Types and features of diagenetic fluids in Shunbei No. 4 strike-slip fault zone in Shuntuoguole Low Uplift, Tarim Basin

Abstract

The Shunbei No. 4 strike-slip fault zone is an important exploration target in the Shuntuoguole Low Uplift of Tarim Basin, and the Middle Ordovician carbonate is a major hydrocarbon-bearing stratum. Fault structures and accompanied fluids play a key role for the distribution of carbonate reservoirs, and it is therefore important to study the fluids accompanied with fault evolution. Petrography, in situ Sr isotopic compositions, in situ rare earth elements (REE) and U-Pb dating were carried out to reveal the fluids from which the calcites in fractures precipitated. The calcites in fractures show 87Sr/86Sr ratios of 0.708 498-0.709 177, and the REE patterns of the calcites are characterized by negative Ce anomaly, positive Eu anomaly and high Y/Ho ratios. The calcite samples show U-Pb isochron age of (433±17) Ma and (449±15) Ma, respectively. The 87Sr/86Sr ratios and REE patterns of the calcites suggest that parent fluids experienced elevated temperature environment and buffered by carbonate host rocks. The U-Pb isochron age implies that the calcites may record the fault-related fluids during the Ⅲ stage of the Middle Caledonian Movement, which might be associated with the Altyn orogeny.

Keywords

• strike-slip fault
• diagenetic fluid
• carbonates
• geochemistry
• shunbei area
• tarim basin