Abstract Abstract Dark-clouded plagioclase, (K0.02Na0.68)Ca0.30Al1.30Si2.70O8, from Bjärnum is characterised structurally and compositionally. The plagioclase consists of andesine and oligoclase. SEM study has revealed microinclusions of hercynite and ilmenite in the clouded andesine. TEM study has showed inclusions of hercynite below 10 nm in size. A crystallographic relationship to the host plagioclase is not observed. The crystal structure of plagioclase has been refined from synchrotron X-ray powder diffraction data. Space group P1, Z=8, T=295(1)K, a=8.1659(5)Å, b=12.8618(5)Å, c=14.2363(7)Å, α=93.606(3)°, β=116.295(3)°, γ=89.789(3)°. The Rietveld study has identified and quantified the hercynite inclusions. The result suggests that the dark clouding is induced by entrapped inclusions of hercynite and ilmenite. Keywords: CloudingdoleritehercyniteilmenitemicroprobeplagioclaseRietveld refinementBjärnumsynchrotron XRD
Abstract The Kullaberg peninsula in NW Skåne renders km-long, continuous exposures of the Proterozoic crystalline basement. We report ion microprobe (SIMS) U–Pb zircon ages for six key lithologies at Kullaberg that constrain the geological history of SW Fennoscandia for a considerable time period. Igneous zircon in three varieties of gneiss granite yield ages of 1694±7 Ma, 1693±7 Ma and 1663±14 Ma, in the same age range as orthogneisses further north in the same crustal segment. Partial melting, manifested by formation of pegmatite dykes and veins, occurred at 1473±6 Ma. Emplacement of mafic dykes, today seen as a large number of north-trending amphibolite sheets across the Kullaberg peninsula, is dated at 961±6 Ma. The dykes, which fall in the same age range as the Blekinge-Dalarna dolerites (978–945 Ma) predate an event of amphibolite facies deformation, which presumably relates to exhumation of the crust following shortly after the Sveconorwegian compressional stage. A pegmatite was emplaced at 934±6 Ma after the crust had been exhumed through the ductile-brittle boundary.
(1986). Mega-lenses and Scandian deformation in the basement in the northern part of Western Gneiss Region, Vestranden, central Norwegian Caledonides. Geologiska Foreningen i Stockholm Forhandlingar: Vol. 108, No. 3, pp. 287-289.
U-Pb zircon dating of granitoids from the northermost part of the Western Gneiss Region (Vestranden) has yielded the oldest ages so far recorded in central and southern Norway. The Geitfjell granite, a coarse-grained granite near Grong, central Norway yielded a U-Pb zircon age of 1828 −65 +88 Ma, whereas a Rb-Sr determination yielded an age of 1770±62 Ma. Its initial 86 Sr/ 87 Sr is 0.7094 and e Nd (1830 Ma) value is -0.04. Petrographically similar granites occur also in large areas in the northern half of the Vestranden region. The petrography, isotope chemistry, age and chemical composition of the Geitfjell granite closely resembles that of granites of the Revsund type, which intrude marine metasedimentary rocks in the Svecofennian Bothnian Basin in north-central Sweden
