National Museum of Nature and Science
Tokyo Institute of Technology
Did a coalition of giant volcanoes occur in the Pacific Ocean?
New evidence for the Ontong Java Nui hypothesis
1. Key Points
- Geological survey and sampling conducted in the Eastern Salient of the Ontong Java Plateau, where the proposed Ontong Java Nui super plateau fragments (Ontong Java Plateau, Manihiki Plateau, and Hikurangi Plateau) were conjoined, provide new geochemical and age data supporting the Ontong Java Nui hypothesis.
- Volcanic rocks having compositions previously found only on Manihiki Plateau were recovered from Ontong Java Plateau for the first time and new ~96-116 Ma and 67-68 Ma eruption ages bridge the temporal gap between Ontong Java Plateau and Hikurangi Plateau.
- The results indicate that OJP, MP, and HP, have a common source and that variation in composition may be explained by a chemically zoned mantle from the seismically anomalous region at the core-mantle boundary, with entrained lower mantle and recycled materials.
JAMSTEC researchers, Maria Luisa Tejada, Takeshi Hanyu, Takashi Miyazaki, Qing Chang, and Bogdan Vaglarov of the Research Institute for Marine Geodynamics and Kenji Shimizu of the Kochi Institute for Core Sample Research, in collaboration with scientists Takashi Sano and Kenichiro Tani from the National Museum of Nature and Science, Masao Nakanishi and Shoka Shimizu of Chiba University, Akira Ishikawa of Tokyo Institute of Technology, and Anthony Koppers of Oregon State University, USA, have discovered new links between the inferred fragments of a super oceanic volcano called the Ontong Java Nui, in the Pacific Ocean. These findings present a breakthrough for the Ontong Java Nui hypothesis.
The Ontong Java Nui hypothesis, which puts together three largest oceanic plateaus in the Pacific, the Ontong Java Plateau (OJP), Manihiki Plateau (MP), and Hikurangi Plateau (HP) as one super volcanic edifice 120 million years ago was first proposed in 2006. However, the hypothesis has been debated given the few evidence and many unresolved issues. For example, the three plateaus differ in crustal thickness, there is a gap in the composition between MP basalts and OJP basalts, and the main stage emplacement of both OJP and MP are apparently older than HP.
In 2016, JAMSTEC researchers and collaborators sailed to the OJP’s eastern margin to conduct geological surveys and collect samples of volcanic rocks using the research vessel R/V Kairei. This region is where the proponents of the Ontong Java Nui hypothesis suggest the three oceanic plateaus were once joined together. Thus, we could expect to find volcanic rocks of similar age and composition among the three plateaus.
The research team obtained geochemical and 40Ar-39Ar age data (*1) for the dredged rocks and found MP-like basalts on OJP for the first time. The ~96-116 Ma and 67-68 Ma 40Ar-39Ar eruption ages also suggest that some of the volcanic rocks erupted during the main formation period of the three plateaus. These data bridge both the compositional gap between OJP and MP and the temporal gap between OJP and HP, which are previously contested. The results provide new evidence for the Ontong Java Nui hypothesis, allowing for a better understanding of the connection among OJP, MP, and HP. The Sr, Nd, Pb, and Hf isotopic data confirm the contribution of four mantle components in the origin of these plateaus, possibly incorporated within an upwelling mantle plume (*2) that is deeply rooted in the seismically anomalous lower mantle region known as the Pacific Large Low-Shear-wave Velocity Province or LLSVP (*3) (Figure 1). The same mantle components also feed present-day South Pacific hotspot volcanism, suggesting that the LLSVP is a long-lived feature that was active for at least 120 million years ago.
This research was supported by the Grant-in-Aid for Scientific Research (6302010 and 18H03746).
These findings will be published in Scientific Reports on May 25 (Japan time).
- Research Institute for Marine Geodynamics, Japan Agency for Marine-Earth Science and Technology
- Department of Geology and Paleontology, National Museum of Nature and Science
- College of Earth, Ocean and Atmospheric Sciences, Oregon State University
- Graduate School of Science, Chiba University
- Department of Earth and Planetary Sciences, Tokyo Institute of Technology
- Graduate School of Science and Engineering, Chiba University
- Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology
Figure 1. Overview of the present study. A hypothesis that currently separated oceanic plateaus, Ontong Java, Manihiki, and Hikurangi, formed a single super oceanic plateau 120 million years (m.y.) ago has been tested by new geochemical and age data using submarine volcanic rocks sampled from the Eastern Salient of the Ontong Java Plateau during R/V Kairei cruise KR16-04.
The Pacific Ocean contains the greatest number and largest submarine volcanic edifices, which are known as oceanic plateaus (Figure 2). Despite their size, oceanic plateaus are little studied due to their remote locations and being at water depths of at least 2000 mbsl. The three largest are Ontong Java Plateau (OJP), Manihiki Plateau (MP), and Hikurangi Plateau (HP), which have attracted attention by researchers due to their apparent simultaneous formation 120 million years ago. Having an area of 1.86 million sq. km and a range of crustal thickness between 30-43 km, the Ontong Java Plateau is the world’s largest oceanic plateau, with an estimated volume of up to 57 million cu. km.
