Using D/V Meng Xiang to drill intact magmatic crust in the Pacific to reveal the petrological nature of the oceanic Moho

Abstract

I have recently published ‘‘Do we really need to drill through the intact ocean crust?” in this journal (Geoscience Frontiors, 2025, Volume 16, 101954), which is a theme talk at the ‘‘ International Workshop on Fulfilling the Quest of Drilling Through the Ocean Crust Using D/V Meng Xiang (‘梦想号’)” held in Guangzhou (November 24 ‒ 27, 2024), and is an objective account of petrological properties of the ocea- nic Moho. The global geoscience community universally acknowledges that Moho is a seismic disconti- nuity representing the boundary between the crust ( V_P ≤ 7 km/s) and mantle ( V_P ≥ 8.0 km/s). However, the longstanding assumption of purely magmatic origin for the ocean crust has misled the sub- ject field. Evidence shows that the ocean crust formed at many slow-spreading ridge localities maintains a globally constant seismic thickness of ∼ 6 ± 1 km yet paradoxically comprises predominantly serpen- tinited mantle peridotite. This observation rationalizes the 60-year-old Hess-type Ocean crust hypothe- sis, while also underscoring the imperative for direct verification through intact ocean crust drilling − the core objective of the abandoned Project Mohole (1957 ‒ 1966). The workshop participants unanimously concurred that D/V Meng Xiang is currently the only operational platform capable of achieving intact ocean crust penetration. However, selection of optimal drilling sites needs further multidisciplinary dis- cussion for successful Moho penetration, allowing addressing the core question on the petrological nature of the oceanic Moho. Here, I suggest the following with justifications for consideration: (1) It is not pos- sible and thus has no significance to drill into the Moho on seafloors formed at slow- and ultraslow- spreading ridges; (2) it is feasible to succeed with well-prepared efforts in drilling through intact mag- matic crust at ideal sites of seafloors produced at the fast-spreading East Pacific Rise; (3) if the Pacific Moho is discovered to be serpentinization front, this will bring about a paradigm shift.

Keywords

Seafloor topography / Spreading rate / Hess-type oceanic crust and Moho / Slow- and ultraslow-spreading ridges / Drilling through intact magmatic crust formed at the fast-spreading East Pacific Rise

CRediT authorship contribution statement

Yaoling Niu: Writing - review & editing, Writing - original draft, Visualization, Validation, Supervision, Software, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization.

Declaration of competing interest

The author declares that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

I thank four journal reviews for useful comments. I also thank the Laoshan Laboratory, China Geological Survey and National Natural Science Foundation of China for delegating me to co-organize the “International Workshop on Fulfilling the Quest of Drilling Through the Ocean Crust Using D/V Meng Xiang (‘梦想号’)” (Guangzhou, November 24‒27, 2024) with my former colleagues XU Yue, ZHANG Xia, CHEN Tienan, WANG Tingting, GUO Pengyuan, SUN Pu, WANG Xiaohong, DUAN Meng and CHEN Yanhong. The workshop was successful and among many relevant issues discussed concerns seafloor site selection for intact crust drilling. I thank Henry Dick, Jim Natland, Andrew McCaig, Jamie Austin, Carl Brenner and many others for sharing their views and drilling experiences and Bob Stern for his view on drilling in the Mariana Trench (which is uncertain for intact ocean crust Moho penetration plus the constraint by the total 11,000 m drill string length). My seafloor petrology and global tectonics research over the past 35 + years has been financially supported by the US NSF, Australian ARC, UK NERC, Chinese NSF, The Royal Society, The Leverhulme Trust, China Geological Survey, Chinese Academy of Sciences, The University of Queensland, Cardiff University, University of Houston, Lanzhou University, China University of Geosciences (Beijing), Durham University and Laoshan Laboratory. This contribution is in particular supported by grants from NSFC (91958215) and the Ministry of Education 111 Project (B18048).

References

[1] AMSOC, Committe, 1959. Drilling Thru the Earth’s Crust - A Study of the Desirability and Feasibility of Drilling a Hole to the Mohorovicic Discontinuity. National Academy of Sciences, National Research Council Publication 717, 1-21.

