IODP Expedition 330: Drilling the Louisville Seamount Trail in the SW Pacific

Abstract

Deep-Earth convection can be understood by studying hotspot volcanoes that form where mantle plumes rise up and intersect the lithosphere, the Earth's rigid outer layer. Hotspots characteristically leave age-progressive trails of volcanoes and seamounts on top of oceanic lithosphere, which in turn allow us to decipher the motion of these plates relative to "fixed" deep-mantle plumes, and their (isotope) geochemistry provides insights into the long-term evolution of mantle source regions. However, it is strongly suggested that the Hawaiian mantle plume moved ~15° south between 80 and 50 million years ago. This raises a fundamental question about other hotspot systems in the Pacific, whether or not their mantle plumes experienced a similar amount and direction of motion. Integrated Ocean Drilling Program (IODP) Expedition 330 to the Louisville Seamounts showed that the Louisville hotspot in the South Pacific behaved in a different manner, as its mantle plume remained more or less fixed around 48°S latitude during that same time period. Our findings demonstrate that the Pacific hotspots move independently and that their trajectories may be controlled by differences in subduction zone geometry. Additionally, shipboard geochemistry data shows that, in contrast to Hawaiian volcanoes, the construction of the Louisville Seamounts doesn’t involve a shield-building phase dominated by tholeiitic lavas, and trace elements confirm the rather homogenous nature of the Louisville mantle source. Both observations set Louisville apart from the Hawaiian-Emperor seamount trail, whereby the latter has been erupting abundant tholeiites (characteristically up to 95% in volume) and which exhibit a large variability in (isotope) geochemistry and their mantle source components. <br><br> doi:<a href="http://dx.doi.org/10.2204/iodp.sd.15.02.2013" target="_blank">10.2204/iodp.sd.15.02.2013</a>

Re‐Os isotope and platinum group elements of a FOcal ZOne mantle source, Louisville Seamounts Chain, Pacific ocean

“…Interestingly, both Canopus and Rigil seamounts data fall along the 72 Ma isochron line, giving an apparent age of 72 ± 2.8 Ma and an initial 187 Os/ 188 Os value of 0.1278 ± 0.0004, suggesting that these two seamounts may have been formed within a short‐time interval (Figure a). Indeed, the Canopus and Rigil seamounts are believed to have been formed within only a few million years of each other (Site U1372, 74.2 ± 0.5 Ma; Site U1374, 70.7 ± 0.6 Ma) [ Koppers et al ., a, ]. In contrast, the Burton seamount data plot along a 65 Ma isochron, consistent with its younger 40 Ar‐ 39 Ar age [ Koppers et al ., ], except for that of sample U1376‐21R‐5, 0–16 cm (Figure a).…”

“… (a) Comparison of LSC Re‐Os data with 80, 72, and 65 Ma isochrons, showing the limited scatter that can be attributed to alteration effects. The isochrons are inferred from available 40 Ar‐ 39 Ar dates [ Koppers et al ., , a, b]. The dashed line is the apparent 72 Ma Re‐Os isochron for Canopus and Rigil seamounts whole rock data with age and initial 187 Os/ 188 Os ratios indicated.…”

“…Excluding this sample with possible Re gain effect, plotting to the right of the 65 Ma isochron, the whole rock and olivine data for Burton seamount define an isochron age of 64.9 ± 3.2 Ma and an initial 187 Os/ 188 Os value of 0.1272 ± 0.0008 (Figure b). These Re‐Os ages are very close to the 40 Ar‐ 39 Ar data for Site U1376 (64.1 ± 0.5 Ma) [ Koppers et al ., a, ]. The agreement between Re‐Os ages and available 40 Ar‐ 39 Ar data further indicates that the Re‐Os data for these samples are not significantly disturbed by alteration or contamination.…”

“…Recent IODP Expedition 330 recovered in situ volcanic rocks from four of the five drilled seamounts that range in age from 50 to 74 Ma (Figure ): Canopus (Site U1372, 74.2 ± 0.5 Ma); Rigil (Sites U1373, 69.5±0.4 Ma and U1374, 70.7±0.6 Ma); Burton (Site U1376, 64.1 ± 0.5 Ma); Achernar (Site U1375, 58.5 Ma); and Hadar (Site U1377, 50 ± 0.3 Ma) [ Expedition 330 Scientists , ; Koppers et al ., a, ]. Before this expedition, information on the composition and geochemistry, as well as the age of the LSC was exclusively based on data obtained from dredged volcanic rocks [ Cheng et al ., ; Hawkins et al ., ; Lonsdale , ; Watts et al ., ; Beier et al ., ; Koppers et al ., ].…”

Deep plume origin of the Louisville hotspot: Noble gas evidence

“…The basement rocks include lava flows, pillow basalts, intrusive lavas, scoriaceous and blocky breccias, and peperites. The variety of rock types drilled from the seamounts documents the change in eruption environment from submarine to subaerial [ Expedition 330 Scientists , ; Koppers et al ., ]. Although the drilled rocks were variously altered, we occasionally found fresh basalts in which olivine phenocrysts and submarine glasses were well preserved.…”