Linking erosion and the sediment record : detrital thermochronology in the Taiwan

究竟是构造活动还是气候是新生代山脉主要隆升的驱动力，是构造地貌学中一个活跃的现代争论。自从1990年彼得·莫尔纳（Peter Molnar）和菲利普·英格兰（Philip England）发起鸡还是蛋的争论以来，人们投入了大量精力来确定构造活动是否驱动了长期气候变化，反之亦然。然而，我们才刚刚开始了解气候和构造之间的复杂相互作用，以及这如何塑造我们周围的景观。现在需要的是以更大的决心，通过综合、跨学科的办法来解决问题。我建议使用现代和古代记录的沉积物供应从台湾东部的中央山脉调查长期的侵蚀速率和文件是否气候或构造活动主导的侵蚀记录在这个活跃的造山带。气候或构造活动主导信号的端元情景将使用表面动力学模型独立建模，从而可能在古代沉积记录中识别气候与构造作用力。为了解决这个问题，我打算把重点放在台湾，因为那里记录的岩石隆起和侵蚀的高速率反映了会聚构造环境和亚热带气候。台湾虽然小，但对全球有重大影响，因为在过去30年中，它贡献了全球进入海洋的悬浮沉积物总量的近2%。如此高的侵蚀率在长时间内是不可持续的，因为在造山带的核心没有高级变质岩被挖掘出来，但自晚中新世碰撞开始以来的平均侵蚀率与历史平均侵蚀率相当。了解是什么推动了这种环境下的侵蚀，这是这个项目的目标。最终的结果将有助于确定气候和/或构造强迫的影响是如何保存在古代沉积物档案，并在未来有助于评估地质时期的沉积记录中的气候与构造强迫的重要性。将记录在一个先行河流系统中的河流对折返的反应，并使用低温热时计或地质钟确定现代和古代碎屑沉积物的长期侵蚀速率。时钟的概念可以作为一个基本工具，用来研究岩石从深处向地表移动，然后被侵蚀，最后沉积在盆地中时会发生什么。这里应用的概念是基于这样一个事实，即矿物在特定温度下变得接近特定元素的扩散。一旦关闭，时钟开始滴答作响，并积累有关样品冷却历史的信息。如果样品的沉积年龄是已知的，无论是从磁性地层学或纳米化石，然后所花费的时间由样品通过关闭和被挖出从深度和沉积在盆地可以计算。然后可以通过热模型推断出侵蚀速率。目前的调查往往是模型偏置或现场偏置，没有很好地整合。因此，一旦我收集了有关的数据，无论是在上新世和第四纪序列的侵蚀速率，我的目标是应用表面动力学模型儿童模拟沉积物通量和河流的长期折返被迫气候和/或构造变化的响应。将生成的模型结果将密切反映沉积物档案中保存的内容，并有助于区分侵蚀记录中的气候和构造作用力。如果这一点得以实现，我将提高我们对这些过程如何塑造地球表面的理解，并朝着将侵蚀历史与沉积记录联系起来迈出一大步。

Whether tectonic activity or climate is the driving force behind the major uplift of mountains during Cenozoic times is a lively modern controversy in tectonic geomorphology. Since this chicken or egg debate was instigated by Peter Molnar and Philip England in 1990 much effort has been invested in determining whether tectonic activity has driven long term climate change or vice versa. However we are only just beginning to understand some of the complex interplay between climate and tectonics and how this shapes the landscape that surrounds us. What is required is greater resolution to solve the problem through an integrated, cross-disciplinary approach. I propose to use both the modern and ancient record of sediment supply from the Central Ranges of eastern Taiwan to investigate long term erosion rates and document whether climate or tectonic activity dominates the erosion record in this active orogen. End member scenarios where climate or tectonic activity dominates the signal will be modelled independently using a surface dynamic model thereby potentially fingerprinting climate versus tectonic forcing in ancient sedimentary records. To tackle this problem I intend to focus on Taiwan due to the high rates of rock uplift and erosion recorded there which reflect both the convergent tectonic setting and sub-tropical climate. Taiwan although small has a major global impact as it contributed almost 2% of the total global suspended sediment entering the ocean in the last 30 years. Such high rates of erosion are not sustainable over prolonged periods of time, as no high grade metamorphic rocks have been exhumed in the core of the orogen, yet average erosion rates since the beginning of collision in the Late Miocene are comparable with average historic erosion rates. Understanding what drives erosion in this setting through time is the ambition of this project. Ultimately the results will help determine how the effects of climate and/or tectonic forcing are preserved in ancient sediment archives and in future help to evaluate the importance of climate versus tectonic forcing in the sedimentary record over geological time. The fluvial response to exhumation in an antecedent river system will be documented and long term erosion rates in both modern and ancient detrital sediments determined using low temperature thermochronometers or geological clocks. The clock concept can be used as a basic tool in investigating what happens to a rock as it first moves from depth towards the surface and then is eroded and finally deposited in a basin. The concept as applied here is based on the fact that minerals become closed to the diffusion of particular elements at particular temperatures. Once closed the clock start to tick and information on the cooling history of the sample is accumulated. If the depositional age of the sample is known, from either magnetostratigraphy or nanofossils, then the time taken by the sample to pass through closure and be exhumed from depth and deposited in the basin can be calculated. The erosion rate can then be inferred by thermal modelling. Current investigations tend to be either model biased or field biased and not well integrated. As a result, once I have collected the data concerning erosion rates both in the Pliocene and Quaternary sequences I aim to apply the surface dynamic model CHILD to modelling sediment flux and fluvial response to long term exhumation forced by climate and/or tectonic variation. The model results will be generated to closely mirror what is preserved in the sediment archive and help distinguish between climate and tectonic forcing in the erosion record. If this is achieved I shall have improved our understanding of how these processes shape the Earth's surface and taken a large step towards linking erosion history with the sediment record.