Three gravity structures

Huomatu sliding block

Tuositai sliding folds and Gaoquan gypsum-salt diapir

are recognized in the west part of the south margin of the Junggar Basin.Huomatu sliding block is located at the north Tianshan Mountains foreland to the south of Hutubi—Dushanzhi region.It is 140 km long from east to west

28 km wide inN-S direction

3.5 km thick on average.It covers an area of 2740 km

2

and the volumeis 9450 km

3

.The sliding mass consists of Tertiary sediments.The sliding sheet is formedby less-compacted argillaceous rock of the Eogene Anjihaihe Formation.The high-pressureanomaly was resulted from the unbalance between compaction and liquor draining as wellas its hydrocarbon generation.With the methods of balanced section

bow and arrow andwidth compensation of unload area

maximum slide distance was determined to be 15 km

and primitive slide angle 5-6°.The Tuositai sliding fold is located at the north Tianshan Mountains to the south ofWusu.It is a big gravity-slide structure mainly formed by Mesozoic sediments.The slidingmass stretches 30 km long in E-W direction

10 km wide in S-N direction

2 km thick.It covers an area of 260 km

2

and the volume is 540 km

3

.The bottom sliding sheet consistsof the Upper Triassic Xiaoquangou Formation and the less-compacted argillaceous rock ofthe Lower Jurassic Sangonghe Formation.The high-pressure anomaly is resulted by largeamount of unloading due to denudation of the upper strata in the late stage and the impe-diment of the release of argillaceous pore-pressure.Its primitive slide angle is measured tobe 8°by quantitative calculation.The Gaoquan embryonic diapir was developed in the Upper Tertiary Taxihe Forma-tion in the Sikeshu sag.It stretches nearly E-W direction

covers an area of 140 km

2

andis buried at 2000 km deep.The diapir was resulted from gypsum and rock-salt that archedthe overlying strata.The formation cause of this structure are:1.the reverse of densitiesfrom gypsum and salt to overlying strata;2.the induction of fault movement;3.the dif-ferentia compaction of the overlying strata.