Resolving the Bombardment history of the early Earth using ancient zircons
Meteorite impacting is an important geologic process within the solar system and has been invoked to explain loss and introduction of volatiles to the planets, magmatic activity, modifications of magnetic field and even introduction of life to Earth. However, the nature of the impact flux rate of the early solar system is debated and early impact craters on the Earth have been completely erased by subsequent tectonic activity. Hyper-velocity impacts create unique microstructural phenomena known as ‘shock metamorphism’ within the lithologies of the target rocks and impactor. Zircon, an important mineral for crustal studies, displays shock metamorphic features such as planar deformation features (PDFs), low-angle boundaries and deformation twins. Zircon can also record the age of an impact event because the U-Pb geochronometer in zircon can be locally reset during shock metamorphism . The aim of this study is to better determine the early impact history of Earth. An integrated scanning electron microscopy (SEM) and Sensitive High Resolution Ion Microprobe (SHRIMP) in situ U-Pb geochronology study of zircons collected from sediments containing Hadean and Eoarchaean detritus will be undertaken to identify and determine the oldest impact evidence on Earth. Additionally shocked zircon and quartz from the Ries Impact structure in Germany will be analyzed to help better refine the shocked zircon impact barometer. Ultimately, this study will help to refine the Earth’s early impact record and will both improve previous impact flux models and develop new ones. The results will also provide test of conflicting models for Solar system evolution.
Resolving the Bombardment history of the early Earth using ancient zircons
Meteorite impacting is an important geologic process within the solar system and has been invoked to explain loss and introduction of volatiles to the planets, magmatic activity, modifications of magnetic field and even introduction of life to Earth. However, the nature of the impact flux rate of the early solar system is debated and early impact craters on the Earth have been completely erased by subsequent tectonic activity. Hyper-velocity impacts create unique microstructural phenomena known as ‘shock metamorphism’ within the lithologies of the target rocks and impactor. Zircon, an important mineral for crustal studies, displays shock metamorphic features such as planar deformation features (PDFs), low-angle boundaries and deformation twins. Zircon can also record the age of an impact event because the U-Pb geochronometer in zircon can be locally reset during shock metamorphism . The aim of this study is to better determine the early impact history of Earth. An integrated scanning electron microscopy (SEM) and Sensitive High Resolution Ion Microprobe (SHRIMP) in situ U-Pb geochronology study of zircons collected from sediments containing Hadean and Eoarchaean detritus will be undertaken to identify and determine the oldest impact evidence on Earth. Additionally shocked zircon and quartz from the Ries Impact structure in Germany will be analyzed to help better refine the shocked zircon impact barometer. Ultimately, this study will help to refine the Earth’s early impact record and will both improve previous impact flux models and develop new ones. The results will also provide test of conflicting models for Solar system evolution.
