Tectonic evolution of the Arctic Norwegian Caledonides from a texturally- and structurally-constrained multi-isotopic (Ar-Ar, Rb-Sr, Sm-Nd, U-Pb) study
Tectonic evolution of the Arctic Norwegian Caledonides from a texturally- and structurally-constrained multi-isotopic (Ar-Ar, Rb-Sr, Sm-Nd, U-Pb) study
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来自结构和结构约束的多同位素（Ar-Ar、Rb-Sr、Sm-Nd、U-Pb）研究的北极挪威喀里多尼德斯的构造演化
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发表时间：
2007
影响因子：
2.9
通讯作者：
Martin J. Whitehouse
中科院分区：
文献类型：
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作者：
Christopher L. Kirkland;J. Daly;E. Eide;Martin J. Whitehouse
本文介绍了挪威北极芬马克地区Kalak推覆杂岩（KNC）和上覆Magerøy推覆岩的Ar-Ar、Sm-Nd、U-Pb和Rb-Sr同位素和结构综合研究结果。结果表明，古生代构造变质的历史不同于以前推断的区域。Kalak推覆杂岩（KNC）一直被认为是波罗的海陆缘的重要组成部分，受到两次古生代构造变质事件的影响，这两次事件在时间上相隔甚远，（晚寒武世，距今490 - 510 Ma）首次从围岩与辉长岩侵入体的野外关系中确定，（志留纪至泥盆纪早期，距今400 - 428 Ma）。Magerøy推覆体中的一条片理化花岗质岩脉产生的锆石U-Pb年龄为438 ± 3 Ma，与该推覆体中横切早期变形构造的侵入体的年龄相同。KNC中早世代白云母的加权平均Ar-Ar冷却年龄为438 ± 2 Ma，KNC中褶皱脉岩中石榴石的Sm-Nd结晶年龄为436 ± 21 Ma。因此，KNC内的早志留世变质作用与上/最上外来岩的上覆Magerøy推覆体内的变形和岩浆作用同时发生。斯堪的纳维亚大陆-大陆碰撞在Magerøy推覆体和KNC中都有记录。KNC中428 ± 4 Ma的热液锆石U-Pb定年被解释为Scandian变质作用的高温条件。Ar-Ar白云母年龄为422 ± 2 Ma，与叠加纹理相关，Rb-Sr黑云母年龄为413 ± 3 Ma，记录了该事件后的冷却。Magerøy推覆体中的Engesfjellet花岗岩产生的Ar-Ar角闪石年龄为423 ± 8 Ma，归因于Scandian碰撞后的冷却，因此为该单元侵位到KNC上的时间提供了最小年龄。KNC中晚期未变形的横切伟晶岩的锆石U-Pb年龄为425 ± 5 Ma，表明Scandian碰撞在此之前完成。黑云母Ar-Ar炉逐步加热分析具有普遍的过量放射性氩污染。Ar-Ar紫外激光探针黑云母分析也被过量氩污染，但显示未受影响的部分年龄为401 ± 6 Ma。在一个来自Magerøy推覆体的样品中，有两个表观年龄，一个在410 ± 8 Ma，另一个在404 ± 4 Ma，对应于具有独特捕获氩组分的不同组构。较老的年龄受到过量氩的影响。然而，年轻的黑云母织物的分析揭示了大气成分的40 Ar/36 Ar值，并被解释为黑云母的年龄冷却。这是一致的普遍过剩的氩通量记录整个北方挪威在斯堪的纳维亚造山运动的一个短暂的事件。这些结果有重要的意义，了解北挪威的加里东造山带的发展，但不支持的前提下，Finnmarkian造山运动（在原来的意义上的术语）在其典型的地方。结果表明，KNC的影响，约10马前的气候Scandian碰撞，可能与板卷在俯冲Iapetus海洋的构造变质事件。
This study presents the results of an integrated Ar-Ar, Sm-Nd, U-Pb, and Rb-Sr isotopic and structural investigation from the Kalak Nappe Complex (KNC) and overlying Magerøy Nappe in Finnmark, Arctic Norway. The results indicate a Paleozoic tectonometamorphic history dissimilar to that previously inferred for the region. The Kalak Nappe Complex (KNC) has been classically regarded as a major component of the allochthonous margin of Baltica variably affected by two Paleozoic tectonometamorphic events separated widely in time -an earlier Finnmarkian event (late Cambrian, ∼490 – 510 Ma) first defined from field relationships of country rocks to gabbroic intrusions, and a later over printing Scandian event (Silurian to early Devonian, ∼400 –428 Ma). A foliated granitic dike within the Magerøy Nappe yields a U-Pb zircon age of 438 ± 3 Ma, an age identical to intrusive bodies that cross cut early deformation structures within this nappe. An early generation of muscovite within the KNC produces a weighted mean Ar-Ar cooling age of 438 ± 2 Ma and garnet from a folded dike, also in the KNC, yields a Sm-Nd crystallization age of 436 ± 21 Ma. Thus early Silurian metamorphism within the KNC occurred at the same time as deformation and magmatism within the overlying Magerøy Nappe of the Upper / Uppermost Allochthon. The Scandian continent-continent collision is recorded both within the Magerøy Nappe and within the KNC. U-Pb dating of hydrothermal zircon in the KNC at 428 ± 4 Ma is interpreted to date high temperature conditions during Scandian metamorphism. Ar-Ar muscovite ages of 422 ± 2 Ma, associated with overprinting textures, and Rb-Sr biotite ages of 413 ± 3 Ma record cooling after this event. The Engesfjellet Granite in the Magerøy Nappe yields an Ar-Ar amphibole age of 423 ± 8 Ma, ascribed to cooling after the Scandian collision and thus provides a minimum age for the time of emplacement of this unit onto the KNC. A late, undeformed cross-cutting pegmatite within the KNC yields a U-Pb zircon age of 425 ± 5 Ma and indicates that the Scandian collision was completed prior to this time. Biotite Ar-Ar furnace step-heating analyses have pervasive excess radiogenic argon contamination. Ar-Ar UV laser-probe biotite analyses are also contaminated with excess argon but reveal unaffected portions of grains with ages of 401 ± 6 Ma. In one sample from the Magerøy Nappe, two apparent ages, one at 410 ± 8 Ma and another at 404 ± 4 Ma, correspond to different fabrics with distinctive trapped argon components. The older ages are affected by excess argon. However analyses of the younger biotite fabric reveal 40Ar/36Ar values of atmospheric composition and are interpreted as dating cooling in biotite. This is consistent with the pervasive excess argon flux recorded throughout northern Norway having developed during a short-lived event in the Scandian Orogeny. These results have significant implications for understanding the development of the Caledonian orogenic belt in North Norway, but do not support the premise of a Finnmarkian Orogeny (in the original sense of the term) within its type locality. The results show that the KNC was affected by a tectonometamorphic event some 10 Ma prior to the climactic Scandian collision, likely related to slab roll back in the subducting Iapetus Ocean.