摘要
为研究南岭—武夷交汇区深部动力学过程提供深部背景资料和科学依据,本文利用远震P波接收函数H-κ叠加和共转换点(CCP)叠加两种方法获取了研究区66个宽频带流动台站及24个固定台站下方的地壳厚度、泊松比和Moho面起伏形态,揭示了扬子地块与华夏地块地壳结构及泊松比变化特征,给出了南岭和武夷之间一条莫霍凸起带的高分辨图像.结果显示:(1)研究区内地壳厚度平均值为31.2km,泊松比平均值为0.23,总体呈现薄地壳、低泊松比的特点.地壳厚度从西北往东南由厚变薄,与区域地壳伸展特征相一致.(2)在韶关—赣州—吉安—南昌一线存在条带状薄地壳结构,平均值为28km,呈南西—北东向展布,对应的泊松比值略微升高.推测地壳减薄带的形成可能与来自南海方向的地幔热流上涌有关.(3)江南造山带的泊松比整体偏低,存在两处平均值小于0.21的区域.华夏地块内地壳厚度与泊松比之间存在弱的负相关,表示随着地壳厚度的增大,铁镁质的下地壳厚度在整个地壳厚度中所占的比例减小.
Knowing the structures of the crust and upper mantle is fundamental for understandingof the geodynamics of the orogenic belt.To provide observational seismic evidences on deep structures of crust and mantle beneath the intersection zone of Nanling and Wuyi,we conduct the crustal imaging obtained from P-wave receiver functions.In this study,P-wave receiver functions are calculated using teleseismic waveforms recorded by 66 portable broadband stations and 24 permanent stations.We also obtain the crustal thickness,Poisson′s ratio and image of the Moho interface by using the H-κ stacking method and Common Conversion Point(CCP)stacking method,which indicate the variationsin crustal thickness and Poisson′s ratio between the Yangtze block and the Cathaysia block.The results show that:(1)The average thickness of the crust is 31.2 km with the average Poisson′s ratio of 0.23.The study area(Both the Yangtze block and the Cathaysia block are)is characterized by thin crust and low Poisson′s ratio.Further,the thickness of crust gradually decreases from northwest to southeast,which is consistent with the regional extension of the crust.(2)Along the Shaoguan-Ganzhou-Jian-Nanchang profile,a strip of thin(about 28 km)crustal thickness is observed,indicating a southwest-northeast spreading,with a slight increase of the Poisson′s ratio.The results suggest that the upwelling of mantle heat flow from the South China Sea leads to the formation of a weak zone in the crust and plays an important role in regulating the crustal stress field in the South China.(3)The Poisson′s ratio in the Jiangnan orogenic belt is relatively low,with average value of two areas less than 0.21.There is a weak negative correlation between the crustal thickness and the Poisson′s ratio in the Cathaysia block,indicating a decrease of the proportion of the ferromagnesian lower-crust thickness in the entire crust with the increase of crustal thickness.The Poisson′s ratio of the Cathaysia block is smaller than that of the Yangtze block,which may be related to the late formation of the crust and the multiple tectonic activities that have occurred since the Phanerozoic.