首页> 外文期刊>Tectonophysics: International Journal of Geotectonics and the Geology and Physics of the Interior of the Earth >Geochronological constraints on Paleoarchean thrust-nappe and Neoarchean accretionary tectonics in southern West Greenland
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Geochronological constraints on Paleoarchean thrust-nappe and Neoarchean accretionary tectonics in southern West Greenland

机译:西格陵兰南部古古生界逆冲推覆和新古生增生构造的年代学约束

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Major regional deformation and metamorphic events in the Godthabsfjord region, southern West Greenland, occurred at similar to 3650 and 2820-2720 Ma (e.g. Precambrian Res. 78 (1996) 1). New geochronological constraints (U-Pb zircon, Sensitive High Resolution Ion Microprobe [SHRIMP] and thermal ionisation mass spectrometry [TIMS]) have been obtained from a stack of mylonitic, crystalline thrust-nappes in the footwall of the western part of the Paleoarchean (similar to3.8-3.7 Ga) Isua Greenstone Belt, Isukasia. A mylonitic tonalite sheet, interpreted to have intruded synkinematically with respect to mylonitisation, yields a magmatic crystallisation age of 3640 3 Ma. A cross-cutting pegmatite and a post-kinematic tonalite pluton yield magmatic crystallisation ages of 2948+/-8 and 2991+/-2 Ma, respectively. Accordingly, we interpret the thrust-nappe stack to have formed during the Paleoarchean (similar to 3640 Ma), making it the oldest example known on Earth. The similarity of this structural regime to that of modem mountain belts suggests that Paleoarchean and modem continental crust were comparable in terms of mechanical strength and constitution. Southern West Greenland has been interpreted in terms of Neoarchean accretion, comparable with modem plate tectonics (e.g. Earth Planet. Sci. Lett. 142 (1996) 353). Isukasia lies just east of a purported Neoarchean accretionary boundary between the Akia terrane to the Northwest and the Akulleq terrane to the Southeast. The Akia terrane was previously considered to overthrust the Akulleq terrane at similar to 2820-2720 Ma. Our geochronological and geological data indicate (i) that the two "terranes", as presently defined, were stitched at 2991+/-2 Ma and (ii) that thrusting across the boundary was directed toward the Akia terrane. Therefore, we suggest that the Akia-Akulleq interface was not a fundamental tectonic structure during the Neoarchean, and we question its identification as an accretionary boundary. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 49]
机译:西格陵兰南部Godthabsfjord地区的主要区域变形和变质事件发生的时间与3650和2820-2720 Ma相似(例如Precambrian Res.78(1996)1)。新的地质年代学限制条件(U-Pb锆石,敏感的高分辨率离子微探针[SHRIMP]和热电离质谱[TIMS])已从古古西部西部下盘的一堆长隆体,结晶质推覆管中获得(类似于3.8-3.7 Ga)Isua的Isua绿宝石带。解释为从运动学上讲,相对于mylonitisation侵入的mylonitic孔雀石薄片的岩浆结晶年龄为3640 3 Ma。横切伟晶岩和运动学上的斜长石岩体产生的岩浆结晶年龄分别为2948 +/- 8 Ma和2991 +/- 2 Ma。因此,我们解释了古古宙时代(类似于3640 Ma)形成的逆冲推覆叠层,使其成为地球上已知的最古老的例子。这种结构形式与现代山地带的相似之处表明,在机械强度和构造方面,古始古纪和现代大陆壳具有可比性。格陵兰岛南部已被解释为与新近的板块构造相类似的新陈代谢,例如现代地球构造学(Earth Planet。Sci。Lett。142(1996)353)。伊苏卡西亚(Isukasia)位于西北部的阿基亚(Akia)地带和东南部的阿库利克(Akulleq)地体之间的一个据称的新奇时代的增生边界的东部。先前认为,Akia地形在类似于2820-2720 Ma时会推翻Akulleq地形。我们的地质年代和地质数据表明,(i)目前定义的两个“地形”以2991 +/- 2 Ma缝合,(ii)越过边界的推力指向Akia地形。因此,我们认为Akia-Akulleq界面不是新古构造时期的基本构造构造,因此我们质疑其是否为增生性边界。 (C)2002 Elsevier Science B.V.保留所有权利。 [参考:49]

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