New U‐Pb geochronology constrains the timing of the Acadian orogeny in the Central Maine Terrane of northern New Hampshire. Sixteen fractions of one to six grains each of zircon or monazite have been analyzed from six samples: (1) an early syntectonic diorite that records the onset of the Acadian; (2) a schist, a migmatite, and two granites that together record the peak of the Acadian; and (3) a postkinematic pluton that records the end of the Acadian. Zircon from the syntectonic Wamsutta Diorite gives a 207Pb/206Pb age of circa 408 Ma, the time at which the boundary between the deforming orogenic wedge and the foreland basin was in the vicinity of the Presidential Range. This age agrees well with the Emsian position of the northwest migrating Acadian orogenic front and records the beginning of the Acadian in this part of the Central Maine Terrane. We propose a possible Acadian tectonic model that incorporates the geochronologic, structural, and stratigraphic data. Monazite from the schist, migmatite, Bigelow Lawn Granite, and Slide Peak Granite gives 207Pb/206U ages, suggesting the peak of Acadian metamorphism and intrusion of two‐mica granites occurred at circa 402–405 Ma, the main pulse of Acadian orogenesis. Previously reported monazite ages from schists that likely record the peak metamorphism in the Central Maine Terrane of New Hampshire and western Maine range from circa 406–384 Ma, with younger ages in southeastern New Hampshire and progressively older ages to the west, north, and northeast. Acadian orogenesis in the Presidential Range had ended by circa 355 Ma, the 207Pb/235U age of monazite from the Peabody River Granite. From 408 to perhaps at least 394 Ma, Acadian orogenesis in the Presidential Range was typical of the tectonic style, dominated by synkinematic metamorphism, seen in central and southern New Hampshire, Massachusetts, and Connecticut. From no earlier than 394 Ma to as late as 355 Ma, the orogenesis was typical of the style in parts of Maine dominated by postkinematic metamorphism.

中文翻译：

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新罕布什尔州北部阿卡迪亚造山运动的时间

新的 U-Pb 年代学限制了新罕布什尔州北部缅因州中部阿卡迪亚造山运动的时间。从六个样品中分析了 1 到 6 个锆石或独居石颗粒的 16 个部分：(1) 早期同构造闪长岩，记录了阿卡迪亚的开始；(2) 一块片岩、一块混合岩和两块花岗岩，共同记录了阿卡迪亚的顶峰；(3) 一个记录阿卡迪亚末期的后运动岩体。来自同构造的 Wamsutta 闪长岩的锆石给出了大约 408 Ma 的 207Pb/206Pb 年龄，这是变形造山楔和前陆盆地之间的边界在总统山脉附近的时间。这个时代与西北迁移的阿卡迪亚造山带的埃姆西亚位置非常吻合，并记录了缅因州中部这一部分阿卡迪亚的开始。我们提出了一个可能的阿卡迪亚构造模型，该模型结合了地质年代学、构造学和地层学数据。片岩、混合岩、毕格罗草坪花岗岩和滑峰花岗岩的独居石给出了 207Pb/206U 年龄，表明阿卡迪亚变质作用和双云母花岗岩侵入的峰值发生在大约 402-405 Ma，这是阿卡迪亚造山作用的主要脉冲。先前报道的片岩独居石年龄可能记录了新罕布什尔州中部缅因州和缅因州西部的峰值变质作用，范围约为 406-384 Ma，新罕布什尔州东南部的年龄较小，西部、北部和东北部的年龄逐渐变大. 总统山脉的阿卡迪亚造山作用在大约 355 Ma 结束，即皮博迪河花岗岩中独居石的 207Pb/235U 年龄。从 408 到也许至少 394 Ma，总统山脉的阿卡迪亚造山带是典型的构造风格，以同运动变质作用为主，见于新罕布什尔州、马萨诸塞州和康涅狄格州的中部和南部。从不早于 394 Ma 到晚至 355 Ma，缅因州部分地区的造山作用是典型的后运动变质作用。