15:45 〜 16:00
[SCG61-08] Coalescing microstructural studies and carbonate clumped isotope thermometry in fault zone research: insights from the calcite veins in Himalayan Frontal Fold Thrust Belt
★Invited Papers
キーワード：Carbonate Clumped Isotope Thermometry, Calcite e-twins, Himalayan Frontal Fold Thrust Belt, MBT, MFT
Calcite is one of the dominant minerals occurring in the host rock or in the veins of inland fault zones, subduction zones, and accretionary prisms. Furthermore, remobilized carbonate fluids often occur as veins associated with the fractures generated in fault rocks and surrounding damage zone. Hence, calcite is one of the well-studied minerals in perspective of fault strength and fault zone deformation. Deformation microstructures provide important insights into the deformation mechanisms, however for comprehensive deformation models accurate temperature reconstructions are also a necessity. In case of deformation in the brittle zone (<15 km depth) only limited options for temperature estimations are available (Raman spectroscopy of carbonaceous material, Beyssac et al., 2002; illite crystallinity analysis, Hara and Kurihara, 2010). Additionally, the temperature estimations from the morphology of calcite e-twins (deformation twins) also provide limited information on temperature estimation. In this context, this study incorporates carbonate clumped isotope thermometry to estimate temperatures of calcite occurring in the veins and host rocks of the Himalayan Frontal Fold Thrust Belt.
The study includes calcite occurring in the fault zones and adjacent host rocks bounded by the two major regional thrusts, the Main Boundary Thrust (MBT) and the Main Frontal Thrust (MFT) of the Himalayan Frontal Fold Thrust Belt. Additionally, calcite from the splay faults within the MBT and MFT are also incorporated within the study.
The temperatures estimated from the carbonate clumped isotope analysis (Sarkar et al., 2021) of syn-kinematic calcite precipitates occurring as veins along MBT (262±30 ℃) and Nahan Thrust (close to MFT) (170±10 ℃) indicate a difference of 100 ℃. The e-twin morphology from the same calcite samples shows coherence with the estimated temperatures. The temperature estimates from the calcite in the fault zone of fault splays also show consistent temperatures.
Additionally, the detailed fault zone architecture of the Nahan thrust indicates lithology-dependent heterogeneity within a single fault zone (Sarkar et al., 2022). The principal slip zone which occurs as a black gouge indicates the marked absence of calcite, and exhibits cataclastic textures, and vapor escape structures suggesting possible seismic nucleation in the zone. However, the calcite grains in the adjacent layers of the principal slip zone indicate a temperature of 170±10 ℃ while the fault rock microstructures indicate foliations (in brittle regime) and pressure solution seams indicative of possible aseismic creep. Thus, carbonate clumped isotope thermometry can also provide very localized temperature estimations.
The present study discusses the robustness and applicability of carbonate clumped isotope thermometry and attempts to integrate it with the existing microstructural studies for refinement of shallow crustal fault zone research.
References: Beyssac et al., (2002), Metamorph. Geol.; Hara and Kurihara, (2010), Tectonophysics; Sarkar et al., (2021), Prog. earth planet. Sci.; Sarkar et al., (2022), GSA bulletin.
The study includes calcite occurring in the fault zones and adjacent host rocks bounded by the two major regional thrusts, the Main Boundary Thrust (MBT) and the Main Frontal Thrust (MFT) of the Himalayan Frontal Fold Thrust Belt. Additionally, calcite from the splay faults within the MBT and MFT are also incorporated within the study.
The temperatures estimated from the carbonate clumped isotope analysis (Sarkar et al., 2021) of syn-kinematic calcite precipitates occurring as veins along MBT (262±30 ℃) and Nahan Thrust (close to MFT) (170±10 ℃) indicate a difference of 100 ℃. The e-twin morphology from the same calcite samples shows coherence with the estimated temperatures. The temperature estimates from the calcite in the fault zone of fault splays also show consistent temperatures.
Additionally, the detailed fault zone architecture of the Nahan thrust indicates lithology-dependent heterogeneity within a single fault zone (Sarkar et al., 2022). The principal slip zone which occurs as a black gouge indicates the marked absence of calcite, and exhibits cataclastic textures, and vapor escape structures suggesting possible seismic nucleation in the zone. However, the calcite grains in the adjacent layers of the principal slip zone indicate a temperature of 170±10 ℃ while the fault rock microstructures indicate foliations (in brittle regime) and pressure solution seams indicative of possible aseismic creep. Thus, carbonate clumped isotope thermometry can also provide very localized temperature estimations.
The present study discusses the robustness and applicability of carbonate clumped isotope thermometry and attempts to integrate it with the existing microstructural studies for refinement of shallow crustal fault zone research.
References: Beyssac et al., (2002), Metamorph. Geol.; Hara and Kurihara, (2010), Tectonophysics; Sarkar et al., (2021), Prog. earth planet. Sci.; Sarkar et al., (2022), GSA bulletin.