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CITATION Neal, C.R., M.F. Coffin, and W.W. Sager OceTHE OFFICIALa MAGAZINEn ogOF THE OCEANOGRAPHYra SOCIETYphy CITATION Neal, C.R., M.F. Coffin, and W.W. Sager. 2019. Contributions of scientific ocean drilling to under- standing the emplacement of submarine large igneous provinces and their effects on the environ- ment. Oceanography 32(1):176–192, https://doi.org/10.5670/oceanog.2019.142. DOI https://doi.org/10.5670/oceanog.2019.142 PERMISSIONS Oceanography (ISSN 1042-8275) is published by The Oceanography Society, 1 Research Court, Suite 450, Rockville, MD 20850 USA. ©2019 The Oceanography Society, Inc. Permission is granted for individuals to read, download, copy, distribute, print, search, and link to the full texts of Oceanography articles. 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DOWNLOADED FROM HTTPS://TOS.ORG/OCEANOGRAPHY SPECIAL ISSUE ON SCIENTIFIC OCEAN DRILLING: LOOKING TO THE FUTURE Contributions of Scientific Ocean Drilling to Understanding the Emplacement of Submarine LARGE IGNEOUS PROVINCES and Their Effects on the Environment By Clive R. Neal, Millard F. Coffin, and William W. Sager Thin section production in progress, Integrated Ocean Drilling Program Expedition 324, Shatsky Rise. Photo credit: John Beck, IODP/TAMU 176 Oceanography | Vol.32, No.1 ABSTRACT. The Ontong Java Plateau (OJP), Shatsky Rise (SR), and Kerguelen Plateau/ Alaska, Greenland, or Western Europe Broken Ridge (KP/BR) represent three large igneous provinces (LIPs) located in oce- (Fitton and Goddard, 2004). However, anic settings. The basement lavas have been investigated through scientific ocean drill- OJP-like basalts also have been recov- ing and, in the case of the OJP, fieldwork on the emergent obducted portions of the pla- ered from the Nauru, East Mariana, and teau in the Solomon Islands. Such studies show that these three LIPs have very different Pigafetta basins that surround the OJP characteristics. For example, the KP/BR still has an active hotspot, whereas the OJP and (e.g., Saunders, 1986; Castillo et al., 1992, the SR do not. The OJP is remarkable in its compositional monotony across the plateau 1994), more than doubling the area of (the Kwaimbaita geochemical type), with minor compositional variation found at the these basalts to ~4 × 106 km2. Based on margins (the Kroenke, Singgalo, and Wairahito types). Shatsky Rise shows more com- a variety of geophysical data, the crustal positional variation and, like the OJP, has a dominant lava type (termed the “normal” thickness of the OJP is estimated to type) in the early stages (Tamu Massif), but subsequent eruptions at the Ori and be between 30 km and 43 km, with an Shirshov massifs comprise isotopically and trace element enriched lavas, likely reflect- average around 36 km (e.g., Furumoto ing a change in mantle source over time. The KP/BR has highly variable basement lava et al., 1970, 1976; Murauchi et al., 1973; compositions, ranging from lavas slightly enriched above that of normal mid-ocean Hussong et al., 1979; Miura et al., 1996; ridge basalt in the northern portion (close to the South East Indian Ridge) to more Richardson and Okal, 1996). Gladczenko enriched varieties to the south and on Broken Ridge, with a continental crust signature et al. (1997) estimated the volume of present in lavas from the southern and central KP/BR. The OJP and the KP/BR appear the OJP to be between 44.4 × 106 km3 to have formed through punctuated magmatic events, whereas the SR was formed by and 56.7 × 106 km3; the lower estimate one relatively long, drawn out event. The formation of oceanic LIPs has in many (but is assuming the plateau formed on pre- not all) cases been synchronous with oceanic anoxic events. This paper focuses on three existing older oceanic crust and the oceanic plateaus to emphasize the debate surrounding the environmental impact such higher assumes it formed on young crust LIPs may have had, and also highlights the contributions of scientific ocean drilling to at a spreading center. The OJP consists of our knowledge of oceanic LIP formation and evolution. This new knowledge allows two parts: the main, or High Plateau in planning for future oceanic LIP drilling. the west and north and the Eastern Salient to the east, the latter having been split INTRODUCTION and environmental impacts of three oce- during the opening of the Stewart Basin Volcanic plateaus on the ocean crust anic LIPs—the Ontong Java Plateau and (e.g., Neal et al., 1997; Figure 1a). The OJP represent the oceanic equivalents of the Shatsky