Geochronology and Tectonic Implications of the "Proterozoic" Seluohe Group at the Northern Margin of the North China Craton
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The Seluohe Group in southern Jilin Province, northeastern China, is traditionally considered to be Mesoproterozoic in age and to represent a Grenville collisional belt at the northern margin of the North China craton, related to the assembly of the Rodinia supercontinent. Investigations indicate that this group is comprised of volcanic and sedimentary rocks that underwent amphibolite- to greenschist-facies metamorphism and intensive deformation. Zircon U-Pb ages indicate that the gneiss and amphibolites were formed in the Archean and underwent amphibolite metamorphism at ~2.5 Ga. However, rhyolite was erupted at 264 ± 10 Ma and andesites formed during the Late Jurassic at 169-162 Ma. These age data indicate that the Seluohe Group is composed by Late Paleozoic and Mesozoic volcanic rocks, with minor Archean metamorphic rocks. They are not a "group" in the stratigraphic sense, but represent a tectonic mélange. Interestingly, no Proterozoic rocks have been identified. Inherited zircons from volcanic rocks (rhyolite, andesite) and granitic gneiss provide no evidence of a Grenvillian collision. Therefore, the new geochronological data do not support the traditional view that Proterozoic tectono-magmatic events affected the northern margin of the North China craton; hence the conclusion that it took part in the formation and evolution of Rodinia during the Proterozoic is questioned. Ar-Ar mineral ages suggest that the Archean metamorphic rocks were later deformed at ~ 160 Ma, establishing a Jurassic deformational event in the area.Keywords:
Rodinia
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Greenschist
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Protolith
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Large igneous province
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Abstract The periodic dispersal and assembly of continental fragments has been an inherent feature of the continental crust. Based on the discovery of large-scale supercontinent cycle and the theory of plate tectonics, several supercontinents have been identified, such as Columbia/Nuna, Rodinia, Gondwana and Pangaea. Neoproterozoic magmatic events related to the break-up of Rodinia are globally well preserved. Although Neoproterozoic magmatic events were very weak in the North China Craton (NCC), they are crucial in reconstructing the geometries of the NCC and could facilitate the completion of the Neoproterozoic configuration of the supercontinent. In this study, c . 853–835 Ma magmatic rocks are identified in the western margin of the NCC. Precise zircon U–Pb age determination yields 206 Pb/ 238 U average ages of 835.5 ± 5.3 Ma (HL-39) and 853.7 ± 4.5 Ma (HL-30). In situ zircon Hf isotope compositions of the samples reveal that their parental magma was formed by the reworking of ancient crust evolved from Mesoproterozoic mantle. In summary, the discovery of Neoproterozoic magmatic rocks in the western margin of the NCC, and reported synchronous rocks in other parts of the NCC indicate that the NCC might be conjoined with the supercontinent Rodinia during the Neoproterozoic. This discovery is of significant help in unravelling the early Neoproterozoic history of the NCC and the evolution of the supercontinent Rodinia.
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标明日期的 U-Pb 在 Delingha 从变形 leucosomes 在锆石的不同领域上被进行() 复杂， Olongbuluke 的更低的基岩() 微大陆，北方 Qaidam，以便考察它的复杂 tectonothermal 历史。锆石核心由高度修改的 magmatic 锆石寡妇组成，锆石披风响应一个迟了的 Protoproterozoic 热事件的深溶酌被生产；锆石核心和锆石披风的年龄和同位素组成严重由于与锆石增生边界的生长联系的热事件被扰乱了。(207 ) 增生边界的 Pb/(206 ) Pb 明显的年龄被估计是 1 030 妈。这个迟了的 Mesoproterozoic 热事件在 Olongbuluke 微大陆作为对全球 Rodinia 超级大陆集会事件的回答被解释了，西北中国。给词调音：锆石增生；U-Pb 年龄；变形 leucosome；Rodinia 超级大陆汇编；西北 Qaidam
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Geosphere, December 2007, v. 3, p. 511-526, doi: 10.1130/GES00091.1. Animation 3 - QuickTime movie of the diachronous assembly and breakup of Rodinia from 1100 Ma to 530 Ma. Positions of continental fragments (white) relative to Laurentia (multi-colored) at key time slices (e.g., 1100 Ma, 1000 Ma, 900 Ma, 700 Ma, 550 Ma) based on the IGCP 440 reconstruction of the Rodinia supercontinent, as summarized in Li et al. (2007 and references therein). Development of Laurentia during this time period based on Whitmeyer and Karlstrom (2007). Early Cambrian rifting of the Precordillera micro-continent from Laurentia based on Thomas and Astini (1996). Neoproterozoic-Cambrian assembly of Gondwana following breakup of Rodinia largely based on Powell et al. (1993) and Dalziel (1997). File size is 4.9 MB.
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The work of Alfred Wegener against the theory of expanding Earth. A b s t r a c t. Wegener‘s Pangea comprised all the continents during Permian times, surrounded by the Panthalassa all-ocean, much wider than the recent Pacific. The process of widening of new oceans (Atlantic, Arctic and Indian) during the Pangea breakup should be simultaneous with the shrinking of the pra-Pacific. However, there is much evidence that there are close biogeographic links between continents surrounding the Pacific, and the perimeter of the ocean becomes larger. If the Pacific expands like the other oceans, the Earth expansion is inevitable. The plate-tectonic fundamentals of supercontinent reconstructions refer to the hypothesis of the cyclic evolution of continental plates and to the assumption that plate collisions result in amalgamation of successive supercontinents followed by their break-up. As the result, the term “supercontinental cycle” was introduced. Thus, the Pangea history becomes a sequence of different consecutive Pangeas. Two periods of Precambrian supercontinent amalgamation were distinguished based on the supercontinent cyclicity hypothesis, leading to the formation of Meso-Neoproterozoic Rodinia and the Early Proterozoic Pre-Rodinia supercontinent. Pre-Rodinia, Rodinia and Pangea were strikingly similar to one another. To explain this phenomenon, a process of self-organization of tectonic plates is invoked. On an expanding Earth, there was only one supercontinent – Pangea – composed of continental lithosphere surrounding the planet smaller than the present Earth. The break-up process of the supercontinent occurred only once during Earth‘s history. Earth expansion offers a reasonable solution to the main plate-tectonic paradox that the continents could have been repeatedly separated and returned to the same unique configuration.
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