HR: 15:10h
AN: T43C-07    [Abstracts]
TI: Crustal Thickness Along the Central American Volcanic Front
AU: * MacKenzie, L S
EM: lauger@bu.edu
AF: Boston University, Deparmtent of Earth Sciences 685 Commonwealth Avenue, Boston, MA 02215, United States
AU: Abers, G A
EM: abers@bu.edu
AF: Boston University, Deparmtent of Earth Sciences 685 Commonwealth Avenue, Boston, MA 02215, United States
AU: Rondenay, S
EM: rondenay@mit.edu
AF: Massachusetts Institute of Technology, 77 massachusetts ave, 54-512, Cambridge, MA 02139, United States
AU: Fischer, K M
EM: karen_fischer@brown.edu
AF: Brown University, Geological Sciences 324 Brook Street, Providence, RI 02912,
AU: Syracuse, E M
EM: syracuse@bu.edu
AF: Boston University, Deparmtent of Earth Sciences 685 Commonwealth Avenue, Boston, MA 02215, United States
AU: Protti, J M
EM: jprotti@una.ac.cr
AF: Universidad Nacional, Apartado 86-3000, Heredia, 0000, Costa Rica
AU: Gonzalez, V
EM: vgonzale@una.ac.cr
AF: Universidad Nacional, Apartado 86-3000, Heredia, 0000, Costa Rica
AU: Strauch, W
EM: wilfried.strauch@gf.ineter.gob.ni
AF: INETER, Postal Apdo. 2110, Managua, 0000, Nicaragua
AB: Subduction zone processes alter the upper plate in a number of ways, including accretion, magmatic addition, serpentinization of the mantle wedge and formation of mafic cumulates in the lower crust. All of these changes affect seismic velocities, and characterizing the structure of underlying terranes in Central America establishes a baseline for composition and continental growth. Tomography Under Costa Rica and Nicaragua (TUCAN) is a PASSCAL deployment of broadband seismometers over an 18-month period. The network has two dense cross arc lines and two along arc lines that cross terrane boundaries. Teleseismic P and PP arrivals recorded on the TUCAN network have been used to estimate crustal thickness and Vp/Vs, and to develop receiver function images. Surface reflected mode conversions (Ppms and Psms) enhance resolution. Crustal thickness ranges from 25 to 44 km with formal errors ranging 1.6-9.2 km. The thinnest crust (24.6 +/- 3.5 km) lies directly beneath the arc in Nicaragua, whereas the thickest crust (43.5 +/- 2.5 km) lies in the backarc in Nicaragua and beneath the Costa Rican arc (37.9 +/- 5.2). Changes in crustal thickness and Vp/Vs show two distinct terrane boundaries crossing the arc. Vp/Vs indicate continental crust (Vp/Vs=1.71-1.77) in Nicaragua, with a transition to gabbroic crust (Vp/Vs=1.82-1.88) in Costa Rica where fragments of the Caribbean large Igneous Province have been found. Crustal thickness beneath the arc in Costa Rica yields a crustal growth rate of 16-36 km3/km/Ma, assuming a base crustal thickness of 30-32 km with 6-14 Ma of magmatism. The Moho shows strong velocity contrasts throughout the study area, and is the only interface seen in the backarc, but it is complicated by interferences caused by shallow structure beneath the arc and forearc. Forward modeling indicates that reverberations in sediment layers interfere with the Ps arrival, however surface reflected arrivals (Ppms) require a velocity contrast on the order of 0.5–1.0 km/s at the Moho. Strong velocity contrasts across the Moho indicate that if melt or serpentinization are present in the upper mantle, they have minimal effect on velocities. Initial migration results are also presented.
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
DE: 9350 North America
SC: Tectonophysics [T]
MN: 2007 Fall Meeting