Oceanography The Official Magazine of
The Oceanography Society
Volume 32 Issue 01

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Volume 32, No. 1
Pages 138 - 149

What Lies Beneath: The Formation and Evolution of Oceanic Lithosphere

Katsuyoshi Michibayashi Masako TominagaBenoît IldefonseDamon A.H. Teagle
Article Abstract

Sampling the upper mantle via scientific ocean drilling remains elusive. Although the technologies required for drilling to the Moho still don’t exist, we have made significant progress over the last five decades in piecing together the complex geology of the oceanic crust. Here, we highlight key findings that reveal the architecture of oceanic crust and the thermal, physical, and chemical processes that are responsible for the growth and structure of the oceanic lithosphere. These advances result from enduring efforts to drill and collect downhole geophysical logs of oceanic crust near both slow and fast spreading ridges.

Citation

Michibayashi, K., M. Tominaga, B. Ildefonse, and D.A.H. Teagle. 2019. What lies beneath: The formation and evolution of oceanic lithosphere. Oceanography 32(1):138–149, https://doi.org/10.5670/oceanog.2019.136.

References

Alt, J.C., J. Honnorez, C. Laverne, and R. Emmermann. 1986. Hydrothermal alteration of a 1 km section through the upper oceanic crust, Deep Sea Drilling Project Hole 504B: Mineralogy, chemistry, and evolution of seawater-basalt interactions. Journal of Geophysical Research 91(B10):10,309–10,335, https://doi.org/10.1029/JB091iB10p10309.

Alt, J.C., H. Kinoshita, L.B. Stokking, and the Shipboard Scientific Party. 1993. Proceedings of the Ocean Drilling Program, Initial Reports, vol. 148. College Station, TX (Ocean Drilling Program), https://doi.org/10.2973/odp.proc.ir.148.1993.

Alt, J.C., H. Kinoshita, L.B. Stokking, and P.J. Michael, eds. 1996. Proceedings of the Ocean Drilling Program, Scientific Results, vol.148. College Station, TX (Ocean Drilling Program), https://doi.org/​10.2973/​odp.proc.sr.148.1996.

Anderson, R.N., J. Honnorez, K. Becker, and the Shipboard Scientific Party. 1985. Initial Reports, DSDP, Vol. 83. Washington (U.S. Government Printing Office). https://doi.org/10.2973/dsdp.proc.83.1985.

Anonymous. 1972. Ophiolites. Prepared by Participants of Penrose Field Conference. Geotimes 17:24–25.

Arculus, R.J., M. Gurnis, O. Ishizuka, M.K. Reagan, J.A. Pearce, and R. Sutherland. 2019. How to create new subduction zones: A global perspective. Oceanography 32(1):160–174, https://doi.org/​10.5670/oceanog.2019.140.

Aumento, F., and H. Loubat. 1971. The Mid-Atlantic Ridge near 45°N. XVI. Serpentinized ultramafic intrusions. Canadian Journal of Earth Sciences 8:631–663, https://doi.org/10.1139/e71-062.

Aumento, F., W.G. Melson, and DSDP Leg 37 Scientific Party. 1977. Initial Reports of the Deep-Sea Drilling Project, Vol. 37. US Government Printing Office, Washington, DC, 1,008 pp., https://doi.org/10.2973/dsdp.proc.37.1977.

Bahcall, J.N. 1990. Science with the Hubble Space Telescope. Statement to the Subcommittee on Space Science and Applications of the US House of Representatives, Washington, DC, 15 pp.

Bascom, W. 1961. A Hole in the Bottom of the Sea: The Story of the Mohole Project. Doubleday and Company, Garden City, NY, 352 pp.

Becker, K., H. Sakai, and Shipboard Scientific Party. 1988. Proceedings of the Ocean Drilling Program, Initial Reports, Part A, vol. 111. College Station, TX, https://doi.org/10.2973/odp.proc.ir.111.1988.

