Вестник МГТУ. 2018, том 21, № 1.

Вестник МГТУ. 2018. Т. 21, № 1. С. 61–79. DOI: 10.21443/1560-9278-2018-21-1-61-79 71 Moving to the under-rift zones above the ascending convective mantle currents, metal carbides, solid particles of the crustal substance, and gas-liquid inclusions come up to the levels of oceanic lithosphere hydration (Fig. 6). Entering the stability field of mineralized water fluids, carbides are easily decomposed with the release of various hydrocarbons and metal hydroxides. It shall therefore be noted that the melting temperature for many carbon compounds with metals significantly exceeds the temperature of the upper mantle (≈1300–1600 ○ C) and fall within the range of 1000–4000 ○ C. This fact seems extremely important and indicates that metal carbides in the almost dry mantle may occur in a stable balanced state and preserve geochemical markers of exogenic origin. For example, entering the near-surface zones of rifts and undergoing hydrolysis, calcium and sodium carbides decompose with the release of acetylene [29]: СаС 2 + 2Н 2 О → Са(ОН) 2 + С 2 Н 2 ↑ + T ○ C, (34) Na 2 C 2 + 2H 2 O → 2NaOH + C 2 H 2 ↑ + T ○ C. (35) Fig. 6. Geochemistry of hydrothermal process and mechanisms of carbon compounds generation in rift zones of the mid-oceanic ridge: 1: sediments; 2: basalts (pillow lavas); 3: dolerite dikes (dike-in-dike unit); 4: serpentinite layer; 5: undercrustal lithospheric layer; 6: mantle: а for igneous hearth under the mid-oceanic ridge crest, б for asthenosphere; 7: structures in black ( а ) and white ( б ) smokers; 8: trend of the oceanic waters in the oceanic crustal mass; 9: critical level of water stability; 10: metal carbides and encapsulated solid mineral compounds and gas-liquid inclusions of degraded sedimentary units moved from the subduction zone; 11: metal carbide decomposition area; 12: metal carbide decomposition product degassing Рис. 6. Геохимия гидротермальных процессов и механизмы генерации соединений углерода в рифтовых зонах срединно-океанического хребта: 1 – осадки; 2 – базальты (подушечные лавы); 3 – долеритовые дайки (комплекс дайка в дайке); 4 – серпентинитовый слой; 5 – подкоровый слой литосферы; 6 – мантия: а – магматический очаг под гребнем срединно-океанического хребта, б – астеносфера; 7 – постройки черных ( а ) и белых ( б ) "курильщиков"; 8 – направление движения океанических вод в толще океанической коры; 9 – критический уровень устойчивости воды; 10 – карбиды металлов и закапсулированные твердые минеральные соединения и газово-жидкие включения деградированных осадочных комплексов, перенесенных из зоны субдукции; 11 – область разложения карбидов металлов; 12 – дегазация продуктов распада карбидов металлов Similar exothermic reactions proceed at the decomposition of potassium (K 2 C 2 ), sodium, and other metal carbide. In the presence of metals, acetylene hydrates and may be transformed to ethane in two stages: C 2 H 2 + H 2 → C 2 H 4 + H 2 → C 2 H 6 ↑. (36)