The Ontong Java Nui (OJN) hypothesis postulates that a super plateau existed ~120 million (m.y.) ago, with the Ontong Java Plateau as the main component together with Manihiki and Hikurangi plateaus that are now located thousands of kilometers away due to the movement of oceanic plates that carried them apart from each other since then (Figure 1). If the hypothesis is correct, the world’s largest massive volcanism that formed the OJP may have reached 90 million cu. km to form the OJN super plateau, larger in volume by 60%! Such massive volcanism is unique on Earth but common in other neighboring planets, Mars and Venus, and the moon. The origin of this massive volcanism is debated but must have involved mantle volumes much larger than the shallow mantle currently tapped by present-day oceanic ridge magmatism. A possible origin from the seismologically detected large low shear-wave velocity provinces (LLSVPs) at the core-mantle boundary region is proposed.
Proponents of the hypothesis compose the OJN from the three plateaus together in different jigsaw-like configuration (Figure 2). However, whether such a jigsaw-like reconfiguration occurred is still debated because there are parts of the puzzle that do not match well. The OJP, MP, and HP formed during the Cretaceous Magnetic Quiet Period (CMQP) when the Earth’s magnetic pole did not flip from N-oriented (normal) to S-oriented (reverse). Such flips in orientation occurred before and after the CMQP, leaving magnetically detected “lines” on the oceanic plate, called magnetic lineations. The formation of these plateaus during CMQP means there are no magnetic lineations to guide researchers in bringing the three plateaus back to their exact original location 120 m. y. ago. Thus, available paleo-reconstructions evolved from one showing Ontong Java and Manihiki plateaus forming separately to another where both plateaus, together with Hikurangi Plateau, form a single super plateau.
Several other attributes of the three plateaus do not match well. For example, 1) they have varying crustal thicknesses; 2) 40Ar-39Ar age range for the HP (96-118 Ma) is younger than both OJP and MP, for which previously dated samples indicate formation prior to 120 Ma; 3) available geochemical data from MP basalts show two types, one of which are unlike any found so far on OJP and HP. If evidence to resolve one or more of these gaps and discrepancies are found, then the OJN may have indeed existed, and this knowledge will lead to better understanding of such massive volcanic event and how it shaped the evolution of our planet Earth until today.
Figure 2. a) Present-day location of the Ontong Java Plateau (OJP), Manihiki Plateau (MP), and Hikurangi Plateau (HP) in the Pacific Ocean. Crustal thicknesses of OJP, MP, and HP are indicated by red numbers. Also shown is the Louisville hotspot (orange star) believed to be the plume mantle source of the OJP. b) and c) Two model projections back to their location 120 million years ago as separate volcanic platforms after Larson (1991) and as one super plateau after Taylor (2006), which is later known as the Ontong Java Nui after Chandler et al. (2012). Also labeled are surrounding basins and rises: PB= Pigafetta Basin; EMB= East Mariana Basin; NB= Nauru Basin; MR= Magellan Rise.
Bathymetric surveys conducted during the KR16-04 cruise of R/V Kairei mapped several elongated ridges protruding from the northern margin of the OJP’s Eastern Salient (Figure 3).
Figure 3. a) Map of the OJP and inset showing the KR16-04 survey area just north of Ocean Drilling Program Site 1184 (red star) on the Eastern Salient. Blue dots represent previous ocean drilling sites. b) Detailed bathymetry and KR16-04 dredge locations; c) and d) Bathymetry profiles along the cross-section lines (yellow dashed lines in b), showing the dredged depth ranges and the 40Ar-39Ar age data.
Topographic analysis revealed that these ridges may have been eroded platforms on top of which younger volcanism formed seamounts. Dredging from two of these eroded platforms recovered samples that are indeed older than initially expected and yielded ages of 96 and 116 Ma, which were determined by 40Ar-39Ar dating technique (Figure 4). These ages are contemporaneous with the timing of the main plateau building episode on Hikurangi Plateau (96-118 Ma) and the younger phase of volcanism on Manihiki Plateau (MP). Surprisingly, only 3 out of 21 recovered samples that were suitable for geochemical analysis showed compositions expected for post-plateau seamounts. Instead, most of the samples (18 out of 21) had geochemical compositions that are like the so-called “low-Ti” basalts that until now were exclusively found on Manihiki Plateau and are unlike any samples recovered on the OJP so far (Figure 5). The results show that MP-like basalts erupted on OJP at the same time when HP was also forming where the three plateaus were supposed to be still connected with or very close to each other (Figure 6).
Figure 4. Published 40Ar-39Ar age data for submarine Ontong Java Plateau (OJP), Manihiki Plateau (MP), and Hikurangi Plateau (HP) basement basalts. The blue line indicates the average age of 123 million years (Ma) for OJP basalts, with another minor cluster at ~90 Ma from one site. The new data from samples dredged during KR16-04 cruise on the OJP’s Eastern Salient overlap with the 96-118 Ma range for Hikurangi plateau basement basalts and with the age of younger Manihiki plateau basalts, suggesting that volcanism occurred on all three plateaus at the same time around 116-118 Ma (inset).