Becker, K., G. Foss, and Shipboard Scientific Party. 1992. Proceedings of the Ocean Drilling Program, Initial Reports, vol. 137. College Station, TX, https://doi.org/10.2973/odp.proc.ir.137.1992.

Becker, K., J.A. Austin Jr., N. Exon, S. Humphris, M. Kastner, J.A. McKenzie, K.G. Miller, K. Suyehiro, and A. Taira. 2019. Fifty years of scientific ocean drilling. Oceanography 32(1):17–21, https://doi.org/​10.5670/oceanog.2019.110..

Blackman, D., J.R. Cann, B. Janssen, and D.K. Smith. 1998. Origin of extensional core complexes: Evidence from the Mid-Atlantic Ridge at Atlantis Fracture Zone. Journal of Geophysical Research 103:21,315–21,321, https://doi.org/​10.1029/98JB01756.

Blackman, D., J.A. Karson, D.S. Kelley, J.R. Cann, G.L. Früh-Green, J.S. Gee, S.D. Hurst, B.E. John, J. Morgan, S.L. Nooner, and others. 2002. Geology of the Atlantis Massif (Mid-Atlantic Ridge, 30°N): Implications for the evolution of an ultramafic oceanic core complex. Marine Geophysical Researches 23:443–469, https://doi.org/​10.1023/​B:MARI.0000018232.14085.75.

Blackman, D., B. Ildefonse, B.E. John, Y. Ohara, D.J. Miller, C.J. MacLeod, and the Expedition 304/305 Scientists. 2006. Proceedings of the Integrated Ocean Drilling Program, Volume 304/305. Integrated Ocean Drilling Program Management International Inc., Washington, DC, https://doi.org/10.2204/iodp.proc.304305.2006.

Blackman, D., B. Ildefonse, B.E. John, Y. Ohara, D.J. Miller, N. Abe, M. Abratis, E.S. Andal, M. Andreani, S. Awaji, and others. 2011. Drilling constraints on lithospheric accretion and evolution at Atlantis Massif, Mid-Atlantic Ridge 30°N. Journal of Geophysical Research 116, B07103, https://doi.org/​10.1029/2010JB007931.

Boudier, F. and A. Nicolas. 1985. Harzburgite and lherzolite subtypes in ophiolite and oceanic environments. Earth and Planetary Science Letters 76:84–92, https://doi.org/​10.1016/​0012-821X(85)90150-5.

Bryan, W.B., T. Juteau, and Shipboard Scientific Party. 1988. Proceedings of the Ocean Drilling Project, Initial Reports (Part A), Vol. 109. Ocean Drilling Program, College Station, TX, https://doi.org/​10.2973/odp.proc.ir.106109.1988.

Buck, W.R. 1988. Flexural rotation of normal faults. Tectonics 7:959–973, https://doi.org/10.1029/TC007i005p00959.

Canales, J.P., B.E. Tucholke, and J.A. Collins. 2004. Seismic reflection imaging of an oceanic detachment fault: Atlantis megamullion (Mid-Atlantic Ridge, 30°10'N). Earth and Planetary Science Letters 222:543–560, https://doi.org/10.1016/​j.epsl.2004.02.023.

Cann, J.R., M.G. Langseth, J. Honnorez, R.P. Von Herzen, S.M. White, and Shipboard Scientific Party. 1983. Initial Reports of the Deep Sea Drilling Project, vol. 69. US Government Printing Office, Washington, DC, https://doi.org/10.2973/dsdp.proc.69.1983.

Cannat, M. 1993. Emplacement of mantle rocks in the seafloor at mid-ocean ridges. Journal of Geophysical Research 98:4,163–4,172, https://doi.org/​10.1029/​92JB02221.

Cannat, M., J.A. Karson, D.J. Miller, and Shipboard Scientific Party. 1995. Proceedings of the Ocean Drilling Project, Initial Reports, vol. 153. College Station, TX, https://doi.org/10.2973/odp.proc.ir.153.1995.

