哥斯达黎加汇聚边缘俯冲剥蚀的古地磁学制约-IODP344航次后研究

Subduction erosion at convergent margins removes material from the front and base of the overriding plate, causing the subsidence in the forearc area and the landward migration of trench. It is critical to quantify the mass loss by subduction erosion as it is closely related to crustal recycling and mass balance. Because the part of the convergent margin that is affected most by subduction erosion is typically under the sea, it is difficult to study the effect of subduction erosion by direct observations. Previous studies of subduction erosion often estimate the subduction-caused mass loss on the basis of biostratigraphy as an age control that is low in resolution and can lead to large errors in the estimates. Integrated Ocean Drilling Program Expedition 344 cored at the subducting Co-cos ridge and the forearc area that is directly affected by the subduction at the Costa Rican convergent margin. And the cores recorded the vertical motions at the convergent margin that were interpreted to result from the subduction erosion. Here we propose to conduct a detailed study of magnetostratigphy and rock magnetism that is based on down hole variation of rock magnetic parameters of the cores from three representative sites, namely, Site U1381 from the subducting plate, Site U1380 from the middle slope, and Site U1413 from the upper slope of the forearc area. Together with the constraint from biostratigraphy, the paleomagnetic work will aim to establish high-resolution timescales for these three sites. The high resolution timescales will provide an important basis for examining the impact of the subduction erosion by the Co-cos ridge on the Central American convergent margin, and contribute to better quantify the mass loss by subduction erosion at the convergent margin.

汇聚边缘的俯冲剥蚀作用将上覆板块的前缘和底部物质带回到地球内部，从而导致弧前区沉降和海沟陆向迁移。因此，定量估算俯冲剥蚀产生的物质亏损对于理解地壳物质再循环至关重要。然而，由于受俯冲剥蚀影响的汇聚边缘通常处于海面以下，不易直接取样观察，而研究程度较低；而且,现有的研究中，地层时代通常由生物地层控制而较粗略，并导致对俯冲剥蚀的估算误差较大。IODP 344航次在哥斯达黎加汇聚边缘实施了钻探，直接从位于俯冲板块之上的科科斯脊及受其俯冲剥蚀影响的弧前区钻取了岩芯；而且,所取岩芯清晰记录到了俯冲剥蚀引起的垂向运动。本项目拟对该航次的U1381、U1380和U1413等三个有代表性站位的岩芯开展详尽的磁性地层和岩石磁学综合研究；同时，结合生物地层，为这些站位的岩芯建立高分辨率的年代标尺, 从而为探讨科科斯脊俯冲剥蚀对中美洲汇聚边缘的影响, 以及为准确地估算俯冲剥蚀引起的物质亏损提供可靠的年代学基础。