Dynamics of Cambro–Ordovician rifting of the northern margin of Gondwana as revealed by the timing of subsidence and magmatism in rift-related basins

ABSTRACT

The Bohemian Massif of Central Europe is a Variscan collage of lithospheric fragments that formed at the northern margin of Gondwana during the late Neoproterozoic. A key geodynamic process that shaped this margin before it became involved in the Variscan orogen was the Cambro–Ordovician rifting that opened the Rheic Ocean. This rifting event has been studied extensively, yet a number of issues remain unresolved, among which are its geodynamic causes. New U–Pb zircon ages of orthogneisses from the mid-crustal Moldanubian unit, in combination with available information on magmatism and basin subsidence in the upper-crustal Teplá–Barrandian unit of the Bohemian Massif, are here used to reconstruct in detail the mechanism of the Cambro–Ordovician rifting. We argue that extension occurred in three phases defined by (1) protracted ~524–480 Ma intermediate to felsic plutonism (including the dated ~490–480 Ma orthogneisses), (2) basaltic submarine volcanism at ca. 470 Ma, and (3) rapid subsidence at ca. 458–452 Ma. This relative timing is interpreted to reflect stretching of the lower lithosphere before upper lithospheric rifting. In a broader context, these inferences are compatible with contrasting, rheologically controlled modes of northern Gondwana break-up during the early Ordovician, in which the westerly Avalonian-type terranes were rifted away from Gondwana, whereas the easterly Cadomian-type terranes formed a hyperextended Gondwanan shelf.

KEYWORDS:

• Avalonian–Cadomian belt
• Bohemian Massif
• hyperextension
• passive margin
• Rheic Ocean
• laser ablation ICP-MS
• U–Pb zircon geochronology
• rifting

Acknowledgments

We gratefully acknowledge constructive reviews by Gernold Zulauf and Armin Zeh as well as careful editorial handling by Robert J. Stern. Data are available as the Supplemental Material to this article.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00206814.2023.2172619

Additional information

Funding

This work was supported by Charles University [Center for Geosphere Dynamics (UNCE/SCI/006), Cooperatio Programme (Research Area GEOL)]; Czech Science Foundation [20-05011J]; Czech Operational Programme Research, Development and Education [CZ.02.2.69/0.0/0.0/16_015/0002362]; Grant Agency of Charles University [952220]; and Institute of Geology of the Czech Academy of Sciences [RVO 67985831].