Apatite fission-track and Re-Os geochronology of the xuefeng uplift, China: Temporal implications for dry gas associated hydrocarbon systems

Abstract

Hydrocarbon evolution is extremely challenging to determine, both temporally and spatially, in complex tectonic settings. Here we investigate the western margin of the Xuefeng uplift (southern China), which records multiple and protracted tectonic and hydrocarbongeneration events. This timing of initial oil generation is recorded by low-maturity bitumen (type A), which yields an Re-Os bitumen date of ca. 430 Ma, consistent with basin models and a ca. 405 Ma bitumen Rb-Sr date. In contrast, apatite fission-track (AFT) data yield considerably younger dates that reflect the timing and tectonic evolution of the Yanshan orogeny from the northwest (ca. 150 Ma) to the southeast (ca. 70 Ma). The youngest AFT date coincides with the western margin of Xuefeng uplift, where high-maturity bitumen (type B) occurs that yields a ca. 70 Ma Re-Os date. The Re-Os and AFT dates imply that both the last stage of the Yanshan orogeny and, by inference, the cessation of dry gas generation, occurred ca. 70 Ma. The Re-Os data of this study imply that the Re-Os chronometer can aid in constraining the timing of oil generation and secondary and/or more mature hydrocarbon processes (e.g., thermal cracking and/or gas generation) in hydrocarbon systems worldwide.