Electron spin resonance dating for the Central Churia Thrust of the Nepal Himalaya

doi:10.13745/j.esf.sf.2023.4.1

Abstract

Abstract:

A temporal pattern of Quaternary fault activity of the Central Churia Thrust (CCT) in the southern Nepal Himalaya has been investigated using Electron Spin Resonance (ESR) signals of quartz grains in fault gouge samples. In order to better understand the reset process, the study of the variations in ESR signal, accumulated dose, and age in various quartz grain sizes was analysed. The results of the E1’ center (a type of signal for ESR dating) of sample CCT3 show a significant spatial variation in the bulk, coarse (200-250 μm), and fine (40-80 μm) grain-size fractions. The ESR date of Quaternary faults, coarser age of (5±0.5) ka and finer fraction mean age of (50±10) ka, demonstrates the latest extension event in the Siwalik region.

Key words: tectonics, geochronology, Central Churia Thrust (CCT), ESR dating, fault gouge, Quaternary fault

CLC Number:

P597
P542

NEUPANE Bhupati, ZHAO Junmeng, LIU Chunru, PEI Shunping, MAHARJAN Bishal, DHAKAL Sanjev. Electron spin resonance dating for the Central Churia Thrust of the Nepal Himalaya[J]. Earth Science Frontiers, 2023, 30(4): 260-269.

Figures/Tables 9

Fig.1 A—Tectonic map of the Nepal Himalaya. B—Geological map of the study area (Modified after Mugner et al., 1999) showing a sample location. MFT, Main Frontal Thrust; MBT, Main Boundary Thrust; MCT, Main Central Thrust; STDS, South Tibetan Detachment system; CCT, Central Churia Thrust.

Fig.2 a—Field photographs of the fault gouge locations and sampling locations near Dobhan village, Palpa District, western Nepal. b—Columnar section along the traverse section to delineate the fault gouge location and its associative country rock.

Fig.3 a—XRD analysis chart of sample CCT-2 showing a peak in the quartz. b—XRD analysis chart of sample CCT-3 showing maximum count for quartz.

Fig.4 The ESR signal intensity of quartz for E’ and Ge centers from the CCT quartz samples.

Table 1 ESR dating results using quartz E’ center signal from samples of the CCT

	Microns/μm	w(U)/ (μg·g^-1)	w(Th)/ (μg·g^-1)	w(K₂O)/%	Cosmic/ (Gy·ka^-1)	W/%	Dose Rate/ (Gy·ka^-1)	Equivalent Dose/Gy	ESR age/ka
CCT2	40-80	6.21	21.9	2.8	0.25	5	5.47	312±48	57±9
	80-100				0.25	5	5.43	417±57	77±10
	100-140				0.25	5	5.39	426±20	79±4
CCT3	40-80	5.26	23.5	2.77	0.25	5	5.34	227±71	43±13
	80-100				0.25	5	5.30	113±90	21±17
	100-140				0.25	5	5.26	51±14	10±3
	140-160				0.25	5	5.22	113±21	22±4
	160-200				0.25	5	5.19	76±17	15±3
	200-250				0.25	5	5.13	25±2.5	5±0.5

Fig.5 The dose response curves of quartz Ti-Li center ESR signals (CCT2 40-80μm).

Table 2 Study of Carbon and Oxygen isotopes of the fault samples

Sample	δ¹³C_PDB/‰	δ¹⁸O_PDB/‰	Z	δ¹⁸O_SMOW/‰
CCT1	-7.986	-6.300	107.807	23.014 15
CCT2	-7.904	-8.322	106.968	20.932 501
CCT3	-7.868	-9.527	106.442	19.691 953 5

Table 3 Total Organic Content and Total Carbon content of the respective fault gouge samples

SN	Sample	w(TOC)/%	w(TC)/%
1	CCT1	0.027	0.011
2	CCT2	0.089	0.045
3	CCT3	0.004	0.011

Fig.6 General view of the active fault area (CCT) shown just after the MFT. CCT—Central Churia Thrust; MFT—Main Frontal Thrust.

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