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Abstract
The Ale granite west of Luleå in northern Sweden forms an irregular, almost elliptical exposure covering an area of roughly 30 by 15 km in size. The central part of the intrusion consists of a homgeneous, quartz- and microcline-rich porphyritic granite, whereas its marginal parts are made up of a heterogeneous granite slightly less rich in quartz. Pegmatites and aplites are common in the surroundings. Zircons from two samples, one from the central part of the Ale granite and one from the border zone, were dated at 1802±3 (2σ) Ma and 1796±2 (2σ) Ma, respectively, by using the U-Pb method. An analysis of Sm-Nd istopes of these samples gave initital εNd values of −5.2 and −3.2, respectively, indicating a significant contribution of Archaean crustal material. Thirteen samples were analysed for major and trace elements. The isotopic and geochemical results suggest that the Ale granite was formed in a compressional environment 1.80 Ga ago, and that mature sediments were not an important source material.