Anorthosites relations with Misho mafic rocks and using age as a guide to identify the Misho mafic rocks paleotectonics (NW of Iran)


1 دانشگاه تبریز گروه علوم زمین احمد جهانگیری

2 بیرجند- دانشگاه بیرجند- دانشکده علوم گروهزمین شناسی

3 Department of Geology, Faculty of Sciences, University of Ferrara, Ferrara, Italy

4 Faculty of Geology, University of Miami, Oxford, America

5 Industry, Mine and Trade Organization of East Azerbaijani, Tabriz, Iran


The Misho Mafic magmatic massif (in NW of Iran) with complex and un-clear paleotectonic is situated in the Soltaniye- Misho zone, in SW of Marand city between the north and the south of the Misho faults. This mafic massif intruded into the PreCamberian Kahar sedimentary rocks and is covered by Permian sedimentary rocks. The lithological units of this massif are gabbro, norite, anorthosite, pyroxenite, olivine gabbro and troctolite. Diabasic dykes with gabbroic composition cut the mafic massif. The main mineral in these leucocratic rocks with cumulate texture is plagioclase which is mainly bitownite and labradorite in composition. Anorthosites are not distinguishable from gabbros on different discrimination diagrams. Anorthosites and gabbros are related to tholeiitic to calc-alkaline magmatic series indicating similar source for both rock types. Gabbros and anorthosites are meta-aluminous and show MORB affinity. Dating of anorthosites by zircon U-Pb method and considering this age for the Misho mafic massif helps us to identify the Misho paleotectonic. Dating results show that the emplacement time for gabbros and anorthosites is early Carboniferous (356.7  3.4 Ma), which is also confirmed by stratigraphy relation (between Kahar Cambrian sediments and Permian sedements). We suggest that Misho mafic massif is formed by an extension event related to plume- type magmatism in early Carboniferous. This is the reason for initiation of spreading of Paleotethys oceanic crust in NW Iran.