Investigation of Metamorphic Timescales

变质时间尺度的研究

基本信息

批准号：
1321777
负责人：
Frank Spear
金额：
$ 26.47万
依托单位：
Rensselaer Polytechnic Institute
依托单位国家：
美国
项目类别：
Continuing Grant
财政年份：
2013
资助国家：
美国
起止时间：
2013-07-01 至 2016-06-30
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1321777&HistoricalAwards=false
关键词：
Investigation Metamorphic Timescales

项目摘要

The theory of Plate Tectonics provides an explanation for the formation of mountain chains as the crumpling of the Earth's crust where two plates collide. Based on the apparent longevity of mountain belts, the slow progress of plate motions, and calculations of the time scales required to heat the crust to the temperatures recorded by metamorphic rocks in mountain belts, it has generally been assumed that mountain building processes take many tens to hundreds of millions of years. Preliminary studies of the principal investigator, however, have revealed that the entire cycle of heating and cooling for at least some metamorphic rocks occurred over no more than a few million years and perhaps in as little as a few hundred thousand years. These time scales are one to two orders of magnitude faster than previously believed and are on the same order as human evolutionary timescales (a few million years at most). That is not to imply that mountains appear out of flat lands in a few generations of humans, but it does present the radically new proposition that mountain belt evolution may have affected human migratory pathways and associated climate conditions.This proposal seeks to test this new hypothesis by conducting a comprehensive study of the timescales of metamorphic cycling in the classic metamorphic terrane of central New England, USA. The study will involve extensive sample collection along strike from northern Vermont to southern Connecticut, analysis of the samples by standard petrographic techniques (optical microscopy, microstructural analysis, elemental mapping using the electron microprobe, cathodoluminescence imaging, trace element analysis, reaction history analysis, thermobarometry, and pressure-temperature path calculation. The novel aspect of this research is to apply newly developed transport models to samples that display clear evidence for diffusional modification of chemical zoning. The theoretical justification for this approach is the fact that diffusion is thermally activated, so most diffusion occurs within 25-50 degrees of the maximum temperature experienced by a sample. Indeed, the largest uncertainty stems from uncertainty in this maximum temperature and new thermodynamic models are being developed to better constrain this value. The initial application of this new method by the PI revealed the short time scale described above and provided the impetus for this proposal. Cursory examination of samples already in the PIs collection indicate that samples appropriate for this type of analysis are readily available, and several extensions of the method to other minerals and diffusion couples will be explored. The goal of this specific proposal is to constrain the temperature-time history of the entire metamorphic belt of central New England. The insights gained from this study will provide justification for its application in other terranes which will ultimately provide greater understanding and appreciation for the true dynamic nature of the Earth.

板块构造的理论为山链形成的解释提供了一种解释，因为在两个板块碰撞的地球地壳的折断中。基于山带的明显寿命，板块运动的缓慢进展以及将地壳加热到山带变质岩石记录的温度所需的时间尺度的计算，通常认为山区建筑过程需要数十至千万年。然而，对主要研究者的初步研究表明，至少一些变质岩石的加热和冷却周期不超过几百万年，甚至只有几十万年。这些时间尺度比以前想象的要快一到两个数量级，并且与人类进化时间尺度（最多只有几百万年）的顺序相同。 That is not to imply that mountains appear out of flat lands in a few generations of humans, but it does present the radically new proposition that mountain belt evolution may have affected human migratory pathways and associated climate conditions.This proposal seeks to test this new hypothesis by conducting a comprehensive study of the timescales of metamorphic cycling in the classic metamorphic terrane of central New England, USA.该研究将涉及从佛蒙特州北部到康涅狄格州南部的大量样品收集，通过标准岩石学技术对样品进行分析（光学显微镜，微观结构分析，使用电子微螺旋体，降压元素成像，痕量元素分析，痕量元素分析，反应历史分析，热力学分析和压力 - 体系校准的新迹象。化学分区的扩散是对这种方法的理论理由，即扩散是热的，因此大多数扩散发生在样本的最大温度的25-50度之内这个建议。对PIS集合中已经已经存在的样本的粗略检查表明，适用于此类分析的样品很容易获得，并且将探索该方法的几种扩展，并将探索其他矿物质和扩散夫妇。该特定建议的目的是限制新英格兰中部整个变质带的温度时间历史。从这项研究中获得的见解将为其在其他地形中的应用提供理由，这最终将对地球的真实动态性质提供更多的理解和欣赏。