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Four billion years of ophiolites reveal secular trends in oceanic crust formation

Geoscience Frontiers 2014年第4期5卷 571-603页

作者： Harald Furnes maarten de wit Yildirim Dilek department of Earth Science and Centre for Geobiology University of BergenAllegt.415007 BergenNorway AEON and Earth Stewardship Science Research Institute Nelson Mandela Metropolitan University 7701Port Elizabeth 6031South Africa department of Geology and Environmental Earth Science Miami University State Key Laboratory of Geological Processes and Mineral Resources and School of Earth Science and Mineral ResourcesChina University of Geosciences

We combine a geological, geochemical and tectonic dataset from 118 ophiolite complexes of the major global Phanerozoic orogenic belts with similar datasets of ophiolites from 111 Precambrian greenstone belts to construct an overview of oceanic crust generation over 4 billion years. Geochemical discrimi- nation systematics built on immobile trace elements reveal that the basaltic units of the Phanerozoic ophiolites are dominantly subduction-related （75%）, linked to backarc processes and characterized by a strong MORB component, similar to ophiolites in Precambrian greenstone sequences （85%）. The remaining 25% Phanerozoic subduction-unrelated ophiolites are mainly （74%） of Mid-Ocean-Ridge type （MORB type）, in contrast to the equal proportion of RiftlContinental Margin, Plume, and MORB type ophiolites in the Precambrian greenstone belts. Throughout the Phanerozoic there are large geochemical variations in major and trace elements, but for average element values calculated in 5 bins of 100 million year intervals there are no obvious secular trends. By contrast, basaltic units in the ophiolites of the Precambrian greenstones （calculated in 12 bins of 250 million years intervals）, starting in late Paleo- to early Mesoproterozoic （ca. 2.0-1.8 Ga）, exhibit an apparent decrease in the average values of incom- patible elements such as Ti, P, Zr, Y and Nb, and an increase in the compatible elements Ni and Cr with deeper time to the end of the Archean and into the Hadean. These changes can be attributed to decreasing degrees of partial melting of the upper mantle from HadeanJArchean to Present. The onset of geochemical changes coincide with the timing of detectible changes in the structural architecture of the ophiolites such as greater volumes of gabbro and more common sheeted dyke complexes, and lesser occurrences of ocelli （varioles） in the pillow lavas in ophiolites younger than 2 Ga. The global data from the Precambrian ophiolites, representative of nearly 50% of all known

关键词： Phanerozoic and Precambrian greenstonebeltsOphiolite classificationSubduction-related ophiolitesSubduction-unrelated ophiolitesPrecambrian plate tectonics

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Paleoarchean bedrock lithologies across the Makhonjwa Mountains of South Africa and Swaziland linked to geochemical,magnetic and tectonic data reveal early plate tectonic genes flanking subduction margins

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Geoscience Frontiers 2018年第3期9卷 603-665页

作者： maarten de wit Harald Furnes Scott MacLennan Moctar Doucouré Blair Schoene Ute Weckmann Uma Martinez Sam Bowring AEON-ESSRI (Africa Earth Observatory Network-Earth Stewardship Science Research Institute) Nelson Mandela University department of Earth Science & Centre for Geobiology University of Bergen department of Geosciences Princeton University department of Geosciences Nelson Mandela University department Geophysics GFZ-German Research Centre for GeosciencesHelmholtz Centre GISCAPETOWN Earth Atmosphere and Planetary SciencesMassachusetts Institute of Technology

The Makhonjwa Mountains, traditionally referred to as the Barberton Greenstone Belt, retain an iconic Paleoarchean archive against which numerical models of early earth geodynamics can be tested. We present new geologic and structural maps, geochemical plots, geo- and thermo-chronology, and geophysical data from seven silicic, mafic to ultramafic complexes separated by major shear systems across the southern Makhonjwa Mountains. All reveal signs of modern oceanic back-arc crust and subductionrelated processes. We compare the rates of processes determined from this data and balance these against plate tectonic and plume related models. Robust rates of both horizontal and vertical tectonic processes derived from the Makhonjwa Mountain complexes are similar, well within an order of magnitude, to those encountered across modern oceanic and orogenic terrains flanking Western Pacific-like subduction zones. We conclude that plate tectonics and linked plate-boundary processes were well established by 3.2-3.6 Ga. Our work provides new constraints for modellers with rates of a 'basket' of processes against which to test Paleoarchean geodynamic models over a time period close to the length of the Phanerozoic.

关键词： Paleoarchean Barberton Greenstone Belt Onverwacht Suite Geologic bedrock and structural maps Geochemistry and geophysics Plate tectonics

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南非(阿扎尼亚)巴伯顿绿岩带一个3500Ma蛇绿杂岩:太古宙洋壳及其大地构造意义

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华北地质 1980年第3期 85-87页

作者： maarten J.de wit Charles R.Stern 闻桂芹南非约翰内斯堡维特瓦特斯兰德大学伯纳德王子地球物理研究所美国科罗拉多博尔德科罗拉多大学地质科学系

测定年龄为3540±30Ma的巴伯顿绿岩带,由于具有保存良好的地区,而在太古宙构造模式中具有重要意义。从斯泰因曼的三位一体观点考虑,有几个工作者注意到了这个绿岩带下部地层单位的蛇绿岩性质,如今被认为是翁韦瓦克特群。但是目前承认的... 详细信息

测定年龄为3540±30Ma的巴伯顿绿岩带,由于具有保存良好的地区,而在太古宙构造模式中具有重要意义。从斯泰因曼的三位一体观点考虑,有几个工作者注意到了这个绿岩带下部地层单位的蛇绿岩性质,如今被认为是翁韦瓦克特群。但是目前承认的翁韦瓦克特群的地层是一个15公里厚的火山喷发和沉积堆积物。这一地层与显生宙蛇绿岩“假地层”不同,这种蛇绿岩可与在洋脊扩张中形成的洋壳相对比。由于这个原因,巴伯

关键词：蛇绿岩地层巴伯超基性岩太古宙太古代前寒武纪绿岩带显生宙显动宙洋壳大洋型地壳

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