Previously, the gap in geochemical composition made it difficult to say that the Ontong Java and Manihiki plateaus have the same mantle source. With these results it is now possible to say that the same mantle source gave rise to all the three plateaus, as part of a single super plateau called the Ontong Java Nui (OJN). Combined geochemical data from the three plateaus indicate a four-component mantle source: 1) primitive mantle, possibly from the Pacific LLSVP; 2) ancient continental materials; 3) prevalent lower mantle material surrounding the LLSVP; and 4) ancient, altered oceanic crust materials. All four of these components are also expressed in Polynesian ocean island basalt compositions.
Figure 5. Available Pb isotope data for Ontong Java Plateau, Manihiki Plateau, Hikurangi Plateau. Note the limited range of OJP data (gray fields) with 206Pb/204Pb values <18.7. Prior to KR16-04 cruise, high-206Pb/204Pb plateau basalts were only recovered from Manihiki Plateau. Such compositional types are now also recovered from the eastern margin of the Ontong Java Plateau. The KR16-04 data also overlap with the composition of the Louisville seamounts basalts, consistent with the Louisville hotspot as the OJN plume mantle source. The data indicate four mantle components are involved in the origin of OJN basalts: primitive mantle, prevalent lower mantle, and recycled ancient continental and oceanic lithospheric materials. Points marked D3-12 and D4-01 are affected by alteration and are not considered magmatic values. OJP= Ontong Java Plateau; MP= Manihiki Plateau; HP= Hikurangi Plateau; Kr-Kw= Kroenke and Kwaimbaita-type composition; Sg= Singgalo-type composition.
These data indicate that OJN may have originated from the same mantle source underlying the present location of Polynesian hotspots, which are rooted from the seismologically delineated Pacific LLSVP. The LLSVP could represent plastic lower mantle material heated by the core and rise adiabatically, driven by the subduction of old, cold, dense oceanic crust thrusted deep into the core-mantle boundary. Paleoreconstructions indicate that when projected down to the core-mantle boundary region, OJN straddled the edge of the LLSVP with the OJP at the inner side and the MP at the outer side (Figure 6). This scenario may explain the isotopic variations within the OJN source: an upwelling thermochemically zoned plume head dominated by primitive mantle component rises from the inner side of the LLSVP, entraining ambient prevalent lower mantle at the margins, with both containing recycled continental and oceanic lithosphere materials. It is also consistent with suggestions that ambient lower mantle at the margins of the LLSVP is entrained in the upwelling mantle plumes.
Figure 6. Paleoreconstruction of Ontong Java Nui straddling the edge of the Pacific Large Low Shear-wave Velocity Province (LLSVP): a) inferred formation of the OJN with Ontong Java Plateau tapping more of the primitive mantle material within the LLSVP and Manihiki Plateau incorporating more of the prevalent lower mantle material at the edge of the LLSVP. Recycled oceanic and continental materials were also entrained in the upwelling mantle plume.
5. Future outlook
The massive volcanism represented by the Ontong Java Nui and its components Ontong Java, Manihiki, and Hikurangi plateaus, may have altered not only the Earth’s evolution but also the atmosphere, biosphere, and hydrosphere since then. Many studies have linked this massive volcanism to 1) global marine anoxia known as the oceanic anoxic event 1a (OAE-1a); 2) ocean acidification, which affected the evolution of marine microorganisms, such as nannoconids; and 3) the so-called “Cretaceous Greenhouse Climate”, when the Earth’s average temperature were roughly 5-10℃ and sea levels were 50-100 meters higher than today.
There are still uncertainties with the original paleo-latitudes of the three plateaus, making the connection among them equivocal and the configuration of the Ontong Java Nui subject to change depending on future results. Thus, the researchers are keen on further testing the Ontong Java Nui hypothesis by ocean drilling. Ocean drilling is the only way to ascertain the stratigraphic correlation of basalts with similar compositions across the three plateaus and to obtain fresh samples for dating and geochemical analyses. Improved 40Ar-39Ar dating techniques applied on appropriate fresh samples can better constrain the eruption ages and have a better handle on the eruption rates. The eruption rates can vary depending on the duration of emplacement of the three plateaus and whether multiple phases of eruption occurred to form such huge volcanic platforms. Only then can we better understand the origin of these super massive eruptions on Earth and, by extension, on the other planets. Understanding this unique period of Earth’s evolution when massive outpouring of magmas ascended from deep down in the mantle is essential in understanding the present warming trends and its impact on life and environment.
- For this study
- Maria Luisa Tejada, Senior Researcher, Research Institute for Marine Geodynamics (IMG) Volcanoes and Earth’s Interior Research Center (VERC) Solid Earth Geochemistry Research Group, JAMSTEC
Chief Curator, Division of Mineral Sciences, Department of Geology and Paleontology, National Museum of Nature and Science
- For press release
- Press Office, Marine Science and Technology Strategy Department, JAMSTEC
Research Promotion and Management Division, National Museum of Nature and Science
Public Relations Division, Tokyo Institute of Technology