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Paleomagnetism and ore mineralogy of some basalts of the geirud formation of Late Devonian - early carboniferous age from the Southern Alborz, Iran

By H. Wensink, J.D.A. Zijderveld and J.C. Varekamp

Abstract

Basaltic lavas from the southern Alborz, an area about 40 km northeast of Tehran, Iran, have been paleomagnetically\ud investigated. The lavas are of Late Devonian-Early Carboniferous age, and belong to the basal member of the\ud Geirnd Formation. At 11 sites a total of 80 cores was drilled.\ud Detailed analyses by means of progressive demagnetization of the natural remanent magnetization (NRM) were\ud made both by the application of alternating magnetic fields and by heating. Also, on a number of specimens a study was\ud done both with thin sections and with polished sections. There proved to be general agreement between the properties\ud of the characteristic NRM and the kind of Fe-Ti oxides in the lavas. In the case of specimens containing magnetite\ud only the characteristic NRM was entirely removed at temperatures just below 600°C, or in alternating fields up\ud to 1500/2000 Oe peak value; on the other hand, in specimens containing both magnetite and a substantial part of\ud hematite (martite) the final part of the characteristic remanence was removed at temperatures above 600°C, and this\ud remanence resisted alternating fields above 2000 Oe peak value. From the characteristic site-mean directions of 5\ud sites an average paleomagnetic direction is computed with D = 210.8 °, 1 = 66.9 °, and c~95 = 3.9 °.\ud This result might be taken as an indication that at the Devono-Carboniferous transition the southern part of the\ud Alborz was located in the present Indian Ocean off the Arabian coast

Topics: Aardwetenschappen
Year: 1978
OAI identifier: oai:dspace.library.uu.nl:1874/19110
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