Deep seismic sounding data reveal the crustal structures beneath Zoigê basin and its surrounding folded orogenic belts
Deep seismic sounding data reveal the crustal structures beneath Zoigê basin and its surrounding folded orogenic belts
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DOI：
10.1007/s11430-009-0166-0
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发表时间：
2010-02
期刊：
影响因子：
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通讯作者：
Shixu Jia;Xian-kang Zhang;Jin-ren Zhao;Fu-yun Wang;Cheng-ke Zhang;Zhao-fan Xu;Ji-shun Pan;Z. L
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文献类型：
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作者：
Shixu Jia;Xian-kang Zhang;Jin-ren Zhao;Fu-yun Wang;Cheng-ke Zhang;Zhao-fan Xu;Ji-shun Pan;Z. L
松潘-甘孜盆地位于青藏高原东北缘由近东西向近南北向构造的转折部位，若尔盖盆地位于松潘-甘孜盆地的中心。本文利用若尔盖盆地的深地震测深资料，建立了若尔盖盆地及其周边褶皱造山带的地壳结构模型。本文还讨论了若尔盖盆地基底的结构与性质、高地与周边褶皱造山带的构造关系、青藏高原东北缘地壳的变形与增厚以及地壳的拆离与松弛过程。结果表明，若尔盖盆地三叠系岩石具有高密度（2.65- 2.75g/cm ~ 3）和高速度（5.6km/s），形成了一个特殊的“中生代基底”。松潘-甘孜构造带转化为两类地壳结构不同的构造单元，相对稳定的若尔盖高地盆地和盆地周边活动的褶皱造山带，是青藏高原地壳物质向东流动并受到周边稳定地块阻挡的过程中形成的。青藏高原东北缘地壳增厚主要发生在中、下地壳，在若尔盖盆地周边褶皱造山带中明显出现低速多反射构造。这表明褶皱造山带的中、下地壳曾经历过强烈的构造变形。若尔盖盆地及其南、北方两侧的褶皱造山带地壳厚度约50 km。“山根”无法识别。推测造山晚期，向东流动的深部物质在周围刚性岩石的阻挡下，围绕东部构造结沿相对松弛的南侧顺时针沿着运动，导致若尔盖盆地周边褶皱造山带的强烈拉伸作用。
Songpan-Garze massif is located at the turning position of tectonics from the near west-east direction to the near north-south direction in the northeastern margin of Qinghai-Tibet Plateau, with Zoigê basin in the centre of the massif. In this paper, we build a crustal structure model of Zoigê basin and its surrounding folded orogenic belts using the deep seismic sounding data in this region. We also discuss structures and properties of the basement in Zoigê basin, tectonic relations between Zoigê upland basin and its surrounding folded orogenic belts, crustal deformation and thickening in the northeastern margin of Tibetan Plateau, and decoupling and relaxing processes in the crust. The results indicate that a special “Mesozoic basement” is formed of Triassic rocks with high density (2.65–2.75 g/cm3) and high velocity (5.6 km/s) in Zoigê basin. Songpan-Garze tectonic massif was transformed into two types of tectonic units with different crustal structures, i.e., relatively stable Zoigê upland basin and active folded orogenic belts around the basin, in the course of the crustal material of Tibetan Plateau flowing eastward and obstructed by surrounding stable blocks. The thickening of the crust in the northeastern margin of Tibetan Plateau mainly occurred in the mid and lower crust, and the structure characterized by low velocities and multiple reflectors obviously appears in the folded orogenic belts around Zoigê basin. It implies that the mid and lower crust underwent a strong tectonic deformation in the folded orogenic areas. The thickness of the crust is about 50 km in Zoigê basin and the folded orogenic belts at the both southern and northern sides of Zoigê basin. The “Mountain root” cannot be identified. It is inferred that during the later orogenic period the eastwards flowing deep materials moved clockwise along the relatively relaxing southern side around the eastern tectonic knot under the obstructing of surrounding rigid massifs, and it resulted in the strong stretching action of the folded orogenic belts around Zoigê basin.