Garnet-Biotite-Tourmaline Thermometry at High Mn Content

知识价值。该提案要求为新的实验项目提供资金，以扩大现有Fe-Mg交换地温计的效用，并可能引入基于共存电气石成分的新温度计。如果成功，该研究将把石榴石-黑云母测温的应用范围扩大到一些常见的富锰变质岩，以及石榴石和电气石共存的各种硅质火成岩中，有或没有辅助的黑云母和白云母。虽然锰在普通镁铁硅酸盐中很容易取代铁，但以前这些矿物之间的平衡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，当矿物成分偏离实验设计时，现有温度计的准确性会下降。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置信度范围。使用含锰起始材料的新实验将有助于解决目前对石榴石热力学混合参数估计的差异，并导致改进的固溶体模型。实验还提出了校准电气石晶体双极端之间的主要和次要元素（Fe, Mg, Mn, Ca， Ti和V）作为温度函数的分异，以期开发单相地温计。最后，对电气石与黑云母、堇青石、石榴石之间的铁镁交换进行定量实验，研制新型电气石-镁铁硅酸盐温度计。如果成功的话，可以在同一块岩石中同时使用多个电气石温度计来确认内部平衡或记录其缺乏。对于火成岩，电气石-石榴石测温从本质上来说比传统的云母（黑云母或白云母）测温更准确，因为与黑云母和白云母相比，石榴石和电气石具有难熔性，因此火成岩的低闭合温度和低模态丰度阻碍了它们在热压测量中的价值。更广泛的影响。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，对矿物热气压测量的贡献可能对岩石成因解释产生深远的影响。

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.