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

• Published in: International geology review Vol. 65; no. 19; pp. 3004 - 3027
• Main Authors: Žák, Jiří, Sláma, Jiří, Syahputra, Reza, Nance, R. Damian
• Format: Journal Article
• Language: English
• Published: Philadelphia Taylor & Francis 28.10.2023; Taylor & Francis Ltd
• Subjects: Avalonian-Cadomian belt; Bohemian Massif; Gondwana; hyperextension; laser ablation ICP-MS; Lithosphere; Magma; Massifs; Ordovician; Orogeny; passive margin; Rheic Ocean; Rheological properties; Rifting; Subsidence; U-Pb zircon geochronology; Volcanic activity; Volcanism; Zircon; Gondwana
• ISSN: 0020-6814; 1938-2839
• DOI: 10.1080/00206814.2023.2172619

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.