{"title":"通过 P 波慢度异常解析东海海底的 Dʺ 结构","authors":"Jiewen Li, Dongdong Tian, Daoyuan Sun, Ping Tong","doi":"10.1029/2024JB029584","DOIUrl":null,"url":null,"abstract":"<p>The Dʺ layer, defined as 200–400 km in the lowermost mantle, is a thermal and chemical boundary layer between the solid silicate mantle and the liquid outer core. Deciphering the detailed structures of the Dʺ region is essential for unlocking the thermal and chemical states in the deep Earth. Here, we precisely measure the slowness and back-azimuth of the direct P-waves by beamforming based on the <i>F</i>-trace stack at the KZ Array in Kazakhstan, to investigate the detailed Dʺ structures beneath the East China Sea. The P-wave slowness for rays turning beneath the East China Sea exhibits a significant anomaly as a function of the P-wave turning depth. Strong correlations between slowness and back-azimuth anomalies for rays from different directions suggest a tilted Moho, with a tilting direction of ∼103° and a dip angle of ∼15°, beneath the KZ Array, further supported by radial receiver functions. After correcting for the slowness anomalies caused by the tilted Moho and heterogeneities outside the Dʺ layer, we construct a series of <i>Vp</i> Dʺ models to fit the remaining slowness anomalies for rays sampling the East China Sea. We obtain the best Dʺ model with a height of 360 km, a maximum <i>δVp</i> of +1.4%, a Dʺ discontinuity thickness of 120 km, and an 80-km low-velocity layer at the base of the mantle by minimizing residuals between the predicted and observed slowness anomalies. Combining the sharpness of the Dʺ discontinuity imaged here with mineralogical analysis suggests a Fe-enriched region in a cold subduction environment beneath the East China Sea.</p>","PeriodicalId":15864,"journal":{"name":"Journal of Geophysical Research: Solid Earth","volume":null,"pages":null},"PeriodicalIF":3.9000,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Dʺ Structures Beneath the East China Sea Resolved by P-Wave Slowness Anomalies\",\"authors\":\"Jiewen Li, Dongdong Tian, Daoyuan Sun, Ping Tong\",\"doi\":\"10.1029/2024JB029584\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<p>The Dʺ layer, defined as 200–400 km in the lowermost mantle, is a thermal and chemical boundary layer between the solid silicate mantle and the liquid outer core. Deciphering the detailed structures of the Dʺ region is essential for unlocking the thermal and chemical states in the deep Earth. Here, we precisely measure the slowness and back-azimuth of the direct P-waves by beamforming based on the <i>F</i>-trace stack at the KZ Array in Kazakhstan, to investigate the detailed Dʺ structures beneath the East China Sea. The P-wave slowness for rays turning beneath the East China Sea exhibits a significant anomaly as a function of the P-wave turning depth. Strong correlations between slowness and back-azimuth anomalies for rays from different directions suggest a tilted Moho, with a tilting direction of ∼103° and a dip angle of ∼15°, beneath the KZ Array, further supported by radial receiver functions. After correcting for the slowness anomalies caused by the tilted Moho and heterogeneities outside the Dʺ layer, we construct a series of <i>Vp</i> Dʺ models to fit the remaining slowness anomalies for rays sampling the East China Sea. We obtain the best Dʺ model with a height of 360 km, a maximum <i>δVp</i> of +1.4%, a Dʺ discontinuity thickness of 120 km, and an 80-km low-velocity layer at the base of the mantle by minimizing residuals between the predicted and observed slowness anomalies. Combining the sharpness of the Dʺ discontinuity imaged here with mineralogical analysis suggests a Fe-enriched region in a cold subduction environment beneath the East China Sea.</p>\",\"PeriodicalId\":15864,\"journal\":{\"name\":\"Journal of Geophysical Research: Solid Earth\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":3.9000,\"publicationDate\":\"2024-11-01\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Journal of Geophysical Research: Solid Earth\",\"FirstCategoryId\":\"89\",\"ListUrlMain\":\"https://onlinelibrary.wiley.com/doi/10.1029/2024JB029584\",\"RegionNum\":2,\"RegionCategory\":\"地球科学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q1\",\"JCRName\":\"GEOCHEMISTRY & GEOPHYSICS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Geophysical Research: Solid Earth","FirstCategoryId":"89","ListUrlMain":"https://onlinelibrary.wiley.com/doi/10.1029/2024JB029584","RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}