[2] Bach, W., Früh-Green, G.L., 2010. Alteration of the oceanic lithosphere and implications for seafloor processes. Elements 6, 173-178.

[3] Batiza, R., Melson, W.G., O’Hearn, T., 1988. Simple magma supply geometry inferred beneath a segment of the Mid-Atlantic Ridge. Nature 335, 428-431.

[4] Bideau, D., Hékinian, R., Sichler, B., Gracia, E., Bollinger, C., Constantin, M., Guivel, C., 1998. Contrasting volcanictectonic processes during the past 2 Ma on the Mid-Atlantic Ridge: submersible mapping, petrological and magnetic results at lat. 34 ° 52’N and 33 ° 55’N. Mar. Geophys. Res. 20, 425-458.

[5] Bown, J.W., White, R.S., 1994. Variation with spreading rate of oceanic crustal thickness and geochemistry. Earth Planet. Sci. Lett. 121, 435-449.

[6] Buck, W.R., Poliakov, A.N.N., 1998. Abyssal hills formed by stretching oceanic lithosphere. Nature 392, 372-374.

[7] Buck, W.R., Lavier, L.L., Poliakov, A.N.B., 2005. Modes of faulting at mid-ocean ridges. Nature 434, 719-723.

[8] Cannat, M., 1993. Emplacement of mantle rocks in the seafloor at mid-ocean ridges. J. Geophys. Res. 98, 4163-4172.

[9] Cannat, M., 1996. How thick is the magmatic crust at slow-spreading oceanic ridges? J. Geophys. Res. 101, 2847-2857.

[10] Cannat, M., Mevel, C., Maia, M., Deplus, C., Durand, C., Gente, P., Agrinier, P., Belarouchi, A., Dubuisson, G., Humler, E., Reynolds, J., 1995. Thin crust, ultramafic exposures, and rugged faulting patterns at the Mid-Atlantic Ridge ( 22 ° -24 ° N). Geology 23, 49-52.

[11] Chen, Y.J., 1992. Oceanic crustal thickness versus spreading rate. Geophys. Res. Lett. 19, 753-756.

[12] Chen, Y.H., Niu, Y.L., Wang, X.H., Gong, H.M., Guo, P.Y., Gao, Y.J., Shen, F.Y., 2019. Petrogenesis of ODP Hole 735B (Leg 176) oceanic plagiogranite: Partial melting of gabbros or advanced extent of fractional crystallization? Geochem. Geophys. Geosyst. 20, 2717-2732.

[13] Chen, Y.H., Niu, Y.L., Duan, M., Gong, H.M., Guo, P.Y., 2021. Fractional crystallization causes iron isotope contrast between mid-ocean ridge basalts and abyssal peridotites. Commun. Earth Environ. 2, 65. https://doi.org/10.1038/s43247-021-00135-5.

[14] Christensen, N.I., 1972. The abundance of serpentinites in the oceanic crust. J. Geol. 80, 709-719.

[15] Christensen, N.I., 2004. Serpentinites, peridotites, and seismology. Int. Geol. Rev. 46, 795-816.

[16] Coleman, R.G., 1977. Ophiolites:Ancient Oceanic Lithosphere? Springer Verlag, 229 p.

[17] Cormier, M.-H., Sloan, H., 2017. Abyssal hills and abyssal plains. In: Micallef A., Krastel S., Savini A. (Eds.),Submarine Geomorphology. Springer Geology, pp. 389-408.

[18] Davis, E.E., Lister, C.R.B., 1974. Fundamentals of ridge crest topography. Earth Planet. Sci. Lett. 21, 405-413.

[19] Dick, H.J.B., 1989. Drilling the oceanic lower crust and mantle. JOI/USSAC Workshop Report. Woods Hole Oceanographic Institution, Woods Hole, MA, 115 pp.

[20] Dick, H.J.B, Natland, J.H., Miller, D.J., et al., 1999. Proc. ODP, Init. Repts. College Station, TX. Ocean Drilling Program. 1997, Vol. 176. https://doi:10.2973/odp.proc.ir.176.1999.