Carlson, R.L. 2010. How crack porosity and shape control seismic velocities in the upper oceanic crust: Modeling downhole logs from Holes 504B and 1256D. Geochemistry, Geophysics, Geosystems 11, Q04007, https://doi.org/​10.1029/​2009GC002955.

Casey, J.F., D. Banerji, and P. Zarian, 2007. Leg 179 synthesis: Geochemistry, stratigraphy, and structure of gabbroic rocks drilled in ODP Hole 1105A, Southwest Indian Ridge. Pp. 1–125 in Proceedings of the Ocean Drilling Program, Scientific Results, vol. 179. J.F. Casey and D.J. Miller, eds, College Station, TX, https://doi.org/10.2973/odp.proc.sr.179.001.2007.

Detrick, R., J. Collins, R. Stephen, and S. Swift. 1994. In situ evidence for the nature of the seismic Layer 2/3 boundary in oceanic crust. Nature 370:288–290, https://doi.org/​10.1038/​370288a0.

Dick, H.J.B. 1989. Abyssal peridotites, very slow spreading ridges and ocean ridge magmatism. Pp. 71–105 in Magmatism in the Ocean Basins. A.D. Saunders and M.J. Norry, eds, Geological Society Special Publication London, vol. 42, https://doi.org/10.1144/GSL.SP.1989.042.01.06.

Dick, H.J.B., J. Erzinger, L.B. Stokking, and Shipboard Scientific Party. 1992. Proceedings of the Ocean Drilling Program, Initial Reports, vol. 140. College Station, TX, https://doi.org/10.2973/odp.proc.ir.140.1992.

Dick, H.J.B., J.H. Natland, D.J. Miller, et al. 1999. Proceedings of the Ocean Drilling Program, Initial Reports, vol. 176. Texas A&M University, College Station, TX, https://doi.org/10.2973/odp.proc.ir.176.1999.

Dick, H.J.B., J.H. Natland, J.C. Alt, W. Bach, D. Bideau, J.S. Gee, S. Haggas, J.G.H. Hertogen, G. Hirth, P.M. Holm, and others. 2000. A long in situ section of the lower ocean crust: Results of ODP Leg 176 drilling at the Southwest Indian Ridge. Earth and Planetary Science Letters 179:31–51, https://doi.org/​10.1016/S0012-821X(00)00102-3.

Dick, H.J.B., J. Lin, and H. Schouten. 2003. An ultraslow-spreading class of ocean ridge. Nature 426:405–412, https://doi.org/10.1038/nature02128.

Dick, H.J.B., J.H. Natland, and B. Ildefonse. 2006. Past and future impact of deep drilling in the oceanic crust and mantle. Oceanography 19(4):72–80, https://doi.org/10.5670/oceanog.2006.06.

Dilek, Y., E.M. Moore, D. Elthon, and A. Nicolas, eds. 2000. Ophiolites and Oceanic Crust: New Insights from Field Studies and the Ocean Drilling Program. Geological Society of America Special Paper 349, Boulder, Colorado, 552 pp.

Fisher, R.L., H.J.B. Dick, J.H. Natland, and P.S. Meyer. 1986. Mafic/ultramafic suites of the slowly spreading Southwest Indian Ridge: Protea exploration of the Antarctic Plate Boundary, 24°E–47°E. Ophioliti 11:147–178.

Früh-Green, G.L., B.N. Orcutt, S.L. Green, C. Cotterill, and the Expedition 357 scientists. 2016. Atlantis Massif Serpentinization and Life. Proceedings of the International Ocean Discovery Program, vol. 357, College Station, TX, https://doi.org/​10.14379/iodp.proc.357.2017.

Gass, I.G. 1968. Is the Troodos massif of Cyprus a fragment of Mesozoic ocean floor? Nature 220:39–42, https://doi.org/​10.1038/​220039a0.

Gass, I.G. 1990. Ophiolites and oceanic lithosphere. Pp. 1–10 in Ophiolites, Oceanic Crustal Analogues, Proceedings of the Symposium ‘TROODOS 1987.’ J. Malpas, E.M. Moores, A. Panayiotou, and C. Xenophontos, eds, Geological Survey Department, Nicosia, Cyprus.

