbles, gneiss, anatectic granites and greenschists with an angular unconformity and a basal conglomerate overlain by Lower Jurassic deposits. Absolute age determinations by K-Ar method show 3377.7 Ma (Middle - Upper Carboniferous) for gneiss and anatectic granite on the biotite and muscovite, 245 ± 7.4 Ma (Permian) for gabbro- pegmatoidic dykes cutting the mafic- ultramafic cumulates on the amphibole, 220 ± 8 Ma (Middle Triassic) on the hornblendes of the basic migmatites in the contact of isotropic gabbroes and Paleozoic metamorphics (Age of gabbro emplacement) and 165 ± 12.35 Ma (Upper Jurassic) on the whole rock for diabasic dykes. Field observations, petrographic, mineralogic and geochemistry studies indicate that this complex is not similar to ophiolitic complexes and resulted form mantle upwelling in an extensional tectonic environment.
Keywords
Mafic-Ultramafic complex
Sikhoran
Southeast of Iran

Subjects

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Scientific Quarterly Journal of Geosciences
Volume 8, 29-30
Autumn & Winter 1999, vol. 8, No. 29-30
Winter 1999
Pages 32-45