库车坳陷西段新生代盐构造特征及演化

库车坳陷古-始新世沉积厚层膏盐岩,在沉积差异形成的重力负载作用下,膏盐岩发生塑性流动,山前的膏盐岩流向盆地内侧,发育盐底辟构造,形成吐孜玛扎盐墙、却勒盐丘,膏盐岩的塑性流动发生在膏盐层沉积后不久,并且持续到上新世库车早期,盐底辟构造主要通过被动底辟作用完成。上新世晚期,库车坳陷受到强烈的挤压作用,发生大规模的逆冲推覆,吐孜玛扎盐墙、却勒盐丘(应变强度薄弱部位)的北侧发育断层,盐岩沿断层刺穿地表,形成底辟型盐墙和喷出型盐席,同时发育整合型米斯坎塔克盐背斜和大宛齐盐枕。库车坳陷的盐构造分为两个阶段:构造平静期(渐新世-上新世),以重力差异负载作用为主,发育底辟型盐构造;构造挤压期(上新世晚期-现今),挤压作用强烈,形成逆冲推覆断层,在不同的构造部位分别形成盐席、盐墙、盐背斜,早期的盐构造对于后续挤压作用下盐构造的形成和演化具有重要的控制作用。

Cenozoic Salt Structures and Evolution in the Western Kuqa Depression, Tarim Basin, China

The salt anticlines and diapirs in the Kuqa depression have previously been considered to be formed through the late Pliocene to nowadays regional compression.We present evidence that the diapirs,which grew mainly by sedimentary differential loading during Oligocene to Pliocene,is preexisting dispirs amplified by the late Pliocene to nowadays regional compression.Compression created thrust faults in the north margin of the diapirs and above the diapirs crests.Where the source layer was thick,the diapirs reactively rose along the thrust faults,the salt pierced ground surface,forming salt walls and salt sheets over the diapirs,and salt anticline and salt pillow at the southern side of the diapirs.Elsewhere the source layer was depleted,the dispirs is inactively during regional compression.The field and seismic profile observation suggest that the folds and thrust faults formed mainly by the late Pliocene to nowadays regional compression across the Kuqa depression.This compression rejuvenated the preexisting diapirs that grew mainly during the Oligocene to Pliocene time by sedimentary differential loading gravity.Because salt is much weaker than its surrounding rocks,the preexisting diapirs localized thrust faults within the diapirs and their roofs and formed salt anticline and salt pillow in the southern side of the diapirs.The salt structure can be divided into two stages in the Kuqa depression:During Oligocene to Pliocene,diapirs grew mainly by sedimentary differential loading gravity;In late Pliocene to nowadays,the early diapirs have been amplified by regional compression,and then formed salt sheet,salt wall and salt anticline.