Polar wander analysis from paleomagnetic data

Utilizing marine magnetic anomalies and paleomagnetic pole positions, paleogeographic maps were constructed for three time intervals back to the Early Cretaceous. From the maps lithospheric plate motions were calculated and these global displacement fields were analyzed to determine best-fitting rigid rotations, which then could be ascribed to true polar wander. The values so obtained are no larger than a few degrees and are within the magnitude of the uncertainties involved

Ordovician paleogeography and the evolution of the lapetus ocean

Paleomagnetic data from northern Appalachian terranes identify several arcs within the lapetus ocean in the Early to Middle Ordovician, including a peri-Laurentian arc at ∼10°-20°S, a peri-Avalonian arc at ∼50°-60°S, and an intra-oceanic arc (called the Exploits arc) at ∼30°S. The peri-Avalonian and Exploits arcs are characterized by Arenigian to Llanvirnian Celtic fauna that are distinct from similarly aged Toquima-Table Head fauna of the Laurentian margin, and peri-Laurentian arc. The Precorclillera terrane of Argentina is also characterized by an increasing proportion of Celtic fauna from Arenig to Llanvirn time, which implies (1) that it was in reproductive communication with the peri-Avalonian and Exploits arcs, and (2) that it must have been separate from Laurenfia and the peri-Laurentian arc well before it collided with Gondwana. Collectively, the paleomagnetic and faunal data require an open Ordovician ocean adjacent to the Appalachian margin and argue against a Taconic-Famatinian collision between North and South America

A Plate-tectonic Speed Limit

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62630/1/363216a0.pd

Magnetostratigraphic dating of river terraces: Rapid and intermittent incision by the Yellow River of the northeastern margin of the Tibetan Plateau during the Quaternary

Up to 23 paleosols have been identified in loess sequences that overlie fluviatile sediments on seven terraces of Huang He (the Yellow River) and Daxia He in the Linxia Basin at the northeastern margin of the Tibetan Plateau. The magnetostratigraphic record in the oldest sequence appears to be fairly complete and spans the entire Quaternary. It includes evidence for the Jaramillo and Olduvai normal polarity subchrons within the Matuyama chron, as well as the Cobb Mountain and "stage 54" (formerly Gilsa) events. Age constraints within the Brunhes are provided by 14C and thermoluminescence/optical stimulated luminescence dating. The magnetostratigraphic chronology of the Quaternary sediments indicates that terraces were formed at about 1.66, 1.4, 1.1, 0.6, 0.12, 0.055, and 0.01 Ma. The terraces may represent climatically induced pauses in long-term tectonically induced incision by the rivers. On the basis of terrace heights and ages, incision rates were highest from 1.66 to 1.4 Ma (∼ 1 m/kyr), decreased from 1.4 to 0.12 Ma (∼ 0.1 m/kyr), and increased from 0.12 Ma to present (∼ 0.75 m/kyr). If river incision is attributed solely to uplift of the Tibetan Plateau, then this uplift appears to have been rapid as well as intermittent following the first evidence of the existence of Huang He in this area at about 1.75 Ma. However, the effects of uplift cannot be fully separated from incision caused by changes in climate. Copyright 1997 by the American Geophysical Union