Wang Jingchuan, Lekić Vedran, Schmerr Nicholas C, Gu Yu J, Guo Yi, Lin Rongzhi
Department of Geology, University of Maryland, College Park, MD 20742, USA.
Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1, Canada.
Sci Adv. 2024 Sep 27;10(39):eado1219. doi: 10.1126/sciadv.ado1219.
The Pacific large low-shear-velocity province (LLSVP), as revealed by cluster analysis of global tomographic models, hosts multiple internal anomalies, including a notable gap (~20° wide) between the central and eastern Pacific. The cause of the structural gap remains unconstrained. Directly above this structural gap, we identify an anomalously thick mantle transition zone east of the East Pacific Rise, the fastest-spreading ocean ridge in the world, using a dense set of precursors. The area of the thickened transition zone exhibits faster-than-average velocities according to recent tomographic images, suggesting perturbed postolivine phase boundaries shifting in response to lowered temperatures. We attribute this observation to episodes of Mesozoic-aged (250 to 120 million years ago) intraoceanic subduction beneath the present-day Nazca Plate. The eastern portion of the Pacific LLSVP was separated by downwelling because of this ancient oceanic slab. Our discovery provides a unique perspective on linking deep Earth structures with surface subduction.
通过对全球层析成像模型进行聚类分析发现，太平洋大型低剪切速度省（LLSVP）存在多个内部异常，包括太平洋中部和东部之间明显的间隙（约20°宽）。这种结构间隙的成因仍未确定。在这个结构间隙正上方，我们利用密集的一组前驱体，在世界上扩张速度最快的大洋中脊——东太平洋海隆以东，识别出一个异常增厚的地幔过渡带。根据最近的层析成像图像，增厚过渡带区域的速度高于平均水平，这表明后橄榄石相边界因温度降低而发生扰动并移动。我们将这一观测结果归因于中生代（2.5亿至1.2亿年前）现今纳斯卡板块下方的洋内俯冲事件。由于这块古老的大洋板块，太平洋LLSVP的东部区域因下沉而被分隔开。我们的发现为将地球深部结构与地表俯冲联系起来提供了独特视角。