Rise in the Pacific Ocean, lies generally between 2 km and 3 km continental flood basalts. Some of and the Kerguelen Plateau/Broken Ridge water depth, although the central High these formed in nascent ocean basins in the Indian Ocean. Plateau region rises to ~1,700 m below (e.g., Kerguelen Plateau/Broken Ridge in sea level. The OJP is isostatically com- the southern Indian Ocean), and the ear- Ontong Java Plateau pensated (e.g., Sandwell and McKenzie, liest outpourings contain the geochem- The Ontong Java Plateau (OJP) is situ- 1989), with much of the plateau surface ical signature of continental crust con- ated in the Southwest Pacific and cov- being relatively smooth, but the top of tamination (e.g., Storey et al., 1992; Neal ers an area of 1.86 × 106 km2 (Coffin and the plateau is punctuated by several large et al., 2002; Kinman et al., 2009). Others Eldholm, 1994; Table 1), about the size of seamounts, including Ontong Java atoll, formed within an oceanic setting and are free from the contamination of continen- tal crust, which allows an examination TABLE 1. Sizes of oceanic large igneous provinces. Area Volume of the deeper mantle source regions for Name References (106 km2) (106 km3) these voluminous eruptions (e.g., Shatsky Ontong Java Plateau 1.86 44 –57 1,2,3 Rise, Ontong Java Plateau, Hikurangi Manihiki Plateau 0.77 9–14 1,4 Plateau, and Manihiki Plateau in the Hikurangi Plateau 0.4–0.8 6.4–18.8 5 Pacific Ocean; Heydolph et al., 2014; Shatsky Rise 0.48 6.9 6 Fitton et al., 2004; Hoernle et al., 2010; Kerguelen Plateau/Broken Ridge 2.3 15–24 1 Timm et al., 2011). This paper outlines scientific ocean drilling contributions 1 = Coffin and Eldholm (1994) 2 = Neal et al. (1997) 3 = Gladczenko et al. (1997) 4 = Eldholm and Coffin (2000) to understanding the origins, evolution, 5 = Hoernle et al. (2010) 6 = J. Zhang et al. (2016) Oceanography | March 2019 177 Tauu atoll to the west, and Nukumanu scenario, the impact of the plume head Arc along its southern and southwest- atoll to the north (Figure 1a). The pla- on the rigid lithosphere should induce ern borders (Figure 1a), which pro- teau has been considered the product uplift (e.g., Griffiths et al., 1989; Hill, moted a change in subduction direc- of plume volcanism, formed through 1991), but the lack of subaerial volca- tion from the southwest to the northeast the pressure release melting of a large nism at the thickest part of the OJP High around 27–23 million years ago (Ma; packet of mantle material rising from the Plateau, coupled with a lack of any iden- Coleman and Kroenke, 1981; Cooper deep interior as a bulbous plume head tifiable plume tail evidence, has called the and Taylor, 1985; Petterson et al., 1997, with a long tail that extends back to the origin of the OJP via a surfacing plume 1999). Consequently, subaerial out- source region (e.g., Richards et al., 1989; head into question (e.g., Korenaga, 2005). crops of OJP basalt are present on the Campbell and Griffiths, 1990). In this The OJP collided with the Solomon islands of Malaita, Santa Isabel, Makira, a c b FIGURE 1. (a) Ontong Java Plateau with location names and previ- ous scientific ocean drilling sites. (b) Shatsky Rise with previous sci- entific ocean drilling sites identified (modified from Sano et al., 2012). (c) Locations of the Kerguelen Plateau/Broken Ridge, the Ninetyeast Ridge, and the Southeast Indian Ridge with scientific ocean drilling and dredge sites identified (modified from Neal et al., 2002). 178 Oceanography | Vol.32, No.1 and Ramos, which have been exam- 2005). However, Shatsky Rise is unique Plateau/Broken Ridge (Coffin et al., 1990; ined through a number of field seasons among the large western Pacific oceanic Schaming and Rotstein, 1990). Magma (e.g., Petterson et al., 1997, 1999, 2009; plateaus because it formed during a time output has varied significantly through Petterson, 2004; Tejada et al., 1996, 2002). of magnetic reversals (Late Jurassic and time, beginning with low volumes con- Recently, it has been argued that the OJP Early Cretaceous, ~145–125 Ma) so that temporaneous with or postdating con- may be much bigger than previously spreading ridge magnetic anomalies were tinental breakup in Early Cretaceous thought, as the Manihiki (~0.8 × 106 km2; recorded within the plateau, promising time, extending through at least one and Coffin and Eldholm, 1994. Table 1) and to allow the connection with mid-ocean possibly two peaks in Early and Late Hikurangi (~0.5 × 106 km2; Hoernle ridges to be examined (Sager, 2005).
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