Investigation of Metamorphic Timescales

变质时间尺度的研究

• 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

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.

板块构造理论解释了山脉的形成是由于两个板块碰撞时地壳的挤压造成的。基于造山带的明显寿命、板块运动的缓慢进展以及将地壳加热到造山带中变质岩记录的温度所需的时间尺度的计算，通常认为造山过程需要数十年的时间。至数亿年。然而，主要研究者的初步研究表明，至少某些变质岩的整个加热和冷却循环发生的时间不超过几百万年，甚至可能只有几十万年。这些时间尺度比之前认为的要快一到两个数量级，并且与人类进化时间尺度（最多几百万年）处于同一数量级。这并不是说，在人类的几代人中，山脉从平地中出现，但它确实提出了一个全新的命题，即山地带的演化可能影响了人类的迁徙路径和相关的气候条件。该提议旨在检验这一新假设通过对美国新英格兰中部经典变质地体的变质循环时间尺度进行全面研究。该研究将涉及从佛蒙特州北部到康涅狄格州南部沿线进行广泛的样品收集，通过标准岩相学技术（光学显微镜、微观结构分析、使用电子探针的元素测绘、阴极发光成像、痕量元素分析、反应历史分析、热压测定）对样品进行分析和压力-温度路径计算这项研究的新颖之处是将新开发的传输模型应用于显示化学分区扩散改变的明确证据的样本。热激活，因此大多数扩散发生在样品所经历的最高温度的 25-50 度范围内。事实上，最大的不确定性源于该最高温度的不确定性，并且正在开发新的热力学模型以更好地限制该值的初始应用。 PI 的这一新方法揭示了上述的短时间范围，并为该提案提供了动力。对 PI 收集中已有样品的粗略检查表明，适合此类分析的样品很容易获得，并且将探索该方法对其他矿物和扩散偶的几种扩展。该具体提案的目标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体中的​​应用提供理由，最终将提供对地球真正动态性质的更深入的理解和欣赏。

项目成果

Regional Quartz Inclusion Barometry and Comparison with Conventional Thermobarometry and Intersecting Isopleths from the Connecticut Valley Trough, Vermont and Massachusetts, USA

美国佛蒙特州和马萨诸塞州康涅狄格谷槽的区域石英包裹体气压测定法以及与传统温压测定法和相交等值线的比较

• DOI: 10.1093/petrology/egaa076
• 发表时间: 2020
• 期刊: Journal of Petrology
• 影响因子: 3.9
• 作者: Wolfe, Oliver M;Spear, Frank S
• 通讯作者: Spear, Frank S

Pronounced and rapid exhumation of the Connecticut Valley Trough revealed through quartz in garnet Raman barometry and diffusion modelling of garnet dissolution–reprecipitation reactions

通过石榴石拉曼气压测定中的石英和石榴石溶解再沉淀反应的扩散模型揭示了康涅狄格河谷的明显和快速折返

• DOI: 10.1111/jmg.12601
• 发表时间: 2021
• 期刊: Journal of Metamorphic Geology
• 影响因子: 3.4
• 作者: Wolfe, Oliver M.;Spear, Frank S.;Harrison, T. Mark
• 通讯作者: Harrison, T. Mark

Overstepping the garnet isograd: a comparison of QuiG barometry and thermodynamic modeling

超越石榴石等梯度：QuiG 气压测量法和热力学模型的比较

• DOI: 10.1007/s00410-014-1059-6
• 发表时间: 2014
• 期刊: Contributions to Mineralogy and Petrology
• 影响因子: 3.5
• 作者: Spear, Frank S.;Thomas, Jay B.;Hallett, Benjamin W.
• 通讯作者: Hallett, Benjamin W.

Determining the amount of overstepping required to nucleate garnet during Barrovian regional metamorphism, Connecticut Valley Synclinorium

• DOI: 10.1111/jmg.12284
• 发表时间: 2018-01
• 期刊: Journal of Metamorphic Geology
• 影响因子: 3.4
• 作者: Oliver M. Wolfe;F. Spear

The duration of near-peak metamorphism from diffusion modelling of garnet zoning

石榴石分带扩散模型的近峰变质作用持续时间

• DOI: 10.1111/jmg.12099
• 发表时间: 2014
• 期刊: Journal of Metamorphic Geology
• 影响因子: 3.4
• 作者: Spear, F. S.