[21] Dick, H.J.B., Natland, J.H., Alt, J.C., Bach, W., Bideau, D., Gee, J.S., Haggas, S., Hertogen, J.G.H., Hirth, G., Holm, P.M., Ildefonse, B., Iturrino, G.J., John, B.E., Kelley, D.S., Kikawa, E., Kingdon, A., LeRoux, P.J., Maeda, J., Meyer, P.S., Miller, D.J., Naslund, H.R., Niu, Y.L., Robinson, P.T., Snow, J., Stephen, R.A., Trimby, P.W., Worm, H.-U., Yoshinobu, A., 2000. A long in situ section of the lower ocean crust: results of ODP Leg 176 drilling at the Southwest Indian Ridge. Earth Planet. Sci. Lett. 179, 31-51.

[22] Dick, H.J.B., Lin, J., Schouten, H., 2003. An ultraslow-spreading class of ocean ridge. Nature 426, 405-412.

[23] Dick, H.J.B., Natland, J.H., Ildefonse, B., 2006. Past and future impact of deep drilling in the oceanic crust and mantle. Oceanography 19, 72-80.

[24] Dick, H.J.B., Tivey, M.A., Tucholke, B.E., 2008. Plutonic foundation of a slow-spreading ridge segment: Oceanic core complex at Kane Megamullion, 23 ° 30’N, 45 ° 20’W. Geochem. Geophys. Geosys. 9, Q05014. doi:10.1029/2007GC001645.

[25] Dick, H.J.B., MacLeod, C.J., Blum, P., Abe, N., Blackman, D.K., Bowles, J.A., Cheadle, M.J., Cho, K., Cia˛zela, J., Deans, J.R., Edgcomb, V.P., Ferrando, C., France, L., Ghosh, B., Ildefonse, B.M., Kendrick, M.A., Koepke, J.H., Leong, J.A.M., Liu, C., Ma, Q., Morishita, T., Morris, A., Natland, J.H., Nozaka, T., Pluemper, O., Sanfilippo, A., Sylvan, J.B., Tivey, M.A., Tribuzio, R., Viegas, L.G.F., 2017. Expedition 360 summary. In: MacLeod C.J., Dick H.J.B., Blum P., and Eds.), Southwest Indian Ridge Lower Crust and Moho. Proceedings of the International Ocean Discovery Program, 360. College Station, TX (International Ocean Discovery Program). http://dx.doi.org/10.14379/iodp.proc.360.101.2017.

[26] Duvernay, T., Jiang, S.H., Ball, P.W., Davies, D.R., 2024. Coupled geodynamical-geochemical perspectives on the generation and composition of mid-ocean ridge basalts. Geochem. Geophys. Geosyst. 25, e2023GC011288. https://doi.org/10.1029/2023GC011288.

[27] Fowler, C.M.R., 2005. The Solid Earth - an Introduction to Global Geophysics. Cambridge University Press, New York, p. 685.

[28] Friðleifsson, G.O., Elders, W.A., Zierenberg, R.A., Stefánsson, A., Fowler, A.P.G., Weisenberger, T.B., Harðarson, B.S., Mesfin, K.G., 2017. The Iceland deep drilling project 4.5 km deep well, IDDP-2, in the seawater-recharged Reykjanes geothermal field in SW Iceland has successfully reached its supercritical target. Scientific Drilling 23, 1-12. https://doi.org/10.5194/sd-23-1-2017.

[29] Gale, A., Langmuir, C.H., Dalton, C.A., 2014. The global systematics of ocean ridge basalts and their origin. J. Petrol. 55, 1051-1082.

[30] Goff, J.A., 1991. A global and regional stochastic analysis of near-ridge abyssal hill morphology. J. Geophys. Res. 96, 21713-21737.

[31] Goff, J.A., Ma, Y., Shah, A.K., Cochran, J.R., Sempéré J.-C., 1997. Stochastic analysis of seafloor morphology on the flank of the Southeast Indian Ridge: the influence of ridge morphology on the formation of abyssal hills. J. Geophys. Res. 102, 15521-15534.