Gilbert, L.A., and M.H. Salisbury. 2011. Oceanic crustal velocities from laboratory and logging measurements of Integrated Ocean Drilling Program Hole 1256D. Geochemistry, Geophysics, Geosystems 12, Q09001, https://doi.org/​10.1029/​2011GC003750.

Gillis, K.M., C. Mével, J. Allan, and Shipboard Scientific Party. 1993. Proceedings of the Ocean Drilling Program, Initial Reports, Vol. 147. College Station, TX (Ocean Drilling Program), https://doi.org/​10.2973/odp.proc.ir.147.1993.

Gillis, K.M., J.E. Snow, A. Klaus, N. Abe, A.B. Adrião, N. Akizawa, G. Ceuleneer, M.J. Cheadle, K. Faak, T.J. Falloon, and others. 2014a. Primitive layered gabbros from fast-spreading lower oceanic crust. Nature 505:204–207, https://doi.org/10.1038/nature12778.

Gillis, K.M., J.E. Snow, A. Klaus, G. Guerin, N. Abe, N. Akizawa, G. Ceuleneer, M.J. Cheadle, Á. Adrião, K. Faak, and others. 2014b. Proceeding of the Integrated Ocean Drilling Program, Vol. 335. Integrated Ocean Drilling Program Management International Inc., Washington, DC, https://doi.org/​10.2204/iodp.proc.345.2014.

Hess, H.H. 1962. History of ocean basins. Pp. 599–620 in Petrological Studies: A Volume in Honor of A.F. Buddington. A.E.J. Engel, H.L. James, and B.F. Leonard, eds, Geological Society of America, Boulder, CO, https://doi.org/10.1130/Petrologic.1962.599.

Hsü, K.J. 1992. Challenger at Sea: A Ship That Revolutionized Earth Science. Princeton University Press, Princeton, NJ, 464 pp.

Ildefonse, B., D.K. Blackman, B.E. John, Y. Ohara, D.J. Miller, C.J. MacLeod, and Integrated Ocean Drilling Program Expeditions 304/305 Science Party. 2007a. Oceanic core complexes and crustal accretion at slow-spreading ridges. Geology 35:623–626, https://doi.org/10.1130/G23531A.1.

Ildefonse, B., P.A. Rona, and D. Blackman. 2007b. Drilling the crust at mid-ocean ridges: An “in depth” perspective. Oceanography 20:66–77, https://doi.org/​10.5670/oceanog.2007.81.

Ildefonse, B., N. Abe, D.K. Blackman, J.P. Canales, Y. Isozaki, S. Kodaira, G. Myers, M.R. Nedimovic, D.A.H. Teagle, S. Umino, and D.S. Wilson. 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.

Ildefonse, B., N. Abe, M. Godard, A. Morris, D.A.H. Teagle, and S. Umino. 2014. Formation and evolution of oceanic lithosphere: New insights on crustal structure and igneous geochemistry from ODP/IODP sites 1245, U1309, and U1415. Pp. 449–505 in Earth and Life Processes Discovered from Subseafloor Environments: A Decade of Science Achieved by the Integrated Ocean Drilling Program (IODP). R. Stein, D.K. Blackmand, F. Inagaki, and H.-C. Larsen, eds, Developments in Marine Geology, vol. 7, https://doi.org/​10.1016/B978-0-444-62617-2.00017-7.

Ishizuka, O., K. Tani, M.K. Reagan, K. Kanayama, S. Umino, Y. Harigane, I. Sakamoto, Y. Miyajima, M. Yuasa, and D.J. Dunkley. 2011. The timescales of subduction initiation and subsequent evolution of an oceanic island arc. Earth and Planetary Science Letters 306:229–240, https://doi.org/10.1016/​j.epsl.​2011.04.006.

Kelemen, P.B., E. Kikawa, D.J. Miller, and Shipboard Scientific Party. 2004. Proceedings of the Ocean Drilling Program, Initial Reports, vol. 209. Ocean Drilling Program, College Station, TX, https://doi.org/​10.2973/odp.proc.ir.209.2004.

