Deformation, Fluid Generation, and Seismogenesis in a Transitional Subduction Environment, the Marlborough Region, New Zealand, Revealed with a Magnetotelluric Resistivity Transect

研究的智力价值。-新西兰的马尔伯勒走滑断裂系统清楚地表明，板块会聚从真正俯冲的上、下板块之间的近脱钩(北岛北部)过渡到地壳和上地幔几乎连续增厚且没有俯冲的板块之间的基本完全耦合(南岛中部)。在马尔伯勒，与现今澳大利亚-太平洋板块汇聚方向成小角度的四个主要的右旋断裂带容纳了平行于板块边界的大部分运动分量。将进行该地区的大地电磁(MT)地球物理断面，以澄清对走滑断裂带内部物理状态的控制，并填补在不耦合和完全耦合情况下对变压造山带的认识空白。要解决的基本问题包括：1)发震断层的流态化程度有多大，这可能影响应力积累？2)断裂带的流体状态是累积位移或活动程度的函数吗？3)主要断裂带的流体是在当地获得的，还是从下地壳获得的？4)当主要走滑断层开始时，地壳的物理条件是什么？5)是什么使俯冲和俯冲板块之间的耦合得以发展？6)俯冲界面是尖锐的，还是存在广泛的扩散变形？7)如果流体有助于控制俯冲界面附近的流变性，它们的来源是什么？8)板材脱水反应是否对下行板材的地震活动有贡献？研究的更广泛影响。-该提案是美国犹他大学和新西兰地质与核科学研究所(IGNS)在研究一个重要的固体地球问题方面的全面合作努力。对一名女研究生的支持可用于教授最先进的地球物理仪器、野外勘测设计参数、海外环境中的实际后勤问题、现代反演方法以及电阻率与地球物理化学状态之间的关系。对现成的商业地球物理仪器用于专门的固体地球研究的效用进行了测试，该项目提高了电学方法在固体地球科学中未得到充分利用的地位。其他社会益处包括更广泛地了解对断层强度的控制，以及建立破坏性压力的能力。

Intellectual Merit of Research. - The Marlborough strike slip fault system of New Zealand clearly exemplifies the transition in plate convergence from near decoupling between upper and lower plates in true subduction (northern North Island), to essentially complete coupling between the plates with near-continuous thickening of the crust and upper mantle and no subduction (central South Island). In Marlborough, four major dextral fault zones at a low angle to the present Australian-Pacific plate convergence direction accommodate most of the component of motion parallel to the plate boundary. A magnetotelluric (MT) geophysical transect of the region is to be carried out to clarify controls on internal physical state of strike slip fault zones, and fill a gap in understanding of transpressional orogens between uncoupled and fully coupled situations. Basic questions to be addressed include: 1) How much are seismogenic faults fluidized, which may influence stress buildup?, 2) Is the fluid state of fault zones a function of cumulative displacement or degree of activity?, 3) Do major fault zones acquire their fluids locally, or from the lower crust?, 4) What are the physical conditions in the crust as major strike slip faults initiate?, 5) What enables coupling between subducting and overriding plates to develop?, 6) Is the subduction interface sharp, or is there a broad zone of diffuse deformation?, 7) If fluids help control rheology near the subduction interface, what is their origin?, and 8) Do slab dehydration reactions contribute to seismicity of the downgoing slab?Broader Impacts of the Research. - The proposal is a fully cooperative effort between the University of Utah of the United States and the Institute of Geological and Nuclear Sciences (IGNS) of New Zealand in research into an important solid earth problem. Support for a female graduate student is made available for education into state of the art geophysical instrumentation, parameters of field survey design, practical logistical matters in overseas settings, modern methods of inversion, and the relationship between electrical resistivity and physico-chemical state in the Earth. The utility of off-the-shelf commercial geophysical instrumentation for specialized solid earth studies is tested and the project raises the profile of electrical methods, an underutilized field, in solid earth science. Additional societal benefits include broader understanding of the controls on fault strength and ability to build up damaging stresses.