热液活动区数目和洋脊扩张速率的关系及其在冲绳海槽的应用

RELATIONSHIP BETWEEN THE NUMBER OF HYDROTHERMAL ACTIVITY FIELDS AND SPREADING RATE AND ITS APPLICATION IN THE OKINAWA TROUGH

根据11段洋脊上已经公布的热液活动区数目和扩张速率,建立了洋脊扩张速率和热液活动区数目之间的关系,发现洋脊的扩张速率越高,其上发育的热液活动区数目就越多。两者之间可用一个线性关系式来描述:Ph=0.000 199 294 89Us-0.000 625 479 19,其中,Us为洋脊的扩张速率(mm/a),Ph为单位洋脊上热液活动区的数目(个/km)。依据上述关系,在已知洋脊扩张速率的情况下可以预测洋脊上热液活动区的数目。冲绳海槽前期的扩张(拉张)速率很低,一般为15 mm/a左右。根据地震剖面计算了冲绳海槽现代扩张速率约为42 mm/a。总体上,冲绳海槽直到目前仍为一个低速扩张(拉张)的孤后盆地,但扩张(拉张)速率有明显加快的趋势,所得到的关系式能够较好地符合冲绳海槽的情况,这一方面验证了给出的热液活动区数目和扩张速率之间关系的合理性,另一方面也说明我们对冲绳海槽近期扩张(拉张)速率讨论的合理性。根据在冲绳海槽的应用结果,我们预测冲绳海槽仍然存在尚未查明的热液活动区。

The relationship between the number of hydrothermal activity fields and the sea floor spreading rate has been created based on the number of hydrothermal activity fields and the sea floor spreading rate of 11 segments of the ridge. The paper points out that there will be a larger number of hydrothermal fields on the faster spreading ridges than the lower ones. The linear equation： Ph=0.0002Us-0. 0005 is obtained for the relationship between the number and the spreading rate, here Us for the spreading rate （in ram/a）, and Ph for the possibility of number of hydrothermal activity fields （in 1/km）. Based on the above given equation, the number of possible hydrothermal activity fields can be calculated if we know the spreading rate of a given ridge, and also we can calculate the spreading rate of the given ridge if we know the number of the hydrothermal activity fields along the given ridge. The spreading rate of Okinawa Trough has been discussed in this paper. During the past extension phase of Okinawa Trough, it has a lower spreading （extension） rate around 15 mm/a. The present spreading rate both based on the seismic profile and on the equation given by this paper is around 40 mm/a. The paper also points out that the spreading of the Okinawa Trough goes faster from past to present. There is possibly one or two more hydrothermal activity fields in the Okinawa Trough that we have not detected until now based on the equation and the current spreading rate of the Okinawa Trough.