Publication
The origin of celestine-quartz-calcite geodes associated with a basaltic dyke, Makhtesh Ramon, Israel
Publisher:
Cambridge University Press (CUP)
Date:
29-10-2014
DOI:
10.1017/S0016756813000800
Abstract: Spectacular celestine geodes occur in a Jurassic peri-evaporitic sequence (Ardon Formation) exposed in Makhtesh Ramon, southern Israel. The geodes are found only in one specific location: adjacent to an intrusive contact with a Lower Cretaceous basaltic dyke. Celestine, well known in sedimentary associations worldwide and considered as a low temperature mineral, may therefore be associated with magmatic-induced hydrothermal activity. Abundant fluid inclusions in celestine provide valuable information on its origin: gas-rich inclusions in celestine interiors homogenized at T≥200°C whereas smaller liquid-rich inclusions record the growth of celestine rims at T≤200°C. Near 0°C melting temperatures of some fluid inclusions and the occurrence of hydrous Ca-sulphate solid crystals in other inclusions indicate that celestine precipitated from variably concentrated Ca-sulphate aqueous solutions of meteoric origin. Celestine crystallized from meteoric water heated by the cooling basaltic dyke at shallow levels ( c. 160 m) during a Lower Cretaceous thermal perturbation recorded by regional uplift and magmatism. The 87 Sr/ 86 Sr ratio of geode celestine, 0.7074, is similar to that measured in the dolostones of the host Jurassic sequence, but differs markedly from the non-radiogenic ratio of the dyke. Strontium in celestine was derived from dolostones preserving the 87 Sr/ 86 Sr of Lower Jurassic seawater, while sulphur (δ 34 S = 19.9‰) was provided by in situ dissolution of precursor marine gypsum (δ 34 S = 16.8‰) indicated by relict anhydrite inclusions in celestine. Low-temperature meteoric fluid flow during the C anian caused alteration of the dyke into secondary clays and alteration of geodal celestine into quartz, calcite and iron oxides.