Geology and petrology of eclogites in the Samylino area (Belomorian Province of the Fennoscandian Shield)

Abstract

New geological and petrological data are presented for the Precambrian eclogites of Gridino area, Belomorian Province. The detailed optical and microprobe studies of eclogites in the Samylino locality allow distinguishing the essential features of eclogitic metamorphism in this area. The early stage of high-pressure metamorphism in this tholeiitic series mafic rocks is recognized by the presence of diopside-plagioclase symplectitic inclusions (symplectites I) in the central parts of large omphacite (jadeite 30–35 %) crystals and in the cores of zoned garnet grains. The eclogitic metamorphism is distinguished by omphacite in the matrix and its inclusions in the garnet (pyrope 27–30 %, almandin 48–52 %, grossular 19–23 %) inner zones. The high-pressure amphibolite faciesoverprinting is represented by garnet rims (pyrope 22–24 %, almandin 52–56 %, grossular 22 %) and diopside-plagioklase (± hornblende) symplectites II. These data suggest a two-stage character of eclogitic metamorphism in Gridino area.

Keywords

• эклогит
• метаморфизм
• докембрий
• беломорская провинция
• феносканднавский щит.