Gneiss domes are an integral element of many orogenic belts and commonly provide tectonic windows into deep crustal levels. Gneiss domes in the New England segment of the Appalachian orogen have been classically associated with diapirism and fold interference, but alternative models involving ductile flow have been proposed. We evaluate these models in the Gneiss Dome belt of western New England with U-Th-Pb monazite, xenotime, zircon, and titanite petrochronology and major and trace element thermobarometry. These data constrain distinct pressure–temperature–time (P-T-t) paths for each unit in the gneiss dome belt tectono-stratigraphy. The structurally lowest units, Laurentia-derived migmatitic gneisses of the Waterbury dome, document two stages of metamorphism (455–435 and 400–370 Ma) with peak Acadian metamorphic conditions of ~1.0–1.2 GPa at 750–780°C at 391 ± 7 to 386 ± 4 Ma. The next structurally higher unit, the Gondwana-derived Taine Mountain Formation, records Taconic (peak conditions: 0.6 GPa, 600°C at 441 ± 4 Ma) and Acadian (peak: 0.8–1.0 GPa, 650°C at 377 ± 4 Ma) metamorphism. The overlying Collinsville Formation yielded a 473 ± 5 Ma crystallization age and evidence for metamorphic conditions of 650°C at 436 ± 4 Ma and 1.2–1.0 GPa, 750–775°C at 397 ± 4 to 385 ± 6 Ma. The structurally higher Sweetheart Mountain Member of the Collinsville Formation yielded only Acadian zircon, monazite, and xenotime dates and evidence for high-pressure granulite facies metamorphism (1.8 GPa, 815°C) at circa 380–375 Ma. Cover rocks of the dome-mantling The Straits Schist records peak conditions of ~1 GPa, 700°C at 386 ± 6 to 380 ± 4 Ma. Garnet breakdown to monazite and/or xenotime occurred in all units at circa 375–360 and 345–330 Ma. Peak Acadian metamorphic pressures increase systematically from the structurally lowest to highest units (from 1.0 to 1.8 GPa). This inverted metamorphic sequence is incompatible with the diapiric and fold interference models, which predict the highest pressures at the structurally lowest levels. Based upon P-T-t and structural data, we prefer a model involving, first, circa 380 Ma thrust stacking followed by syn-collisional orogen parallel extension, ductile flow, and rise of the domes between 380 and 365 Ma. Garnet breakdown at circa 345–330 Ma is interpreted to reflect further exhumation during collapse of the Acadian orogenic plateau. These results highlight the power of integrating petrologic constraints with paired geochemical and geochronologic data from multiple chronometers to test structural and tectonic models and show that syn-convergent orogen parallel ductile flow dramatically modified earlier accretion-related structures in New England. Further, the Gneiss Dome belt documents gneiss dome development in a syn-collisional, thick crust setting, providing an ancient example of middle to lower crustal processes that may be occurring today in the modern Himalaya and Pamir Range.

中文翻译：

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阿巴拉契亚造山带北部片麻岩穹窿带反转变质作用、地体增生、逆冲堆积和延性流的岩石年代学约束

片麻岩穹丘是许多造山带的组成部分，通常为深入地壳层提供构造窗口。阿巴拉契亚造山带新英格兰段的片麻岩穹顶通常与底辟作用和褶皱干扰相关，但也有人提出了涉及延性流的替代模型。我们利用 U-Th-Pb 独居石、磷钇矿、锆石和钛矿岩石年代学以及主量和微量元素热压测定法评估了新英格兰西部片麻岩穹窿带的这些模型。这些数据限制了片麻岩穹顶带构造地层中每个单元的不同压力-温度-时间（PTt）路径。结构最低的单元，沃特伯里圆顶的劳伦体衍生混合岩片麻岩，记录了两个变质阶段（455-435 Ma 和 400-370 Ma），阿卡迪亚变质峰值条件为 ~1.0-1.2 GPa，温度为 750-780°C，温度为 391 ± 7 至 386 ± 4 Ma。下一个结构较高的单元是冈瓦纳大陆衍生的泰恩山地层，记录了塔科尼岩层（峰值条件：0.6 GPa，600°C，441 ± 4 Ma）和阿卡迪亚岩层（峰值：0.8–1.0 GPa，650°C，377 ± 4 Ma） ) 变质作用。上覆的 Collinsville 地层结晶年龄为 473 ± 5 Ma，并且有证据表明 436 ± 4 Ma 时温度为 650°C，397 ± 4 至 385 ± 6 Ma 时压力为 1.2–1.0 GPa、750–775°C。柯林斯维尔组的结构较高的甜心山段仅产生了阿卡迪亚锆石、独居石和磷钇矿年代和约 380-375 Ma 高压麻粒岩相变质作用（1.8 GPa，815°C）的证据。海峡片岩的穹顶覆盖岩石在 386 ± 6 至 380 ± 4 Ma 时记录了约 1 GPa、700°C 的峰值条件。所有单元中石榴石分解为独居石和/或磷钇矿的时间大约为 375–360 和 345–330 Ma。阿卡迪亚峰值变质压力从结构上最低的单位到最高单位（从 1.0 GPa 到 1.8 GPa）系统地增加。这种倒转的变质序列与底辟和褶皱干扰模型不相容，后者预测结构最低水平处的最高压力。根据 PTt 和结构数据，我们更喜欢一个模型，首先涉及约 380 Ma 逆冲堆积，然后是同碰撞造山带平行伸展、延性流和 380 至 365 Ma 之间穹顶的上升。石榴石在大约 345-330 Ma 的分解被解释为反映了阿卡迪亚造山高原塌陷期间的进一步折返。这些结果凸显了将岩石学约束与来自多个计时器的成对地球化学和地质年代学数据相结合来测试结构和构造模型的力量，并表明同步汇聚造山带平行延性流极大地改变了新英格兰早期的增生相关结构。此外，片麻岩穹窿带记录了在同碰撞厚地壳环境中片麻岩穹窿的发育，提供了今天可能在现代喜马拉雅山和帕米尔山脉发生的中下地壳过程的古老例子。