Comparison of Cretaceous granitoids of the Chaun tectonic zone to those of the Taigonos Peninsula, NE Asia: rock chemistry, composition of rock forming minerals, and conditions of formation
The Cretaceous granitoid complexes of the East- ern Taigonos and the Prybrezhny Taigonos belts (south- ern part of the Taigonos Peninsula), Tanyurer pluton of the Okhotsk-Chukotka volcanic belt, and the Peekiney, Moltykan, and Telekay plutons of the Chaun tectonic zone are discussed in relation to their structural position, pet- rography, rock and mineral chemistry and physicochemical conditions of melt crystallization. These granitoid plutons were generated through melting of a compositionally hetero- geneous crustal source, with direct contribution from mafic melts produced in the mantle wedge above active or extinct Benioff zones. Variations of the trace-element composition of granitoids are controlled to a greater extent by local com- positional peculiarities of the source regions than by the geo- dynamic regime as such. The final crystallization of these plutons occurred at comparatively shallow depths, between 1-2 and 6-7 km, in a temperature interval of 700-770 C. The depth of emplacement of the bodies decreases with in- creasing distance from the areas with oceanic and transitional type crust, as does the degree of incompatible element en- richment of the mantle and crustal sources of melts. Varia- tions in fo2 values at the late stages of crystallization of the plutons reach 3-4 orders of magnitude, exceeding the limits of the quartz-fayalite-magnetite (QFM) and nickel-nickel ox- ide (NNO) buffer equilibria, which likely results from local variations of the source composition.