Na-metasomatism in the form of albitisation is regionally extensive in the Precambrian crust of southern Scandinavia and is particularly widespread in the Bamble Sector, the Kongsberg-Modum Sector and the Norwegian pa...Na-metasomatism in the form of albitisation is regionally extensive in the Precambrian crust of southern Scandinavia and is particularly widespread in the Bamble Sector, the Kongsberg-Modum Sector and the Norwegian part of the Mylonite Zone. Sites of albitisation outside these belts are associated with hy- drothermal breccia pipes and fracture-bound alteration. The albitites are composed of near end-member sodic plagioclase （Ano 5Ab94-99） with minor carbonate （calcite and dolomite）, rutile, clinopyroxene （En30Fs21-23W047 49）, amphibole （edenite-pargasite）, quartz, titanite, tourmaline, epidote （Fe3＋ - 0.20 -0.85 a.p.f.u） and chlorite （Mg# = 0.81-0.89）. The albitites have been studied in detail in the region around the town of Kragem, and are described as albitisation along veins, as breccias, alhitic felsites, massive carbonate-bearing albitites and megascale clinopyroxene-titanite-bearing albitite. The strong fluid control on their formation is illustrated by the veining and mineral replacement reactions, showing fluid transport by a H20-CO2 fluid rich in Na, depleting Fe and Mg from the host rock, in accordance with calculated mass transfer. A study of the mineralogical replacement reactions in combination with a regional compilation has demonstrated the relationship between metasomatic processes and the for- mation of apatite, ruti｜e and Fe deposits. The albitites occur spatially associated with other metasomatic rocks such as scapolitised metagabbros. We document that metasomatism is an important mineral- and rock-forming process in the continental crust, which in the Bamble Sector is a part of the tectonome- tamorphic evolution of the Sveconorwegian orogen.展开更多
文摘Na-metasomatism in the form of albitisation is regionally extensive in the Precambrian crust of southern Scandinavia and is particularly widespread in the Bamble Sector, the Kongsberg-Modum Sector and the Norwegian part of the Mylonite Zone. Sites of albitisation outside these belts are associated with hy- drothermal breccia pipes and fracture-bound alteration. The albitites are composed of near end-member sodic plagioclase （Ano 5Ab94-99） with minor carbonate （calcite and dolomite）, rutile, clinopyroxene （En30Fs21-23W047 49）, amphibole （edenite-pargasite）, quartz, titanite, tourmaline, epidote （Fe3＋ - 0.20 -0.85 a.p.f.u） and chlorite （Mg# = 0.81-0.89）. The albitites have been studied in detail in the region around the town of Kragem, and are described as albitisation along veins, as breccias, alhitic felsites, massive carbonate-bearing albitites and megascale clinopyroxene-titanite-bearing albitite. The strong fluid control on their formation is illustrated by the veining and mineral replacement reactions, showing fluid transport by a H20-CO2 fluid rich in Na, depleting Fe and Mg from the host rock, in accordance with calculated mass transfer. A study of the mineralogical replacement reactions in combination with a regional compilation has demonstrated the relationship between metasomatic processes and the for- mation of apatite, ruti｜e and Fe deposits. The albitites occur spatially associated with other metasomatic rocks such as scapolitised metagabbros. We document that metasomatism is an important mineral- and rock-forming process in the continental crust, which in the Bamble Sector is a part of the tectonome- tamorphic evolution of the Sveconorwegian orogen.
