Title: A petrographical and geochemical study of granitoids from the southeastern part of the Linderödsåsen Horst, Skåne
Abstract: The Precambrian crystalline basement in Skane only outcrops in the large NW striking Horsts that are roughly parallel to the Tornquist Zone. In the south-easternmost part of the Linderodsasen Horst in SE Skane, the Stenshuvud porphyritic granitoids previously considered to be Palaeoproterozoic volcanic rocks, have been recently dated to 1458 Ma. This indicates that these rocks are coeval with the Karlshamn granitoids in Blekinge as well as other granitoids in southern Sweden. This poses questions regarding the relationship between the granitoids at Stenshuvud and the surrounding rocks. In this study, the area around Sankt Olof, west of Stenshuvud, was mapped in the field and structural, as well as petrographical, investigations were carried out. The main part of the present thesis is a presentation of these new data, which also have been included in the structural-geological map of SE Linderodasen presented in a previous publication. The aim of this study was to compare the obtained structural, petrographical and geochemical data with previous work on the Stenshuvud area.
The crystalline bedrock west of Stenshuvud mainly consists of fine-grained, markedly foliated gneisses and weakly foliated fine-grained granitoids. Some of these rocks have a porphyritic texture similar to the one found in the granitoids from Stenshuvud. Thin aplitic, sometimes ptygmatic, veins and younger pegmatites exist in the rocks from both areas. The biotite is phlogopitic in all the analysed samples of fine-grained granites from the study area and in the granites from Stenshuvud. Chemically, the fine-grained granites are all similar to each other, and to the Stenshuvud granites which is particularly true in regard to REE- and other trace-elements. Many features indicate that the fine-grained granites of the study area are of the ‘Stenshuvud type’. West of this area, close to the small village of Taghusa, there is an elongate intrusion composed of fine to medium-grained gneissic granitoids, dated to 1442 Ma. In the field, the distinguishing feature of these rocks is the aggregates of mafic minerals that define the foliation. Another difference is the composition of biotite, which is richer in iron than that in the granites further to the east. The chemistry of the rocks from the Taghusa intrusion, differ somewhat from the easterly granites in regard to the major elements, while the trace elements are similar. The latter could indicate that the rocks were formed by similar source material.
The rocks in an area to the west of the Taghusa intrusion are gneissic to migmatitic, and vary in composition. They are of unclear origin and might represent remnants of older country rock. Occasionally, the gneisses, and the migmatites, are garnet-bearing: the garnet is Mn-rich in the gneisses.
A more or less pronounced NNW-striking foliation has been found in most of the outcrops of the area, indicating that regional deformation had taken place. The foliation varies from magmatic to migmatitic, and in some cases is mylonitic. The elongate shape of the Taghusa intrusion, stretching in the same direction as the foliation, is yet another indication that the area was affected by deformation during, and somewhat later than, the ca. 1.46 to 1.44 Ga magmatism.
Publication Year: 2004
Publication Date: 2004-01-01
Language: en
Type: article
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