Luminescence Characteristics of Terrestrial Jarosite from Kachchh, India: A Martian Analogue

Malika Singhal, Himela Moitra, Souvik Mitra, Aurovinda Panda, Jayant Kumar Yadav, D. Srinivasa Sarma, Devender Kumar, Naveen Chauhan, Saibal Gupta, Ashok Kumar Singhvi

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 chronology of jarosite formation or its transport.
Jarosite exhibited TL, BSL and IRSL signals with varied sensitivities. The TL glow curve of jarosite comprises peaks at 100, 150, 300 and 350°C, reproducible under multiple readout cycles. The least bleachable peak at 350°C reduced to (1/e)th of its peak intensity (i.e. 36%) with ~100 minutes of exposure under a sun lamp. BSL and IRSL optical decay signals comprised three components. The signal exhibited athermal fading of g ~ 6 %/decade, but pIRIR signal at 225°C showed a near zero fading. The saturation doses ranged from 700 Gy to 2600 Gy for different signals, which suggest a dating range of 25 ka using a reported Martian total dose rate of 65 Gy/ka primarily due to cosmic rays. Multiple TL peaks and their widely differing stability also offer promise to discern changes in cosmic ray fluxes over century to millennia time scale through inverse modelling and laboratory experiments