Cambrian sedimentary dykes in the Proterozoic basement of the Västervik area (southeast Sweden): episodic formation inferred from macro- and microfabrics

Abstract

Fabrics of Cambrian sedimentary dykes formed in Proterozoic granites of the Västervik area (Southeast Sweden) evidence repeated opening/filling and mineralisation/cementation events under varying conditions. Diagnostic features include (1) wall-parallel boundaries between epiclastic fillings and (2) early formed dyke sediments that appear as lithoclasts in subsequently formed sedimentary fillings. The psammitic components mostly consist of wellrounded quartz grains related to a coastal environment and fragments from the granitic host rock. Platy calcitic fragments embedded in the epiclastic matrix originally formed as microveins within already-lithified dyke sediments and the adjacent host rock. Convex downward-pointing, internal sagging structures, together with the preferred orientation of compositional boundaries and long axes of grains/rock fragments parallel to the dyke walls, are interpreted as the result of suction-controlled flow of unconsolidated fillings during episodes of downward dyke growth. Pressure solution of quartz grains are evidence of extensional phases with dyke propagation that were interrupted by phases of horizontal compression normal to the dyke walls. The N-S and NE-SW striking sedimentary dykes formed by opening of a preexisting joint set during NW-SE oriented rifting during the Cambrian.

Multi-stage emplacement of the Götemar Pluton, SE Sweden: new evidence inferred from field observations and microfabric analysis, including cathodoluminescence microscopy

“…1c, 4c, d; see also Alm and Sundblad 2002;Röshoff and Cosgrove 2002;Friese et al 2010). The dominantly NW-SE-and NE-SW-striking clastic dikes are crosscut by brittle faults.…”

“…Late Sveconorwegian (1.1-0.9 Ga) and Early Cambrian extension in the working area is indicated by N-S-trending dolerite dikes (Wahlgren et al 2006), and two sets of Cambrian sandstone dikes (Röshoff and Cosgrove 2002;Friese et al 2010). Although the Götemar Granite has been quarried for dimension stone since the 1930s, comparatively little geological work has been carried out, in particular with respect to the emplacement process.…”

Mesoproterozoic Strike-Slip Faulting within the Åland Rapakivi Batholith, Southwestern Finland

“…Due to the stable continental setting of the Fennoscandian shield and consequent slow erosion rates, the current erosional level of the basement bedrock is considered to have been reached during Precambrian times (Kohonen and Rämö, 2005;Hall et al, 2021). This is supported by the occurrence of Cambrian-aged clastic dykes, for example within the Åland rapakivi (Bergman et al, 1982;Tynni, 1982) and Proterozoic granites of southeast Sweden (Friese et al, 2011). Sequences of Paleozoic sediments were later deposited on top of this erosional surface (Van Balen and Heeremans, 1998;Larson et al, 1999).…”

Geologische Exkursion Südost-Schweden

“…VS13.4b). Nach Gefügeuntersuchungen von (Friese et al 2010) wurden diese Gänge mehrphasig durch wiederholte Öffnung, Sedimentation (Füllungen durch Eintrag von der Oberfläche) und Zementation gebildet (s.a. EF "Sedimentgänge" (Kap. 3.1, S1)).…”