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

点击翻译按钮获取中文摘要

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 system3) 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.