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Exhumation of an anatectic complex by channel flow and extrusion tectonics: structural and metamorphic evidence from the Porto–Viseu Metamorphic Belt, Central-Iberian Zone
International Journal of Earth Sciences ( IF 1.8 ) Pub Date : 2021-06-22 , DOI: 10.1007/s00531-021-02067-z
T. Bento dos Santos , J. F. Rodrigues , P. Castro , B. Cotrim , I. Pereira , J. A. Ferreira , C. Meireles , N. Ferreira , P. Ferreira , A. Ribeiro , F. Guimarães

Structural and metamorphic analyses of the Porto–Viseu Metamorphic Belt (PVMB), an anatectic complex located in the Central-Iberian Zone (CIZ), Iberian Variscan Massif, constrain the kinematic features of the polyphase Variscan deformation, as well as the boundary conditions associated with the exhumation and emplacement of the belt onto the CIZ’s lower-grade metasediments. A sharp metamorphic contrast is evident between the lowest grade rocks of the anatectic complex—garnet-staurolite mylonitic schists with a minimum metamorphic peak at P = 5.7 kbar and T = 635 °C—and the host chlorite-biotite metasediments of the CIZ. Additional P–T estimates for metatexites in the PVMB provided P = 7.6–7.9 kbar and T = 770–810 °C, confirming high-grade metamorphic peak conditions. The temperature jump between the anatectic complex and the low-grade host rocks exceeds 400 °C if the anatectic core of the belt (metatexites, diatexites, and S-type granites) is considered, implying a vertical difference of 10–17 km. The PVMB is limited in the NE by a D2 shear zone displaying normal kinematics, which has been explained so far by extensional tectonics. However, the SW boundary is limited by a D2 shear zone showing reverse kinematics. This pair of coeval and antithetical ductile shear zones bordering the PVMB, associated with the increase of the metamorphic grade towards the axial domain of the belt, is consistent with anatectic channel flow, followed by extrusion tectonics of the PVMB within an overall D2 compressive setting.



中文翻译:

通道流和挤压构造对深熔复合体的挖掘:来自伊比利亚中部地区波尔图-维塞乌变质带的构造和变质证据

波尔图-维塞乌变质带 (PVMB) 的结构和变质分析,这是一个位于伊比利亚 Variscan 地块中部 - 伊比利亚带 (CIZ) 的深熔复合体,限制了多相 Variscan 变形的运动学特征,以及相关的边界条件随着带的挖掘和就位到 CIZ 的低品位变质沉积物上。深熔复合体的最低品位岩石——在P  = 5.7 kbar 和T  = 635 °C处具有最小变质峰的石榴石-星形石糜棱质片岩与CIZ 的寄主绿泥石-黑云母变沉积物之间存在明显的变质对比。PVMB 中超纺织物的额外 P-T 估计值提供P  = 7.6-7.9 kbar 和T = 770–810 °C,证实了高级变质峰条件。如果考虑带的深熔岩心(变质岩、硅质岩和 S 型花岗岩),深熔复合体与低品位主岩之间的温度跃变超过 400 °C,意味着垂直差异为 10-17 km。PVMB 在 NE 受 D2 剪切带限制,显示正常的运动学,迄今为止已通过拉伸构造解释了这一点。然而,SW 边界受到显示反向运动学的 D2 剪切区的限制。这对与 PVMB 接壤的同时期和对立的韧性剪切带与向带轴向区域的变质等级增加有关,与深熔通道流动一致,随后是在整体 D2 压缩环境中 PVMB 的挤压构造。

更新日期:2021-06-22
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