Detailed tectonic evolution of the Reykjanes Ridge during the past 15 Ma using magellan, a new tool for modeling magnetic anomalies

Abstract

Chapter 1: Magellan: A new magnetic anomaly modeling program Critical to the theories of seafloor spreading and plate tectonics are seafloor ages and spreading rates determined from modeling marine magnetic anomalies. We have developed a new marine magnetic modeling program, Magellan, which retains the advantages of existing programs and overcomes many of their limitations. Magellan uses open-source and platform-independent code to model two dimensional magnetic fields produced by magnetic polarity intervals created by seafloor spreading. The block model can include seafloor bathymetry and variable magnetization strength and thickness of the source layer. Other variables include an arbitrary number of ridge jumps and spreading rates. The model also treats oblique spreading, variable profile azimuth, extinct spreading centers, and can apply a "contamination coefficient" to simulate broad polarity reversals sometimes observed at slow spreading rates. Suggestions and comments from users have and will contribute to further development of Magellan, allowing them to add new features and fixes which can be included in future releases of the software. Magellan and its manual can be downloaded at www.magellan-project.net. Chapter 2 Detailed Tectonic Evolution of the Reykjanes Ridge During the Past 15 Ma We present a new detailed tectonic model of the Reykjanes Ridge which examines the rift propagation hypothesis for the V-shaped ridges and its asymmetric lithospheric accretion. Four major southward rift propagations extend through our entire survey area and several additional small scale rift propagations are observed, including northward propagators. If plume pules only drive southward propagators, then two mechanically different kinds of propagators must exist. We find that there is a major difference in the crustal accretion asymmetry between the area immediately out the Iceland shelf and that farther south, both in rift propagation pattern and free air gravity lineations. Furthermore, we identify two small offset features coined ponsutransforms, from which rift propagation is both initiated and stopped. The pattern of the V-shaped ridges on the Reykjanes Ridge is not symmetric about the Reykjanes Ridge and the V-shaped ridges are not linear continuous features. Our rift propagation model produces excellent fits to magnetic data and provides a self-consistent model for the evolution of the Reykjanes Ridge during the past 15 Ma.