Testing theOntong Java Nuihypothesis
SANO, TEJADA, NEAL, ET AL. (2020) IODP FULL PROPOSAL 967

Pacific oceanic plateaus and theOntong Java Nui hypothesis

Pacific oceanic plateaus and theOntong Java Nui hypothesis
110-95144-122~125
125-119126-118

118-86The Ontong Java Nui hypothesis is a proposal thatthe three oceanic plateaus (Ontong Java Plateau,
Manihiki Plateau and Hikurangi Plateau) formed
one plateau 120 my ago.

What we know
so far…
KR06-16
SOTW, SO198, HK07

DSDP Site 317

SO168, 193, 225

Southern margin of the OJP

750 mMalaita, Solomon Is.
121-125 Ma

Malaita Alkalic Suite
44 Ma(?)

Alnoites
34 Ma
YoungerSeries
44 Ma>2700 mSigana Alkalic Suite
90 Ma~34 and ~60 Ma alkalic rocks~34, ~60, & ~90 Ma OJP-like rocks
Tejada et al., 1996; Birkhold-Van Dyke et al., 1996;
Petterson et al., 1999; 2009

Tejada et al., 2002

Evidence forOntong Java Nui?
Ages overlap amongplateaus
Similar evolution fromtholeiitic to alkalic
volcanism

Evidence?

Distinct mantle source from MORBs

200-1200 km long OJP flowsIdentical composition andvolatile contents
Sites 1186A, 1185B

CO2 contents = shallow
eruption depths

Michael et al., Goldschmidt 2022

OJP

Melt fraction

MP+HPTrace element patterns
differ from MORBs
Indicate larger degrees
of melting required, ~30%

Implications

OJP
MP+HP

Combined OJP-MP-HP
requires larger volume ofmantle melted, 200-680
million cu. Km
Equivalent to a spherewith 760-1100 km diameter
Large eruption rates arerequired, >global MORB

Implications

Models for OJP-MP-HP origin
Not a single model
can account for allobservations

Potential problems?
Ontong Java crust >>Manihiki and Hikurangi crustal
thickness
Paleolatitudes differ
Majority of Manihiki
tholeiitic flows arecompositionally distinct fromOJP and HP

Ontong Java Nuiconfiguration?

Hochmuth et al., 2015??

Evidence?

MP and OJP-HP composition mismatch?

Ontong Java Nuisource?
LLSVP root for theOntong Java Nui?
(“JASON” = Pacific
Large Low-Shear
Velocity Province)

Torsvik et al., G-cubed 2019

IODP Full 967
proposal
Focus on:
True extent of the OJPor OJNOrigin and mechanismof formation
Magmatic/source
evolution
Environmental impacts

Primaryobjectives

Primaryobjectives

Primaryobjectives

Secondary objectives
Examine new models oforigin based on newgeophysical observations
and geochemical data
e.g., LLSVP source for theOntong Java Nui?

Secondary objectives
Investigate geodynamicevolutionEffect of chemical root on
the OJP?

Richardson et al., 2000

Suetsugu et al., 2019; Isse et al., 2021

Secondary objectives

New ages:OJP = 118 – 103 Ma(Davidson & Koppers, 2022)

Selli Level = 119.30 – 118.38 Ma(Leandro et al., 2022)

Paleoenvironmental impacts??

Summary(What do we need to test the OJN hypothesis?)
Obtain 100 m of basement rocks from all 5 sites in the eastern OJP and adjacent basinsObtain freshest as possible, stratigraphcally controlled samples
Improved dating technology for high-precision age controls
Volcanological study and paleodepth estimation
Geochemical fingerprinting
Paleomagnetic study for paleolocation

Borehole heat flow measurements
Obtain a complete sedimentary section at MagellanCapture the paleoenvironmental record before, during and after the OJN event
Biostratigraphy to monitor impact on marine lifeThanks for your attention!

Japan OJP Working Group