A new view of the thermal structure of continental mountain ranges: the importance of igneous heat transport

当大陆板块碰撞形成山脉时，山脉内部的岩石温度会升高到足以融化。这些熔岩从地壳中升起，在较浅的深处结晶，或者从火山喷发出来。然而，我们不知道这些熔岩在穿过地壳时携带了多少热量。这种不确定性很重要，因为这是我们不了解的主要问题之一，即是什么控制了地球内部的温度分布。我们关心温度的原因是它控制着岩石的强度，以及地球内部矿物的分布。这些主题具有广泛的重要性，从它们在控制山脉的大小、形状和随时间的演变中所起的作用，到经济矿物的分布。我们提出的研究将通过测试熔融岩石在山脉内部传递了多少热量来解决目前的不确定性。这一目标将通过结合三个研究主题来实现：1。当岩石融化时，它们是在一定的温度范围内逐渐融化的，而产生的岩浆的成分取决于岩石的温度。通过观察岩浆冷却时产生的岩石中的矿物类型，我们可以知道熔点的温度。当熔融的岩石位于地壳的上部时，它们会加热周围的环境，导致新的矿物质生长，我们可以利用这些矿物质来估计周围岩石的温度。我们将把这种方法应用于四个已经放置了熔融岩石的区域，这样我们就可以计算出不同位置之间有多少可变性。我们可以使用计算机模型将主题(1)中的观测结果转化为对安置熔岩体所需时间的估计，以及当这一过程发生时它们的温度。本提案中描述的新计算表明，在侵入体周围生长的新矿物的分布足以对这些数量进行良好的估计。这一目标之所以成为可能，是因为对地壳性质如何随温度变化的新测量方法，以及现代计算机的强大功能——这意味着我们能够进行所有必要的计算。通过结合主题(1)和(2)的结果，我们可以制作山脉内温度的新计算机模型。这些模型将包括岩石融化的影响，以及我们在目标(2)中能够估计的那些岩石携带的热量。因此，我们将能够对山带的温度结构有一个新的、更准确的认识。通过将这些信息与我们对岩石的温度依赖强度的了解相结合，我们将能够解决一个长期存在的争议，即在山带的深处发生了什么，因此它们是如何随着时间的推移而演变的（例如，岩石是否能够在地壳中以“通道”流动，就像牙膏从管子中挤出一样）。我们提出的研究的最后一部分将是检查我们的结果对地球科学其他领域的影响。目前争论的是熔岩侵入是作为一个单一的大体发生，还是作为一系列不同时间到达的小体。我们对侵入物出现和加热周围岩石的时间的研究结果将使我们能够在我们研究的地区回答这个问题。最后，我们将能够利用我们的结果来更新我们的知识，我们预计哪些岩石会在地球的哪些位置产生，因为这取决于温度。这个主题的更广泛的重要性在于，它使我们能够利用今天的岩石分布来推断地质过去发生了什么，也有助于我们努力了解具有重要经济意义的矿物的分布。

When continental tectonic plates collide and build mountain ranges, the rocks in the interior of these ranges get hot enough to melt. This molten rock rises through the crust, and crystallises at shallower depths or is erupted at volcanoes. However, we don't know how much heat these molten rocks transport with them as they move through the crust. This uncertainly is important, because it is one of the main things we don't understand about what controls the distribution of temperature within the Earth. The reason we care about temperature is that it controls the strength of rocks, and the distribution of minerals within the Earth. These topics have wide-ranging importance, from the role they play in controlling the sizes, shapes, and evolution through time of mountain ranges, to the distribution of economic minerals.Our proposed research will resolve the current uncertainty by testing how much heat is moved through the interiors of mountain ranges by molten rocks. This aim will be achieved by combining three research themes:1. When rocks melt, they do so gradually over a range of temperatures, and the composition of the resulting magma depends on how hot the rocks became. Looking at the types of minerals in the rocks produced when the magma cools therefore tells us the temperature in the melting zone. As molten rocks are emplaced in the upper part of the crust, they heat up the surroundings, causing new minerals to grow, which we can use to estimate how hot these surrounding rocks became. We will apply this approach in four regions where molten rocks have been emplaced, so that we can work out how much variability there is between different locations.2. We can use computer models to turn the observations in theme (1) into estimates of how long it took to emplace the bodies of molten rock, and how hot they were when this happened. New calculations described in this proposal demonstrate that the distribution of new minerals grown around intrusions is sufficient to make well-constrained estimates of these quantities. This objective is made possible by new measurements of how the properties of the crust vary as a function of temperature, and by the power of modern computers that means we are able to run all of the necessary calculations.3. By combining the results of themes (1) and (2) we can make new computer models of the temperature within mountain ranges. These models will include the effects of the melting of rocks, and those rocks transporting with them the amount of heat that we have been able to estimate in objective (2). We will therefore be able to create a new and more accurate understanding of the temperature structure of mountain belts. By combining this information with our knowledge of the temperature-dependent strength of rocks, we will be able to address a long-running controversy over what happens in the deep interiors of mountain belts, and therefore how they evolve through time (for example whether the rocks are able to flow in 'channels' through the crust, much like toothpaste being squeezed from a tube). The final part of our proposed research will be to examine the implications of our results for other areas of Earth Science. It is currently debated whether intrusions of molten rock occur as a single large body, or as a series of smaller bodies arriving at different times. Our results for how long the intrusions were appearing and heating the surrounding rocks will allow us to answer this question in the regions we study. Finally, we will be able to use our results to update our knowledge of which rocks we would expect to be produced in which locations within the Earth, as this depends on the temperature. The wider importance of this topic is that it allows us to use the distribution of rocks at the present day to infer what happened in the geological past, and also aids our efforts to understand the distribution of economically important minerals.