OROCLINES: WHAT WE KNOW AND WHAT WE DON’T

In the tectonic community, accepted paleogeographic reconstructions are founded in the idea of continental lithospheric rigidity. Nevertheless, recent work has conclusively shown that continental lithosphere can accommodate large deformations, especially related with differential rotations around vertical axes. Present-day geodetic measurements and other, mainly paleomagnetic, evidences indicate that throughout earth’s history, continental lithosphere has undergone dramatic shape changes - identified as oroclines - whose origins and geodynamical implications are not fully understood. Probably the best-known orocline in the world is the Cantabrian Orocline that formed ca. 300 My ago. Studies of the Cantabrian Orocline indicate that oroclinal development is lithospheric in scale with profound implications for geodynamic processes in the lithospheric mantle - including its ultimate delamination and subsequent replacement. Similar processes can be imaged with seismic tomography in present-day developing oroclines – e.g., in the Vrancea region (East Carpathians) where mantle lithospheric delamination is presently occurring. The kinematic and dynamic lithospheric-scale evolution of many of the world’s oroclines remain enigmatic (e.g., Andes, Alaska, East Australia, and the peri-Mediterranean realms). It is clear that much work remains in order to better understand how, when and what the driving forces are that produce oroclines. This is particularly relevant when it comes to incorporating initial oroclinal geometries into paleogeographic reconstructions and to generating a better understanding of lithospheric mantle involvement in oroclinal development, orogeny and continental construction. Finally, our current understanding of oroclines should be incorporated into the Earth Science paradigm and should be used to modify our basic tectonic model of a rigid continental lithosphere.