龙门山冲断带的隆升和川西前陆盆地的沉降

THE UPLIFT OF THE LONGMENSHAN THRUST BELT AND SUBSIDENCE OF THE WESTERN SICHUAN FORELAND BASIN

通过龙门山地区和川西前陆盆地岩石样品的裂变径迹和镜质体反射率的测定和计算机模拟得出:(1)松潘-甘孜褶皱带10Ma以来至少隆升了3—4km,隆升速率最低为0.3—0.4mm/a;(2)龙门山逆冲推覆构造带10Ma以来至少隆升了5—6km,隆升速率最低为0.5—0.6mm/a;(3)龙门山滑脱拆离带60Ma以来隆升1—2km,隆升速率为0.016—0.032mm/a;(4)川西前陆盆地60Ma以来隆升了1.7—3km,隆升速率为0.028—0.05mm/a;(5)10Ma以来北川—映秀—小关子断裂西侧的隆升速率是其东侧隆升速率的40倍;(6)60Ma以前松潘—甘孜褶皱带的隆升与川西前陆盆地的沉降曲线呈镜象关系,即松潘—甘孜褶皱带隆升较快时,盆地沉降也较快。60Ma以来,川西前陆盆地也以隆升为主,但松潘—甘孜褶皱带的隆升速率要大得多;(7)川西前陆盆地的古地温梯度为25℃/km。

Through the measurement and computer modelling of the apatite fission track data and vitrinite reflectance, the uplift history of the Longmenshan thrust belt and uplift (subsidence) history of the Western Sichuan foreland basin have been studied in details. The Songpan-Garze fold belt has been uplifted at least 3-4km since 10Ma B. P., with an uplift rate of at least 0.3-0.4mm/a. The Logmenshan thrust nappe belt has been uplifted 5-6km at least since 10Ma B. P., with an uplift rate of more than 0.5-0.6mm/a. The Longmenshan foreland detachment belt has been uplifted 1-2km since 60 Ma B. P., with an uplift rate of 0.016-0.032mm/a. The Western Sichuan foreland basin has been uplifted 1.7-3km since 60Ma B.P., with an uplift rate of 0.028-0.05mm/a. The uplift rate on the western side of the Beichuan-Yingxiu-Xiaguanzi fault is 40 times as much as that on its eastern side since 10Ma B. P. The palaeo-temperature gradient was 25℃/km in the Western Sichuan foreland basin.