Diachronous collision in the Seve Nappe Complex: Evidence from Lu–Hf geochronology of eclogites (Norrbotten, North Sweden)
Diachronous collision in the Seve Nappe Complex: Evidence from Lu–Hf geochronology of eclogites (Norrbotten, North Sweden)
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Seve Naappe 杂岩中的历时碰撞：来自榴辉岩 LuâHf 地质年代学的证据（北瑞典北博滕）
DOI：
10.1111/jmg.12591
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发表时间：
2021
影响因子：
3.4
通讯作者：
Münker
中科院分区：
文献类型：
--
作者：
Fassmer;Froitzheim;Janák;Strohmeyer;Bukala;Münker
加里东造山运动期间，波罗的海和劳伦大陆发生碰撞。400-420毫安。然而，俯冲和碰撞过程也发生在这个主碰撞阶段之前，这些构造历史仍然没有完全解决。瑞典的塞夫推覆复合体记录了这些早期阶段。诺尔博滕（瑞典北部加里东山脉）的塞夫推覆复合体由四个叠加推覆体组成，它们是由向东逆冲推覆而成的（根据传统的构造解释，从底部到顶部）：下塞夫推覆体、瓦伊莫克、萨雷克和策科克透镜体。榴辉岩产于Vaimok和Tsäkkok透镜体。Vaimok透镜代表了被新元古代粗玄岩脉侵入的波罗的海大陆边缘的岩石，这些粗玄岩脉后来被榴辉岩化和石香肠化。相比之下，Tsäkkok透镜的榴辉岩是与钙片岩有关的前大洋玄武岩，可能代表波罗的海和土卫八之间的洋-陆过渡。以前榴辉岩年龄的测定得出了不同的年龄。500和480 Ma，与Jämtland更南部的Seve推覆复合体中更年轻（460-450 Ma）的超高压变质作用形成对比。采用Lu-Hf石榴石年代学对Vaimok（一个样品）和Tsäkkok（三个样品）透镜体中的榴辉岩进行了定年。所有样品中石榴石的主量元素和Lu含量均呈现明显的分带性，并获得了以下年龄的等时线：480.4 ± 1.2 Ma（Vaimok）; 487.7 ± 4.6 Ma，486.2 ± 3.2，484.6 ± 4.6 Ma（Tsäkkok）。Tsäkkok的年龄被解释为约1000年左右西倾俯冲带中Iapetus-Baltica海洋-大陆过渡的埋葬。485 Ma，构造上更深的Vaimok推覆体的年龄为大陆边缘俯冲的后续。本研究不支持以前报道的500 Ma及以上的年龄。Jämtland的Seve Nappe Complex中榴辉岩之间的年龄差异（c。460-450 Ma）和Norrbotten（c. 488-480 Ma）可能反映了岛弧与波罗的海不规则形状的被动大陆边缘的碰撞，或者反映了平直边缘与上板块增生的微大陆（Sarek透镜）的碰撞。
The collision of Baltica and Laurentia during the Caledonian Orogeny happened atc. 400–420 Ma. However, subduction and collision processes also took place before this main collisional phase and the tectonic history of these is still not fully resolved. The Seve Nappe Complex in Sweden has recorded these earlier phases. The Seve Nappe Complex in Norrbotten (North Swedish Caledonides) comprises four superimposed nappes emplaced by eastward thrusting (from base to top according to the conventional structural interpretation): Lower Seve Nappe, Vaimok, Sarek, and Tsäkkok Lenses. Eclogites occur in the Vaimok and Tsäkkok Lenses. The Vaimok Lens represents rocks of the Baltican continental margin intruded by Neoproterozoic dolerite dikes which were later eclogitized and boudinaged. By contrast, eclogites of the Tsäkkok Lens are former oceanic basalts associated with calcschists, possibly representing the ocean–continent transition between Baltica and Iapetus. Previous age determinations for eclogitization yielded various ages betweenc. 500 and 480 Ma, in contrast to younger (460–450 Ma) ages of ultra high‐Pmetamorphism in the Seve Nappe Complex further south in Jämtland. Eclogites from the Vaimok (one sample) and Tsäkkok (three samples) lenses were dated using Lu–Hf garnet geochronology. Garnet from all samples shows prograde zoning of major element and Lu contents and yielded well‐defined isochrons of the following ages: 480.4 ± 1.2 Ma (Vaimok); 487.7 ± 4.6 Ma, 486.2 ± 3.2, 484.6 ± 4.6 Ma (Tsäkkok). The ages from Tsäkkok are interpreted to date the burial of the Iapetus–Baltica ocean–continent transition in a west‐dipping subduction zone aroundc. 485 Ma, and the age from the structurally deeper Vaimok Nappe the following subduction of the continental margin. Previously reported ages of 500 Ma and older are not supported by this study. The age difference between eclogites in the Seve Nappe Complex in Jämtland (c. 460–450 Ma) and Norrbotten (c. 488–480 Ma) may reflect the collision of an island arc with an irregularly shaped passive continental margin of Baltica or alternatively the collision of a straight margin with a microcontinent (Sarek Lens) accreted to the upper plate.
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