[32] Guo, P.Y., Niu, Y.L., Sun, P., Zhang, J.J., Chen, S., Duan, M., Gong, H.M., Wang, X.H., 2021. The nature and origin of upper mantle heterogeneity beneath the Mid-Atlantic Ridge 33-35 ° N: a Sr-Nd-Hf isotopic perspective. Geochim. Cosmochim. Acta 307, 72-85.

[33] Hess, H.H., 1960. The AMSOC hole to the Earth’s mantle. Am. Sci. 48, 254-263.

[34] Hess, H.H., 1962. History of ocean basins. In: Engel A.E.J., James, H.L., Leonard B.F. (Eds), Petrologic Studies: A Volume to Honor A. F. Buddington. Geol. Soc. Am., pp. 599-620.

[35] Ildefonse, B., Abe, N., Blackman, D.K., Pablo Canales, J., Isozaki, Y., Kodaira, S., Myers, G., Nakamura, K., Nedimovic, M., Skinner, A.C., Seama, N., Takazawa, E., Teagle, D.A.H., Tominaga, M., Umino, S., Wilson, D.S., Yamao, M., 2010. The MoHole: a crustal journey and mantle quest. Workshop in Kanazawa, Japan, 3-5 June 2010. Scientific Drilling 10, 56-63. https://doi.org/10.2204/iodp.sd.10.07.2010.

[36] Kelemen, P.B., Kikawa, E., Miller, D.J., 2007. Leg 209 summary: processes in a 20-km-thick conductive boundary layer beneath the Mid-Atlantic Ridge, 14 ° -16 ° N. Proc. ODP. Sci. Results 209, 1-33. https://doi.org/10.2973/odp.proc.sr.209.001.2007.

[37] Kelley, D.S., Karson, J.A., Fruh-Green, G.L., et al., 2005. A serpentine-hosted ecosystem: the lost City hydrothermal field. Science 307, 1428-1434.

[38] Koppers, A.A.P., Coggon, R., 2020. Exploring Earth by Scientific Ocean Drilling: 2050 Science Framework. UC San Diego Library Digital Collections. https://doi.org/10.6075/J0W66J9H.

[39] Langmuir, C.H., Klein, E.M., Plank, T., 1992. Petrological systematics of mid-ocean ridge basalts:Constraints on melt generation beneath ocean ridges. In: Phipps Morgan J., Blackman D.K., Sinton J.M. (Eds.),Mantle Flow and Melt Generation at Mid-Ocean Ridges. Am. Geophys. Uni. Monogr. 71, 183-280.

[40] Le Pichon, X., 1968. Sea-floor spreading and continental drift. J. Geophys. Res. 73, 3661-3697.

[41] Lissenberg, C.J., McCaig, A.M., Lang, S.Q., Blum, P., et al., 2024. A long section of serpentinized depleted mantle peridotite. Science 385, 623-629.

[42] Macdonald, K.C., 1982. Mid-ocean ridges: Fine scale tectonic, volcanic and hydrothermal processes within the plate boundary zone. Ann. Rev. Earth Planet. Sci. 10, 155-190.

[43] MacLeod, C.J., Escartin, J., Banerji, D., Banks, G.J., Gleeson, M., Irving, D.H.B., Lilly, R.M., McCaig, A.M., Niu, Y., Allerton, S., Smith, D.K., 2002. Direct evidence for oceanic detachment faulting: the Mid-Atlantic Ridge, 15 ° 45’N. Geology 30, 879-882.

[44] McCaig, A., Lang, S.,the Scientific participants, 2023. Building Blocks of Life, Atlantis Massif. IODP 399. International Ocean Discovery Program JOIDES Resolution Science Operator.

[45] McKenzie, D.P., Parker, R.L., 1967. The North Pacific: an example of tectonics on a sphere. Nature 216, 1276-1280.

[46] McKenzie, D.P., Parker, R.L., 1967. The North Pacific: an example of tectonics on a sphere. Nature 216, 1276-1280.

[47] Michael, P.J., Forsyth, D.W., Blackman, D.K., Fox, P.J., Hanan, B.B., Harding, A.J., Macdonald, K.C., Neumann, G.A., Orcutt, J.A., Tolstoy, M., Weiland, C.M., 1994. Mantle control of a dynamically evolving spreading center: Mid-Atlantic Ridge 31 ° -34 °. Earth Planet. Sci. Lett. 121, 451-468.