引用次数: 0
摘要
Dʺ 层位于地幔最下层 200-400 公里处,是固态硅酸盐地幔和液态外核之间的热和化学边界层。破译 Dʺ 区域的详细结构对于揭示地球深部的热和化学状态至关重要。在此,我们利用哈萨克斯坦KZ阵列的F-轨迹堆栈,通过波束成形技术精确测量了直接P波的慢度和后方位角,以研究中国东海地下的Dʺ区详细结构。中国东海海底转向射线的 P 波慢度与 P 波转向深度呈显著的反常关系。来自不同方向的射线的慢度与后方位角异常之间的强相关性表明,KZ 阵列下方的莫霍面倾斜,倾斜方向为 ∼103°,倾角为 ∼15°,径向接收函数进一步证实了这一点。在校正了倾斜莫霍和Dʺ层外异质引起的慢度异常后,我们构建了一系列Vp Dʺ模型来拟合东海采样射线的剩余慢度异常。通过最小化预测和观测慢度异常之间的残差,我们得到了最佳的Dʺ模型,其高度为360千米,最大δVp为+1.4%,Dʺ不连续厚度为120千米,地幔底部为80千米的低速层。结合Dʺ不连续面的锐度和矿物学分析表明,中国东海下方的冷俯冲环境中存在一个富铁区。
Dʺ Structures Beneath the East China Sea Resolved by P-Wave Slowness Anomalies
The Dʺ layer, defined as 200–400 km in the lowermost mantle, is a thermal and chemical boundary layer between the solid silicate mantle and the liquid outer core. Deciphering the detailed structures of the Dʺ region is essential for unlocking the thermal and chemical states in the deep Earth. Here, we precisely measure the slowness and back-azimuth of the direct P-waves by beamforming based on the F-trace stack at the KZ Array in Kazakhstan, to investigate the detailed Dʺ structures beneath the East China Sea. The P-wave slowness for rays turning beneath the East China Sea exhibits a significant anomaly as a function of the P-wave turning depth. Strong correlations between slowness and back-azimuth anomalies for rays from different directions suggest a tilted Moho, with a tilting direction of ∼103° and a dip angle of ∼15°, beneath the KZ Array, further supported by radial receiver functions. After correcting for the slowness anomalies caused by the tilted Moho and heterogeneities outside the Dʺ layer, we construct a series of Vp Dʺ models to fit the remaining slowness anomalies for rays sampling the East China Sea. We obtain the best Dʺ model with a height of 360 km, a maximum δVp of +1.4%, a Dʺ discontinuity thickness of 120 km, and an 80-km low-velocity layer at the base of the mantle by minimizing residuals between the predicted and observed slowness anomalies. Combining the sharpness of the Dʺ discontinuity imaged here with mineralogical analysis suggests a Fe-enriched region in a cold subduction environment beneath the East China Sea.
期刊介绍:
The Journal of Geophysical Research: Solid Earth serves as the premier publication for the breadth of solid Earth geophysics including (in alphabetical order): electromagnetic methods; exploration geophysics; geodesy and gravity; geodynamics, rheology, and plate kinematics; geomagnetism and paleomagnetism; hydrogeophysics; Instruments, techniques, and models; solid Earth interactions with the cryosphere, atmosphere, oceans, and climate; marine geology and geophysics; natural and anthropogenic hazards; near surface geophysics; petrology, geochemistry, and mineralogy; planet Earth physics and chemistry; rock mechanics and deformation; seismology; tectonophysics; and volcanology.
JGR: Solid Earth has long distinguished itself as the venue for publication of Research Articles backed solidly by data and as well as presenting theoretical and numerical developments with broad applications. Research Articles published in JGR: Solid Earth have had long-term impacts in their fields.
JGR: Solid Earth provides a venue for special issues and special themes based on conferences, workshops, and community initiatives. JGR: Solid Earth also publishes Commentaries on research and emerging trends in the field; these are commissioned by the editors, and suggestion are welcome.