Observations and modeling of the crustal structure and Moho strength variation along the Lesser Antilles Arc

Abstract:

Subduction processes influence the crustal structure in their vicinity. The Mohorovičić discontinuity (Moho), separating the crust from the mantle, can be influenced both in its depth and strength. Normally it is stronger than any crustal discontinuity, but a change in subducted material can weaken the Moho.

We are investigating the change in crustal structure along the Lesser Antilles Arc using three component broadband stations on various islands along the arc. This arc is formed by the slow subduction (~2cm/yr) of the North and South American plates beneath the Caribbean plate. We are using receiver functions and H-κ stacking to constrain the depth (H) of the strongest discontinuity and the average crustal P-to-S wave velocity ratio (κ) to that depth. The ratio constrains the subsurface material. Results in this field of study can easily be ground-truthed with the composition of materials found in samples from the same area to find uniform patterns.

Our results show significant depth variations of the discontinuity. Some of our results match the depth of an inter-crustal boundary (Conrad) found in a previous study (Boynton, 1979, GJRAS). This suggests a comparably weak Moho in these areas, a theory that is supported by models based on petrological results.

We compare our results to synthetic data from inversion models that determine the depth location of the Conrad and the Moho. For this purpose we use a combined method of different inversion approaches and include petrological constraints. Where we previously see agreement between the depth of the Conrad in Boynton’s study and the H-κ stacking, the models now confirm this result.