Costa Rica Seismogenesis Project
Deformation mechanisms within an erosive plate margin: The Cocos-Caribbean plate boundary
Proposal P 26634-N29 funded by the Austrian Science Fund (FWF); project started by Oct. 1st 2014.
The Costa Rica Seismogenesis Project (CRISP) was designed to elucidate the processes that control nucleation and seismic rupture of large earthquakes at erosional subduction zones. CRISP is located at the only known seismogenic zone at an erosional margin within reach of scientific drilling. With a low sediment supply, fast convergence rate, abundant seismicity, subduction erosion, and a change in subducting plate relief along strike, CRISP offers excellent opportunities to better understand earthquake nucleation, rupture propagation, and the mechanisms of deformation along the updip sections of a convergent plate margin.
This project aims to test various hypotheses related to the transition from aseismic to seismic behaviour along erosive plate boundaries, that are mainly related to the activity of fluids within the subduction zone: 1) The architecture of the subduction megathrust evolves down dip and the transition from stable to unstable slip corresponds to the transition from a fluid-rich, broad fault zone to a thinner and drier fault. Geological, physical and structural characteristics of material in the subduction channel influence fault mechanics and the transition from stable to unstable slip. 2) Fluid advection affects the localization of faulting and locking of erosional plate boundaries. Fluid chemistry, P-T conditions and residence time affect the state of eroded material through upper-plate basement alteration, diagenesis and low-grade metamorphism. Variations in material/fluid properties and distribution affect fault propagation.
This study will focus on constraining the boundary conditions of lithology and fluid flow that control the deformation mechanisms in the seismogenic and aseismic zone along the IODP Expedition 344 drilling transect.
Simplified tectonic sketches of the Middle Miocene tectonic situation of the Cocos Plate (not to scale). (a) The Cocos Plate was formed at the Cocos-Nazca spreading center (CNS) and subducted under the Caribbean Plate. The activity of the Galapagos hotspot (GHS) resulted in the formation of the Cocos Ridge. Basaltic eruptions and advective heat transfer led to lithification of sediments of Unit III accompanied with first vein formation. The Cocos Ridge and Unit III underwent heating by a second event. The heat source was either (b) the CNS, due to the ridge jump at 14.5 Ma, (c) a combination of CNS and GHS activity or (d) seamount volcanism in the area of Cocos Island (Co. Is.). (Brandstätter et al., 2016)
BRANDSTÄTTER, J., KURZ, W., KRENN, K. & MICHEUZ, P.: Fluid inclusion petrology and microthermometry of the Cocos Ridge hydrothermal system, IODP Expedition 344 (CRISP 2), Site U1414.- Geochemistry, Geophysics, Geosystems, DOI: 10.1002/2015GC006212, 2016.
BRANDSTÄTTER, J., KURZ, W. & ROGOWITZ, A.: Microstructural analysis and calcite piezometry on hydrothermal veins: insights into the deformation history of the Cocos Plate at Site U1414 (IODP Expedition 344). Tectonics, 36, 1562-1579, DOI: 10.1002/2017TC004490, 2017.
Brandstätter, J., Kurz, W., Richoz, S., Cooper, M. J., TEAGLE, D. A. H.: The origin of carbonate veins within the sedimentary cover and igneous rocks of the Cocos Ridge: Results from IODP HoleU1414A. G3: Geochemistry, Geophysics, Geosystems: an electronic journal of the earth sciences, 19, doi.org/10.1029/ 2018GC007729. DOI: doi.org/10.1029/ 2018GC007729, 2018.