Dating Very Young Submarine Basalts
70% of global crustal magmatism occurs at mid-ocean ridges, where heat budget controls crustal structure, hydrothermalism, and a vibrant biosphere. Yet, the tempo of magmatic inputs remains poorly understood there. Such timescales can be assessed with natural Actinide-series decay chains because chemical disruption to secular equilibrium systems initiates parent-daughter disequilibria, which re-equilibrate by the shorter half-life (t½) in a pair (see Fig. 2 below).
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Figure 1 view through the submersible Alvin of a small piece of mid-ocean ridge basalt in on of the manned-sub's manipulator arms. |
The temporal variability of crustal and mantle processes occurring at the Mid-Ocean Ridge (MOR) system is a key component for understanding the dynamics of these globally important volcanic structures. Time series observations of the MOR have demonstrated that eruptive and tectonic events can take place on very short time scales and they can cause dramatic hydrologic, biologic and geologic changes at these undersea volcanoes. Additionally, detailed geochemical and geophysical studies in some ridge locales have shown that physical conditions in the underlying mantle directly influencing magma generation and transport can vary in strong coherence with conditions in the MOR crust. Figure 2 Diagram illustrating the decay of radioactive disequilibria in 4 parent-daughter pairs within the U-series decay chain. The different half-lives involved cause the signals to decay over different timescales. "A" stands for "activity", and "o" stands for "initial". In this case daughter excesses are depicted, and only the excess part of the disequilibria changes with time. Note the log scale on the x-axis | |
The methods we utilize focus on radioactive disequlibria amongst naturally occuring isotopes in the Uranium decay series, which as a group cover a wide range of chemistries and half-lives. Focus applications of my research group include:
See more info at the links above or in please see:
KH Rubin, SA Soule, WW Chadwick, DJ Fornari, DS Clague, RW. Embley, ET Baker, MR Perfit, DW Caress, RP Dziak (2012) Volcanic Eruptions in the Deep Sea, Oceanography, 25(1), 142–157, http://dx.doi.org/10.5670/oceanog.2012.12. Rubin, K.H. Smith, M.C. Perfit, M.R., Christie, D.M. and Sacks, L.F. (1998) Geochronology and Geochemistry of lavas from the 1996 North Gorda Ridge eruption, Deep Sea Research II, 45, 2751-2599. Garcia, M.O., Rubin, K.H., Norman, M.D., Rhodes, M., Graham, D.W., Muenow, D., Spencer, K. (1998) Petrology and geochronology of basalt breccia from the 1996 earthquake swarm of Loihi Seamount, Hawaii: Magmatic history of its 1996 eruption, Bulletin of Volcanology, vol 59, 577-592. Rubin, K.H., Macdougall, J.D. and Perfit, M.R. (1994) 210Po-210Pb dating of recent volcanic eruptions on the sea floor, Nature, 368, 841-844. K.H. Rubin and J.D. Macdougall, (1990) A radioactive decay technique for dating neovolcanic MORB, Earth Planet. Sci. Lett., 101, 313-322. K.H. Rubin and J.D. Macdougall, (1988) 226Ra excesses in mid-ocean-ridge basalts and mantle melting, Nature 335, 158-161.
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