Multistage Tectonism and Metamorphism During Gondwana Collision: Baladiyah Complex, Saudi Arabia
Multistage Tectonism and Metamorphism During Gondwana Collision: Baladiyah Complex, Saudi Arabia
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冈瓦纳碰撞期间的多期构造作用和变质作用：沙特阿拉伯巴拉迪亚杂岩
DOI：
10.1093/petrology/egu046
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发表时间：
1964
影响因子：
3.9
通讯作者：
Passchier
中科院分区：
文献类型：
--
作者：
Abu-Alam;Hassan;Stüwe;Passchier
来自沙特阿拉伯阿拉伯-努比亚地盾北方Baladiyah杂岩的现场证据表明，几个侵蚀不整合面分隔了不同的高级和中级变质沉积层序。这表明，东冈瓦纳和西冈瓦纳之间的碰撞涉及几个周期的挖掘和埋葬，提供了一个独特的机会来研究这个造山运动的多个阶段。矿物平衡的方法和热力学建模被用来放置这些周期的形成条件的约束。结果表明，该杂岩的特点是由三个区域变质事件，其次是第四次变质事件有关的剪切加热，由于逆冲后构造花岗岩。在第一次变质事件期间，变质作用的峰值约为705-715°C和5.2 - 5.6 kbar，随后减压到地球表面。随后沉积的沉积物在第二次变质事件期间达到635-670°C和4.2 -5 kbar，随后是磨拉石沉积物的剥露、侵蚀和沉积。岩石随后被第三次埋藏，并在磨拉石沉积物的负荷下变质至绿片岩相变质条件（330 ± 30°C和3.6 - 4.6 kbar）。最后，后构造花岗岩在最后的泛非折返过程中被侵入和冲断，导致第四次变质事件（700 ± 25°C）。与变形历史的对比表明，第一次和第二次变质作用发生在挤压体制下（D1和D2），分别与东西冈瓦纳大陆第一次（750 Ma）和第二次（676 Ma）碰撞有关。第三变形期以挤压体制开始，导致第三次变质事件，然后转变为斜向扭压体制，导致逃逸构造和大规模Najd走滑剪切带系统的发展。
Field evidence from the Baladiyah complex in the northern part of the Arabian–Nubian Shield of Saudi Arabia indicates several erosional unconformities separating different high- and medium-grade metasedimentary sequences. This suggests that the collision between East and West Gondwana involved several cycles of exhumation and burial, providing a unique opportunity to study the multiple stages of this orogeny. A mineral equilibria approach and thermodynamic modeling are used to place constraints on the formation conditions of each of these cycles. It is shown that the complex is characterized by three regional metamorphic events followed by a fourth metamorphic event related to shear heating owing to the thrusting of post-tectonic granites. During the first metamorphic event peak metamorphism was at around 705–715°C and 5·2–5·6 kbar followed by subsequent decompression to the Earth’s surface. Subsequently deposited sediments attained 635–670°C and 4·2–5 kbar during a second metamorphic event, followed by exhumation, erosion and deposition of molasse sediments. The rocks were then buried for a third time and metamorphosed to greenschist-facies metamorphic conditions (330 ± 30°C and 3·6–4·6 kbar) under the load of the molasse sediments. Finally, post-tectonic granites were intruded and thrust during the final Pan-African exhumation, causing a fourth metamorphic event (700 ± 25°C). Correlation of this metamorphic evolution with the deformation history shows that the first and the second metamorphic events occurred in a compressional regime (D1and D2), interpreted to be related to the first (750 Ma) and the second (676 Ma) collision stages between East and West Gondwana, respectively. The third deformation phase began with a compressional regime causing the third metamorphic event, and then turned into an oblique transpressive regime, which led to escape tectonics and the development of the large-scale Najd strike-slip shear zone system.
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