用磷灰石裂变径迹研究西湖凹陷的古地温

对西湖凹陷HY1411井的岩心和岩屑样品中的磷灰石进行了系统的裂变径迹测定 ,并对该井所代表的西湖凹陷地热史进行了分析和模拟。研究结果表明 ,西湖凹陷磷灰石裂变径迹退火带深度为 2 0 0 0～ 390 0m ,相应的古地温为 70～ 12 5℃ ,古地温梯度为 2 .8℃ / (10 0m)。西湖凹陷主要生油岩是下第三系暗色泥页岩 ,其大量生成油气的温度约为 90℃ ,生油门限是 2 80 0m左右。西湖凹陷的磷灰石裂变径迹长度为单峰分布 ,说明此地区自第三纪以来仅经历了一次热事件作用 ,且与该地区大地构造活动一致。这说明此方法是可信的 ,值得进一步推广。

ESTIMATION OF ANCIENT SUBSURFACE TEMPERATURES IN XIHU DEPRESSION WITH APATITE FISSION TRACKS

Apatite fission tracks are measured for the estimation of the ancient temperatures in the Tertiary in the Xihu depression of the East China Sea basin. The investigation concluded that the annealing temperatures of the apatite fission tracks are in the range of 70～125℃, which are corresponding to the depths of 2000～3900 m in the Xihu depression and its ancient subsurface temperature gradient of 2.8 ℃ in one hundred meters. Dark shales are believed as major oil source rocks in Xihu depression, which got to the oil generating threshold at about 2800 m corresponding to 90 ℃. As the apatite fission tracks are in single peak distrbution, the authors believe that the subsurface temperature evolution was resulted from one thermal event which was controlled by tectonic activity in the Xihu depression. Therefore, estimation of ancient temperatures with apatite fission tracks is believable,and can be applied to other depressions in the East China Sea basin.