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

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 Sr-87-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.