Thermal maturity structures in an accretionary wedge by a numerical simulation

Ayumu Miyakawa,Makoto Otsubo,Yohei Hamada,Masataka Kinoshita

doi:10.1186/s40645-018-0252-z

Abstract

This study investigates the thermal maturity structure of the accretionary wedge along with the thermal history of sediments during wedge formation using a numerical simulation. The thermal maturity, which is described in terms of vitrinite reflectance, is determined using the temperature and duration of exposure based on the particle trajectories within the accretionary wedge. This study revealed the variability in the thermal maturity even though sediments are observed to originate at an identical initial depth and thermal conditions. We propose two end-member pathways of sediment movement in the accretionary wedge during wedge growth: a shallow, low thermal maturity pathway and a deep, high thermal maturity pathway. These shallow path sediments, which move into the shallow portion of the wedge during wedge growth through accretion, rarely experience high temperatures; therefore, their thermal maturity is low. However, the sediments subducted in the deep portion of the wedge experience high temperatures and obtain high thermal maturity as a function of the deep high thermal maturity pathway. Simultaneously, a geological deformation event, such as faulting, defines the steps of thermal maturity. The small step of thermal maturity is formed by the frontal thrusting and can be preserved as a function of the shallow low thermal maturity pathway. However, the step is overprinted and is observed to disappear through the deep high thermal maturity pathway. The large step of thermal maturity is formed by long-term displacement along an out-of-sequence thrust (OOST) in the deep portion of the wedge.

Highlights

Previous studies have depicted that the relative duration of peak heating within any accretionary wedge, especially during specific stages of deformation, can be ascertained by determining whether any discordance exists between megascopic structural geometries and paleothermal gradients
The faults in the accretionary wedge were reactivated at times during the shortening process the displacement was smaller than that observed for the active frontal thrust
These results and observations lead to the conclusion that the thermal maturity in the numerical simulation is highly representative of the thermal maturity that occurs in the natural accretionary wedge

Summary

Introduction

Previous studies have depicted that the relative duration of peak heating within any accretionary wedge, especially during specific stages of deformation, can be ascertained by determining whether any discordance exists between megascopic structural geometries and paleothermal gradients. Miyakawa et al Progress in Earth and Planetary Science (2019) 6:8 materials (e.g., Beyssac et al 2007; Jehlička et al 2003; Sakaguchi 1996; Sweeney and Burnham 1990; Yamamoto et al 2017), which are most frequently used as preservation indices of thermal history, is the integration of the entire history of the material (c.a., temperature and exposed time). These indices can reveal the thermal history either as a function of the heating temperature or as a function of the duration. The unique trajectory of the sediments cannot be inferred by only using the observed thermal maturity indices because of the tradeoff between the exposed temperature and its duration

Results

Discussion

Conclusion