Neoproterozoic to early Paleozoic extensional and compressional history of East Laurentian margin sequences: The Moine Supergroup, Scottish Caledonides
Neoproterozoic to early Paleozoic extensional and compressional history of East Laurentian margin sequences: The Moine Supergroup, Scottish Caledonides
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DOI：
10.1130/b31068.1
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发表时间：
2015-03
影响因子：
4.9
通讯作者：
Peter A. Cawood;R. Strachan;R. Merle;I. Millar;S. Loewy;I. Dalziel;P. Kinny;F. Jourdan;A. Nem
中科院分区：
文献类型：
--
作者：
Peter A. Cawood;R. Strachan;R. Merle;I. Millar;S. Loewy;I. Dalziel;P. Kinny;F. Jourdan;A. Nem
新元古代硅屑岩占主导地位的层序广泛分布在劳伦蒂亚东部边缘，与劳伦蒂亚从罗迪尼亚超大陆爆发有关的裂谷作用有关。来自苏格兰西北部莫因超群的碎屑锆石产生了太古代至新元古代早期的U-Pb年龄，这与格伦维尔-斯维科诺夫造山带及其周围地区的形成和1000 Ma后的堆积相一致。长英质侵入岩及其伴生岩浆的U-Pb锆石年龄确定了大约870 Ma与伸展有关的广泛的岩浆活动脉动。伟晶岩的锆石U-Pb年龄为830~745 Ma，制约了与主脉岩诺伊达特造山作用有关的一系列变形和变质脉动。另外的锆石和独居石U-Pb数据以及伟晶岩和寄主片麻岩的40Ar/39Ar年龄表明，在加里东造山旋回期间发生了约458-446 Ma和约426 Ma的高级变质事件。北大西洋附近新元古代早期硅质碎屑沉积和变形的存在以及北美东部沿走向的硅质碎屑沉积和变形的存在，与罗迪尼亚裂解时期的劳伦斯古地理形成了鲜明对比。北大西洋地区占据了劳伦西亚边缘的一个外部位置，该地区充当了来自格伦维尔-斯维孔诺威造山带的碎屑(Moine超群及其等价物)的聚集地，这些碎屑是由于Rodinia的碰撞组装而形成的。新元古代造山活动与超大陆外围汇聚的铂金活动发展相对应。相比之下，在位于罗迪尼亚内部的北美东部，沉积作用直到新元古代中期(约760 Ma)才开始，当时是超大陆碎裂的初始阶段。在北大西洋地区，这一时间框架对应于以达拉迪亚超群等单元为代表的第二次伸展脉冲，该超群不整合地覆盖了预先变形的莫因序列。
Neoproterozoic siliciclastic-dominated sequences are widespread along the eastern margin of Laurentia and are related to rifting associated with the breakout of Laurentia from the supercontinent Rodinia. Detrital zircons from the Moine Supergroup, NW Scotland, yield Archean to early Neoproterozoic U-Pb ages, consistent with derivation from the Grenville-Sveconorwegian orogen and environs and accumulation post–1000 Ma. U-Pb zircon ages for felsic and associated mafi c intrusions confi rm a widespread pulse of extension-related magmatism at around 870 Ma. Pegmatites yielding U-Pb zircon ages between 830 Ma and 745 Ma constrain a series of defor ma tion and metamorphic pulses related to Knoydartian orogenesis of the host Moine rocks. Additional U-Pb zircon and monazite data, and 40 Ar/ 39 Ar ages for pegmatites and host gneisses indicate high-grade metamorphic events at ca. 458–446 Ma and ca. 426 Ma during the Caledonian orogenic cycle. The presence of early Neoproterozoic silici clastic sedimentation and deformation in the Moine and equivalent successions around the North Atlantic and their absence along strike in eastern North America refl ect contrasting Laurentian paleogeography during the breakup of Rodinia. The North Atlantic realm occupied an external location on the margin of Laurentia, and this region acted as a locus for accumulation of detritus (Moine Supergroup and equivalents) derived from the Grenville-Sveconorwegian orogenic welt, which developed as a consequence of collisional assembly of Rodinia. Neoproterozoic orogenic activity corresponds with the inferred development of convergent platemargin activity along the periphery of the supercontinent. In contrast in eastern North America, which lay within the internal parts of Rodinia, sedimentation did not commence until the mid-Neoproterozoic (ca. 760 Ma) during initial stages of supercontinent fragmentation. In the North Atlantic region, this time frame corresponds to a second pulse of extension represented by units such as the Dalradian Supergroup, which unconformably overlies the predeformed Moine succession.