Detrital zircon signatures of the Baltoscandian margin along the Arctic Circle Caledonides in Sweden: The Sveconorwegian connection
Detrital zircon signatures of the Baltoscandian margin along the Arctic Circle Caledonides in Sweden: The Sveconorwegian connection
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瑞典北极圈 Caledonides 沿线 Baltoscandian 边缘的碎屑锆石特征：Sveconorwegian 连接
DOI：
10.1016/j.precamres.2015.05.012
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发表时间：
2015
影响因子：
3.8
通讯作者：
J. Majka
中科院分区：
文献类型：
--
作者：
D. Gee;P. Andreasson;H. Lorenz;D. Frei;J. Majka
新的证据表明，斯维康诺威造山带继续从斯堪的纳维亚西南部的典型地区沿着巴尔托斯卡尼亚外缘向北进入北极高地。穿过瑞典北极圈66-67°N的斯堪的纳维亚加里多尼德山脉的Silver Road(Silvervägen)剖面提供了整个巴尔托斯卡迪亚边缘的构造地层剖面，从自体到下阿洛奇松，一直到中阿勒契桑的上部。变质程度通过推覆体向上递增，最低为低绿片岩相，最高部分为榴辉岩级，后者与早期奥陶纪俯冲巴尔托斯珊瑚最外缘有关。这些沉积岩的年龄范围从新元古代到奥陶纪，提供了从巴尔托斯珊瑚地台向西越过低温裂谷边缘到陆洋过渡带的环境变化的证据，也提供了奥陶纪前陆盆地的证据。来自不同构造地层层的12个砂岩样品获得了反映其源区变化特征的碎屑锆石U/Pb年龄特征。原地砂岩起源于晚古元古代(1800-1950 Ma)逆冲前缘以东附近的结晶岩。下奥陶纪埃迪卡拉纪-早寒武世石英岩也以晚古元古代锆石特征为主，但具有从属于中元古代和晚太古代的特征，而中奥陶世W衍生的前陆盆地浊积岩以斯维康诺威(950-1100 Ma)特征为主，从属于较老的中元古代和最新的古元古代群体。所有来自中阿勒契顿下部(缺乏辉绿岩岩墙)的样品都具有以古元古代晚期和中元古代早期为主的特征，其从属种群可追溯到斯维孔诺夫时代；后者主导着上覆的Särv推覆构造和塞夫推覆杂岩，此前已在那里报道了约945 Ma的流纹岩。这一证据表明，北极圈更南端和更北端的斯维康诺威造山带源岩，再加上之前公布的碎屑锆石数据，显然支持这样一种解释，即新元古代斯维康诺威造山带沿着整个巴尔托斯考古外缘延伸到北极高地。
New evidence is presented here that the Sveconorwegian Orogen continued northwards from type areas in southwestern Scandinavia along the Baltoscandian outer margin into the high Arctic. The Silver Road (Silvervägen) profile through the Scandinavian Caledonides, located in Sweden along the Arctic Circle at 66–67° N, provides a full section through the tectonostratigraphy of the Baltoscandian margin from the Autochthon, via the Lower Allochthon to the upperment parts of the Middle Allochthon. Metamorphic grade increases upwards through the nappes, being low greenschist facies at lowest levels and increasing to eclogite grade in the highest parts of the Seve Nappe Complex, the latter being related to early Ordovician subduction of the Baltoscandian outermost margin. The sedimentary rocks range in age from Neoproterozoic to Ordovician and provide evidence of the changes of environment from the Baltoscandian platform, westwards out over the Cryogenian rifted margin to the continent-ocean transition zone; also the Ordovician foreland basin. Twelve samples of psammites from the different tectonostratigraphic levels have yielded U/Pb detrital zircon age-signatures that reflect the changing character of their provenance. Autochthonous sandstones are derived from late Paleoproterozoic (1800–1950 Ma) crystalline rocks in the vicinity to the east of the thrust front. Ediacaran-early Cambrian quartzites of the Lower Allochthon also yield mainly late Paleoproterozoic zircon signatures, but with subordinate Mesoproterozoic and late Archaean populations, whilst mid Ordovician, W-derived foreland basin turbidites are dominated by Sveconorwegian (950–1100 Ma) signatures, with subordinate older Mesoproterozoic to latest Paleoproterozoic populations. All samples from the lower parts of the Middle Allochthon (lacking dolerite dykes) have signatures that are dominated by latest Paleoproterozoic and early Mesoproterozoic ages, with subordinate populations down to Sveconorwegian ages; the latter dominate the overlying Särv nappes and also the Seve Nappe Complex, where c. 945 Ma rhyodacites have been previously reported. This evidence of Sveconorwegian source rocks in the hinterland, taken together with previously published detrital zircon data farther south and north of the Arctic Circle, clearly favours the interpretation that the Sveconorwegian Orogen, during the Neoproterozoic, extended along the entire Baltoscandian outer margin into the high Arctic.