Preface

Abstract

In 2007 the AGU Joint Assembly moved to Mexico, taking place in the popular holiday resort of Acapulco. In this successful meeting, a large number of contributions belonging to many different fields of Earth Sciences was presented. Among 14 specific sessions devoted to Geomagnetism and Paleomagnetism, one of them, titled Magnetism of Volcanic Materials, was held as homage to Michel Prévot's scientific career in the fields of rock-magnetism, paleointensity and paleomagnetism. The idea to publish the present special issue of Earth, Planets and Space stems from that session, and it has resulted in a collection of 21 works. Many of these contributions had been previously presented in the session and others were included subsequently. It soon appeared that a special issue thought of as a homage to Michel Prévot's work should not be only restricted to volcanic materials senso stricto, allowing for the inclusion of rock-magnetic studies without limitation to any specific lithology. In the present special issue of Earth, Planets and Space 21 contributions dealing with paleomagnetic, rock-magnetic and paleointensity studies can be found. Paleomagnetic studies include investigations on Paleozoic volcanics in Argentina (Tomezzoli et al.) as well as on Tertiary volcanic rocks in Mexico (Sbarbori et al.), a study of paleosecular variation in New Zealand (Tanaka et al.) and an investigation on volcanic ashes and rocks in one of the sites of earliest human occupation in the Americas (Goguitchaichvili et al.). Many of the submitted papers deal with absolute paleointensity determinations, carried out on materials ranging in age from Archean to historic times: Biggin et al. discuss the geomagnetic field intensity in late-Archean and early-Proterozoic, Brandt et al. report new high quality determination on Early Cretaceous rocks from southern Brazil, Shcherbakova et al. present paleointensity results from Mesozoic baked contacts in Armenia, Perrin et al. study the paleointensity of Cenozoic-Mesozoic basalts in Egypt, Calvo-Rathert et al. present a paleointensity study on Mio-Pliocene volcanics from Spain and Goguitchaichvili et al. analyse the Gilbert-Gauss geomagnetic reversal on Georgian flows. In addition, also two archeointensity studies on Pre-Columbian potteries (Morales et al.) and Portuguese potteries (Hartmann et al.) and a methodological study about a Vibrating Thermo-Magnetometer (Poidras et al.), a useful device to optimize paleointensity determinations, are included in this issue. A large fraction of the contributions is devoted to rock-magnetic measurements: Muxworthy et al. discuss thermal fluctuation fields in basaltic rocks, Kosterov et al. present results of low-temperature magnetic properties of andesitic rocks and Alva-Valdivia et al. study rock-magnetic properties in an ore-deposit in Brazil. Several articles deal with magnetic properties of magnetite:Özdemir et al. study its susceptibility at low temperature, Smirnov the grain-size dependence of its low-temperature remanence, Carvallo et al. the formation of m...