Collaborative Research: Lithospheric Evolution in Response to Triple Junction Migration: Seismic Images of the Mendocino Triple Junction Region

加利福尼亚州北部的沿海地区，从北纬38度到北纬41度，代表了现今构造体制从俯冲到门多西诺三联结(MTJ)运动转换的突变区域。由于三重结点沿北美海岸向北迁移，了解该地区的地壳和上地幔结构将有助于深入了解整个美国西海岸大陆边缘以及全球其他汇聚边缘的构造演化。该项目涉及一项综合地震实验，以成像MTJ通过之前和之后的地壳和上地幔结构。这项研究是许多研究人员长期、多学科努力的重要组成部分，目的是将这一明确界定的系统作为一个现场实验室，研究与转换和汇聚构造环境中的地幔上涌、熔体分离和迁移、构造吸积和地壳变形有关的物理化学过程，并评估这些过程对大陆生长和演化的影响。这项研究包括两个田间季节。一个季节涉及采集八条多道地震(MCS)剖面，旨在成像下面的深部地壳结构：1)铂。Arena盆地、圣安德烈亚斯断裂和MJ以南的消亡海沟；2)门多西诺转换断层；3)MJ以北的Eel River盆地和Cascadia俯冲带。这些剖面与MTJ北部和南部的井相交，以提供地层控制。MCS剖面还将记录在海底水听器和地震仪以及部署在陆地上的REFTEK地震仪上，以提供补充的大口径数据。另一个季节涉及获取三条陆上爆炸源折射剖面，其中两条延伸了MTF南北拍摄的陆上/近海断面，以便穿过弧前和无奴隶窗口。第三条折射剖面将跟随方济各会地体的走向，以穿过戈尔达板块的南缘，绘制地壳结构可能沿走向的变化，并将两个主要的陆上-近海剖面联系在一起。所有三个陆地剖面都将使用REFTEK和SGR地震仪进行密集测量。

The coastal region of northern California from latitude of 38o to 41oN represents a region in which the present tectonic regime changes abruptly from subduction to transform motion at the Mendocino Triple Junction (MTJ). Because the triple junction is migrating north along the coast of North America, an understanding of the crust and upper mantle structure in this region will provide insights into the tectonic evolution of the entire U.S. west coast continental margin as well as other convergent margins worldwide. This project involves an integrated seismic experiment to image the structure of the crust and upper mantle immediately before and after passage of the MTJ. This study represents an important part of a long-term, multi-disciplinary effort on the part of many investigators to exploit this well defined system as an in-situ laboratory to study physical and chemical processes associated with mantle upwelling, melt segregation and migration, tectonic accretion, and crustal deformation in both transform and convergent tectonic settings, and to evaluate the implications of these processes for continental growth and evolution. The study encompasses two field seasons. One season involves acquisition of eight multichannel seismic (MCS) profiles designed to image deep crustal structure beneath: 1) Pt. Arena basin, San Andreas fault, and extinct trench south of the MTJ; 2) the Mendocino Transform fault; and 3) the Eel River basin and Cascadia subduction zone north of the MTJ. The profiles intersect wells both north and south of the MTJ to provide stratigraphic control. The MCS profiles will also be recorded on ocean-bottom hydrophones and seismographs and on REFTEK seismographs deployed onshore to provide complementary large aperture data. The other season involves acquisition of three onshore explosive-source refraction profiles, two of which extend onshore/offshore transects shot north and south of the MTF, in order to cross the fore-arc and slabless window. The third refraction profile will follow the trend of the Franciscan terrane in order to cross the southern edge of the Gorda plate, map possible along-strike variations in crustal structure and tie together the two primary onshore-offshore profiles. All three land profiles will be densely instrumented with REFTEK and SGR seismographs.