TERRANE WRECKS AND INCLINATION ANOMALIES

Paleomagnetic studies of cratonic regions are instrumental in constraining Earth’s paleogeographic evolution. Paleomagnetic data from the mobile belts that flank Precambrian cratons, however, are often difficult to interpret, as a number of such belts are characterized by inclinations that differ significantly from cratonic reference values. Orogens associated with ‘inclination anomalies’ include 1) the North American Cordillera, where shallow inclinations in Late Cretaceous rocks require the bulk of the belt to have been translated 2000 to 3000 km northward relative to cratonic North America, 2) the Carpathian – Balkan segment of the eastern Alpine system, which lies directly NNE of an Eastern Mediterranean region where inclinations in Upper Oligocene to Mid Miocene rocks require post-depositional northward translation between 500 and 1000 km, and 3) the Western Variscan belt, where shallow inclinations in passive margin strata require their deposition 40 degrees north of autochthonous Gondwana in the Devonian. These belts boast a second common feature: they are characterized by coupled oroclines. Oroclines, arcuate segments of orogenic belts, form by buckling of an originally linear orogen about a vertical axis of rotation. Coupled oroclines (terrane wrecks) result from buckling into two or more contiguous bends. In Alaska, the Cordilleran orogen is characterized by a Z-shaped oroclinal pair that accommodated 3000 km of orogen parallel shortening. The coupled Z-shaped oroclines of the Carpathian – Balkan belt similarly accommodated 1000 km of translation. Formation of the coupled S-shaped Iberian oroclines of the Variscan orogen required 1100 km of translation. Restoration of the Alaskan and Carpathian – Balkan oroclines fully accounts for the translations recorded by the Cordilleran and Eastern Mediterranean inclination anomalies, respectively. Restoration of the Iberian oroclines accounts for one third of the translation recorded by the Variscan inclination anomaly. Apparent inclination anomalies are resolvable when oroclinal buckling is considered, suggesting that significant post-orogenic margin-parallel translation is common. Fully resolving the Variscan inclination anomaly requires the recognition of additional oroclinal bends continuous with the Iberian coupled oroclines.