利用接收函数方法研究海南地幔柱上地幔间断面精细结构

Previous seismological studies have suggested the existence of the Hainan plume. However, due to the limitation of station distribution and lateral resolution in seismic tomography, the fine structure of the major seismic discontinuities in the upper mantle beneath the Hainan and surrounding regions has not been precisely depicted, especially for the lithosphere-asthenosphere boundary (LAB) and mantle transition zone discontinuities (410 km/660 km). Therefore, the origin and deep structure of the Hainan plume are still debated. Here, we plan to use P- and S-receiver functions to image the high-resolution structure of the upper mantle discontinuities beneath the Hainan and surrounding regions, based on dense broadband teleseismic data recorded by permanent regional and national seismic networks, combined with our temporary seismic observations. The lithospheric structure and the mantle transition zone thickness under the Hainan hotspot will be mainly discussed. Our study will provide more seismological constraints on the origin and deep structure of the Hainan plume and will also be of great significance for further discussion on the cause and tectonic evolution of the volcanoes in Hainan region.

已有地震学研究为海南地幔柱的存在提供了证据。但受台站分布及地震层析成像横向分辨率的限制，海南及其周边地区上地幔间断面结构，特别是岩石圈与软流圈边界(LAB)和地幔过渡带间断面(410 km/660 km)的精细形态未能清晰描绘。对于形成地表热点的海南地幔柱深部结构及起源，目前仍存在较大的争议。本项目拟利用海南及其周边地区区域和国家固定台网所记录的地震波形资料，联合课题组近几年布设的高密度宽频带流动地震台站的观测数据，基于远震P波和S波接收函数方法，构建海南及其邻区高分辨率的上地幔间断面结构成像，着重探讨海南热点地区现今岩石圈界面的几何形态和地幔过渡带间断面厚度变化，为揭示海南地幔柱深部结构及起源提供更多的地震学约束，对于进一步探讨海南地区火山成因及其深部构造演化动力学过程有极为重要的意义。

海南地幔柱的深部结构和起源一直存在较大的争议。本项目收集和处理了海南及其邻区大量的地震波形数据，开展了P波和S波接收函数以及接收函数偏移成像等工作。研究结果表明，海南地幔柱起源于海南岛北部以及雷州半岛东侧的下地幔，一部分地幔热物质穿过地幔过渡带上升至岩石圈底部并与岩石圈相互作用，造成该地区地壳、岩石圈和地幔过渡带厚度的显著减薄；而另一部分热物质在下地幔顶部从源区向北北东方向流动，造成了广东沿海地区660km界面的抬升。我们同时发展并完善了三维接收函数克希霍夫偏移成像方法，该方法的成像结果具有更高的分辨率，对于其他地区的三维深部结构研究也有很好的应用前景。