A Paleolatitude Calculator for Paleoclimate Studies
(A) Example of a plate circuit. The motion of India versus Eurasia cannot be directly constrained since these plates are bounded by a destructive plate boundary (trench). Relative motions between these plates can be reconstructed by restoring the opening history of the North Atlantic ocean between Eurasia and North America, the Central Atlantic Ocean between Africa and North America, and the Indian Ocean between India and Africa. With the relative positions of all these plates known through time, a paleomagnetic pole of one of these plates can be used to constrain all of these plates relative to the geodynamo. (B) schematic outline of plate and mantle motions and reference frames. Plates move relative to the mantle (plate tectonics), and plates and mantle together can undergo phases of motion relative to the liquid outer core (true polar wander). Both processes lead to motion of a rock record relative to the Earth’s spin axis, and hence both influence the angle of insolation that is relevant for paleoclimate study. Mantle reference frames A-C (see text for explanation of these frames) can only reconstruct plate motion relative to the mantle, but cannot reconstruct true polar wander. These frames are therefore used for analysis of geodynamics, but should not be used for paleoclimate studies. Instead, a paleomagnetic reference frame should be used. On geological timescales, the geodynamo coincides with the Earth’s spin axis. The orientation of the paleomagnetic field in a rock can be used to restore a rock record into its original paleolatitude relative to the spin axis.