首都圈及其邻区的电性莫霍面探测

The detection of the electrical Moho in the Capital Circle region and its vicinity

  • 摘要: 使用首都圈地区电磁台网部分台站的长周期大地电磁数据,反演得到了首都圈地区的深部电性结构,该结果与前人使用地震、电磁、重力等资料得到的研究区地下结构具有较好的一致性。研究表明首都圈地区的地震学莫霍面附近也存在着电阻率变化特征,为了解首都圈地区eMoho分布情况,本文采用对反演所得的电阻率曲线求取一阶导数的方式来刻画测点下方的电性莫霍面的深度位置,通过建立三类地层模型验证了该方法的可行性,并对实测资料反演结果求取一阶导数,结果凸显了电性莫霍面的分布,所得电性莫霍面与地震、重力等资料得到的莫霍面在深度分布上整体基本一致。结合前人的研究,推测在华北部分地区出现的高导薄层可能归结于下地壳物质部分熔融后发生重新结晶分异所导致的硫化物富集。大连台、无棣台下方壳-幔电阻率变化有别于理论模型,这可能是由于临海地区的特殊岩石圈结构,无棣台下方的低阻特征推测可能是该台站下方存在一个软流圈物质上涌通道。

     

    Abstract: The Moho discontinuity, also known as the Mohorovičić discontinuity, represents a critical boundary within the Earth’s lithosphere and plays a significant role in the processes of lithospheric formation and evolution. As a key parameter for describing both the thickness and structural characteristics of the Earth’s crust, variations in the depth and thickness of the Moho are direct manifestations of the long-term dynamic processes that the crust has experienced. Therefore, accurately determining the depth of the Moho is of great importance for understanding the global processes of crustal formation and evolution. One of the most distinct features of the Moho is the pronounced change in seismic wave velocities as seismic waves cross this boundary, making seismic methods become the most widely used approach in Moho-related research. Over the years, numerous researchers have employed a range of seismological techniques to carry out extensive studies on the global distribution of Moho depths. Although the Moho is universally recognized as a continuous first-order discontinuity at the global scale, its structure in tectonically complex regions remains highly intricate and variable. Since the early 21st century, the focus of scientific inquiry has increasingly expanded beyond seismic characteristics to the electrical properties of the crust-mantle boundary. With the ongoing accumulation of long-period magnetotelluric (MT) data and the deepening of global research on the Moho, particularly following the introduction of the concept of the electrical Moho (eMoho) and breakthroughs in its study, there has been growing recognition of the potential of magnetotelluric methods for probing the electrical properties of the Moho. The application of MT methods in this context has demonstrated significant scientific potential and feasibility for revealing the electrical characteristics of the crust-mantle interface. This study, based on long-period broadband MT data from four stations in the North China region, investigates the depth distribution of the electrical Moho in the region. It aims to provide a solid foundation of electrical evidence for gaining a comprehensive understanding of the depth distribution of the Moho across North China, elucidating the mechanisms behind the destruction of the North China Craton, and contributing to the understanding of the seismogenic processes in the Capital Circle region. In this research, long-period MT data from several stations within the electromagnetic network of the Capital Circle region were utilized to invert the deep electrical structure of the area. The results exhibit a high degree of consistency with previous studies that used seismic, electromagnetic, and gravity data to determine subsurface structures at the same stations. The findings indicate that significant resistivity variations are present near the seismologically determined Moho within the Capital Circle region. To further investigate this, the study developed three stratigraphic models, validating the feasibility of employing the first derivative of the inverted resistivity curve as a method for delineating the depth of the electrical Moho beneath individual measurement points. After applying this method to the inversion results, the distribution of the electrical Moho became clearly evident. The results demonstrated that the derived electrical Moho is generally consistent with the Moho depth obtained from seismic, gravity, and other geophysical data, indicating a robust agreement across multiple methods. By integrating findings from previous studies, the research hypothesizes that the high-conductivity thin layer observed in some parts of North China may result from the partial melting and subsequent recrystallization of lower crustal materials, leading to the accumulation of sulfides. In particular, the resistivity variations observed beneath the Dalian and Wudi stations deviate from theoretical expectations, likely due to the unique lithospheric structure associated with the coastal regions. Specifically, the low-resistivity anomaly detected beneath the Wudi station may suggest the presence of an asthenospheric upwelling channel, which could provide a pathway for the movement of deeper mantle materials toward the surface. The findings of this study not only enhance our understanding of the distribution and characteristics of the electrical Moho in the Capital Circle region but also provide a valuable reference for the study of Moho-related processes in other regions with similar geological contexts. The research contributes important insights into the geodynamic mechanisms governing lithospheric evolution, particularly in tectonically active regions, and underscores the complementary nature of seismic and magnetotelluric methods for investigating complex subsurface structures. Through continued accumulation of MT data and further development of interpretative models, magnetotelluric methods are poised to offer increasingly refined insights into the nature of the crust-mantle boundary and its role in broader geophysical processes. These results are not only significant for understanding regional tectonics but also for advancing global studies of the Earth’s lithospheric dynamics.

     

/

返回文章
返回