中国南方存在印支期的油气藏——Re-Os同位素体系的制约

Indosinian Hydrocarbon Accumulation in South China:A Re-Os Isotope Constrain

利用Re-Os同位素方法开展富含有机质的沥青、原油等的研究,是确定油气成藏时间和破坏时间有效的但极富挑战性的新途径,在国内尚无研究实例报道。以我国南方最大的古油藏之一的麻江古油藏中的沥青为主要对象,采用Re-Os同位素方法试图限定油气的成藏时间和破坏时间。研究表明,麻江古油藏的固体沥青Re、Os同位素质量分数分别在41.5×10-6～642×10-6和0.21×10-6～12.15×10-6之间,N(187Re)/N(188Os)比值较高,且变化范围较大,在270.90～4074.99之间,Os同位素组成指示中等放射成因,其N(187Os)/N(188Os)比值在0.3400～3.6557之间变化。所有沥青样品的模式年龄在28～144Ma之间变化,集中在85Ma左右。通过沥青Re-Os同位素研究,结合详细地质资料,认为麻江古油藏的成藏时间为印支期—早燕山期(144Ma之前),而油藏破坏时间为燕山晚期即85Ma左右。

Rhenium-Osmium isotope system is a new and challenging method used to determined the hydrocarbon accumulation and date of desdtruction. This paper reports a Re-Os approach to date the hydrocarbon accumulation and destruction time of the Majiang paleo-oil pool,one of the largest paleo-oil reservoirs in South China. The Re and Os contents in the bitumen vary from 41.5×10-6 to 642×10-6 and 0.21×10-6 to 12.15×10-6,respectively. Their 187Re/188Os ratios are characterized by high and variable range of 270.90 to 4 074.99,while their 187Os/188Os ratios are moderately radiogenic,ranging from 0.340 0 to 3.655 7. The Re-Os model ages for the bitumen vary between 28 Ma and 144 Ma,with an average of ~85 Ma. With conbination of the documented geological researches,the paper suggests that the Majiang hydrocarbon deposit should be finally accumulated at ~144 Ma of Indosinian to Early Yanshanian period,and destroyed at ~85 Ma of Late Yanshanian period.