Leinen, M., D.K. Rea, and Shipboard Scientific Party. 1986. Initial Reports, DSDP, vol. 92. US Government Printing Office, Washington, https://doi.org/​10.2973/dsdp.proc.92.1986.

McCarthy, J., J.C. Mutter, J.L. Morton, N.H. Sleep, and G.A. Thompson. 1988. Relic magma chamber structures preserved within the Mesozoic North Atlantic crust? Geological Society of America Bulletin 100:1,423–1,436, https://doi.org/10.1130/0016-7606(1988)100​<1423:RMCSPW>2.3.CO;2.

MacLeod, C.J., H.J.B. Dick, P. Blum, and the Expedition 360 Scientists. 2017. Southwest Indian Ridge Lower Crust and Moho. Proceedings of the International Ocean Discovery Program, vol. 360. College Station, TX, https://doi.org/10.14379/iodp.proc.360.2017.

Maxwell, A.E., and the Shipboard Scientific Party. 1970. Initial Reports of the Deep Sea Drilling Project, Volume III. Prepared for the National Science Foundation by the University of California Scripps Institution of Oceanography, US Government Printing Office, Washington, 806 pp., https://doi.org/10.2973/dsdp.proc.3.1970.

Michibayashi, K., M. Reagan, S. Umino, A. Okamoto, K. Takai, T. Morishita, O. Ishizuka, Y. Harigane, J. Kimura, T. Hanyu, and others. 2016. Oceanic to Proto-Arc Mantle Transformation: Fore Arc M2M (Moho-to-Mantle) in the Bonin Trench, Northwestern Pacific. IODP Proposal 898-Pre, http://www.iodp.org/proposals/active-proposals.

Miyashiro, A. 1973. The Troodos ophiolitic complex was probably formed in an island arc. Earth and Planetary Science Letters 25:217–222, https://doi.org/​​10.1016/​0012-821X(73)90118-0.

Morishita, T., G. Fujie, S. Ono, J. Morgan, D. Teagle, M. Yamano, S. Saito, S. Kodaira, J. Kimura, N. Abe, P. Kelemen, B. Ildefonse. 2015. Bend-fault Hydrology in the Old Incoming Plate. IODP Proposal 886-Pre, http://www.iodp.org/proposals/active-proposals.

Morishita, T. 2017. Drilling into deep-seated hard rocks of the oceanic plate formed at the Mid-Ocean Ridge: Results and future perspectives: Deep-seated hard rock drilling. Journal of the Geological Society of Japan 123:185–205, https://doi.org/10.5575/geosoc.2016.0063.

Morgan, J., T. Henstock, D. Teagle, P. Vannucchi, G. Fujie, S. Kodaira, I. Grevemeyer, L. Ruepke, H. Villinger, C. Ranero, and others. 2014. Bend-Fault Serpentinization: Oceanic Crust and Mantle Evolution from Ridge through Trench. IODP Proposal 876-Pre, http://www.iodp.org/proposals/active-proposals.

Morris, A., J.S. Gee, N. Pressling, B.E. John, C.J. MacLeod, C.B. Grimes, and R.C. Searle. 2009. Footwall rotation in an oceanic core complex quantified using reoriented Integrated Ocean Drilling Program core samples. Earth and Planetary Science Letters 287:217–228, https://doi.org/​10.1016/​j.epsl.2009.08.007.

Müller, R.D., M. Sdrolias, C. Gaina, and W.R. Roest. 2008. Age, spreading rates, and spreading asymmetry of the world’s ocean crust. Geochemistry, Geophysics, Geosystems 9, Q04006, https://doi.org/​10.1029/2007GC001743.

Mutter, J.C., and North Atlantic Transect (NAT) Study Group. 1985. Multichannel seismic images of the oceanic crust’s internal structure: Evidence for a magma chamber beneath the Mesozoic Mid-Atlantic Ridge. Geology 13:629–632, https://doi.org/​10.1130/​0091-​7613​(1985)13​<629:​MSIOTO>​2.0.CO;2.

