EAPSI:Determining the characteristics of deformation and role of fluids along deep faults associated with mountain belt formation in South Korea

Austin Sarah E, Rochester NY

Investigators

Abstract

During the formation of a mountain belt (orogeny), two tectonic plates collide and the compression and shortening associated with this collision result in slices of rocks stacking up on one another. This forms a series of faults and folds, known as a fold-thrust belt. The lowest fault (basal detachment), which allows everything above it to move, plays an important role in the evolution of the fold-thrust belt but is seldom found exposed at the surface. The Okcheon Belt in South Korea formed during a tectonic collision ~250 million years ago. It has a well-exposed basal detachment providing a rare opportunity to directly study it. Field data and rock samples will be gathered, in addition to field mapping, to look at the large scale and small scale deformation and flow of fluids occurring along the basal detachment. This research will be conducted in collaboration with Dr. Sanghoon Kwon at Yonsei University, a noted expert on the structural geology of the Permo-Triassic Collision. This collaboration will provide the first direct evidence of the processes occurring along basal detachments associated with the formation of mountain belts and will give further understanding of the processes by which mountains form. A fold-thrust belt (FTB) is an important component of any orogenic belt. In existing models, the basal decollement plays a key role in the evolution of the FTB, but it is rarely exposed at the surface. The structurally lowest fault of the Okcheon Belt in South Korea is the well-exposed basal decollement of the collisional Permo-Triassic orogeny, which brought together the Gyeonggi and Yeongnam Massifs .This project will examine this decollement in collaboration with Dr. Sanghoon Kwon at Yonsei University in Seoul, South Korea. To record observations and collect data, a series of structural transects will be studied both along and across the decollement zone. Hand samples will be taken along the transects to be used for microstructural analysis of deformation structures in the fault rocks (e.g. mylonites, cataclasites). To determine the role of fluids along the decollement samples of veins will be collected along the transects to conduct stable isotope and fluid inclusion analyses. In addition to these microscopic and chemical analyses, mesoscopic analysis of deformation structures will be conducted to determine the kinematics, mechanics, and role of fluids in a basal decollement deformation zone. This will lead to a more complete understanding of the effects of decollement rheology on the geometry and evolution of fold-thrust belts. This award under the East Asia and Pacific Summer Institutes program supports summer research by a U.S. graduate student and is jointly funded by NSF and the National Research Foundation of Korea.