[48] Michael, P.J., Langmuir, C.H., Dick, H.J.B., Snow, S.E., Goldstein, S.L., Graham, D.W., 2003. Magmatic and amagmatic seafloor generation at the ultraslow-spreading Gakkel ridge, Arctic Ocean. Nature 423, 956-961.

[49] Morgan, W.J., 1968. Rises, trenches, great faults, and crustal blocks. J. Geophys. Res. 73, 1959-1982.

[50] Natland, J.H., Steering Committee Members, 1989. Deep drilling in the ocean crust and upper mantle:Past commitments, present prospects and future plans. In: Dick H.J.B. (Ed.), Drilling the Oceanic Lower Crust and Upper Mantle. Woods, Hole, MA, pp.9-19.

[51] Nicolas, A., 1989. Structures of Ophiolites and Dynamics of Oceanic Lithosphere. Kluwere Academic Publishers, The Netherlands, p. 369.

[52] Niu, Y.L., 1992. Mid-ocean ridge magmatism: style of mantle upwelling, partial melting, crustal level processes, and spreading rate dependence: a petrologic approach. Ph.D. thesis, University of Hawaii, Honolulu.

[53] Niu, Y.L., 1997. Mantle melting and melt extraction processes beneath ocean ridges: evidence from abyssal peridotites. J. Petrol. 38, 1047-1074.

[54] Niu, Y.L., 2016. The meaning of global ocean ridge basalt major element compositions. J. Petrol. 57, 2081-2104.

[55] Niu, Y.L., 2020. On the cause of continental breakup: a simple analysis in terms of driving mechanisms of plate tectonics and mantle plumes. J. Asian Earth Sci. 194, 104367.

[56] Niu, Y.L., 2021. Lithosphere thickness controls the extent of mantle melting, depth of melt extraction and basalt compositions in all tectonic settings on Earth - a review and new perspectives. Earth-Sci. Rev. 217, 103614.

[57] Niu, Y.L., 2022. Paradigm shift for controls on basalt magmatism: Discussion with Lustrino et al on the paper I recently published in Earth-Science Reviews. Earth-Sci. Rev. 226, 103943.

[58] Niu, Y.L., 2023. The 60-year-old quest of ocean drilling into the mantle remains unfulfilled and we must persevere. Sci. Bull. 68, 2893-2895.

[59] Niu, Y.L., 2025a. Do we really need to drill through the intact ocean crust? Geosci. Front. 16, 101954.

[60] Niu, Y.L., 2025b. Shallow origin of continental mantle materials beneath slow-spreading ocean ridges. Sci. Bull. 70, 1533-1537.

[61] Niu, Y.L., Batiza, R., 1993. Chemical variation trends at fast and slow spreading ridges. J. Geophys. Res. 98, 7887-7902.

[62] Niu, Y.L., Batiza, R., 1994. Magmatic processes at a slow spreading ridge segment: 26 ° S Mid-Atlantic ridge. J. Geophys. Res. 99, 19719-19740.

[63] Niu, Y.L, Green, D.H., 2018. The petrological control on the lithosphere-asthenosphere boundary (LAB) beneath ocean basins. Earth-Sci. Rev. 185, 301-307.

[64] Niu, Y.L., Hékinian, R., 1997. Spreading rate dependence of the extent of mantle melting beneath ocean ridges. Nature 385, 326-329.

[65] Niu, Y.L., O’Hara, M.J., 2008. Global correlations of ocean ridge basalt chemistry with axial depth: a new perspective. J. Petrol. 49, 633-664.

[66] Niu, Y.L., Langmuir, C.H., Kinzler, R.J., 1997. The origin of abyssal peridotites: a new perspective. Earth Planet. Sci. Lett. 152, 251-265.

[67] Niu, Y.L., Bideau, D., Hékinian, R., Batiza, R., 2001. Mantle compositional control on the extent of melting, crust production, gravity anomaly, ridge morphology, and ridge segmentation: a case study at the Mid-Atlantic Ridge 33-35 ° N. Earth Planet. Sci. Lett. 186, 383-399.

