Аннотация

This paper reports isotopic and geochemical studies of eclogites from the western ultrahigh pressure (UHP) and eastern high-pressure (HP) blocks of the Kokchetav subduction-collision zone. These HP and UHP eclogites exhumed in two stages: (1) The rocks of the western block metamorphosed within the field of diamond stability (e.g., Kumdy-Kol and Barchy); (2) In contrast, the metamorphic evolution of the eastern block reached the pressure peak within the stability field of coesite (e.g., Kulet, Chaglinka, Sulu-Tyube, Daulet, and Borovoe). The eclogites vary widely in the ratios of incompatible elements and in the isotope ratios of Nd (143Nd/144Nd = 0.51137-0.513180) and Sr (87Sr/86Sr = 0.703930.78447). The Sulu-Tyube eclogites display isotope-geochemical features close to N-MORB, while those from the other sites are compositionally similar to E-type MORB or island arc basalts (IAB). The model ages TNd(DM) of eclogites vary between 1.95 and 0.67 Ga. The Sulu-Tyube eclogite yields the youngest age; it has the values of εNd(T) (7.2) and 87Sr/86Sr (0.70393) close to the depleted mantle values. The crustal input to the protolith of the Kokchetav eclogites is evident on the εNd(T)-86Sr/87Sr and εNd(T)-T plots. The eclogites make up a trend from DM to country rocks. Some eclogites from the Kulet, Kumdy-Kol, and Barchy localities display signs of partial melting, such as high Sm/Nd (0.65-0.51) and low (La/Sm)N (0.34-0.58) values. The equilibrium temperatures of these eclogites are higher than 850 °C. The geochemical features of eclogites testify to the possibility of the eclogite protolith formation in the tectonic setting of passive continental rift margin subducted to depths over 120 km.

Язык оригиналаанглийский
Страницы (с-по)1560-1576
Число страниц17
ЖурналRussian Geology and Geophysics
Том59
Номер выпуска12
DOI
СостояниеОпубликовано - 1 дек 2018

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