Publication Date:
2017-03-01
Description:
Most Central American volcanoes occur in an impressive volcanic front that
trends parallel to the strike of the subducting Cocos Plate. The volcanic front is a
chain, made of right-stepping, linear segments, 100 to 300 Km in length.
Volcanoes cluster into centers, whose spacing is random but averages about 27
Km. These closely spaced, easily accessible volcanic centers allow mapping of
geochemical variations along the volcanic front. Abundant back-arc volcanoes in
southeast Guatemala and central Honduras allow two cross-arc transects. Several
element and isotope ratios (e.g. BalLa, Uffh, B/La, IOBe/9Be, 87Sr/86Sr) that are
thought to signal subducted marine sediments or altered MORB consistently
define a chevron pattern along the arc, with its maximum in Nicaragua. BalLa, a
particularly sensitive signal, is 130 at the maximum in Nicaragua but decreases
out on the limbs to 40 in Guatemala and 20 in Costa Rica, which is just above the
nominal mantle value of 15. This high amplitude regional variation, roughly symmetrical
about Nicaragua, contrasts with the near constancy, or small gradient, in
several plate tectonic parameters such as convergence rate, age of the subducting
Cocos Plate, and thickness and type of subducted sediment. The large geochemical
changes over relatively short distances make Central America an important
margin for seeking the tectonic causes of geochemical variations; the regional
variation has both a high amplitude and structure, including flat areas and gradients.
The geochemical database continues to improve and is already adequate to
compare to tectonic models with length scales of 100 Km or longer.
Type:
Book chapter
,
NonPeerReviewed
Format:
text