青藏高原北缘昆仑山中段构造隆升的磷灰石裂变径迹记录

Apatite fission-track records of the tectonic uplift of the central segment fo the Kunlun Mountains on the northern margin of the Qinghai-Tibet Plateau

3组磷灰石裂变径迹年龄分别反映出阿尔金地块白垩纪末(69.5±2.9)Ma、昆仑山前山地带和昆仑山后山地带(高原区北缘)上新世晚期(4.2±0.8)Ma和(3.9±0.6)Ma、早更新世中期(1.66±0.31)Ma等3次构造抬升事件。根据磷灰石裂变径迹分析样品的古埋深及据前人有关资料推测的古地表高程,换算出样品的古海拔高程,再由高程差得出绝对构造抬升量,绝对抬升速率为绝对抬升量与时间(裂变径迹年龄)差之比。计算结果:阿尔金山北缘69Ma以来总共抬升了4940m,平均抬升速率为0.072mm/a。昆仑山前山地带4.15Ma至1.66Ma间总共抬升了1380m,平均抬升速率为0.55mm/a;1.66Ma以来总共抬升了4140m,平均抬升速率为2.49mm/a。昆仑山后山地带3.85Ma至1.66Ma间总共抬升量约为1500m,平均抬升速率为0.70mm/a;1.66Ma以来总共抬升量约为5140m,平均抬升速率为3.19mm/a。结合有关阶地特征及年龄,推算出21ka左右的晚更新世末以来昆仑山后山的抬升速率可能达11mm/a。昆仑山后山地带较前山地带4Ma以来相对抬升了1120m,二者的平均隆升速率比约为1.2。

Three groups of apatite fission-track ages indicate three tectonic uplift events:the uplift of the Altyn Tagh block at the end of the Cretaceous(69.5±2.9Ma BP)and the uplifts of the front of the Kunlun Mountains and rear zone of the Kunlun Mountains(on the northern margin of the plateau region)in the late Pliocene(4.2±0.8Ma BP and3.9±0.6Ma BP)and in the middle Early Pleistocene(1.66±0.31Ma BP).The paleo-altitudes of the apatite fission-track samples are calculated on the basis of the paleo-burial depths of the samples and paleo-altitudes of the surface inferred according previous relevant data,and then the absolute tectonic uplift amount is calculated,which is equivalent to the altitude difference and the absolute rate of tectonic uplift is equivalent to the ratio of the absolute uplift amount to the difference of apatite fission-track ages.The results of the calculation are as follows:the northern margin of the Altyn Tagh has risen4940m since69Ma BP,with an average uplift rate of0.072mm/a;the front zone of the Kunlun Mountains has risen1380m from4.15to1.66Ma BP,with an average uplift rate of0.55mm/a,and risen4140m since1.66Ma BP,with an average uplift rate of2.49mm/a;the rear zone of the Kunlun Mountains has risen1500m from3.85to1.66Ma BP,with an average uplift rate of0.70mm/a,and it has risen5140m since1.66Ma BP,with an average uplift rate of3.19mm/a.In combination with the relevant terrace features and ages,it may be estimated that the average uplift rate of the rear zone of the Kunlun Mountains may have reached11mm/a since the end of the late Pleistocene(21ka BP).The rear zone of the Kunlun Mountains may have risen1120m relative to the front zone of the Kunlun Mountains since4Ma BP and the ratio of the average uplift rates of the two zones is about1.2.