Zircon trace-element and isotopes (U–Pb, Lu–Hf, δ ¹⁸ O) response to fluid-deficient metamorphism of a subducted continental terrane (North Muya, Eastern Siberia)

The orogenic continental crust of accretionary and collisional belts worldwide is dominated by felsic and metasedimentary rocks, which show variable responses to high-grade metamorphism. Transformation of felsic rocks is commonly limited as compared to that of the enclosed mafic rocks (including eclogites sensu stricto ), which is widely attributed to availability of H 2 O–CO 2 fluids, kinetically controlled growth of high-grade assemblages, and their preferential preservation in metabasites more competent to rehydration. We report on the results of studies of the geochemical behaviour of zircon (trace-element, U–Pb, Lu–Hf and δ 18 O) in three felsic samples (two metagranitoids and one paragneiss), which are spatially (geographically and at the outcrop-scale) juxtaposed with mafic eclogites within the North Muya block (Neoproterozoic Baikalides, northern Central Asian Orogenic Belt). The data imply that metagranitoids and metasediments within the buried continental lithosphere might follow a single subduction-related P – T – t trend, whereas contrasting degrees of mineralogical and zircon transformation were governed by mineral buffer reactions in the absence of external fluids. The latter was significant only in an H 2 O-enriched protolith of metasediments. The formation of 18 O-depleted zircon recrystallization rims together with Mn enrichment of garnet rims indicate a distinct metamorphic stage without or with minor localized fluid infiltration, most likely, related to peak temperature conditions during collision. Supplementary material: The data on the mineral composition, trace-element and U–Pb–Lu–Hf–O isotopic composition of zircon are available at https://doi.org/10.6084/m9.figshare.c.6794043