CENOZOIC EVOLUTION AND TECTONIC RECONSTRUCTION OF THE QAIDAM BASIN: EVIDENCE FROM SEISMIC PROFILES
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摘要: 柴达木盆地是青藏高原内部最大的坳陷。柴达木盆地构造成因的研究, 可以揭示青藏高原形成机制和生长历史。本文分析了柴达木盆地区域地震勘探剖面, 得到如下认识:柴达木盆地一级构造为新生代宽缓复向斜, 其振幅和半波长分别从柴西的> 16km和~170km变化为柴东的 < 4km和~50km。褶皱首先在柴西贴近阿尔金断裂附近形成(65~50.5Ma), 并向柴东扩展(23.3Ma)。复向斜的形成与较老的柴北缘逆冲断层系(65~50.5Ma)和较年轻的柴南缘逆冲断层系(35.5~23.3Ma)有关。盆地内部新生代上地壳缩短作用, 由柴西的> 48%, 向柴东减小到 < 1%, 说明在柴西和柴东之间, 存在地壳加厚机制的渐进转换:柴西主要为上地壳缩短, 柴东主要为下地壳缩短。Abstract: The Qaidam basin is the largest topographic depression inside the Tibetan plateau. Understanding the tectonic origin of the Qaidam basin has important implications for unraveling the formation mechanism and growth history of the Tibetan plateau.In this paper, the authors analyze regional seismic-reflection profiles across the basin.The first-order structure of the basin is a broad Cenozoic synclinorium, with an amplitude ranging from > 16 km in the west to < 4 km in the east.The fold axis propagated from the western Qaidam basin against the Altyn Tagh fault at 65-50.5Ma to the eastern basin at 23.3Ma; its half-wavelength changes from ~170 km in the west to ~50 km in the east. The formation of the synclinorium was induced by an older thrust system initiated at ~65-50.5Ma at the northern margin and a younger thrust system initiated at 35.5-23.3Ma at the southern margin.Cenozoic upper-crustal shortening decreases across the basin from > 48% in the west to < 1% in the east, suggesting a progressive shift in crustal thickening mechanisms across the Qaidam basin, from dominantly upper-crustal shortening in the west to dominantly lower-crustal shortening in the east.
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Key words:
- seismic reflection profile /
- tectonic reconstruction /
- Cenozoic /
- Qaidam basin
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图 1 柴达木盆地地质构造简图与6条穿盆地震剖面分布
NZF-北宗务隆山断裂带；NQF-柴北缘断裂带；QTF-祁漫塔格北缘断裂带；SQF-柴达木南缘断裂带；KLF-昆仑断裂带；ATF-阿尔金断裂带；WHF-哇洪山断裂带(温泉断裂带)：LDF-拉配泉拆离断层。
Figure 1. Geological sketch map of the Qaidam Basin and locations of six transect seismic lines
图 2 地震测线地质平衡剖面与恢复剖面
(a)、(c)、(e)、(g)、(i)、(k)分别为CDM-7、CDM-160、CDM-200、CDM-246、CDM-330、CDM-392地震测线的地质平衡剖面; (b)、(d)、(f)、(h)、(j)、(l)分别为CDM-7、CDM-160、CDM-200、CDM-246、CDM-330、CDM-392地震测线的地质恢复剖面。地层代号:Q-第四系; Sh-狮子沟组; SY-上油砂山组; XY-下油砂山组; SG-上干柴沟组; XGs-下干柴沟组上段; XGx-下干柴沟组下段; XG-下干柴沟组; Lu-路乐河组; J-侏罗系; pre-Mz-前中生界
Figure 2. Balanced geo-sections and restored sections of transect seismic lines
图 3 地震测线CDM-160平衡剖面的构造重建
阶段1, 白垩纪末(65Ma); 阶段2, 古新世-早始新世(65~50.5M a); 阶段3, 中始新世(50.5~ 35.5Ma); 阶段4, 晚始新世-上新世(35.5~2.6Ma); 阶段5, 第四纪(2.6~0M a)。地层代号同图 2
Figure 3. Restoration of balanced cross section CDM-160 showing 5-stage evolution
图 4 柴达木盆地缩短应变的分布与盆地南界的重建
(A)柴达木盆地变形时间与缩短应变的分布; (B)根据地壳缩短量进行的柴达木盆地南界的重建; (C)根据东昆仑山的旋转进行的柴达木盆地南界的重建。
Figure 4. Summary of timing and shortening strain across the Qaidam basin and reconstruction of the southern Qaidam margin
图 5 柴达木盆地上地壳变形与下地壳变形之间的关系
(A)上地壳缩短、下地壳和地幔岩石圈俯冲形成的地壳增厚; (B)下地壳纯剪切收缩形成的地壳增厚; (C)下地壳缩短形成地壳增厚; (D)通道流地壳增厚模式; (E)下地壳逆冲重复导致的地壳增厚。
Figure 5. Relationship between upper-crustal and lower-crustal deformations across the Qaidam basin
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