华北克拉通北缘(怀来-苏尼特右旗)地壳结构

2009年，中国地质科学院地质研究所与美国俄克拉荷马大学合作实施了一条长453 km的深地震反射、宽角反射与折射、三分量反射地震联合探测剖面. 剖面南起怀来盆地，向北依次穿过燕山造山带西缘、内蒙地轴、白乃庙弧带、温都尔庙杂岩带，到达索伦缝合带. 其中，宽角反射与折射剖面采用8个0.5~1.5 t炸药震源激发，使用300套Texan单分量数字检波器接收，获得了高质量的地震资料. 通过资料分析和处理，识别出沉积层及结晶基底的折射波（Pg）、来自上地壳底界面的反射波（Pcp），中地壳底界面的反射波（Plp），莫霍界面的反射波（Pmp）及上地幔顶部的折射波（Pn）等5个震相. 分别采用Hole有限差分层析成像和Rayinvr算法对华北克拉通北缘及中亚造山带南部进行了上地壳P波速度结构成像和全地壳二维射线追踪反演成像. 结果显示：（1）中亚造山带地壳厚度~40 km，变化平缓，低于全球平均造山带地壳平均厚度，可能为造山后区域伸展的结果. 阴山-燕山带附近莫霍明显加深，推测其为燕山期造山过程形成的山根，但该山根很可能在后期被改造. （2）测线中部地壳上部速度较高，对应地表大面积花岗岩出露，而下地壳速度较低，速度梯度低，呈通道状，推测其可能曾为古亚洲洋向南俯冲消亡的主动陆缘，并在碰撞后演变为伸展环境下岩浆侵入的通道. （3）华北克拉通北缘与中亚造山带显示出不同速度变化特征，前者变化相对缓而后者则变化剧烈，二者的分界出现在赤峰-白云鄂博断裂附近.

Crustal structure of the northern margin of north China craton from Huailai to Sonid Youqi profile

The SinoProbe-02 North China joint seismic experiment consisted of three seismic recording efforts along 453 km long profile. The profile extended from the Huailai basin, across the Yinshan-Yanshan belt, Inner Mongolia paleo-uplift, Bainaimiao arc, Ondor Sum accretion complex to the Solonker suture zone. We processed, analyzed, and modeled the data collected during the wide-angle reflection and refraction effort. The seismic waves from 8 explosions were recorded by 300 Texan recorders. The P-wave field provided good quality data for most of the profile. Arrivals of refracted and reflected waves from sediments and basement (Pg), intracrustal phases (PcP, PlP), and the Moho (PmP, Pn) were typically observed. Hole's first arrival tomography program was used to obtain the upper crustal velocity structure. And Zelt's 2D travel time raytracing and inversion program (Rayinvr) was used to obtain the full crustal structure. The final 2D P-wave velocity model contains many features of tectonic significance: (1) The flat and relatively shallow Moho in the Central Asia Orogeny Belt (CAOB) may be attributed to the extension; thicker crust appears beneath the Yinshan-Yanshan belt and was probably generated by compression in the Jurassic-Cretaceous and modified during the later extension; (2) The velocity structure varies significantly from the NCC to the CAOB, and the boundary between them appears at the Chifeng-Bayan Obo fault; (3) Relatively high velocities in the upper crust of the middle part of the profile may represent the outcrop of large area granites; strong velocity variations beneath the Bainaimiao arc and Ondor Sum subduction accretion complex indicate that multiple pulses of magmatism occurred during the complex tectonic evolution of this area.