Cruise support for Dr Christopher Smith-Duque to sail as a Petrologist on IODP Expedition 344 - CRISP II

The subduction of tectonic plates is one of the fundamental processes of plate tectonics, and the most potent source of earthquakes near the Earth's surface. The process occurs at convergent boundaries where one tectonic plate moves under another tectonic plate sinking into the Earth's mantle. Despite the wealth of research that has been dedicated to understand the role of subduction in earthquake generation (seismogenesis) direct sampling of the seismogenic region of subduction zones has, until now been beyond the reach of direct sampling and observation.

Integrated Ocean Drilling Program (IODP) Expedition 344 forms an integral part of an ambitious project to understand the processes that control the formation and rupture of large earthquakes at subduction zones. We will collect sediment and basement cores from 4 sites across the Central American margin offshore the Osa Peninsula of Costa Rica, spanning the area immediately preceding subduction through to the area above the seismogenic zone preparing the groundwork for a later expedition to drill and sample this zone.

Aboard ship, I will be part of an international team of scientists using a multi-disciplinarily approach to characterise the geological nature of seafloor sediments, underlying volcanic rocks and accreted sediment and basement that make up the subducting oceanic plate (Cocos-Nazca) and the upper (Caribbean) plate of Costa Rica. The erosive Costa Rican subduction system is targeted since the majority of subduction systems are erosive (Upper plate material is eroded and drawn into subduction), it is an area of intense seismic (earthquake) activity, and crucially earthquake nucleation in this region occurs at a sufficiently shallow depth to be sampled by ocean drilling.

IODP Expedition 344 will determine:
1) The geological nature of subducting sediments and basement, including their composition, texture and physical properties.
2) The rate of subduction of the oceanic plate and erosion of the upper plate of the Costa Rican subduction system
3) The interactions between fluids and rock within the upper plate.
4) How the forces acting on the subduction system change as the subduction system enters the seismogenic zone.

My role as a petrologist on Expedition 344 will be to describe and characterise rocks of igneous origin that occur beneath the sediments of the subducting oceanic crust and within the upper plate basement. The volcanic material in the subducting plate and the upper plate originally formed millions of years ago at mid-ocean ridges and during back-arc volcanism respectively. Describing and analysing these rocks during Expedition 344 will allow me to infer the styles of the original eruptive processes and classify them.

Thermally driven chemical processes known as hydrothermal alteration, results in the exchange of elements and compounds between seawater and rock to form new minerals in voids between fragments of rock, in cooling fractures, and within bubbles known as vesicles that were once occupied by gases escaping from the magmas during eruption. In the upper plate, basement of volcanic origin (e.g., accreted seamounts) may have been subjected to similar seafloor alteration processes prior to their emplacement. However, an additional consideration will be the chemical exchange processes that have taken place during accretion and during subduction, a potentially significant factor in how earthquakes form.

I will interpret hydrothermal alteration features within igneous rock recovered during Expedition 344 to determine how seawater and subduction-related fluids interacted with oceanic basement and upper plate basement respectively. My work will contribute to our understanding of the hydrogeological system of the subduction zone which will help us to understand the setting at which earthquakes can form.

Participation as the principal petrologist aboard JOIDES Resolution during IODP Expedition 344 Costa RIca Seismogenisis Project (CRISP) II will be of immediate benefit to my shipboard research partners as well as a broad range of researchers across several disciplines worldwide. My work will specifically focus on providing detailed information regarding the volcano-stratigraphic make-up of the basaltic igneous basement, the nature and extent of hydrothermal alteration, and the geochemical and thermal setting in which alteration took place.

Benefits to: IODP
Our work helps addresses one of the fundamental objectives in the Initial Science Plan of the IODP which is to explore the seismogenic zone within a convergent margin (subduction zone).

Benefits to Academic Researchers:
Our work will have significant impact in a wide range of researchers in many disciplines that are focussed on understanding the processes of subduction, seismogenesis, and hydrothermal activity at convergent margins. Our research will impact on geophysicists and structural geologists who will use our findings to understand the controls on physical properties of igneous basement rocks, which in turn impacts on studies of the stress regime and geometry of subduction systems. Our research will be fundamental to other petrologists and geochemists that seek to understand subduction related volcanism and the hydrogeological processes surrounding subduction zones.

Benefits to Public:
The goal of CRISP (to which Exp 344 forms a major component) is to learn about the nature of earthquakes at subduction zones. Given that large portions of our society live within earthquake prone regions, our contribution to CRISP through Expedition 344 is of great societal relevance. Our links to school teachers (Teacher at Sea Program), journalists, and museums will be utilized to ensure that wider society is both informed and inspired.

How does my participation generate impact?

Detailed documentation of the nature and extent of hydrothermal alteration and crustal composition, together with inferences on the hydrogeological regime during Expedition 344 will be central to assessing the impact of ocean basement-influenced properties such as permeability, fluid pressure, and composition on seismogenic zones, all major aims of Expedition 344 and the wider CRISP project.

Detailed description of the upper plate basement through to igneous oceanic crust will be essential for estimating the composition, texture, physical properties and subduction channel thickness of the upper plate material entering the subduction channel. Since upper plate material is dragged into the subduction channel it enters the seismogenic zone which likely affects the seismogenic behaviour along the subduction megathrust. Detailed descriptions of the upper plate basement will be critical for placing structural and mechanical constraints on the mechanisms at work during this process.

IODP Expedition 344 is the second stage of a major project that ultimately aims to sample an erosive subduction system from the aseismic zone and into the seismogenic region. 90% of Earth's seismogenesis takes place at convergent margins and of these convergent margins, at least 50% are erosive. Due to the wealth of previous study at the central American margin, the erosive nature of the Costa Rican subduction zone, and the relative ease of access to the seismogenic zone, our collective efforts during Expedition 344 will represent a major step forward in achieving the long standing goal of understanding the nature of seimogeneisis at subduction zones.

Researchers from the wider academic community will benefit from our research since all the shipboard scientific results are publicly available in the 'Proceedings of the Integrated Ocean Drilling Program'. As part of our commitment to high quality output our scientific findings will be published in peer reviewed publications within 48 months post cruise.