National Research Council. 1957. The AMSOC Project to Drill a Hole to the Mohorovicic Discontinuity. Prepared for the AMSOC committee by H.H. Hess, Division of Earth Sciences, Washington, DC, 5 pp.

National Research Council. 1959. A Report by the AMSOC Committee on Drilling Thru the Earth’s Crust: A Study of Desirability and Feasibility of Drilling a Hole to the Mohorovicic Discontinuity. Publication 717, National Academy of Sciences/National Research Council, Washington, DC, 20 pp.

National Research Council (U.S.) AMSOC Committee. 1961. Experimental Drilling in Deep Water at La Jolla and Guadalupe Sites. Issue 914 of National Research Council Publication, National Academy of Sciences/National Research Council, Washington, DC, 183 pp.

Ohara, Y., K. Michibayashi, H.J.B. Dick, J.E. Snow, Y. Harigane, S. Ono, N. Akizawa, M. Fujii, O. Ishizuka, M.P. Loocke, and others. 2018. The nature of the back-arc basin lower crust and upper mantle at the Godzilla Megamullion. IODP Proposal 941-Full, http://www.iodp.org/proposals/active-proposals.

Ohira, A., S. Kodaira, G.F. Moore, M. Yamashita, T. Fujiwara, Y. Kaiho, S. Miura, and G. Fujie. 2018. Active-source seismic survey on the northeastern Hawaiian Arch: Insights into crustal structure and mantle reflectors. Earth, Planets and Space 70:121, https://doi.org/10.1186/s40623-018-0891-8.

Panayotou, A., ed. 1980. Proceedings of the International Ophiolite Symposium in Cyprus, 1979. Geological Survey, Nicosia, 781 pp.

Reagan, M.K., J.A. Pearce, K. Petronotis, R.R. Almeev, A.J. Avery, C. Carvallo, T. Chapman, G.L. Christeson, E.C. Ferré, M. Godard, and others. 2017. Subduction initiation and ophiolite crust: New insights from IODP drilling. International Geology Review 59:1,439–1,450, https://doi.org/​10.1080/​00206814.​2016.1276482.

Reagan, M.K., D.E. Heaton, M.D. Schmitz, J.A. Pearce, J.W. Shervais, and A.A.P. Koppers. 2019. Forearc ages reveal extensive short-lived and rapid seafloor spreading following subduction initiation. Earth and Planetary Science letters 506:520–529, https://doi.org/10.1016/j.epsl.2018.11.020.

Schroeder, T., M.J. Cheadle, H.J.B. Dick, U. Faul, J.F. Casey, and P.B. Kelemen. 2007. Nonvolcanic seafloor spreading and corner-flow rotation accommodated by extensional faulting at 15°N on the Mid-Atlantic Ridge: A structural synthesis of ODP Leg 209. Geochemistry, Geophysics, Geosystems 8, Q06015, https://doi.org/​10.1029/​2006GC001567.

Swift, S., M. Reichow, A. Tikku, M. Tominaga, and L. Gilbert. 2008. Velocity structure of upper ocean crust at Ocean Drilling Program Site 1256. Geochemistry, Geophysics, Geosystems 9, Q10O13, https://doi.org/10.1029/2008GC002188.

Tamura, A., S. Arai, S. Ishimaru, and E.S. Andal. 2008. Petrology and geochemistry of peridotites from IODP Site U1309 at Atlantis Massif, MAR 30°N: Micro- and macroscale melt penetrations into peridotites. Contributions to Mineralogy and Petrology 155:491–509, https://doi.org/10.1007/s00410-007-0254-0.

Tatsumi, Y., K. Kelley, R. Arculus, M. Arima, S. Debari, J.B. Gill, O. Ishizuka, Y. Kaneda, J. Kimura, S. Kodaira, and others. 2010. Continental Crust Formation at Intra-Oceanic Arc: Ultra-Deep Drilling to the Middle Crust of the Izu-Bonin-Mariana Arc. IODP Proposal 698-Full3, http://www.iodp.org/proposals/active-proposals.

