Authigenic Green Mica in Interflow Horizons within Late Cretaceous Deccan Volcanic Province, India and Its Genetic Implications

Abstract

Green authigenic mica, i.e., celadonite, is commonly associated with submarine alteration of basic igneous rock. However, very few studies have reported the formation of celadonite under nonmarine conditions. An integrated study involving field investigation, petrography, mineralogy, and mineral chemistry highlighted the origin of celadonite in two clay-rich horizons (green boles) of the Late Cretaceous Deccan volcanic province. Within the Salher green bole, the celadonite occurred as the dissolution and alteration of plagioclase, volcanic glass, and pore-filling cement. In the case of the Pune green bole, the celadonite was formed by the alteration of plagioclase, pyroxene, and precipitation as film within intergranular pores, along with zeolite. The celadonite in the Salher green bole exhibited slightly lower K2O and Fe2O3 and higher Al2O3 than in the Pune. The mineral chemistry of the former showed a composition closer to ferro-aluminoceladonite. Although the mineral chemistry of celadonite overlaps with glauconite, the distinct 10 Å and 15 Å reflections in XRD, euhedral lath and honeycomb morphology under SEM, and characteristic absorption bands in VNIR spectroscopy (0.4–2.5 µm) and FTIR spectroscopy (400–4000 cm−1) identified celadonite and Fe-smectite within green boles. The green boles were formed either by the alteration of a volcaniclastic deposit in local pools of water or by the in situ alteration of the fragmentary flow top. The present study is significant due to the occurrence of celadonite in a nonmarine environment, as it otherwise forms under submarine conditions.

Geochemical biosignature formation in experimental Martian fluvio‐lacustrine and simulated evaporitic settings

“…Rock succession at Mawrth Vallis most likely suggests pedogenic alteration or hydrothermal alteration (T of 20-60°C) of basaltic rocks by groundwater circulation or after deposition into a marine environment (Bishop et al, 2008(Bishop et al, , 2013McKeown et al, 2009;Poulet et al, 2014). On Earth, celadonite forms in amygdales, voids, or fractures in mm to lm deposits not only under hydrothermal conditions (e.g., Odin et al, 1988;Weisenberger & Selbekk, 2009) but also as results of direct precipitation from lowtemperature (>17°C) Fe-rich solutions at the sedimentwater interface (Polg ari et al, 2013) and as results of in situ alteration of basalts in local pools of water in continental settings (Singh et al, 2022). Similar processes may have occurred in Gale and Jezero crater lacustrine systems and, for this reason, celadonite on Mars may be more widespread, although difficult to detect.…”