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Long‐term growth and subsidence of Ascension Island: Constraints on the rheology of young oceanic lithosphere
Author(s) -
Minshull T. A.,
Ishizuka O.,
GarciaCastellanos D.
Publication year - 2010
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2010gl045112
Subject(s) - geology , lithosphere , subsidence , subaerial , volcano , borehole , geothermal gradient , thermal subsidence , geophysics , seismology , paleontology , tectonics , structural basin
The dating of material from deep boreholes drilled in volcanic ocean islands allows constraints to be placed on their growth and long‐term subsidence rates. We dated lavas from a 3 km geothermal borehole at Ascension Island by the laser‐heating 40 Ar/ 39 Ar technique. The samples yield ages of up to 3.4 Ma and volcanic growth rates of ∼0.4 km/Myr. The transition from submarine to subaerial eruption occurs at ∼710 m below present sea level and 2.5 Ma. Since 2.5 Ma, there has been ∼430–500 m of subsidence over and above the expected ∼190–260 m due to lithospheric cooling. Plausible elastic thicknesses and growth histories would generate a maximum elastic subsidence since 2.5 Ma of ∼200 m. We infer that the subsidence includes a component of viscous relaxation resulting from rapid loading prior to 2.5 Ma, and place constraints on the timescale of this relaxation, and hence the viscosity of the underlying lithosphere.