Neoproterozoic palaeomagnetic directions in rocks from a key section of the Protogine Zone, southern Sweden

Abstract

SUMMARY New palaeomagnetic data from the Protogine Zone (PZ) of southern Sweden are presented together with data from east and west of the zone. They confirm previous palaeomagnetic results from the PZ that indicate a diVerence in magnetic properties between rocks north and south of a section at 57°N, here called the Alvesta‐Ljungby Palaeomagnetic Borderzone (ALPB). The results are divided into four groups: group I [declination (D)=297°, inclination (I)=’78.5°, a 95 =2.4°, pole position 42.7°S, 220.9°E]; group II (D=129.4°, I=52.2°, a 95 =4.2°, pole position 9.4°S, 235.5°E); group III (D=155.4°, I=61.3°, a 95 =4.9°, pole position 11.6°S, 211.2°E); group IV (D=125.5°, I=35.4°, a 95 =5.4°, pole position 0.8°N, 244.1°E). A fifth, poorly defined, group has a mean direction D=304.5°, I=5.4°, a 95 =15.1° and pole position 21.3°N, 255.9°E. These palaeopoles fall on the c. 1050‐900 Ma Sveconorwegian Loop of the Fennoscandian apparent polar wander path. Together with previously published data from southern Norway, the group I poles define the high-latitude apex of the loop at c. 950‐930 Ma. The groups II‐V palaeopoles are situated at low latitudes but it is diYcult to place them in chronological order owing to a lack of age data and two possible interpretations, that is of an open or a closed loop. The study shows that the part of the PZ extending south of the ALPB belongs to the Southwest Granulite Region and the rocks became remagnetized during the tectonic stacking and uplift processes that created that region. Dolerites from east of the PZ have primary magnetizations and the data indicate that they belong to the Blekinge‐ Dalarna dolerites, a suite of dykes east of the PZ with ages between 995 and 880 Ma. Dolerites west of the PZ yield low-latitude Sveconorwegian palaeopoles but it is not certain if their magnetizations are primary or are due to remagnetization during the Sveconorwegian Orogeny.