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Abstract
Two granite-granodiorite-tonalite-trondhjemite (TTG) complexes intruded mafic-intermediate volcanic and volcaniclastic rocks at 1954-1940 Ma in the central part of the Knaften area, which lies in the northern part of the Palaeoproterozoic Bothnian Basin, in the central part of the Fennoscandian Shield, northern Sweden. The regional metamorphism was upper greenschist to amphibolite facies. The granitoid complexes are subdivided texturally into three types of intrusions. Contact relationships show that the most coarse-grained type is the oldest, followed by a medium-grained type and finally an aplitic-pegmatitic type intrusion. Felsic dykes that cut the granitoids form the youngest intrusive event. Myrmekitic/symplectitic textures or graphic intergrowths show that the later intrusive phases were more volatile-rich. The granitoids are high-level intrusions, and formed the root-zone of a volcano. Close to, but outside the granitoid complexes, compositionally similar felsic porphyry dykes occur. A package of reworked felsic tuffaceous rocks occurs in the northern part of the Knaften area and may constitute extrusive equivalents of the intrusions. These clastic rocks display primary structures such as cross bedding, which indicate deposition in shallow water. Geochemically, the Knaften intrusions are granites, granodiorites, tonalites and trondhjemites. The northern granitoids are more fractionated than the southern ones, and some felsic dykes are geochemically similar to the southern intrusions. The tuffaceous rocks are intermediate in composition between the felsic and more mafic intrusive phases. All Knaften felsic phases have similar trace element patterns and, their trace element chemistry is similar to other rocks from collisional settings in island arc terrains.
