The fluid origin of calcite veins in Shunnan-Gucheng area of Tarim Basin and its implications for hydrocarbon accumulation.

The high-angle, structural genetic calcite veins of the Ordovician in Shunnan-Gucheng area in Tarim Basin provide a convenient to study the fluid properties and hydrocarbon migration to accumulation events in fault zone of this area. Based on detailed core investigation, studies of fluid inclusions in calcite veins and comparison of geochemical characteristics of limestone matrix and calcite veins were carried out. Multiple types of hydrocarbons inclusion, including dry asphalt inclusion, three-phase hydrocarbon inclusion, oil and water inclusion, gas-rich inclusion, were found in calcite veins. And the coexisted aqueous inclusions with gas-liquid phase had high homogenization temperature (130-160 °C). The distribution characteristics of 18O-depleted (δ18O: -13.1‰ to - 8.7‰), 87Sr-enriched (87Sr/86Sr: 0.708 879 to 0.710 432), relatively high total Rare Earth Elements and positive Europium Anomalies indicated that the structural origin of calcite veins were mainly derived from the dissolution of surrounding rocks and diagenetic-hydrocarbon fluids. Participation signs of meteoric water were not proved. The rich hydrocarbon inclusions in the calcite veins indicated that the north-east strike-slip fault zone in Shunnan- Gucheng area is an important channel for hydrocarbon migration and accumulation. [ABSTRACT FROM AUTHOR]