Fluid regime of the amphibolite-facies metamorphism in the Dzhugdzhur-Stanovoy fold area (Far East)

• Published in: Russian journal of Pacific geology Vol. 3; no. 4; pp. 307 - 318
• Main Authors: Avchenko, O. V., Aleksandrov, I. A., Khudolozhkin, V. O., Mishkin, M. A.
• Format: Journal Article
• Language: English
• Published: Dordrecht SP MAIK Nauka/Interperiodica 01.08.2009; Springer Nature B.V
• Subjects: Carbon dioxide; Earth and Environmental Science; Earth Sciences; Electrochemistry; Geology; Metamorphic rocks; Metamorphism; Oxidation; oxidation state; fluid regime; electrochemistry; metamorphic fluid; Dzhugdzhur-Stanovoy fold area; gas chromatography
• ISSN: 1819-7140; 1819-7159
• DOI: 10.1134/S1819714009040010

Chromatographic and electrochemical measurements, combined with computer simulation of the natural mineral parageneses and estimation of the stability field of muscovite-bearing assemblages, yielded a consistent model of the fluid regime for the amphibolite-facies metamorphism of the Dzhugdzhur-Stanovoy fold area (DSFA). The model allows the fluid differentiation into “internal” and “external” fluids. The “internal” fluid is formed by the volatiles of the rock, while the “external” fluid arrived from an outer source: the mantle or other reservoir. It is established that the chromatographic and electrochemical measurements refer to the “external” fluid, whereas the redox state estimated from the mineral equilibria is related to the “internal” fluid, whose composition is buffered by the equilibrium mineral assemblage. The “external” fluid trapped by rocks preserves its own redox state only at the regtrograde stage, when the solid-phase reactions slacken and the buffer role of the mineral assemblages is minimized. This aspect explains the contradiction between the wide variations in the oxidation state of the mineral equilibria (log fO 2 from −15 to −20), on the one hand, and the persistent oxidation state of the external fluid established by the chromatographic and electrochemical methods, on the other hand. The main reason for the wide development of hornblende-bearing assemblages in the amphibolite-facies metamorphic rocks of the Dzhugdzhur-Stanovoy fold system is the high H 2 O pressure in the “external” fluid. According to the obtained data, the composition of the “external” fluid is determined by the conditions ≥ 0.7 P S and = 0.01–0.3. The oxidation potential of the “external” fluid is close to that of the H 2 O-C system under carbon-saturated vapor conditions.