川南滇北交界处杏仁状玄武岩中的沥青微形貌特征与成因研究

The genesis and micro-morphologic characteristics of bitumen in amygdaloidal basalt in southern Sichuan-northern Yunnan border area

对产出于川南和滇北交界处杏仁状玄武岩中的沥青进行了微形貌特征研究。沥青呈皮壳状、圈层状、杏仁状、致密块状产出于杏仁状玄武岩的晶洞、气孔或裂隙中。沥青的螺旋生长花纹表明沥青是由热液相或气相转变为固相的,沥青中的气孔构造是沥青中的天然气(主要为甲烷)从沥青的气孔逸出的佐证,也表明沥青是成矿热液中的原油受热(>300℃)发生热裂解的产物。沥青的元素组成、H/C比值、反射率以及微区X射线衍射、水晶晶体中的包裹体均一化温度等测试结果表明,川南普格石油热演化与变质程度比滇北昭通石油要高。沥青的碳同位素δ13C在-25‰～-31‰之间变化,表明沥青具生物成因,有机质来自下二叠统的碳酸盐岩。川南普格玄武岩有利于气藏的形成,滇北昭通玄武岩则有利于油藏的形成。

Bitumen in the crustose, circular layer, amygdaloid and dense massive forms occur in vugs, vesicles and fractures of amygdaloidal basalt. The spiral growth patterns of bitumen show that bitumen has experienced transformation from hydrothermal fluid or gas into solid. Vesicle structure in bitumen evidences that natural gas （the main composition being methane） escaped from it, and that bitumen was produced through the thermal cracking of original oil （〉300℃） from the ore-forming hydrothermal solution. The element composition, H/C ratio, reflectivity and micro-XRD of bitumen as well as homogeneous temperature of fluid inclusions in rock quartz crystal show that the degree of thermal evolution and metamorphism of petroleum in Puge area of southern Sichuan was higher than that in Zhaotong area of northern Yunnan. The variation of carbon isotope δ13C content from -25‰ to -31‰ suggests that bitumen was of biogenic origin, and the organic matter came from lower Permian carbonate rock. Basalt of Puge area in southern Sichuan is favorable for the formation of gas reservoirs, and that of Zhaotong area in northern Yunnan is conducive to oil deposition.