Continental crust in Gorny Altai: nature and composition of protoliths

Abstract

The history of the Vendian–Early Paleozoic formation of protoliths of continental crust in the Gorny Altai segment of the Central Asian fold belt is considered, and their composition, isotopic characteristics, and formation mechanisms are estimated. We have established two stages of crust-forming processes in Gorny Altai: Early and Late Caledonian, with the different structures of formed geoblocks and nature and compositions of crustal protoliths. At the Early Caledonian stage, fragments of oceanic lithosphere of basic composition (MORB, OIT, OIB) (TNd(DM-2st) = 0.65–1.1 Ga) formed, as well as island arcs with andesite-basaltic and andesitic protoliths with low contents of incompatible elements (TNd(DM-2st) = 0.7–0.9 Ga). At the Late Caledonian stage, the redistribution of the substance of these blocks and the external supply of material led to the formation of heterogeneous crust of turbidite basins with an oceanic basement and andesite-dacitic upper-crustal protoliths (TNd(DM-2st) varies from 0.8–0.9 Ga in the framing of the volcanic arc of Altaids to 1.4–1.6 Ga at the boundary of the Altai–Mongolian microcontinent).

Geochemistry and Nd isotopic composition of the Early Paleozoic flysch sequence in the Chinese Altai, Central Asia: Evidence for a northward-derived mafic source and insight into Nd model ages in accretionary orogen

“…To the north of Chinese Altai, a large amount of Early Paleozoic to Neoproterozoic mafic rocks occur in Gorny Altay and West Mongolian, e.g. tholeiiteboninite series of island-arc complex and basalt-gabbro-pyroxeniteperidotite series of ophiolitic complex, which provide an ideal mafic source for the flysch sequence (Tomurtogoo, 1997;Buslov et al, 2002;Tomurtogoo, 2002;Dobretsov et al, 2004;Kruk et al, 2010). Therefore, geochemistry of the flysch sequence suggests a northward-derived mafic source, which, in combination with the old felsic sources, favors the interpretation of northward-derived multiple--sources suggested by our previous U-Pb dating of detrital zircons .…”

“…Nance and Taylor, 1976;Dickinson and Suczek, 1979;Bhatia, 1983;Taylor and McLennan, 1985;Roser and Korsch, 1988;McLennan et al, 1990;Cox et al, 1995;Gao et al, 1999;Cullers and Podkovyrov, 2002;Hofmann, 2005;Garzanti et al, 2007;Kruk et al, 2010). In order to investigate source characteristics of the flysch sequence and the timing of crustal formation of the Chinese Altai, we present systemic major element, trace element, and Nd isotopic studies on the flysch in the northwestern Chinese Altai.…”

Early–Middle Paleozoic granitoids in Gorny Altai, Russia: Implications for continental crust history and magma sources

“…The Late Neoproterozoic to Early Cambrian magmatic arc in the periphery of Siberia contains the fragments of two types of volcanic belt systems (Berzin et al, 1994). The first system is mainly composed of submarine basalts with oceanic and back-arc basin major-and trace-element signatures (Gibsher et al, 1997;Safonova et al, 2008;Kruk et al, 2010). Basaltic layers are often buried under carbonate caps.…”

“…Intense erosion of young orogenic structures produced large turbidite basins (Figs. 1 and 2) which lied upon oceanic crust and became filled with thick highAl sediments metamorphosed to low grades (Berzin et al, 1994;Sennikov et al, 2003;Kruk et al, 2010).…”

“…The bulk of crustal protoliths of the Gorny Altai granitoids formed likewise in two stages (for details see Kruk et al (2010) and references therein). In the beginning (late Neoproterozoiclatest Early Cambrian), there appeared oceanic basins, seafloor rises, and Mariana-type island arcs, all upon oceanic crust (see above).…”