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doi:10.2204/iodp.proc.324.202.2013

Introduction

Shatsky Rise is an oceanic plateau that is a large igneous province (LIP) on the Pacific plate thought to be the product of a mantle-melting anomaly interacting with a triple junction. It was formed in Late Jurassic to Early Cretaceous time (Sager et al., 1999; Nakanishi et al., 1999). Three volcanic massifs, Tamu, Ori, and Shirshov, and the Papanin Ridge are the major structures of Shatsky Rise (Fig. F1). Based on magnetic lineations surrounding Shatsky Rise, the age and volume of the plateau decreases from the Tamu Massif to the Papanin Ridge (Sager et al., 1999).

Because Shatsky Rise volcanism was poorly understood, coring on Shatsky Rise during Expedition 324 gathered samples of igneous rocks to better understand its formation. Basaltic lava flows were recovered at four sites (U1346, U1347, U1349, and U1350), whereas volcaniclastic material was recovered at a fifth site (U1348) (Fig. F1) (Sager et al., 2011a, 2011b; see also “Expedition 324 summary” chapter [Expedition 324 Scientists, 2010]). Prior to Expedition 324, significant basaltic material had been cored only once, at Ocean Drilling Program Site 1213 on the south flank of Tamu Massif. At this site, basalt from three massive flows was recovered over a 47 m section (Fig. F2) (Koppers et al., 2010). At Site U1347, also on Tamu Massif, a basement section 159.9 m in length produced both pillow and massive flows, but at Site U1348, on the north flank of Tamu Massif, only volcaniclastics were recovered from ~120 m of core. Two holes at Ori Massif both yielded basalt flows: thin massive flows from 85.3 m of core at Site U1349 and 172.7 m of pillow and thin massive flows from Site U1350 (Fig. F2). Site U1346, on Shirshov Massif, yielded a 52.6 m section of pillow lavas with two small massive flows.

One of the goals of Expedition 324 was to understand the volcanism that built Shatsky Rise. Paleomagnetic measurements can aid in this understanding because the measured paleomagnetic inclinations give clues about the timing and paleolatitude of eruptions. In this study, the remanent magnetization of igneous rock samples was measured to determine changes in inclination with depth at each site. Changes in remanent inclination versus depth from an igneous section constrain the eruptive time span by the amount of observed geomagnetic field secular variation. The main focus of this report is measurements from basalt lava flows from Sites U1346, U1347, and U1350. A small number of samples from Site U1348 were measured to see if the hyaloclastite samples from that hole would produce reliable results (they did not). We did not measure samples from Site U1349 because another member of the shipboard party is working on that site. Paleomagnetic analysis for 120 basalt samples was done onboard the R/V JOIDES Resolution during Expedition 324. In our data tables, we combine those results with ours for completeness.

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