Intense silicification of Ordovician carbonates in the Tarim Basin: Constraints from fluid inclusion Rb–Sr isotope dating and geochemistry of quartz

Abstract

Abstract An unconventional porous silicified carbonate reservoir was unveiled in the Middle Ordovician fractured limestone within a strike‐slip fault zone in the Tarim Basin, NW China. The silicified carbonates are mainly composed of fine‐ to medium‐crystalline fascicular quartz matrix and coarse crystalline bladed to columnar quartz cement. Fluid inclusion leachate‐residue paired Rb–Sr isotopic dating of the quartz cement yields an isochron age of 167 ± 15 Ma, attesting to a causal link to the Jurassic (Yanshanian) orogeny. Pervasive replacement of matrix quartz and subsequent precipitation of cement quartz through nonisothermal effervescence probably induced by episodic influxes of the hot silica‐ and 87 Sr‐rich basinal brines from the neighbouring deeper Manjiaer depression. This study thus signifies the usefulness of using Rb–Sr isotope dating method in constraining the timing of carbonate alteration, enabling to establish the deterministic relationship of basinal fluid evolution with the major tectonic activity.