New palaeomagnetic, petrographic and 40Ar/39Ar data to test palaeogeographic reconstructions of Caledonide Svalbard
New palaeomagnetic, petrographic and 40Ar/39Ar data to test palaeogeographic reconstructions of Caledonide Svalbard
复制标题
新的古地磁、岩相和 40Ar/39Ar 数据用于测试卡利多尼德斯瓦尔巴群岛的古地理重建
作者：
K. Michalski;M. Lewandowski;G. Manby
摘要：提供了斯瓦尔巴群岛西南部寒武纪岩石的新古地磁和岩相数据，首次测试了斯瓦尔巴群岛主要地体的古生代重建。在热退磁过程中，识别出三种 ChRM（特征剩磁）成分，根据其不同的解锁温度，分别标记为 HORNL、HORNM 和 HORNH。 HORNM磁化强度与晚奥陶世-志留纪同变质S1叶理的形成有关。 HORNM 古极点（Φ = −18.5°，Λ = 359°，Dp/Dm = 5.8°/11.4°，Plat = 6°N）与土卫八闭合（455-415 Ma）后波罗的海-劳伦亚明显的极移路径的志留纪扇区完全匹配。根据从分隔中部和东部地体的 Billefjorden 断层带沿线的广阔糜棱岩地带获得的云母年龄确定的 450 Ma 40Ar-39Ar 年龄也表明这两个地体最终在 450 Ma 时合并。 HORNMVGP 还非常靠近源自东部地体（新弗里斯兰）中元古代岩石的古极点，这些岩石在加里东时期变质，表明它非常接近研究区域（中央地体）。本研究表明，斯瓦尔巴群岛至少有两个主要地体（如先前作者所定义）在志留纪时期占据了相似的地理位置，并且先前提出的大规模晚泥盆世左侧向位移的说法并不被支持。
Abstract New palaeomagnetic and petrographic data are presented from Cambrian rocks of SW Svalbard to test, for the first time, Palaeozoic reconstructions of the major terranes of Svalbard. In the course of thermal demagnetization three ChRM (characteristic remanent magnetization) components were identified, which were labelled HORNL, HORNM and HORNH, respectively, on the basis of their different unblocking temperatures. The HORNM magnetization is related to the Late Ordovician–Silurian formation of the synmetamorphic S1 foliation. The HORNM palaeopole (Φ = −18.5°, Λ = 359°, Dp/Dm = 5.8°/11.4°, Plat = 6°N) matches exactly the Silurian sectors of the Baltica–Laurentia apparent polar wander paths after the closure of Iapetus (455–415 Ma). The 450 Ma 40Ar–39Ar age determination from mica ages obtained from the broad zone of mylonites along the Billefjorden Fault Zone which separates the Central and Eastern terranes, also suggests that the two terranes were eventually amalgamated by 450 Ma. The HORNMVGP also lies very near the palaeopole derived from the Middle Proterozoic rocks of the Eastern Terrane (Ny Friesland), metamorphosed during Caledonian time, suggesting its close proximity to the study area (Central Terrane). The present study has shown that at least two of the major terranes of Svalbard, as defined by previous authors, occupied similar geographical locations by Silurian time, and the previously proposed large-scale Late Devonian left lateral displacements are not supported.