It is proposed that the contrasting metamorphic mineral assemblages of the isolated amphibolite facies metamorphic highs in the Penokean orogen of northern Michigan may be caused by different heat production rates in the Archean basement. This hypothesis is based on concentrations of K, U, and Th in the Archean basement gneisses and Paleoproterozoic metasediments that indicate significant contribution of radiogenic heating during Penokean metamorphism. Heat production was anomalously high (∼10.6 μWm−3) where andalusite‐bearing mineral assemblages indicate that high temperatures were attained at shallow crustal levels (∼550°–600°C at ∼3 kbar). In contrast, where exposed metamorphic rocks indicate peak temperatures of 600°–650°C at 6–7 kbar, heat production in the Archean basement was lower (∼3.7 μWm−3). The effect of heat production rates on the metamorphic pressure–temperature paths was tested with numerical thermal models. The calculations show (1) that if the heat production rate, where andalusite‐bearing assemblages formed, was significantly <6.0 μWm−3, the estimated pressure at peak temperatures ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $$P_{T_{\mathrm{max}\,}}$$ \end{document} ) would be much higher and lie in the sillimanite or kyanite stability fields; and (2) differences between \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $$P_{T_{\mathrm{max}\,}}$$ \end{document} estimates for the metamorphic highs based on thermobarometry can be reproduced if thermal history involved significant crustal thickening as well as moderate unroofing rates.

中文翻译：

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对比密歇根北部 Penokean 造山带产热异常的变质记录

有人提出，密歇根州北部 Penokean 造山带中孤立的角闪岩相变质高地的对比变质矿物组合可能是由太古代基底的不同产热率引起的。该假设基于太古代基底片麻岩和古元古代变沉积物中 K、U 和 Th 的浓度，表明在 Penokean 变质过程中放射性加热的显着贡献。产热异常高（~10.6 μWm-3），其中含红柱石的矿物组合表明在浅地壳水平（~550°-600°C，~3 kbar）达到高温。相比之下，暴露的变质岩在 6-7 kbar 下的峰值温度为 600°-650°C，太古宙基底的产热较低（~3.7 μWm-3）。用数值热模型测试了产热速率对变质压力-温度路径的影响。计算表明 (1) 如果红柱石组合形成的产热率显着 <6.0 μWm−3，则峰值温度下的估计压力 ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2, OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty } \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $$P_{T_{\mathrm{max}\,}}$$ \end{document} ) 会更高，并且位于硅线石或蓝晶石稳定场；(2) \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp } \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,