The Northern Giudicarie and the Meran-Mauls fault (Alps, Northern Italy) in the light of new paleomagnetic and geochronological data from boudinaged Eo-/Oligocene tonalites
The Northern Giudicarie and the Meran-Mauls fault (Alps, Northern Italy) in the light of new paleomagnetic and geochronological data from boudinaged Eo-/Oligocene tonalites
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根据来自布丁始/渐新世英云岩的新古地磁和地质年代学数据，研究北朱迪卡里和梅兰-莫尔斯断层（阿尔卑斯山，意大利北部）
DOI：
10.1007/s00531-010-0612-4
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发表时间：
2011
影响因子：
2.3
通讯作者：
B. Fügenschuh
中科院分区：
文献类型：
--
作者：
H. Pomella;U. Klötzli;R. Scholger;M. Stipp;B. Fügenschuh
本研究集中于朱迪卡里断层系统的两个重要断层（北朱迪卡里断层和梅拉-莫尔斯断层）沿线的小型侵入体，这些断层被概括为“英云岩片层”。磁组构分析与构造场数据相结合表明，沿着朱迪卡里断层系（Meran-Mauls 断层）的 NE-SW 走向的右旋走滑变形，受到较年轻的逆冲作用的影响。第三纪区域应力场方向大致为北北西-南南东方向。沿Meran-Mauls断层从右旋走滑到东南顶逆冲的变形的独特变化可能是由于英云长岩侵入并形成水平磁性叶理后断层的旋转或弯曲引起的。基于南高山压头向 NNW 方向推进而弯曲的初步笔直的近地层线的假设，色调岩层可以解释为在压痕过程中从阿达梅洛岩基上剪下的透镜体。新的锆石 U/Pb 数据表明，一些片层属于渐新世（Rupelian），其他的属于晚始新世（Prabonian）年龄。 Meran-Mauls 断层上出现的角闪石-辉长岩透镜体提供了中始新世（巴托阶）年龄。在主要的近洲岩体中，只有阿达梅洛岩基的南部单元也侵入了始新世，这表明英伦岩层和阿达梅洛岩基之间存在很强的相关性。剩余磁化强度的分析和居里点测定表明磁铁矿是在相对较低的温度下被阻挡的粘性磁化强度的主要载体。这表明沿朱迪卡里断层系统所研究的侵入体缓慢冷却至约 300°C，这与目前地表阿达梅洛侵入体单元确定的快速冷却形成鲜明对比。新的锆石裂变径迹数据还显示，与南部的阿达梅洛岩基和北部的莫尔斯薄片相比，沿朱迪卡里断层系的英英闪长岩冷却较晚，表明该地区包含从比阿达梅洛和莫尔斯地区更深的构造层面挖出的岩浆体。这可能是由于北朱迪卡里断层和梅兰-莫尔斯断层下盘有重要的东南向逆冲断层和压断层造成的。
This study concentrates on small intrusions along two important faults of the Giudicarie fault system, the Northern Giudicarie and the Meran-Mauls fault, summarised under the term tonalitic lamellae. Magnetic fabric analyses in combination with structural field data indicate dextral strike slip deformation along the NE–SW striking northern part of the Giudicarie fault system, the Meran-Mauls fault, overprinted by younger thrusting. The regional stressfield was oriented approximately NNW–SSE during Tertiary times. The distinctive change in deformation along the Meran-Mauls fault from dextral strike slip to top-SE thrusting may be caused by a rotation or bending of the fault after the intrusion of the tonalites and the formation of their horizontal magnetic foliation. Based on the assumption of a preliminary straight Periadriatic lineament bent by the NNW-wards advancement of the Southalpine indenter, the tonalitic lamellae may be interpreted as lenses sheared off from the Adamello batholith during indentation. New U/Pb data on zircon show that some of the lamellae are of Oligocene (Rupelian), others of Late Eocene (Priabonian) age. An amphibole-gabbro lens occurring on the Meran-Mauls fault provides a Middle Eocene (Bartonian) age. Among the major Periadriatic plutons, only the southern units of the Adamello batholith also intruded in the Eocene that suggests a strong correlation between the tonalitic lamellae and the Adamello batholith. The analyses of the remanent magnetisation and the Curie point determinations argue for magnetite as the main carrier of a viscous magnetisation blocked at relatively low temperatures. This indicates slow cooling of the investigated intrusions along the Giudicarie fault system down to approximately 300°C, which is in contrast to the fast cooling determined for the Adamello intrusion units currently at the surface. The new zircon fission track data also show later cooling of the tonalites along the Giudicarie fault system when compared with the Adamello batholith in the south and the Mauls lamellae in the north, indicating that this area contains magmatic bodies exhumed from a deeper structural level than in the Adamello and the Mauls region. This may be due to important top-SE thrusting and transpressive faulting in the footwall of the Northern Giudicarie fault and the Meran-Mauls fault.