Paleomagnetic directions and K/Ar dating of 0 to 1 Ma lava flows from La Guadeloupe Island (French West Indies): Implications for time‐averaged field models

Abstract

Abstract. Twenty-six lava flows spanning the last million years were sampled in La Guadeloupe, French West Indies. Because of the lack of continuous volcano-stratigraphic sections in La Guadeloupe, dating is necessary in order to describe the temporal evolution of the geomagnetic field in this time interval. New K/Ar ages ranging from 50 ka to I Ma have been obtained on andesires using the Cassignol-Gillot technique at the Universitd Paris Sud -Institut de Physique du Globe de Paris Orsay laboratory. Additional flows (with K/At ages obtained using the same dating technique) were also sampled for paleomagnetic investigations. More than 200 samples were analyzed using both alternating field AF and thermal stepwise demagnetization techniques. Duplicate samplings of two flows at three different sites demonstrate that within-How dispersion is negligible for the andesitic lava flows sampled in this study. Direct comparison with an earlier paleomagnetic study performed on the island indicates that, for the three investigated flows, modern demagnetization techniques yield much better defined paleomagnetic directions. The MatuyamaBrunhes transition was recorded in a three-flow section and is dated at 781 + 18 ka, in good agreement with other recent radiometric age determinations. The mean paleomagnetic pole calculated from the 23 normal polarity flows is indistinguishable t¾om geographic north, which implies that no significant persistent axial quadrupole term can be identified at this site for the last million years. This result contradicts earlier results and has important implications for models of the time-averaged field (TAF). An Occam algorithm was used to construct a TAF model from the global volcanic database from the last 5 Ma. Substitution of the mean direction calculated from the earlier study for the Lesser Antilles by our new mean value reduces the quadrupole term by more than 30•. This effect, which was produced by changing data from a single site, demonstrates that older paleomagnetic sites may need to be reinvestigated. Furthermore, it also highlights the limitations of TAF models that can be inferred from paleomagnetic databases in their present state.

DEM-based reconstruction of southern Basse-Terre volcanoes (Guadeloupe archipelago, FWI): Contribution to the Lesser Antilles Arc construction rates and magma production

“…However, this does not provide any new constraint about the onset of the GDVC (stage VI, Fig. 7B), the timing of which is still open to debate: a lone age of 445 ± 6 ka for a basal lava flow located south of GDS (Carlut et al, 2000) is the only available constraint, and can either be related to the last phases of STV or to the earliest construction of GDS-1. Nevertheless, our study shows that the GDS volcano was built through three main phases (GTS-1 to 3), probably erupted from the same vent.…”

“…Their occurrences during the last 650 ka have been associated with the on-land termination of the Marie-Galante rift system (Feuillet et al, 2002). Based on a detailed chronology, the Grande Découverte Volcanic Complex effusive volcanism appears as a succession of seven different constructional episodes since 400 ka, with spatially distinct eruptive centers (Blanc, 1983;Carlut et al, 2000;Samper et al, 2007Samper et al, , 2009 …”

“…South of the Septentrional Chain (SC) and since at least 1 Ma, volcanism migrated southeastward. The Axial Chain (AC) was active over about 0.6 Myr, from 1.02 to 0.435 Ma (Blanc, 1983;Carlut et al, 2000;Samper et al, 2007Samper et al, , 2009. The AC defines the northern limit of the Grande Découverte Volcanic Complex (GDVC), which occupies the southern one-third of Basse-Terre since at least 200 ka (Fig.…”

“…Based on the reconstructed primary volcanic landforms and a large amount of K-Ar ages (Blanc, 1983;Carlut et al, 2000;Samper et al, 2007Samper et al, , 2009, the edifices of southern Basse-Terre (Guadeloupe, Lesser Antilles Arc) are good candidates to apply a high-resolution temporal reconstruction of their successive building and destruction phases over the last million years. Although erosion has played a significant part in the current morphology of Basse-Terre, the successive composite volcanoes are spatially separated enough to create a model according to ten construction stages.…”

Retrospective analysis of uncertain eruption precursors at La Soufrière volcano, Guadeloupe, 1975–77: volcanic hazard assessment using a Bayesian Belief Network approach

“…Comprehensive descriptions of the geological setting and volcanic activity Boudon et al 2008;Samper et al 2009;Legendre et al 2010;Legendre 2012) are summarised briefly here. Past activity has ranged from effusive fissure eruptions, explosive magmatic and phreatic episodes, and major sector collapse events (Boudon et al 1987;Carlut et al 2000;Komorowski et al 2008a;Samper et al 2007) ( Table 1).…”