Structural Geology of Santa Cruz Island, Galapagos Archipelago

Darin Schwartz
University of Idaho, Dept. of Geological Sciences Moscow, Idaho, United States
[email protected]

Santa Cruz Island is an extinct hotspot volcano in the Galapagos Archipelago. Sub-vertical faults and fissures, whose origins are unknown, crosscut the island. The primary population center of the Galapagos is Puerto Ayora. The town is located between two of the largest faults on Santa Cruz and utilizes fissures associated with these faults to access water in some places while disposing waste in others. Our goal was to gather structural evidence that could be used to improve the understanding of the fluid interaction and potential for groundwater contamination between these fractures, given their conflicting use. We mapped the length and orientations of faults using satellite imagery and a DEM. During a month in the field, we collected throw profiles and field observations to determine fault scarp heights and opening widths of fissures. We identify ~400 fault segments on the island that have a mean orientation of 084º. The longest of these features are >3 km, have maximum scarp heights of 30 m, and exhibit horizontal opening up to 4 m. Variably intact monoclinal folds are breached by the faults. Mode 1 fractures within the downthrown block trend parallel to the primary fault scarps and exhibit dilation up to 0.5 m. The distributed tension that we have documented, primarily from the fault scarp into the down-dropped block, is predicted by several fault propagation models. Correlating deformation to a single model will help to characterize the mechanism for faulting, which has implications for understanding fluid migration around the island.

AAPG Search and Discovery Article #90157©2012 AAPG Foundation 2012 Grants-in-Aid Projects