(Table 1) Apparent ages from 40Ar/39Ar heating steps for DSDP Hole 72-516F basalts

Submarine basalts are difficult to date accurately by the potassium-argon method. Dalrymple and Moore (1968) and Dymond (1970), for example, showed that, when the conventional K-Ar method is used, pillow lavas may contain excess 40Ar. Use of the 40Ar/39Ar step-heating method has not overcome the problem, as had been hoped, and has produced some conflicting results. Ozima and Saito (1973) concluded that the excess 40Ar is retained only in high temperature sites, but Seidemann (1978) found that it could be released at all temperatures. Furthermore, addition of potassium, from seawater, to the rock after it has solidified can result in low ages (Seidemann, 1977), the opposite effect to that of excess 40Ar. Thus, apparent ages may be either greater or less than the age of extrusion. Because of this discouraging record, the present study was approached pragmatically, to investigate whether self-consistent results can be obtained by the 40Ar/39Ar step-heating method.

海底玄武岩难以通过钾氩法（potassium-argon method）实现精准定年。例如，Dalrymple与Moore（1968年）及Dymond（1970年）的研究证实，采用传统钾氩法定年时，枕状熔岩（pillow lavas）可能含有过剩的40Ar。尽管学界曾预期40Ar/39Ar阶段加热法（40Ar/39Ar step-heating method）能够解决这一难题，但该方法非但未能克服该问题，反而得出了多组相互矛盾的结果。Ozima与Saito（1973年）提出过剩40Ar仅留存于高温位点，而Seidemann（1978年）则发现其可在所有温度区间内被释放。此外，玄武岩固结后，海水带入的钾元素会导致定年结果偏低（Seidemann, 1977），这一效应与过剩40Ar带来的影响恰好相反。因此，测得的视年龄既可能高于火山喷发的真实年龄，也可能低于该真实年龄。鉴于这一不尽如人意的研究现状，本研究采取务实的研究思路，旨在探究通过40Ar/39Ar阶段加热法能否获得自洽的定年结果。