Phase equilibria modeling of sodic-calcic amphibole-epidote assemblages in greenstones in the northern Appalachians, USA, is compatible with relatively shallow subduction of the early Paleozoic Laurentian margin along the Laurentia-Gondwana suture zone during closure of a portion of the Iapetus Ocean basin. Pseudosection and isopleth calculations demonstrate that peak metamorphic conditions ranged between 0.65 GPa, 480 °C and 0.85 GPa, 495 °C down-dip along the subducted Laurentian continental margin between ∼20 km and ∼30 km depth. Quantitative petrological data are explained in the context of an Early Ordovician geodynamic model involving shallow subduction of relatively young, warm, and buoyant Laurentian margin continental-oceanic lithosphere and Iapetus Ocean crust beneath a relatively warm and wet peri-Gondwanan continental arc. A relatively warm subduction zone setting may have contributed to the formation of a thin, ductile metasedimentary rock-rich channel between the down-going Laurentian slab and the overriding continental arc. This accretionary channel accommodated metamorphism and tectonization of continental margin sediments and mafic volcanic rocks (greenstones) of the Laurentian margin and provided a pathway for exhumation of serpentinite slivers and rare eclogite blocks. Restricted asthenospheric flow in the forearc mantle wedge provides one explanation for the lack of ophiolites and absence of a well-preserved ultra-high-pressure terrane in central and northern Vermont. Exhumation of the subducted portion of the Laurentian margin may have been temperature triggered due to increased asthenospheric flow following a slab tear at relatively shallow depths.

中文翻译：

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劳伦边际俯冲俯冲的观点：来自美国北部的钡铁矿绿岩相平衡模型的地球动力学约束阿巴拉契亚人

在美国北部阿巴拉契亚人的绿岩中，钙-钙闪石-闪石组合的相平衡建模与在部分Iapetus海洋盆地关闭期间沿Laurentia-Gondwana缝合带的早期古生代Laurentian边缘相对较浅的俯冲兼容。伪截面和等值线计算表明，沿俯冲的Laurentian大陆边缘，在约20 km至约30 km深度处，最高变质条件范围为0.65 GPa，480°C和0.85 GPa，495°C下倾。在早期奥陶纪地球动力学模型的背景下解释了定量岩石学数据，该模型涉及相对较年轻，温暖和浮力的Laurentian边缘大陆-海洋岩石圈和Iapetus大洋壳在相对温暖和潮湿的冈瓦纳大陆弧以下的浅层俯冲。相对较热的俯冲带环境可能在下降的劳伦式板块与上覆大陆弧之间形成了一条薄而易延展的沉积沉积富岩通道。该增生通道适应了Laurentian边缘的大陆边缘沉积物和镁铁质火山岩（绿岩）的变质作用和构造，为蛇纹石碎片和稀有的榴辉岩块的掘出提供了途径。前臂地幔楔中的软流圈流动受限，这为佛蒙特州中部和北部缺乏蛇绿岩和保存完好的超高压地层提供了一种解释。Laurentian边缘俯冲部分的掘出可能是由于板坯在相对浅的深度撕裂后流软圈流动增加而触发的。