Previous Geological Interpretation

The geology of the Duobblon area was first described briefly by Hogbom (1937), and Gavelin and Kulling (1955). In the 1970s Einarsson published a more detailed geological map of the Duobblon area (Einarsson 1979). He introduced the term "Duobblon Group", which is divided into a lower Bjornknosen Formation with "conglomerates, lithophysae-bearing volcanics and tuffitic sandstone", and an upper Gippervare Formation with "acid volcanics". The Duobblon Group is the name given to the supracrustal rocks on top of brecciated basement. A detailed description of the lithophysae can be found in Lindroos and Smellie (1979) and Smellie (1982). They range in size from 5 mm to 15 cm in diameter and vary in shape from spheroidal, ellipsoidal, to lenticular. Perlitic structures occur in the vicinity of the lithophysae, which often coalesce into amoeboid shape. The mineral assemblage within the lithophysae is dominated by quartz with subordinate feldspar, commonly exhibiting a concentric layering within the lithophysae.

Fig. 2. Geological plan map over the central parts of the Duobblon Structure.

The lower unit is about 450 m thick and the overlying Gippervare rocks are over 1 km thick (Einarsson 1979; Lindroos and Smellie 1979).

Sixty-one drill-holes (11 252 m) penetrate rock sequence down to the brecciated granite rock. The drill-cores allow detailed lithological and mineralogical studies.

According to Einarsson (1979), a major unconformity separates the Duobblon Group from the basement, which is composed of granite and metamorphic pelitic and psammitic metasediments. The greywacke type

Dh TtOOi _______Wt 770(2 Oh 78002 Ol 77019 Dh 78013

Dh TtOOi _______Wt 770(2 Oh 78002 Ol 77019 Dh 78013

Fig3. Geological profile. The position of the profile is indicated in Fig. 2.

Fig3. Geological profile. The position of the profile is indicated in Fig. 2.

metasediments form the Paksjo Group. The Sorsele Granite (1791±22Ma; Skiold 1988) intrudes both the basement rocks and the Duobblon Group. The last Precambrian event is the intrusion of dolerite dykes (younger than 1626 Ma). To the west, the Caledonian nappes have been thrusted over the Precambrian rocks during the Caledonian orogeny at about 450 Ma ago. The general geology of the area is shown in Fig. 1 and Fig. 2; and a cross section is presented in Fig. 3.

Lindroos and Smellie (1979) and Smellie (1982) in general support the stratigraphy introduced by Einarsson (1979) with only minor alterations.

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