Duration of the Intrusion Formation and Its Relation to the Size of Thermal and Maturity Aureoles of the Intrusion Bodies

Abstract

Maturity aureole of the trap and sill complex considered in this chapter determines the depth of oil and gas windows and an ability of the underlying and host sedimentary rocks to generate hydrocarbons. Our study shows that a size of maturity aureoles of the single intrusions and trap complex decreases considerably with increase of duration of these complex is formation. So, the aureole size in for formation of the trap with total thickness of 1000 m underlain by clay complex reduces from 1150–1067 m for the trap formation during time interval 11.4 years and more shorter to less than 1 m for the traps formed during 1200 and more years under condition of steady rate of the trap formation. The modeling demonstrates that a maturation level of organic matter in sedimentary rocks under trap and within the host rocks of single intrusions can be rather moderate if the time span of formation of these structures (or formation of their single layers) was enough long. The size of maturity aureole of the trap complex formed during several stages can be close to the aureole of single trap layer with maximal thickness. Comparison of computed and measured values of vitrinite reflectance within the thermal aureole of some well-dated intrusions shows that traditional calculations of instantaneous intrusion considerably over-estimate temperatures and maturation of organic matter in the host rocks. Models which consider formation of the intrusive body over time (as distinct from instantaneous intrusion) and especially models of emplacement of the intrusive body in the shell of relatively cool magmatic rocks show better agreement between computed and observed data.