[68] Niu, Y.L., Gilmore, T., Mackie, S., Greig, A., Bach, W., 2002. Mineral chemistry, whole-rock compositions and petrogenesis of ODP Leg 176 gabbros:Data and discussion. In: Ocean Drill. Program Sci.results. 176,334-393.

[69] Niu, Y.L., O’Hara, M.J., Pearce, J.A., 2003. Initiation of subduction zones as a consequence of lateral compositional buoyancy contrast within the lithosphere: a petrologic perspective. J. Petrol. 44, 851-866.

[70] Niu, Y.L., Shi, X.F., Li, T.G., Wu, S.G., Sun, W.D., Zhu, R.X., 2017. Testing the mantle plume hypothesis: an IODP effort to drill into the Kamchatka-Okhotsk Sea basement. Sci. Bull. 62, 1464-1472.

[71] Normile, D., 2024. China’s ‘dreamy’ scientific drilling ship takes global command - As U.S. leadership falters, Meng Xiang prepares for bold mission to retrieve rocks from Earth’s mantle. Science 386, 1202-1203.

[72] Richards, F.D., Hoggard, M.J., Cowton, L.R., White, N.J., 2018. Reassessing the thermal structure of oceanic lithosphere with revised global inventories of basement depths and heat flow measurements. J. Geophys. Res. 123, 9136-9161.

[73] Robinson, P.T., Von Herzen, R.P., Adamson, A.C., et al., 1987. Proceedings of the Ocean Drilling Program, 118 Initial Reports. Ocean Drilling Program. College Station, TX. doi:10.2973/odp.proc.ir.118.1989.

[74] Sinton, J.M., Detrick, R.S., 1992. Mid-ocean ridge magma chambers. J. Geophys. Res. 97, 197-216.

[75] Sloan, H., Sauter, D., Goff, J.A., Cannat, M., 2012. Abyssal hill characterization at the ultraslow spreading Southwest Indian Ridge. Geochem. Geophys. Geosyst. 13. https://doi.org/10.1029/2011GC003850.

[76] Small, C., 1994. A global analysis of mid-ocean ridge axial topography. Geophys. J. Int. 116, 64-84.

[77] Standish, J.J., Sims, K.W.W., 2010. Young off-axis volcanism along the ultraslow-spreading Southwest Indian Ridge. Nature Geosci. 3, 286-292.

[78] Stein, C.A., Stein, S., 1992. A model for the global variation in oceanic depth and heat flow with lithospheric age. Nature 359, 123-129.

[79] Sun, Z., Xu, Y., Deng, Y.N., 2025. The Moho is in reach of ocean drilling with the Meng Xiang. Nature Geosci. 18, 275-276.

[80] Xu, Y., Niu, Y.L., Zhang, X., Chen, T.N., Wang, T.T., Guo, P.Y., Sun, P., Wang, X.H., Duan, M., Chen, Y.H., 2025. D/V Meng Xiang is coming to revive the 60-year-old dream of Moho drilling and enter a new phase of international scientific ocean drilling. Sci. Bull. 70, 2023-2024.

[81] Zhang, T., Li, J.B., Niu, X.W., Ding, W.W., Fang, Y.X., Lin, J., Wang, Y.J., Zha, C.C., Tan, P.C., Kong, F.S., Chen, J., Wei, X.D., Lu, J.G., Dyment, J.érôme., Morgan, J.P., 2024. Highly variable magmatic accretion at the ultraslow-spreading Gakkel Ridge. Nature 633, 109-113.

[82] Zhang, T., Li, J.B., Ding, W.W., Kong, F.S., Fang, Y.X., Niu, X.W., Jiang, J., Yu, Z.T., Tan, P.C., Shen, Z.Y., Yang, C.G., Sun, Q.C., Lu, Z.Z., Yang, B., Liu, Y., Wang, Y.J., Zhao, Y.S., 2025. Magnetotelluric evidence for highly focused mantle melting along the ultraslow-spreading Gakkel Ridge, Arctic Ocean. Nat. Sci. Rev. 12, nwaf077.