Structural Detachment Layer Distribution Variation and Trap Controls Along Foreland Thrust Belts in Northern and Southern Tianshan

doi:10.19657/j.geoscience.1000-8527.2021.191

Abstract

Abstract:

The foreland thrust belts in northern and southern Tianshan have strong differential deformation characteristics. The detachment layer variations have great influence on the oil-gas trapping patterns in these belts, and are thus important for oil and gas exploration in both northern and southern Tianshan. Based on seismic data interpretation, fault distance measurement, shortening statistics, and balanced section restoration, we conclude that: (1) properties of the detachment layer in the foreland thrust belts in northern and southern Tianshan are different. The Paleogene gypsum-halite constitutes the detachment layer in the Kuqa foreland thrust belt, and the layered deformation characteristics are significant. Deep faults in the foreland thrust belt on the southern margin of Junggar Basin mostly crosscut the detachment layers with poor stratification; (2) Difference of Cenozoic deformation in the foreland thrust belts in northern and southern Tianshan, with the average shortening rate of 12.1% and 9.93% in the foreland thrust belts at Kuqa and on the southern margin of Junggar Basin, respectively, showing that the deformation intensity of the former was higher; (3) Affected by the detachment layer variations, the average distance between the upper and lower detachment layers of the foreland thrust belts at Kuqa is larger than that of on the southern margin of Junggar Basin. Shortening of the Kuqa foreland thrust belt shows a complex multiple-peak pattern, which is absent for the foreland thrust belt on the southern margin of Junggar Basin. This indicates that the plasticity and delamination ability of foreland thrust belt detachment layers at Kuqa are stronger than that on the southern margin of Junggar Basin; (4) Based on the different fault activity and detachment layers in the northern and southern Tianshan foreland thrust belts, the latter is mainly composed of lithologic and structural composite traps, whereas the former is dominated by large structural traps beneath the halite sequence and supplemented by lithologic-structural traps. Lithologic-structural traps controlled by detachment layers such as the Jurassic-Triassic coal seams and mudstone in the deep foreland thrust belt on the southern margin of Junggar Basin and Kuqa foreland thrust belts are favorable targets for future oil and gas exploration.

Key words: southern and northern Tianshan, structural difference, detachment layer, trap type

CLC Number:

TE121.2

HOU Xiaoxiao, NENG Yuan, QI Jiafu, LI Kuayue, HU Jianning, FU Yonghong, LI Yuan, GUO Man. Structural Detachment Layer Distribution Variation and Trap Controls Along Foreland Thrust Belts in Northern and Southern Tianshan[J]. Geoscience, 2021, 35(06): 1818-1829.

Figures/Tables 11

Fig.1 Division of tectonic units in the foreland thrust belts at Kuqa and on the southern margin of Junggar Basin

Fig.2 Integrated stratigraphic map of the northern and southern Tianshan orogens

Fig.3 Tectonic deformation patterns of the Kuqa foreland thrust belt

Fig.4 Tectonic deformation patterns of the foreland thrust belt on the southern margin of Junggar Basin

Table 1 Shortening distance and rate of balance profiles in the foreland thrust belts (middle section) at Kuqa and on the southern margin of JunggarBasin

位置	测线	现今长度/km	总缩短量/km	总缩短率/%	新生代以来变形强度
位置	测线	现今长度/km	总缩短量/km	总缩短率/%	平均缩短量/km	平均缩短率/%
库车	2-7	92.48	11.22	10.8	12.28	12.1
准南	1-2	47.19	7.85	14.2	7.53	9.93

Fig.5 Tectonic evolution diagram of the Kuqa foreland thrust belt

Fig.6 Tectonic evolution diagram of the foreland thrust belt on the southern margin of Junggar Basin

Fig.7 Histogram of average fault distance above and below the detachment layer for the foreland thrust belts at Kuqa and on the southern margin of Junggar Basin

Fig.8 Histogram of shortening distance above and below the detachment layer for the foreland thrust belts on the southern margin of Junggar Basin and Kuqa

Fig.9 Accumulation model for the Kuqa foreland thrust belt

Fig.10 Accumulation model for the foreland thrust belt on the southern margin of Junggar Basin

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