Cambrian sedimentary basins of northern Gondwana as geodynamic markers of incipient opening of the Rheic Ocean
Abstrakt
Diachronous opening of the Rheic Ocean and separation of Avalonian-Cadomian terranes from Gondwana began with a change from an active to passive margin in the late Ediacaran to early Cambrian. During the Cambrian, extension within these terranes was recorded by magmatism and by the development of sedimentary basins.
However, the timing, style, and kinematics of this transformation still remain poorly understood and plate-scale models vary significantly. To address this issue, the Pribram-Jince basin in the Bohemian Massif was chosen as a case study since it preserves an excellent record of Cambrian rifting.
Here, after Cadomian subduction ceased at similar to 527 Ma, extension initiated and a thick pile of continental siliciclastics was deposited in the basin between similar to 515 Ma and similar to 499 Ma, interrupted by marine transgression at similar to 506-503 Ma. Our field, paleocurrent, and rock-magnetic data suggest that the source areas were located to the similar to ESE and to the similar to SW of the basin during the deposition of the lower and upper formations, respectively.
Sediment sources changed accordingly from distant metamorphic basement (Gondwana?) and Cadomian volcanic arcs and an accretionary wedge underlying the basin. This redirection marked a change in the tectonic evolution of the basin from orthogonal to dextral oblique extension that enlarged the basin into a pull-apart structure.
Integrating this depositional and tectonic record into a large-scale picture, we suggest that strike-slip movements along the former Avalonian-Cadomian belt controlled the diachronous opening of the Rheic Ocean. An inherited suture in the Avalonian ribbon terrane facilitated complete rifting and rift-drift transition while the Cadomian terranes remained attached to Gondwana.
The kinematics of this event remains controversial. Either it was opposite along the westerly (sinistral) and easterly (dextral) segments of the belt, which may be explained by interaction with an intervening spreading center, or it was the same dextral transtension.