Cyril Hochard

Plate tectonics of the Alpine realm

Abstract New field data on the East Mediterranean domain suggest that this oceanic basin belonged to the larger Neotethyan oceanic system that opened in Permian times. A Greater Apulia domain existed in Mesozoic times, including the autochthonous units of Greece and SW Turkey. It also included a united Adria and Apulia microplate since Early Jurassic times. This key information implies that a new post-Variscan continental fit for the western Tethyan area is necessary, where the relationships between the Adriatic, Apulian and Iberian plates are defined with greater confidence. To construct a reliable palinspastic model of the Alpine realm, plate tectonic constraints must be taken into consideration in order to assess the magnitude of lateral displacements. For most of the plates and their different terranes, differential transport on the scale of thousands of kilometres can be demonstrated. This plate tectonic framework allows a better geodynamic scenario for the formation of the Alpine chain to be proposed, where the western and eastern transects have experienced contrasting geological evolutions. The eastern Alps–Carpathians domain evolved from the north-directed roll-back of the Maliac–Meliata slab and translation of the Meliata suture and Austroalpine domain into the Alpine domain. In the western Alps, the changing African plate boundary in space and time defined the interaction between the Iberian–Briançonnais plate and the Austroalpine accretionary wedge.

3D palaeogeographic reconstructions of the Phanerozoic versus sea-level and Sr-ratio variations

Abstract A full global geodynamical model over 600 million years (Ma) has been developed at the University of Lausanne during the past 20 years. We show herein how the 2D maps were converted into 3D (i.e., full hypsometry and bathymetry), using a heuristic-based approach. Although the synthetic topography may be viewed as relatively crude, it has the advantage of being applicable anywhere on the globe and at any geological time. The model allows estimating the sea-level changes throughout the Phanerozoic, with the possibility, for the first time, to flood accordingly continental areas. One of the most striking results is the good correlation with “measured” sea-level changes, implying that long-term variations are predominantly tectonically-driven. Volumes of mountain relief are also estimated through time and compared with strontium isotopic ratio (Sr-ratio), commonly thought to reflect mountain belt erosion. The tectonic impact upon the general Sr-ratio trend is shown herein for the first time, although such influence was long been inferred.

Geodynamic evolution of the Earth over the Phanerozoic: Plate tectonic activity and palaeoclimatic indicators

Abstract During the last decades, numerous local reconstructions based on field geology were developed at the University of Lausanne (UNIL). Team members of the UNIL participated in the elaboration of a 600 Ma to present global plate tectonic model deeply rooted in geological data, controlled by geometric and kinematic constraints and coherent with forces acting at plate boundaries. In this paper, we compare values derived from the tectonic model (ages of oceanic floor, production and subduction rates, tectonic activity) with a combination of chemical proxies (namely CO 2 , 87 Sr/ 86 Sr, glaciation evidence, and sea-level variations) known to be strongly influenced by tectonics. One of the outstanding results is the observation of an overall decreasing trend in the evolution of the global tectonic activity, mean oceanic ages and plate velocities over the whole Phanerozoic. We speculate that the decreasing trend reflects the global cooling of the Earth system. Additionally, the parallel between the tectonic activity and CO 2 together with the extension of glaciations confirms the generally accepted idea of a primary control of CO 2 on climate and highlights the link between plate tectonics and CO 2 in a time scale greater than 10 7 yr. Last, the wide variations observed in the reconstructed sea-floor production rates are in contradiction with the steady-state model hypothesized by some.