平衡剖面反映的柴西新生代变形对青藏高原隆升的响应

柴达木盆地为一中新生代盆地,位于青藏高原北缘,盆内中新生代地层发育很好地记录了印度一欧亚板块自约55Ma以来碰撞传到高原北缘的地质事件.在最新的高精度磁性地层绝对年代控制下,通过盆内西部五条北东-南西向地震大剖面,用平衡剖面方法恢复了新生代以来盆地因两大板块碰撞而引起的地壳收敛缩短量.结果显示:在宏观上柴西地区存在两个相对快速收缩期:早始新世-渐新世和晚中新世或上新世-现今(E_(1+2)末-N_1,43.80～22.00Ma和N~2_2或N_2~3-现今,8.20或2.65～0Ma)和两个相对较弱收缩期:中生代末-早始新世和渐新世-晚中新世(M_z-E_(1+2)初期,65.00～43.80Ma和N_1末-N~2_2,22.00～2.65Ma)以及两个主要的断裂活动期次,早期路乐河组末-下干柴沟组上段时期(E_(1+2)-E_3~2)和晚期上油砂山组至今(N~2_2-Q).在微观上,盆地内部受自身断裂活动的控制,发育了独特的形态.表明在印欧板块碰撞高原隆升的早期,柴西地区就开始变形响应,随后盆地在整个新生代发展过程中,都处于板块碰撞高原隆升的大环境影响下而发生整体的变形缩短,同时自身的断裂活动控制了盆地的微观形态.

Cenozoic deformation history of the western Qaidam Basin responding to the uplift of the Tibetan Plateau by restoration of the balance section

Qaidam Basin in the northern margin of the Tibetan Plateau is a large mesozoic-cenozoic basin and bears huge thick continuous cenozoic strata, recording well the geological events of collision of India with Eurasia since 55 Ma. Based on latest progress in precise dating of stratigraphy, a technique of balanced section was applied to five NE-SW seismic geological profiles in the western Qaidam Basin to reconstruct the crust shortening history from collision and to understand the nature of the basin. Two main rapid deformation periods were determined: the early eocene-oligocene and the late miocene or the pliocene to today (the end of E_(1+2)-N_1, 43.80～22.00 Ma and N~2_2 or N_2~3 to now, 8.20 or 2.65～0Ma) and two main slow shorting periods: the end of mesozoic to the early eocene and the oligocene to the late miocene(the early M_z-E_(1+2),65.00～43.80 Ma and the end of N_1-N~2_2, 22.00～2.65 Ma). At the same time, there were two main the fault activity periods in the western Qaidam Basin. The one movement period was the end of the Lulehe formation to Xiaganchaigou formation(E_(1+2)-E_3~2) and the other was since the Xiayoushashan formation (N~2_2-Q). The Qaidam Basin's evolution was controlled by the faults action in the cenozoic and it shaped the particular modality. The results showed that the western Qaidam Basin began to deform weakly nearly synchronous to the early collision and the Tibetan Plateau uplift, and continued to the present. Qaidam Basin formed the particular shape that is controlled on the fault movement in the interior.