Final Thoughts
It seems fitting that my last sea going experience terminated with this cruise on the
KOK, and that I participated on the last dive of the mission on Volcano #1. I find it
quite ironic that I began documenting my studies of the ocean floor with a paper
about rocks from the Indian Ocean’s spreading ridge where the crust is being
created, and my last sea going experience took place in a subduction zone near
Tonga. During my profession as an oceanographer, I have been privileged to visit
all the world’s oceans and I have tried to answer some of our questions about how
our planet was formed.
I find it comforting to think that once the tectonic plates have been subducted, at
the end of their journey drifting on the asthenosphere from their place of creation
at a spreading ridge, their rocks will be fused once again. It is likely that some day,
in the distant future, a subducted plate’s rocks may once again return as fresh lava
at another spreading ridge somewhere on our planet. It appears that living
organisms and even the rocks of our planet have a period of birth (creation),
existence and death, but in the case of seafloor rocks, we know that their ‘‘death’’
(by melting) in a subduction zone is not at all the end of their existence.
References
Anderson RN, Uyeda S, Miyashiro A (1976) Geophysical and geochemical constraints at
convegent plate boundaries-part I: dehydration of down going slab. Geophys J Roy Soc
London 44:333–357
Barazangi M, Isacks B (1971) Lateral variations of seismic-wave attenuation in the upper mantle
above the inclined earthquake zone of the Tonga Island arc: deep anomaly in the upper
mantle. J Geophys Res 76:8493–8516
Bloomer SH, Ewart A, Hergt JM, Bryan WB, (1994) Geochemistry and origin of igneous rocks
from the outer Tonga fore arc (Site 841). In: Hawkins J, Parson L, Allan J et al. (eds)
Proceedings of the ocean drilling program, scientific results, 135:625–646
de Ronde CEJ, Massoth GJ, Baker ET, Lupton JE (2003) Submarine hydrothermal venting
related to volcanic arcs. In: Simons SF, Graham IJ (eds) Gingebach memorial volume:
volcanic geothermal and ore forming fluids: rulers and processes within the Earth. Soc Econ
Geol Spec Publ 10:91–109
de Ronde CEJ, Hannington MD, Stoffers P, Wright IC, Ditchburn RG, Reyes AG, Baker ET,
Massoth GJ, Lupton JL, Walker SL, Greene RR, Soong J, Ishibashi CWR, Lebon GT, Bray CJ
(2005) Evolution of a submarine magmatic-hydrothermal system: brothers volcano, Southern
Kermadec arc, New Zealand. Econ Geol Bull Soc Econ Geol 100:1097–1134
Ewart A, Bryan WB (1972) Petrography and geochemistry of the igneous rocks from Eua, Tonga
Island. Geol Soc Am 83:3281–3296
Fisher RL, Engel CG (1969) Ultramafic and basaltic rocks dredged from the nearshore flank of
the Tonga trench. Geol Soc Am Bull 80:1373–1378
Hamilton W, (1974) Earthquake map of the Indonesian region.US Geol Surv Map I-875-C
Hekinian R, Mühe R, Worthington T, Stoffers P (2008) Geology of a submarine volcanic caldera
in the Tonga arc: dive results. Jour Volcanol Geoth Res 176:571–582
362
10 Subduction Zones
It seems fitting that my last sea going experience terminated with this cruise on the
KOK, and that I participated on the last dive of the mission on Volcano #1. I find it
quite ironic that I began documenting my studies of the ocean floor with a paper
about rocks from the Indian Ocean’s spreading ridge where the crust is being
created, and my last sea going experience took place in a subduction zone near
Tonga. During my profession as an oceanographer, I have been privileged to visit
all the world’s oceans and I have tried to answer some of our questions about how
our planet was formed.
I find it comforting to think that once the tectonic plates have been subducted, at
the end of their journey drifting on the asthenosphere from their place of creation
at a spreading ridge, their rocks will be fused once again. It is likely that some day,
in the distant future, a subducted plate’s rocks may once again return as fresh lava
at another spreading ridge somewhere on our planet. It appears that living
organisms and even the rocks of our planet have a period of birth (creation),
existence and death, but in the case of seafloor rocks, we know that their ‘‘death’’
(by melting) in a subduction zone is not at all the end of their existence.
References
Anderson RN, Uyeda S, Miyashiro A (1976) Geophysical and geochemical constraints at
convegent plate boundaries-part I: dehydration of down going slab. Geophys J Roy Soc
London 44:333–357
Barazangi M, Isacks B (1971) Lateral variations of seismic-wave attenuation in the upper mantle
above the inclined earthquake zone of the Tonga Island arc: deep anomaly in the upper
mantle. J Geophys Res 76:8493–8516
Bloomer SH, Ewart A, Hergt JM, Bryan WB, (1994) Geochemistry and origin of igneous rocks
from the outer Tonga fore arc (Site 841). In: Hawkins J, Parson L, Allan J et al. (eds)
Proceedings of the ocean drilling program, scientific results, 135:625–646
de Ronde CEJ, Massoth GJ, Baker ET, Lupton JE (2003) Submarine hydrothermal venting
related to volcanic arcs. In: Simons SF, Graham IJ (eds) Gingebach memorial volume:
volcanic geothermal and ore forming fluids: rulers and processes within the Earth. Soc Econ
Geol Spec Publ 10:91–109
de Ronde CEJ, Hannington MD, Stoffers P, Wright IC, Ditchburn RG, Reyes AG, Baker ET,
Massoth GJ, Lupton JL, Walker SL, Greene RR, Soong J, Ishibashi CWR, Lebon GT, Bray CJ
(2005) Evolution of a submarine magmatic-hydrothermal system: brothers volcano, Southern
Kermadec arc, New Zealand. Econ Geol Bull Soc Econ Geol 100:1097–1134
Ewart A, Bryan WB (1972) Petrography and geochemistry of the igneous rocks from Eua, Tonga
Island. Geol Soc Am 83:3281–3296
Fisher RL, Engel CG (1969) Ultramafic and basaltic rocks dredged from the nearshore flank of
the Tonga trench. Geol Soc Am Bull 80:1373–1378
Hamilton W, (1974) Earthquake map of the Indonesian region.US Geol Surv Map I-875-C
Hekinian R, Mühe R, Worthington T, Stoffers P (2008) Geology of a submarine volcanic caldera
in the Tonga arc: dive results. Jour Volcanol Geoth Res 176:571–582
362
10 Subduction Zones