镜质体、海相镜质体和镜质体反射率及其研究实例

Marine Vitrinite:Vitrinite Reflectance as an Indicator of Concealed Pluton

镜质体是一种由高等植物木质素经过生物化学降解作用和凝胶化作用形成的胶状体,在煤和炭质泥页岩中含量高,仅出现在志留纪及其以后的地层中。此外,还有一种海相镜质体,主要由海洋低等生物(藻类、菌类及某些海洋低等动物)经腐殖化作用而形成,主要存在于早古生代及晚古生代页岩和碳酸盐岩地层中。研究表明,海相镜质体反射率(R^o_m)可作为成熟度指标加以应用。海相镜质体成熟作用轨迹不同于镜质体,二者存在一定的相关关系,使用时需把海相镜质体反射率换算为镜质体反射率(R_o)。镜质体反射率是一个寻找隐伏岩体的好方法,作者采用镜质体反射率方法对铜陵地区开展了研究,初步结果表明,铜陵地区全部数值均超过地热增温率理论曲线,说明铜陵地区深部可能有较大的隐伏岩体,深度大约在4~5 km左右。此外,在ZK113号钻孔深度200~260 m处R_o很高(>2%~3%),可能预示钻孔旁侧有规模较小的隐伏侵入体,推测距钻孔距离不超过100 m,但具体方位不详。上述研究表明采用镜质体反射率方法寻找隐伏岩体是可行的,它的最大优点是解释的唯一性,R_o数值仅与温度有关,不受其他因素的干扰。

Vitrinite is a colloid formed by biochemical degradation and gelation of higher plant lignin, which is high in coal and carbonaceous shale and appears only in strata younger than Silurian. Marine vitrinite is a special vitrinite resulted from humification of the marine lower organisms （algae, fungi and some marine animals）, which is mainly found in the Early Paleozoic and Late Paleozoic shale and carbonate rocks. Studies show that marine vitrinite reflectance can be used as indices of maturity. The maturation pathway of marine vitrinite is different from common vitrinite, however, there is correlation between the marine vitrinite reflectance and those of the common vitrinite. In the Tongling region, Ro values of vitrinite reflectance are all over the theoretical geothermal warming rate curve, indicative of large pluton buried about 4-5 km beneath. In addition, Ro is fairly high （〉2%-3%） at 200-260 m depth of ZK113 which indicates that there may be small hidden intrusions around the drilling, the distance from borehole is no more than 100 m, but the specific location is unknown. The study showed that vitrinite reflectance is a feasible method of looking for hidden pluton, and the advantage of this approach is that Ro values are only temperature sensitive.