大兴安岭诺敏河火山群远震P波衰减研究

板内火山活动是板内下方深部物质组成的重要视窗,而中国东北是研究板内火山的热点场所.中国东北火山活动主要沿大兴安岭及松辽盆地周缘分布,隐匿在大兴安岭内的各火山群落鲜有地球物理观测.本研究聚焦于大兴安岭北部的诺敏河火山群,利用围绕诺敏河火山布设的43个流动台站记录到的17个远震事件数据,通过时间域波形匹配法计算了300条直达P波震相的Δt*,并进一步采用贝叶斯蒙特卡洛方法反演得到了研究区的二维Δt*模型,为约束诺敏河火山地区的深部结构提供了新的观测证据.结果显示研究区高衰减区域与火山活动在空间位置上有很好的一致性.诺敏河火山与研究区北端临近小古里河火山区域均观测到高Δt*值,可能由区域下方热地幔物质上涌导致.诺敏河火山东部、科洛河火山西部区域观测到低Δt*值,与高衰减区域最大Δt*差值达约0.3±0.05 s,可能由两部分原因导致:该区域下方残留未被侵蚀的岩石圈,以及局部区域或存在的部分熔融导致的残留地幔矿物脱水.

Study of teleseismic P-wave attenuation beneath the Nuomin River Volcanoes

Intraplate volcanism is a key access to the deep architecture beneath intra-continental. NE China is a worthy experimental site for exploring intraplate volcanism, where abundant Cenozoic volcanic sites are mainly distributed along the Da Hinggan and surrounding the Songliao Basin. Since volcanoes located at the Da Hinggan are lack of geophysical observations, this study is focused on the Nuomin River Volcanic site sitting on the northern Da Hinggan. We estimated the Δt^* value of 300 P-wave phases from 17 teleseismic events received by 43 seismometers deployed around the Nuomin River Volcanoes, using a time-domain waveform matching method. Furthermore, we obtained a 2D map of Δt^* by applying a non-linear Bayesian Monte Carlo inversion. The observed relative attenuation facilitated our comprehensive understanding of the deep structure beneath the Nuomin River Volcanoes. Results suggest that highly attenuated regions are consistent well with the locations of volcanism. Higher Δt^* values are observed beneath the Nuomin River Volcanoes and the northern region near the Xiaoguli River Volcano to the north, where hot mantle upwelling are inferred. Lower attenuation is found to the east of the Nuomin River Volcanic site, where reduction of Δt^* is up to ~0.3±0.05 s when comparing with the highest observation. We attribute these low Δt^* observations to two main causes: the remained thicker lithosphere and the presence of partial melting and consequent mantle dehydration beneath this region.