11:15 AM - 11:30 AM
[SVC34-08] Subsurface structures, ages, and magma types of Ontong Java Plateau revealed by recent research cruises
★Invited Papers
Keywords:Ontong Java Plateau, Large Igneous Province, Oceanic Plateau, MOHO, stagnant slab, magma
The Ontong Java Plateau (OJP) is the largest oceanic plateau and is probably the most voluminous igneous edifice on Earth. Despite its importance, the size, volume, and formation mechanism of the OJP are not yet well constrained. In order to clarify subsurface structure and magma origin of the OJP, several research cruises have been conducted on and around the OJP (MR14-06, KR16-04, KH-17-J01, KM1609) during last decade. I will introduce recent research results related to the research cruises.
Utilizing 2-year-long broadband ocean bottom seismometer data acquired on surveys MR-14-06 and KH-17-J01, geophysical researches have observed specific crust and mantle structures beneath the OJP as follows. (1) The average S velocity in the entire mantle beneath the OJP is estimated to be low because travel time residuals of multiple ScS waves are positive (Suetsugu et al., 2019, Earth, Planets and Space). (2) Depths of the MOHO, seismic velocity discontinuities, beneath central OJP and near eastern edge are estimated to be 30-40 km and 20 km, respectively (Tonegawa et al., 2019, Journal of Geophysical Research). (3) The lithosphere-asthenosphere boundary beneath the OJP is ~40 km deeper than ambient mantle, suggesting possible presence of dehydrated residual mantle (Isse et al., 2021, Communications Earth & Environment). (4) Remnant dipping Pacific slab was detected beneath the center of the OJP at a depth of 200-300 km and stagnant slab was observed in the mantle transition zone beneath and around the OJP (Obayashi et al., 2021, Scientific Reports).
Basaltic rocks recovered from dredge hauls during KR16-04 and KH-17-J01 were used to geochemical and age dating studies as follows (Tejada et al., submitted; Sano et al., in preparation). (1) Kwaimbaita-type basalt, the dominant magma type of main plateau areas, is also present on eastern and southern edge areas. (2) New 40Ar-39Ar plateau age data of basaltic rocks from the eastern area, Eastern Salient, are distinctly younger than previous reports. (3) Basalts with low-Ti compositions on the Eastern Salient, which are found for the first time on the OJP, are geochemically similar to those from Manihiki Plateau, east of the OJP, suggesting that magma genesis of the OJP and Manihiki Plateau were closely related.
Other than the above, I will present the latest research results related to the OJP.
Utilizing 2-year-long broadband ocean bottom seismometer data acquired on surveys MR-14-06 and KH-17-J01, geophysical researches have observed specific crust and mantle structures beneath the OJP as follows. (1) The average S velocity in the entire mantle beneath the OJP is estimated to be low because travel time residuals of multiple ScS waves are positive (Suetsugu et al., 2019, Earth, Planets and Space). (2) Depths of the MOHO, seismic velocity discontinuities, beneath central OJP and near eastern edge are estimated to be 30-40 km and 20 km, respectively (Tonegawa et al., 2019, Journal of Geophysical Research). (3) The lithosphere-asthenosphere boundary beneath the OJP is ~40 km deeper than ambient mantle, suggesting possible presence of dehydrated residual mantle (Isse et al., 2021, Communications Earth & Environment). (4) Remnant dipping Pacific slab was detected beneath the center of the OJP at a depth of 200-300 km and stagnant slab was observed in the mantle transition zone beneath and around the OJP (Obayashi et al., 2021, Scientific Reports).
Basaltic rocks recovered from dredge hauls during KR16-04 and KH-17-J01 were used to geochemical and age dating studies as follows (Tejada et al., submitted; Sano et al., in preparation). (1) Kwaimbaita-type basalt, the dominant magma type of main plateau areas, is also present on eastern and southern edge areas. (2) New 40Ar-39Ar plateau age data of basaltic rocks from the eastern area, Eastern Salient, are distinctly younger than previous reports. (3) Basalts with low-Ti compositions on the Eastern Salient, which are found for the first time on the OJP, are geochemically similar to those from Manihiki Plateau, east of the OJP, suggesting that magma genesis of the OJP and Manihiki Plateau were closely related.
Other than the above, I will present the latest research results related to the OJP.