The Evidence of Hydrothermal Activity and Its Significance of Permian-Triassic Strata, Eastern Longgang Area, Northeastern Sichuan Basin

Key words: 
• hydrothermal activity /
• migration channel /
• activity period /
• Permian-Triassic /
• eastern Longgang area /
• NE Sichuan Basin

Abstract: Based on the analysis of petrology of Changxing Formation-Feixianguan Formation in eastern Longgang Area, NE Sichuan Basin, combing with analytical method such as rare earth elements(REE), fluid-inclusions and laser Laman, it is illustrated that there exist mineral assemblages including saddle dolomite-pyrite, fluorite-quartz and corresponding homogenization temperatures is above normal formation temperature. All the rock samples from reservoirs of Changxing Fm-Feixianguan Fm shares the same positive Ce anomaly with marine sedimentary limestone and most of them are characterized by the similar REE patterns and significant positive Eu anomaly of saddle dolomite. There exist bitumen-bearing inclusions, which are products of oil-bearing inclusions trapped by the period of oil generation peak of Longtan Formation after high-temperature cracking in hydrothermal minerals of fluorite and quartz. The hydrothermal activity can be divided into 2 periods on the basis of relationship between mineral occupation and hydrocarbon charging timing:The first stage corresponding to the late Permian-early Triassic and the action mode of is to promote the formation process and late-reformation of dolomite reservoir; the second stage corresponding to Late Triassic and the action mode is filling of saddle dolomite, quartz and fluorite in reservoir spaces.