Luminescence characteristics of terrestrial Jarosite from Kachchh, India: A Martian analogue

Abstract

In this study, naturally occurring jarosite samples from Kachchh, India (considered to be Martian analogue) were characterized using Fourier Transform Infrared Spectroscopy (FTIR), Cathodoluminescence–Energy Dispersive X-ray Spectroscopy (CL-EDXS), and Luminescence (thermoluminescence [TL], blue and infrared stimulated luminescence [BSL and IRSL]) methods. FTIR and CL-EDXS studies suggested that jarosite preserves its luminescence characteristics even after annealing the samples to 450°C. This facilitated luminescence studies (TL/BSL/IRSL) to assess the potential use of luminescence-dating methods to establish the chronology of jarosite formation or its transport. Jarosite exhibited TL, BSL, and IRSL signals with varied sensitivities. The TL glow curve of jarosite comprised glow peaks at 100, 150, 300, and 350°C, reproducible over multiple readout cycles. The least bleachable TL glow peak at 350°C is reduced to (1/e)^th of its glow peak intensity (i.e., 36%) with ~100 min of light exposure under a sunlamp. BSL and IRSL optical decay signals comprised three components. These signals exhibited athermal fading of g ~ 6%/decade, but pIRIR signal at 225°C showed a near zero fading. The saturation doses (2D₀) ranged from 700 Gy to 2600 Gy for different signals, which suggests a dating range of ~25 ka using a reported Martian total dose rate of 65 Gy/ka, primarily due to cosmic rays. Multiple TL glow peaks and their widely differing stability also offer promise to discern changes in cosmic ray fluxes over a century to millennia time scale through inverse modeling and laboratory experiments.