Kinematics of syneclogite deformation in the Bergen Arcs, Norway: implications for exhumation mechanisms
Kinematics of syneclogite deformation in the Bergen Arcs, Norway: implications for exhumation mechanisms
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挪威卑尔根弧区提辉岩变形的运动学：对折返机制的影响
DOI：
10.1144/gsl.sp.2005.243.01.13
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发表时间：
2005
期刊：
影响因子：
--
通讯作者：
D. Avigad
中科院分区：
文献类型：
--
作者：
H. Raimbourg;L. Jolivet;L. Labrousse;Y. Leroy;D. Avigad
挪威卑尔根岛弧的Holsnøy岛西北部是一个麻粒岩相原岩，在加里东造山作用期间，部分原岩在深部转变为榴辉岩相（700 °C，> 19 kbars）和角闪岩相（650 °C，8-10 kbars）。榴辉岩带主要是平面物体（具有平行反应带和cm至100 m尺度剪切带的裂缝）。榴辉岩带呈两组方向分布，其变形可描述为“书架构造”。主要剪切带走向在N120附近，倾向北，在整个地区表现出一致的自上而下的NE向剪切。在加里东北西向倾斜板片的大尺度运动学框架中，榴辉剪切带被解释为地壳单元从俯冲板片中分离并阻止其进一步下沉的方式。由于退变质斜长角闪岩变形模式与榴辉岩变形模式相似，拆离地壳单元沿着榴辉岩剪切带向上伸展。榴辉岩和角闪岩变质作用的放射性年龄及其与加里东造山作用年代学的比较表明，Holsnøy记录的变形发生在会聚背景下。因此，我们提出的机制可以解释碰撞过程中折返的第一步。
Abstract The northwestern part of Holsnøy island, in the Bergen Arcs, Norway, consists of a granulite-facies protolith partially transformed at depth in eclogite (700 °C, > 19 kbars) and amphibolite (650 °C, 8–10 kbars) facies during the Caledonian orogenesis. Eclogitized zones are mainly planar objects (fractures with parallel reaction bands and cm-to-100 m-scale shear zones). Eclogitic zones are distributed in two sets of orientations and the associated deformation can be described as ‘bookshelf tectonics’. The major shear zones strike around N120 and dip to the North, and show consistent top-to-the-NE shear sense throughout the area. In the large-scale kinematic frame of Caledonian NW-dipping slab, eclogitic shear zones are interpreted as the way to detach crustal units from the subducting slab and to prevent their further sinking. As the retrograde amphibolitic deformation pattern is similar to the eclogitic one, the detached crustal units started their way up along these eclogitic shear zones. Radiometric ages of eclogitic and amphibolitic metamorphism and their comparison with the chronology of Caledonian orogenesis show that the deformation recorded on Holsnøy occurred in a convergent context. The mechanism we propose can thus account for the first steps of exhumation during collision.