Teagle, D.A.H., J.C. Alt, S. Umino, S. Miyashita, N.R. Banerjee, D.S. Wilson, and the Expedition 309/312 Scientists. 2006. Superfast Spreading Rate Crust 2 and 3, Proceedings of the Integrated Ocean Drilling Program, Vol. 309/312. Integrated Ocean Drilling Program Management International Inc., Washington, DC, https://doi.org/​10.2204/iodp.proc.309312.2006.

Teagle, D., and B. Ildefonse. 2011. Journey to the mantle of the Earth. Nature 471:437–439, https://doi.org/​10.1038/​471437a.

Teagle, D.A.H., B. Ildefonse, P. Blum, and the Expedition 335 Scientists. 2012. Superfast Spreading Rate Crust 4, Proceedings of the Integrated Ocean Drilling Program, Vol. 335. Texas A&M University, Integrated Ocean Drilling Program Management International Inc., Washington, DC, https://doi.org/10.2204/iodp.proc.335.2012.

The National Academies of Sciences, Engineering, and Medicine. 2011. Project Mohole: Commemorating the Accomplishments of Project Mohole—​1961–2011, http://www.nationalacademies.org/mohole/index.html.

Thompson, G., and W.G. Melson, 1972. The petrology of oceanic crust across fracture zones in the Atlantic Ocean: Evidence of a new kind of sea-floor spreading. Journal of Geology 80:526–538, https://doi.org/10.1086/627779.

Tominaga, M., B. Orcutt, and P. Blum. In press. Panama Basin Crustal Architecture (504B) & Restoring Hole 896A. IODP Expedition 385T, Scientific Prospectus.

Tucholke, B.E., and J. Lin. 1994. A geological model for the structure of ridge segments in slow-​spreading ocean crust. Journal of Geophysical Research 99:11,937–11,958, https://doi.org/​10.1029/94JB00338.

Umino, S., B. Ildefonse, P.B. Kelemen, S. Kodaira, K. Michibayashi, T. Morishita, D.A.H. Teagle and the MoHole proponents. 2012. MoHole to Mantle (M2M). IODP Proposal 805-MDP, http://www.iodp.org/​proposals/​active-proposals.

Whitehead, J.A., H.J.B. Dick, and H. Shouten. 1984. A mechanism for magmatic accretion under spreading centers. Nature 312:146–148, https://doi.org/​10.1038/312146a0.

Wilson, D.S. 1996. Fastest known spreading on the Miocene Cocos-Pacific plate boundary. Geophysical Research Letters 23(21):3,003–3,006, https://doi.org/10.1029/96GL02893.

Wilson, D.S., D.A.H. Teagle, G.D. Acton, and ODP Leg 206 Scientific Party. 2003. Proceedings of the Ocean Drilling Program, Initial Reports, vol. 206. Ocean Drilling Program, College Station, TX, https://doi.org/10.2973/odp.proc.ir.206.2003.

Wilson, D.S., D.A.H. Teagle, J.C. Alt, N.R. Banerjee, S. Umino, S. Miyashita, G.D. Acton, R. Anma, S.R. Barr, A. Belghoul, and others. 2006. Drilling to gabbro in intact ocean crust. Science 312:1,016–1,020, https://doi.org/10.1126/science.1126090.

Wernicke, B., and G.J. Axen. 1988. On the role of isostasy in the evolution of normal fault systems. Geology 16:848–851, https://doi.org/​10.1130/​0091-7613​(1988)​016​<0848:​OTROII>2.3.CO;2.

Yeasts, R.S., S.R. Hart, and DSDP Leg 34 Scientific Party. 1976. Initial Reports of the Deep Sea Drilling Project, Vol. 34. Washington (US Government Printing Office), 814 pp., https://doi.org/10.2973/dsdp.proc.34.1976.