Transposition of structures in the Neoproterozoic Kaoko Belt (NW Namibia) and their absolute timing
Transposition of structures in the Neoproterozoic Kaoko Belt (NW Namibia) and their absolute timing
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新元古代 Kaoko 带（纳米比亚西北部）的构造转位及其绝对时间
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
L. Tajčmanová
中科院分区：
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作者：
S. Ulrich;J. Konopásek;P. Jeřábek;L. Tajčmanová
在纳米比亚西北部的Kaoko带研究了横跨海岸地体、边界火成杂岩和造山带核的三个构造剖面。已知最古老的硅组构是继承自一个较老的构造变质事件。它只发生在沿海地体中，其改造程度从南到北逐渐增加。S1叶理使沿海地体中的硅组构重新活化或折叠，并在边界火成杂岩的花岗岩类和造山带核域的混合岩中作为早期平面组构出现。叠加的近垂直S2组构对应于直立近等斜褶皱的轴面劈理，其发育程度也由南向北逐渐增大。在造山带核S2发育过程中，部分熔体的活跃迁移表明这种变形开始于~550 Ma。F2褶皱轴和L2拉伸线理的分布表明，在中部剖面中保存了与N-S向S2劈理发育有关的纯剪切变形，而在北方新发育的NW-SE向普遍劈理上则发生了以左旋简单剪切变形为主的变形。这种变形记录的空间变化是由于不规则形状的刚果Dupron压头，这是反映了在沿海地体和边界火成岩复杂的S2裂解前的非均匀发展。L1和L2拉伸线理的共同取向和S1和S2平面上的固态改造表明，自550 Ma以来，应变划分为斜向逆冲（重新激活的S1）和横向左旋剪切（S2和S3）域的单次左行平移挤压事件。这种变形结构的连续性表明，高科带的主要近垂直剪切带并不对应于早期地壳不连续面，而是反映了冷却期间的晚期应变局部化。
Three structural profiles across the Coastal Terrane, the Boundary Igneous Complex and the Orogen Core have been studied in the Kaoko Belt of northwestern Namibia. The oldest known Si fabric is inherited from an older tectono-metamorphic event. It occurs in the Coastal Terrane only and the extent of its reworking increases from south to north. The S1 foliation reactivates or folds Si fabric in the Coastal Terrane and appears as an early planar fabric in granitoids of the Boundary Igneous Complex and migmatites of the Orogen Core domain. Superimposed subvertical S2 fabric corresponds to axial plane cleavage of upright close to isoclinal folds and the extent of its development also increases from south to north. Active migration of partial melt during S2 development in the Orogen Core dates the onset of this deformation at ~550 Ma. Distribution of F2 fold axes and L2 stretching lineations suggests pure shear–dominated deformation associated with development of N–S trending S2 cleavage preserved in the central profile, followed by sinistral simple shear–dominated deformation on newly developed NW–SE trending pervasive cleavage in the northern part of the area. Such spatial variation in the deformation record is attributed to the irregular shape of the Congo Craton indenter that is reflected by heterogeneous development of the S2 cleavage front in the Coastal Terrane and the Boundary Igneous Complex. Common orientation of L1 and L2 stretching lineations and solid-state reworking on both S1 and S2 planes suggest single event of sinistral transpression since 550 Ma with strain partitioning into domains of oblique thrusting (reactivated S1) and transcurrent sinistral shearing (S2 and S3). Such succession of deformation structures suggests that major subvertical shear zones in the Kaoko Belt do not correspond to early crustal discontinuities, but rather reflect late strain localization during cooling.