Subduction dynamics at the middle America trench : new constraints from swath bathymetry, multichannel seismic data, and 10BE
Citable URI
https://hdl.handle.net/1912/2458Location
Middle America TrenchDOI
10.1575/1912/2458Keyword
Subduction zones; Seismic prospecting; Marine sediments; Beryllium; Isotopes; Radioisotopes in oceanography; Maurice Ewing (Ship) Cruise EW0005; Maurice Ewing (Ship) Cruise EW0104; Sonne (Ship) CruiseSO76; Fred H. Moore (Ship) Cruise FM3502; Ida Green (Ship) Cruise IG2402Abstract
The cosmogenic radionuclide 10Be is a unique tracer of shallow sediment subduction in
volcanic arcs. The range in 10Be enrichment in the Central American Volcanic Arc
between Guatemala and Costa Rica is not controlled by variations in 10Be concentrations
in subducting sediment seaward of the Middle America Trench. Sedimentary 10Be is
correlated negatively with 143Nd/144Nd, illustrating that 10Be concentrations varied both
between and within cores due to mixing between terrigenous clay and volcanic ash
endmember components. This mixing behavior was determined to be a function of grain
size controls on 10Be concentrations. A negative correlation of bulk sedimentary 10Be
concentrations with median grain size and a positive correlation with the proportion of
the sediment grains that were <32 μm in diameter demonstrated that high concentrations
of 10Be in fine-grained, terrigenous sediments were diluted by larger grained
volcanogenic material.
The sharp decrease in 10Be enrichment in the Central American Volcanic Arc between
southeastern Nicaragua and northwestern Costa Rica correlates with changes in fault
structure in the subducting Cocos plate. Offshore of Nicaragua, extensional faults
associated with plate bending have throw equal to or greater than the overlying
subducting sediment thickness. These faults enable efficient subduction of the entire
sediment package by preventing relocation of the décollement within the downgoing
sediments. Offshore of Costa Rica, the reduction of fault relief results in basement faults
that do not penetrate the overlying sediment. A conceptual model is proposed in which
the absence of significant basement roughness allows the décollement to descend into the
subducting sediment column, leading to subsequent underplating and therefore removal
of the bulk of the sediment layer that contains 10Be.
Basement fault relief was linearly related to plate curvature and trench depth. The
systematic shoaling of the plate from southeastern Nicaragua to northwestern Costa Rica
is not explained by changes in plate age for this region. Instead, it is hypothesized that the
flexural shape of the plate offshore of southeastern Nicaragua and northwestern Costa
Rica represents a lateral response to a buoyant load caused by the thick crust and elevated
thermal regime in the Cocos plate offshore of southeastern Costa Rica.
Description
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2003
Collections
Suggested Citation
Thesis: Kelly, Robyn K., "Subduction dynamics at the middle America trench : new constraints from swath bathymetry, multichannel seismic data, and 10BE", 2003-09, DOI:10.1575/1912/2458, https://hdl.handle.net/1912/2458Related items
Showing items related by title, author, creator and subject.
-
The subduction experiment : cruise report R/V Knorr : cruise number 138 leg XV : subduction 3 mooring recovery cruise, 13-30 June 1993
Trask, Richard P.; Galbraith, Nancy R.; Robbins, Paul E.; Ostrom, William M.; Regier, Lloyd; Pezzoli, Glenn; McPhee, Neil M. (Woods Hole Oceanographic Institution, 1993-12)Subduction is the mechanism by which water masses formed in the mixed layer and near the surface of the ocean find their way into the upper thermocline. The subduction process and its underlying mechanisms were studied ... -
The Subduction experiment : cruise report R/V Oceanus : cruise number 240 leg 3 : subduction 1 mooring deployment cruise, 17 June-5 July 1991
Trask, Richard P.; Brink, Nancy J. (Woods Hole Oceanographic Institution, 1993-03)Subduction is the mechanism by which water masses formed in the mixed layer and near the surface of the ocean find their way into the upper thermocline. The subduction process and its underlying mechanisms were studied ... -
The Subduction experiment : cruise report R/V Oceanus cruise number 250 legs 1 and 2 subduction 2 mooring deployment and recovery cruise, 25 January-26 February 1992
Trask, Richard P.; Brink, Nancy J.; Regier, Lloyd; McPhee, Neil M. (Woods Hole Oceanographic Institution, 1993-03)Subduction is the mechanism by which water masses formed in the mixed layer and near the surface of the ocean find their way into the upper thermocline. The subduction process and its underlying mechanisms were studied ...