Mesozoic Paleomagnetism in Adria and Africa: Solving a Persistent Puzzle in Alpine Tectonics

University Of Florida, Gainesville FL

Investigators

Abstract

The proposal is addressing the role of Adria (the continental lithosphere encircled by the peri-Adriatic mountain belts) in the evolution of Alpine-Mediterranean tectonics, which has been a subject of debate for over 30 years. The "Adria problem" involves the idea that the Adrian microplate has behaved as a promontory of the African plate. This idea has since been supported by previously obtained paleomagnetic data from Adria, although the issue is complicated by the thrust sheet rotation of sedimentary cover on Adria and by the lack of adequate paleomagnetic data from Africa and Adria. A "cusp" or "hairpin" in the Jurassic and Cretaceous apparent polar wander path (APWP) for Adria (Channell, 1996) appears to fit with the recently published 'synthetic' African APWP (Besse and Courtillot, 2002). The two APWPs are, however, not sufficiently well defined to establish coherency or document offsets that would imply relative rotation between Adria and Africa. To resolve these issues, this study is providing paleomagnetic poles for the critical Late Jurassic-Early Creteceous interval from both Adria and Africa. Sampling sites on Adria (Italy) will allow the shape of the Late Jurassic-Early Cretaceous APWP to be resolved. Comparison of these APWPs with those from Gargano (believed to be unaffected by thrust sheet rotation) with allow the amount of thrust sheet rotation elsewhere on Adria to be ascertained. Our study is providing an Early Cretaceous APWP for NW Africa that can be precisely linked to a polarity stratigraphy and hence to the geologic timescale. These data will augment the very sparse African data for this time interval and provide a means of comparison with the data from Adria and with the 'synthetic' African APWP of Besse and Courtillot (2002). Intercalated basalts and hyaloclastites at the base of the pelagic section on Maio provide a means of linking the polarity stratigraphy to absolute argon-argon isotopic ages for much-needed timescale calibration. Our research will establish whether the stable autochthonous core of Adria has rotated relative to Africa since Early Mesozoic. The question is critical to Alpine tectonics, and hence to understanding the evolution of the Alpine belt. The project is integrated into the learning experience at the University of Florida, and students will participate in fieldwork laboratory acquisition of data, and analysis of results.