پترولوژی توده های الترامافیک-مافیک محدوده ماسوله، استان گیلان

Three small ultramafic-mafic massifs, located in vicinity of the Chepol, Zodel and Gilvandarud villages, in Masuleh area, southwestern Fouman are studied in this paper. These massifs are olivine websterite, websterite, lherzolite, olivine gabbro, hornblende gabbro, gabbro in compositions, and are cut by micro-gabbro-diabase dikes, and quartz-monzodiorite, micro-granite dikes and veins. The crystallization trend of these rocks is olivine-plagioclase-clinopyroxene-ortopyroxene-hornblende-biotite, which is similar to crystallization trend in closed-magma chambers in mid-ocean ridges, however occurrence of heteradcumalate texture with hydrous minerals, such as hornblende and biotite, indicate their crystallization in an open-magma chamber similar to those in arc domains. The gabbroic rocks include harzhburgite microenclaves and garnet xenocrysts, suggesting a mantle origin for their magmas. In discriminating diagrams, most of the samples are tholeiitic and in tectonomagmatic diagrams plot in arc domains. The spider diagrams display enrichment of LREE relative to HFSE which makes them comparable to subduction related magmatism. It seems that the parental magmas are probably produced by partial melting of mantle wedge which were influenced by subduction components and mantle diapirs but are differentiated in shallow magma chambers. Regarding to small to intermediate scale of the studied massifs, lacking of high grade metamorphic rocks and serpentinites, presence of hydrous minerals, and clear relationship between ultramafic-mafic rocks, the massifs may be compared to the Alaskan orogenic massifs