Geothermal systems related to rapid uplift on the Alpine Fault, New Zealand

虽然最大的地震（例如，2004年苏门答腊）发生在构造板块碰撞的地方，大地震（Mag.7 -8+）也发生在走滑断层上，那里的板块水平移动通过彼此。走滑断层，如圣安德烈亚斯或北安纳托利亚断层（土耳其）发生在人口稠密的地区，地震可能会对人类造成毁灭性的后果。虽然断层受到地震监测，但我们对地震发生的原因仍然知之甚少。这是因为我们没有在现代地震中破裂的岩石样本，因为破裂通常发生在地壳深处（>5-10公里）。我们也没有现场测量的热和流体条件，确定如何响应板块的相对运动的材料。古断层岩确实存在，但这些岩石通常被蚀变，并且具有未知的构造背景。阿尔卑斯断层是新西兰南阿尔卑斯山脉西部前缘沿着的主要走滑断层。该断层是澳大利亚板块和太平洋板块之间的边界，澳大利亚地壳以每年约27毫米的速度向东北方向移动。由于板块运动不平行于阿尔卑斯断层，碰撞是以倾斜的角度发生的。这导致了最近（约500万年）太平洋板块在澳大利亚板块上的快速（>6-8 mm/年）隆起，形成了>3000 m高的南阿尔卑斯山。岩石，直到几百万年前在地壳深处超过25公里，现在出现在地表沿着断层。重要的是，几千年前的岩石在阿尔卑斯断层带本身内部断裂和变形，现在出现在地表。这个著名的构造几何学和沿着一个主要的走滑断层的单侧隆起是独一无二的，并提供了一个很好的天然实验室来了解地震过程。令人惊讶的是，在欧洲时代，阿尔卑斯断层上没有发生过大地震。然而，古地震证据表明，在1717年左右发生了一次大地震，大地震每200-400年发生一次。这些地震非常大，每次地震的水平运动高达8米。阿尔卑斯山断层在地震周期中处于晚期，并且早该发生一次大的破坏性地震。这导致一个国际科学家小组建议在阿尔卑斯断层带钻一系列浅和深（~4公里）的钻孔，以就地对断层岩进行取样，并安装仪器（地震活动性，应变，温度，流体压力），以监测最终形成大地震期间的主要断层。阿尔卑斯山断层的数据可以用来了解其他断层带。在我们决定在哪里钻一个深孔之前，我们需要知道在目标深度的温度。我们计划的工作将通过调查沿着阿尔卑斯断层的地热暖泉（高达60摄氏度）来估计岩石的温度。这些暖泉的出现是因为快速的隆起将深层的热岩石带到了地表附近。地质学家通常使用来自间歇泉或海底黑烟囱喷口的流体，作为了解地壳深处情况的窗口。排放的流体和气体的化学性质可以告诉我们流体来自哪里以及它们如何反应。不幸的是，人们对阿尔卑斯断层地热系统知之甚少，因为许多泉水都位于非常偏远的地方，科学家们无法获得现代技术。通过研究其他热液环境中的流体-岩石交换，我们开发了新的方法来了解流体和矿物之间的反应。我们将把温暖的泉水与阿尔卑斯断层带内形成的矿物相匹配，这些矿物是在这些岩石向地表隆起的不同阶段形成的。当匹配可以，我们将知道，反应和条件产生现代流体必须发生在阿尔卑斯山断层今天。

Although the largest earthquakes (e.g., 2004 Sumatra) occur where tectonic plates collide, large earthquakes (Mag. 7-8+) also occur on strike-slip faults where plates are moving horizontally past each other. Strike-slip faults such as the San Andreas or the North Anatolian Fault (Turkey) occur in highly populated areas where earthquakes can have devastating human consequences. Although faults are seismic monitored, our knowledge of why earthquakes occur remains poor. This is because we have no samples of rocks that ruptured during a modern earthquake because failure typically occurs deep in the crust (>5-10 km). Nor do we have in situ measurements of the thermal and fluids conditions that determine how materials respond to the relative motion of the plates. Ancient fault rocks do occur but these rocks are commonly altered and have unknown tectonic context. The Alpine Fault is major strike-slip fault, that runs along the western range front of the Southern Alps, New Zealand. The fault is the boundary between the Australian and Pacific plates with the Australian crust moving to the northeast at ~27 mm/year. Because plate motions are not parallel to the Alpine Fault, collision is occurring at an oblique angle. This has resulted in the recent (~5 million years) rapid (>6-8 mm/yr) uplift of the Pacific plate over the Australian plate forming the >3000 m-high Southern Alps. Rocks, that until a few million years ago where more than 25 km deep in the crust, now crop out at the surface along the fault. Importantly, rocks that as recently as a few 10s of thousands of years ago, were fracturing and deforming within the Alpine Fault zone itself, now occur at the surface. This well known tectonic geometry and one-sided uplift along a major strike-slip fault is unique, and provides an excellent natural laboratory to understand earthquake processes. It is surprising that there have been no large earthquakes on the Alpine Fault in European times. However, paleo-seismic evidence indicates a major earthquake in ~1717, and that large earthquakes occurr every 200-400 years. These quakes were very large with up to 8 m horizontal movement in each event. The Alpine Fault is late in its seismic cycle and overdue for a large, devastating earthquake. This has lead an international group of scientists to propose drilling a series of shallow and deep (~4 km) bore holes into the Alpine Fault Zone to sample the fault rocks in situ, and to install instruments (seismicity, strain, temperature, fluid pressure) to monitor a major fault during the final build up to a large earthquake. Data from the Alpine fault can be used to understand other fault zones. Before we can decide where to drill a deep hole, we need to know how hot it is at the target depth. Our proposed work will make estimates of the temperature of rocks at depth by investigating geothermal warm springs (up to 60 deg C) that occur along the Alpine Fault. These warm springs occur because rapid uplift has brought deep hot rocks near to the surface. Geologists commonly use fluids from geysers or seafloor black-smoker vents, as windows into conditions deep within the crust. The chemistry of fluids and gases emitted can tell us where the fluids come from and how they have reacted. Unfortunately, there is very little known about the Alpine Fault geothermal systems because many of the springs are in very remote locations, and the scientists didn't have access to modern techniques. From investigating fluid-rock exchange in other hydrothermal environments, we have developed new methods to understand reactions between fluids and minerals. We will match warm spring fluids to minerals that formed within the Alpine Fault zone, during different stages of the uplift of these rocks to the surface. When matches can be made, we will be know that the reactions and conditions producing modern fluids must be occurring within the Alpine Fault today.