利用S波接收函数研究红河断裂带及其邻区岩石圈结构

The Lithospheric Structure Beneath Red River Fault Zone and Its Adjacent Areas by S-wave Receiver Function

摘要:

红河断裂带两侧复杂的地质构造背景、剧烈的板块运动和频繁的地震活动,使红河断裂带及其邻区成为研究板块运动及深部动力学特征的焦点区域。本文基于红河断裂带及其邻区 (21° N～26° N,98° E～104° E) 28个固定台记录的2011—2022年远震数据,采用S波接收函数偏移成像方法获得了研究区的地壳与岩石圈厚度,结合已有的地球物理资料分析地壳和岩石圈厚度横向变化特征及其相关的动力学过程。研究结果表明: ①红河断裂带是一条超壳断裂带,其西南侧地区地壳厚度 (30～43km) 较其东北侧地区 (36～45km) 更薄且变化更剧烈,推测可能是由于ES向逃逸的高原物质进入滇中地块,导致断裂带东北侧地壳较西南侧厚; ②研究区岩石圈厚度在70～141km范围内变化,大部分区域的岩石圈较薄且在红河断裂带两侧跨度平缓,推测腾冲火山区薄且上隆的岩石圈底界面与上涌的软流圈物质加热熔融岩石圈底部相关,塑性流动的热物质横跨红河断裂带东向运移,可能导致研究区大部分区域的岩石圈减薄。

Abstract:

The Red River Fault zone and its adjacent regions,located in the southern part of the North-South seismic belt,have emerged as focal areas for research on plate motion and geodynamic characteristics. This is attributed to the complex geotectonic background,vigorous plate motion,and frequent seismic activity in this region. This study employs teleseismic data recorded by 28 permanent seismic stations within the Red River Fault zone and its adjacent areas (21° N—26° N,98° E—104° E) from January 2011 to December 2022. We utilize the S-wave receiver function migration technique to determine the thickness of the crust and lithosphere in the study area. Additionally,we integrate these imaging results with existing geophysical research findings to analyze the lateral variations in crustal and lithospheric thickness and related structural features. The results are as followings: (1) The Red River Fault is an ultra-crustal fault. The crustal thickness on the southwest side (30～43km) is thinner and exhibits more pronounced variations compared to the northeast side (36～45km). It is inferred that crustal material flow escaping from the southeast margin of the Tibetan Plateau and entering the Central Yunnan block has led to a thicker crust on the northeast side of the Red River Fault zone than on the southwest side. (2) The lithospheric thickness in the study area ranges from 70km to 141km. In most regions,the lithosphere is relatively thin,with a gentle gradient observed on both sides of the Red River Fault zone. We hypothesize that the thin and uplifted lower boundary of the lithosphere in the Tengchong volcanic region is associated with upwelling asthenospheric material heating the base of the lithosphere. Furthermore,we propose that the eastward migration of hot,plastic-flowing material across the Red River Fault zone may contribute to the thinning of the lithosphere in many areas within the study region.