Abstract

Metapelites and metabasites within the Yenisei regional shear zone of the Yenisei Ridge underwent strong deformations with substrate recrystallization and blastomylonite formation during the Ediacaran. The geostructural, petrological, and isotopic–geochronological characteristics of development of the Late Neoproterozoic blastomylonite complexes marking the junction zone of the paleocontinental and paleoceanic sectors of the Yenisei Ridge have been analyzed. Two zones of heterogeneous blastomylonite complexes have been recognized from west to east, in order of increasing distance from the paleoceanic structures: (I) high-baric complexes of the suture zone and (II) frontal (above-suture) medium-baric and medium- to low-temperature complexes. The established differences in the Р–Т parameters of metamorphism between strongly and weakly deformed rocks were interpreted using well-known geodynamic models based on different tectonic mechanisms. As a result of the analysis, we found that the polychronous dynamic metamorphism of gneisses of the Angara–Kan block in the south and formation of the bulk of blastomylonites in the northern segment of the shear zone in the Northern Yenisei Ridge occurred with a 1.5–3 kbar increase in pressure along with insignificant increase in temperature and low metamorphic gradient dT/dH < 10°C/km compared to the background values of earlier regional metamorphism. This was probably due to crustal thickening as a result of rapid thrusting/subduction, followed by rapid uplift. The maximum excess values of the thermodynamic parameters of metamorphism were established in apometabasite tectonites of the suture zone with relict glaucophane schist associations that underwent metamorphism with a simultaneous significant increase in pressure by 3–5 kbar and temperature by 180–240°C with a higher dT/dH gradient of 15–20°C/km. Such excess Р–Т values could be due to progressive metamorphism, complicated by local heating of rocks during viscous deformations and excess oriented tectonic pressure over lithostatic in ductile shear zones. The data agree well with the results of numerical experiments, and this confirms the role of tectonic stress as an additional thermodynamic factor of metamorphic alterations in crustal suture zones.

中文翻译：

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西叶尼塞山脊（俄罗斯东西伯利亚）的珠光体复合物：地质位置，变质演化和地球动力学模型

摘要

叶尼撒隆期间叶尼塞海脊叶尼塞地区剪切带内的变质岩和变质岩经历了强烈的变形，并伴有基质的重结晶和珠光体的形成。分析了叶尼塞海岭古大陆和古洋界交界带的新元古代晚期成矿质蒙脱石复合体发育的地理结构，岩石学和同位素-年代学特征。从西部到东部，已识别出两个不均匀的成纤维质次生岩复合物带，其与古海洋结构的距离逐渐增大：（I）缝合带的高气压复合物和（II）额线（缝线以上），中等气压和中等压力-低温配合物。Р–Т的既定差异使用众所周知的基于不同构造机制的地球动力学模型解释了强变形和弱变形岩石之间的变质作用参数。分析的结果是，我们发现南部安加拉-坎区块片麻岩的多时动态变质作用和叶尼塞山脊北部剪切带北段的成纤维硅藻土的形成发生在1.5-压力增加3 kbar，温度增加不明显，变质梯度低dT / dH与早期区域变质的背景值相比，<10°C / km。这可能是由于快速推进/俯冲并随后迅速抬升导致地壳增厚所致。在缝线区的土石棉片岩结合体中发生变质作用的热力学参数的最大超额值，经历了变质作用，同时压力显着增加了3–5 kbar，温度显着增加了180–240°C，温度更高dT / dH梯度为15–20°C / km。这样的多余Р–Т其值可能是由于渐进变质作用，复杂的岩石变形过程中岩石的局部加热以及韧性剪切带中岩石静力学上的定向构造压力过大所致。数据与数值实验结果吻合得很好，这证实了构造应力作为地壳缝合带变质作用的附加热力学因子的作用。