Albite-actinolite (Hedenbergite) containing rocktypes in the Bamble Area, South-west Norway

Albite-actinolite (Hedenbergite) containing rocktypes in the Bamble Area, South-west Norway

Kloprogge, J.T.

Molengraaff Fonds

1987

Several rocktype scontainin albite/hedenbergite or albite/actinolite associations are found in the Bamble area, South Norway. In part 1 of this study several types are described which formed only a minor part of the fieldwork. For diopside layers embedded in quartzite and for actinolite gneisses a sedimentary origin is suggested. The emplacement of the albitites, another group of rocks, resembles that of pegmatites, but their origin is still not clear. A connection with gabbro's or carbonatites is possible. The strongly foliated finegrained albite-actinolite rock found within the Jomasknutene gabbro has probably a tectonic origin, due to strong shearing of the gabbro combined with recrystallisation and alteration. The finegrained albite­actinolite rock is associated with huge, pure quartz deposits. This rock probably represents the altered country-rock, completely recrystallised under influence of fluids connected with the quartz formation. In art 2 the major rocktype studied during this fieldwork is described together with whole rock chemistry and a possible genesis. The main minerals in these rocks are albite (AnO - An2.5) and actinolite. The rocks are thought to originate from deformation and later brecciation of gabbro and country-rock along the gabbro boundary. Fluids rich in elements such as Na and Mg(+ Al and Ca) caused recrystallisation, and formation of albite and actinolite. This may have occured during the brecciation or later. The first possibility is favoured because of veins intruding the blocks in the breccia, which have the same texture and mineralogy as the matrix. The composition of this fluid could be formed by leaching old evaporitic sediments. The existence of small marble bands seems to support this, although an origin in the Fen area with its carbonatites cannot be excluded. A second phase of fluids introduced a great amount of pure quartz and again caused recrystallisation of actinolite.

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