Garnet-Biotite-Tourmaline Thermometry at High Mn Content

高锰含量下石榴石-黑云母-电气石测温

• 批准号: 0946322
• 负责人: David London
• 金额: $ 26.34万
• 依托单位: University of Oklahoma Norman Campus
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-06-01 至 2013-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0946322&HistoricalAwards=false
• 关键词: Garnet; Biotite; Tourmaline; Thermometry; Mn

Intellectual Merit. This proposal requests funding for new experimental programs that will expand the utility of existing Fe-Mg exchange geothermometers, and that may introduce new thermometers based on the composition of coexisting tourmaline. If successful, the research will extend the application of garnet-biotite thermometry to some common Mn-rich metamorphic rocks, and to a variety of silicic igneous rocks in which garnet and tourmaline coexist, with or without accessory biotite and muscovite. Although Mn readily substitutes for Fe in common ferromagnesian silicates, previous calibrations of equilibrium between these minerals were conducted in Mn-free systems thereby raising concern that there may be systematic errors in P-T estimates based on these calibrations. Essentially, the accuracy of existing thermobarometers wanes as mineral compositions diverge from those of the experimental design. Thus, many rock types and conditions are outside of the range of confidence for which most thermometers can be applied. New experiments using Mn-bearing starting materials will help to resolve current discrepancies in the estimation of the thermodynamic mixing parameters for garnet and lead to improved solid solution models. Experiments are also proposed to calibrate the fractionation of major and minor elements (Fe, Mg, Mn, Ca, Ti, and V) between the bipolar ends of tourmaline crystals as a function of temperature, in hopes of developing a single-phase geothermometer. Finally, experiments will be conducted to quantify Fe-Mg exchange between tourmaline and biotite, cordierite, and garnet to develop a new tourmaline- ferromagnesian silicate thermometers. If successful multiple tourmaline-based thermometers could be used simultaneously in the same rock to confirm internal equilibrium or document lack thereof. For igneous rocks, tourmaline-garnet thermometry will be inherently more accurate than conventional thermometry with micas (biotite or muscovite), owing to the refractory nature of garnet and tourmaline as compared to biotite and muscovite, for which low closure temperatures and low modal abundances in igneous rocks hinder their value in thermobarometry.Broader Impacts. This project will support one graduate student. Funding also will support the experimental lab of the PI, and the contributions to mineral thermobarometry could have profound influence on petrogenetic interpretations.

智力上的功绩。这项提案要求为新的实验项目提供资金，这些项目将扩大现有铁镁交换地热温度计的用途，并可能引入基于共存电气石成分的新温度计。如果研究成功，将把石榴石-黑云母测温的应用范围扩大到一些常见的富锰变质岩，以及各种石榴石和电气石共存的硅质火成岩，以及有或没有副黑云母和白云母的硅质火成岩。虽然在普通的铁镁硅酸盐中，锰很容易替代铁，但以前对这些矿物之间的平衡的校准是在无锰体系中进行的，因此引起了人们的关注，即基于这些校准的P-T估计可能存在系统误差。从本质上讲，由于矿物成分与实验设计的不同，现有温度气压计的准确度会下降。因此，许多岩石类型和条件超出了大多数温度计可以应用的可信范围。使用含锰原料的新实验将有助于解决目前石榴石热力学混合参数估计中的差异，并导致改进的固溶体模型。为了研制一种单相地温计，还提出了测量电气石晶体两极端间主次元素(Fe、Mg、Mn、Ca、Ti、V)随温度变化的实验。最后，对电气石与黑云母、堇青石和石榴石之间的铁镁交换进行了实验研究，以开发一种新的电气石-硅酸铁镁温度计。如果成功，可以在同一块岩石中同时使用多个电气石温度计，以确认内部平衡或证明缺乏内部平衡。对于火成岩，电气石-石榴石测温将固有地比云母(黑云母或白云母)的传统测温更准确，这是因为石榴石和电气石的耐火性与黑云母和白云母相比，低封闭温度和火成岩中的低模式丰度阻碍了它们在热压测量中的价值。这个项目将资助一名研究生。资金还将支持PI的实验实验室，对矿物温压测量的贡献可能会对岩石成因解释产生深远影响。