Collaborative Research: Geophysical Investigation of a Modern Continent-Continent Collisional Orogen: The SouthernAlps, New Zealand

在新西兰的南岛，太平洋板块和澳大利亚板块的汇合形成了一个相对狭窄（约80公里宽）的活跃造山带，与世界上大多数其他地区相比，它的构造不那么复杂。板块边界的主要构造元素是南阿尔卑斯山脉，其垂直运动和伴随的侵蚀速率是世界上最高的，以及阿尔卑斯断层，它同时具有走滑和倾滑运动的成分。该项目下的大地电磁工作是一项为期四年的南岛板块边界合作研究的一部分，涉及美国和新西兰的科学家，分别来自南加州大学、麻省理工学院、伍兹霍尔、加州大学伯克利分校、普渡大学、圣地亚哥州立大学、犹他州、地质与核科学研究所（新西兰）、维多利亚大学（新西兰）和奥塔哥大学（新西兰）。两国都提供了支持。该项目的核心是南岛的一对多面地球物理样带，包括主动震源地震学、海上多通道和OBS数据采集、被动地震学、岩石物理学、大地电磁学、重力测量和地表地质学。实验的目的是描绘南阿尔卑斯山及其邻近地区的地壳和上地幔结构。到目前为止，收集到的大地电磁数据已经形成了横跨南岛中部的高质量大地电磁样带。该造山带内部的MT响应为了解南岛深处的热状态和流变学提供了令人兴奋的希望。完整的电阻率结构将为地壳应变分配、下地壳的变质作用、地壳与地幔的相对变形、南岛隆起的补偿以及其他几个重要过程提供必要的边界。然而，由于缺乏陆路车辆通过南岛主分隔带的上行隆起主要区域，目前沿样带的MT覆盖范围存在一个关键缺口。该项目收集的数据将通过直升机运输支持的6 - 8个新的大地电磁学测深来弥补这一覆盖范围的差距。国际情报局的人员将参与这项工作，并提供人力和后勤支持。＊＊＊

9725759 Jiracek On the South Island of New Zealand, convergence of the Pacific and Australian plates has given rise to a relatively narrow (~80 km wide) and less complex zone of active mountain building than in most other regions of the world. The dominant structural elements of the plate boundary are the Southern Alps where vertical movement and accompanying rates of erosion are among the highest in the world, and the Alpine Fault which has components of both strike- slip and dip-slip movement. The magnetotelluric work that willl be done under this project is part of a four year cooperative study of the South Island plate boundary involving U.S. and New Zealand scientists at USC, MIT, Woods Hole, UC Berkeley, Purdue, San Diego State, Utah, Institute for Geological and Nuclear Sciences (IGNS, NZ), Victoria University (NZ), and Otago (NZ). Support is being provided by both countries. The centerpiece of the project is a pair of multifaceted geophysical transects across the South Island including active source seismology, offshore multichannel and OBS data acquisition, passive seismology, petrophysics, magnetotellurics, gravity measurements, and surface geology. Experiments are aimed at delineating the crustal and upper mantle structure beneath the Southern Alps and adjacent regions. MT data collected so far has led to a high-quality magnetotelluric transect across the central South Island. The MT response of the interior of this orogen holds the exciting promise of understanding the thermal regime and rheology of the South Island at depth. The complete resistivity structure will provide essential bounds on crustal strain partitioning, metamorphism in the lower crust, relative deformation of the crust versus the mantle, compensation of the South Island uplift, and several other important processes. However, there presently exists a crucial gap in the MT coverage along the transect due to lack of land vehicle access across the principal region of upl ift through the Main Divide of the South Island. The data collected in this project will close this gap in coverage with six-eight new MT soundings supported by helicopter transport. Personnel from the IGNS will participate in this effort and will provide manpower and logistical support. ***