后裂谷沉积盆地建造的性质

ON THE NATURE OF POSTRIFT SEDIMENTARY BASIN FORMATION

考虑了裂谷作用停止后部分熔融地幔的固结作用,本文提出了后裂谷沉积盆地形成的一种新模式,这一模式与前人的模式的根本区别在于:这一模式认为异常地幔并非一个简单的软流圈隆起,而是一个在Moho-面之下的部分熔融异常地幔透镜体,玄武质熔融物即在此处产生。据岩石学和地震方面的资料可知:部分熔融物占异常地幔的5-20％。岩石圈的冷却、异常地幔内熔融物的固结作用(而非热收缩作用)导致了沉降作用及盆地的形成。文中给出了热历史模式、固结作用的时间范围及作为时间函数的沉积幅度变化的计算公式,以及在岩石圈简单冷却情况下和考虑熔融物固结作用时的沉积盆地沉降曲线。沉积盆地中的沉积物从经验沉降曲线中可分出快速沉积相和相对停止部分。异常地幔中5-20％的熔融物可解释这一现象。快速沉降相的存在使我们可以更精确的确定生油的时限。如果考虑异常地幔的固化效应,则开始生油的时间要比岩石圈简单冷却情况下的生油时间早2-3倍。

A new model for the formation of post-rift sedimentary basin, which takes into account the solidification of the anomalous mantle, has been proposed. The content of 5-20% melts in the anomalous mantle permits to explain the characteristic features of the empirical subsidence curves: presence of the fast phase of subsidence and a relatively stopping part—'step' The existence of the fast subsidence phase makes it possible to determine more accurately the time limits of oil generation. If the effect of the anomalous mantle solidification is taken into account, the starting point of oil generation is 2-3 times earlier than in the case of simple lithosphere cooling.