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doi:10.2204/iodp.proc.324.201.2013

Introduction

Shatsky Rise was cored during Integrated Ocean Drilling Program Expedition 324 because it is a unique oceanic plateau, formed mainly during the Late Jurassic and Early Cretaceous at a rapidly spreading triple junction, with characteristics that could be attributed to either of two competing hypotheses for ocean plateau formation: plume head or plate boundary processes (Sager, 2005). Shatsky Rise is also a monster volcanic construct whose formation style is poorly understood. The goal of Expedition 324 was to core the igneous rocks of Shatsky Rise and the overlying sediments to examine the age, physical volcanology, geochemistry, and tectonic evolution of the rise as well as the sedimentation history.

Thermal and alternating field (AF) demagnetizations were carried out by the shipboard paleomagnetists on discrete samples in order to give an estimate of the inclination of the recorded geomagnetic field. According to the wide variation of coercive field and unblocking temperature spectra, it is clear that the nature and size of the magnetization carriers are very diverse, even within one hole or one lava flow (see the “Expedition 324 summary” chapter [Expedition 324 Scientists, 2010a]).

Approximately 60 samples from Holes U1347A, U1349A, and U1350A were collected for Thellier-Thellier paleointensity experiments. In order to select samples that would have the best chances for successful paleointensity determinations, the samples were chosen from lava flows for which the shipboard-based AF demagnetization spectra (magnetization versus AF demagnetizing field) showed an initial plateau at low demagnetizing field, which is usually characteristic of single-domain behavior. Also, the bulk susceptibility variations, measured after each heating step in the thermal demagnetizations, were selected to be as small as possible in order to avoid samples that would alter during the paleointensity experiments. We selected 14 samples from Hole U1347A, all from the same basaltic massive flow (stratigraphic Unit XV in the “Site U1347” chapter [Expedition 324 Scientists, 2010b); 22 samples from Hole U1349A, from 5 different subunits of the same stratigraphic unit; and 24 samples from Hole U1350A, 2 from stratigraphic Subunit IIc (stack of thin inflation units) and 22 from Unit IV (stack of ~0.1–0.5 m thick plagioclase-phyric pillow lavas) (see the “Site U1350” chapter [Expedition 324 Scientists, 2010c). We tried to take two or three samples per pillow lava unit or thin inflation unit whenever possible. No samples were collected from Hole U1346A because the AF demagnetization behavior described above could not be identified in any lava flow in this hole.

In order to characterize the carriers of the magnetization, several rock magnetic measurements were carried out. The paleointensity experiments are described elsewhere (Carvallo et al., in press). In short, 9 samples out of 60, all from Hole U1349A, gave reliable paleointensity estimates. Samples from Hole U1347A failed because of concave-curved Arai plots, and samples from Hole U1350A failed because of important alteration that took place during the repeated heating, combined with very low Curie temperatures. The goal of this data report is to document the magnetic measurements done on these samples, including scanning electron microscope (SEM) observations, and it contains all measured data; a subset of these data is included in Carvallo et al. (in press).