The Jumping Brook Metamorphic Suite in the western Cape Breton Highlands of Nova Scotia is part of an inverted Barrovian sequence that formed during a Late Silurian–Early Devonian promontory–promontory collision in the Canadian Appalachians. In this study, systematic discrepancies between geochemical observations and thermodynamic model predictions led to the discovery of a systematic relationship linking the style of garnet core isopleth intersection (GCII) to the pyrophanite (MnTiO₃) component of co‐existing ilmenite. Samples that yielded tight GCIIs at or near the garnet‐in curve were found to contain ilmenite with negligible pyrophanite components, whereas samples yielding GCIIs far removed (up to 105°C) from the garnet‐in curve were found to contain ilmenite with significant pyrophanite and/or ecandrewsite (ZnTiO₃) components. Based on petrographic and geochemical observations, Mn(±Zn)‐rich ilmenite are interpreted to have sequestered Mn throughout prograde metamorphism due to sluggish intracrystalline diffusion. The amount of reactive Mn input into the thermodynamic models from whole‐rock analyses were, in some cases, overestimated, resulting in garnet‐in curve topologies that extend to erroneously low P–T conditions. Modifications to the whole‐rock chemistry that account for Mn sequestration into ilmenite, however, yielded robust model results. Our results show that, in addition to uncertainties in thermodynamic data sets and phenomenon related to reaction kinetics, Mn‐rich ilmenite may superimpose additional complexities related to the interpretation of predicted equilibria involving garnet. Numerical simulations of garnet crystallization were used to infer P–T paths of metamorphism for one sample from the garnet zone (Mn corrected) and two samples from the staurolite zone (Mn uncorrected) of the inverted sequence. Model results are remarkably similar among the three samples and indicate that garnet crystallization occurred along relatively steep (31–37°C/km) clockwise P–T paths. The peak conditions of garnet crystallization and metamorphism (560–590°C, 7.4–8.0 kbar) are interpreted to have been attained approximately simultaneously, such that the paths are characterized by tight prograde‐to‐retrograde transitions. The hairpin nature of the P–T paths is interpreted to represent the onset of thrust‐related exhumation and isograd inversion along ductile shear zones, consistent with available field and geochronological constraints.

中文翻译：

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富硒钛铁矿的重要性以及新斯科舍省西布雷顿角高地沉积岩中石榴石分区成岩的P–T路径的确定

新斯科舍省布雷顿角高地西部的布鲁克林变质套房是加拿大阿巴拉契亚山脉晚志留纪-早泥盆纪海角-海角碰撞期间形成的巴罗夫倒置序列的一部分。在这项研究中，地球化学观测与热力学模型预测之间的系统差异导致发现了将石榴石岩心等值相交（GCII）的样式与吡phan石（MnTiO ₃）联系起来的系统关系）共存的钛铁矿成分。在石榴石入曲线处或附近产生紧密GCII的样品被发现含有钛铁矿，其硫氰酸盐组分可忽略不计，而从石榴石入曲线中移出（高达105°C）的产生GCII的样品被发现含有具有显着蛇麻石的钛铁矿。和/或钙矾石（ZnTiO ₃）组分。根据岩相学和地球化学观察，由于缓慢的晶体内扩散，富含Mn（±Zn）的钛铁矿被解释为在整个变质过程中都螯合了Mn。在某些情况下，过高估计了从全岩体分析输入到热力学模型中的反应性锰的数量，导致石榴石形曲线拓扑扩展到错误的低P–T条件。然而，对整个岩石化学的修改（将Mn螯合成钛铁矿）产生了可靠的模型结果。我们的结果表明，除了热力学数据集的不确定性和与反应动力学相关的现象外，富锰钛铁矿可能会叠加与解释石榴石预测平衡有关的其他复杂性。石榴石结晶的数值模拟被用于推断对-叔变质的路径，用于从石榴石区中的一个样本的反相序列的（锰校正），并从十字石带两个样品（MN未校正）。模型的结果是三个样品之间非常相似并且指示沿相对陡峭（31-37℃/公里）顺时针发生石榴石结晶对叔路径。石榴石结晶和变质的峰值条件（560–590°C，7.4–8.0 kbar）被认为是同时达到的，因此路径具有从严格的过渡到过渡的特征。P–T路径的发夹性质被解释为代表与延性剪切带的发掘和沿延性剪切带的等梯度反演的发生，与可用的田野和年代学约束相一致。