Cambrian initiation of the Saxothuringian Ocean: new insights from the Kaczawa Complex, West Sudetes, Poland

Abstract

The Saxothuringian Ocean originated in the Early Palaeozoic from the fragmentation of northern Gondwana. In the Kaczawa basin, a part of the Saxothuringian Ocean, sedimentary-volcanogenic deposition began during the early Cambrian. The clastic material, predominantly composed of Neoproterozoic (c. 75 %) detrital zircons, originated from source areas dominated by 0.64–0.60 Ga and 0.58–0.54 Ga-aged felsic rocks, formed within a continental magmatic arc along the Gondwanan margin. This Ediacaran magmatism facilitated the recycling of older Gondwanan crust, which incorporated Cryogenian (0.75–0.73 Ga), Tonian-Stenian (1.2–0.9 Ga), Paleoproterozoic (2.2–1.8 Ga), and Archean (3.4–2.4 Ga) components. These inputs are reflected in εHf(t) values (–35.0 to +12.8) and TDM(Hf) ages (2.6–0.7 Ga), indicating a complex structure of the Gondwanan margin. The older continental crust of this margin gained juvenile additions from the mantle around 1.0 Ga and 0.72–0.53 Ga, supported by positive Hf zircon and whole rock Nd isotopic evidence. Though absent in the Kaczawa Complex today, such rocks were likely eroded alongside volcanic ash falls during the Cambrian. Detritus is interpreted to be transported from the Saharan Metacraton, the Trans-Saharan Belt, and the Anti-Atlas domain, shaped by the drainage systems of northern Gondwana. Contributions from the West African Craton cannot be ruled out, but the source regions exhibit greater complexity than this single craton. Mafic volcanism, ranging from WPB to OIB types with TDM(Nd) ages of 0.72–0.53 Ga began in the early Cambrian. This was accompanied by intermediate volcanic differentiates (TDM(Nd) 0.7–0.5 Ga) and felsic effusives (TDM(Hf, Nd) ages of 1.2–0.9 Ga), with volcanic activity peaking 500–490 Ma. This early evolution of the Kaczawa Complex reflects a continental rift-back arc basin system linked to oceanic subduction beneath the extended Gondwanan margin. This setting involved mantle wedge melting, differentiation and contamination by subducted sediments and materials from the upper plate.