Jadeitite in the Syum-Keu ultramafic complex from Polar Urals, Russia: insights intofluid activity in subduction zones

Drainage of subduction interface fluids into the forearc mantle evidenced by a pristine jadeitite network (Polar Urals)

“…The P-T estimates derived here are compatible with those proposed by Garcia-Casco (2007 Some inferences on the timing of the crystallization of this dyke can be made by combining existing and new petrochronological data. Whereas previously published zircon U-Pb ages are in the range 412-397 Ma for the white jadeitite (Konovalov & Sergeev, 2015;Meng et al, 2011Meng et al, , 2016, we show here that amphiboles record a broad age range that overlaps with the oldest jadeitite zircon ages (c. 410 Ma) for the most pristine Ab-Pg bearing jadeitite (PU3: 420-409 Ma; Figures 10 and 11). Based on field, petrographic and age relationships, we propose that the albite-paragonite-edenite assemblage formed coevally with the zircon crystals that were extracted from the white jadeitite and dated by Meng et al (2011).…”

“…This interpretation, in line with the findings from Fu et al (2010), Yui et al (2012 and Hertwig et al (2016) highlighting the multiplicity of zircon-forming events in jadeitites, provides an interesting perspective on the paradox raised by Harlow et al (2015), who pointed out that jadeitite zircon ages are in general substantially older than peak burial metamorphic ages for the crustal rocks associated with jadeitites in HP-LT serpentinized mélanges (see also Tsujimori & Harlow, 2012). A magmatic origin of the jadeitite zircon crystals dated by Meng et al (2011) is also compatible with the εHf(t) (mostly in the range 5-10) and δ 18 O zircon isotopic values (5-6 per mil) obtained in Meng et al (2016). Additionally, the 5-10 Ma timespan proposed here between dyke crystallization and jadeitite precipitation (see Figure 13) is similar to the c. 5 Ma window inferred for Sierra del Convento between the tonalitic-trondhjemitic samples (112.8 ± 1.1 Ma;Lazaro et al, 2009) and the P-type jadeitite ages (107.4 ± 0.5 Ma; Cardenas-Parraga et al, 2012; U-Pb SHRIMP zircon ages).…”

“…The study area is located on the western flank of the Syum-Keu massif in the Pus'yerka locality, north of the intersection between the MUT and the Bolshaya Xadata river (Figures 1b and 2a). Previous field investigations have revealed the presence of (a) serpentinized shear zones along and above the MUT (Kuznetsov et al, 1986) and (b) N-S to NE-SWstriking jadeite-bearing lenses embedded in the serpentinized dunite-harzburgite host (Fishman, 2006;Meng et al, 2011Meng et al, , 2016; Figure 1b). The regional foliation in the serpentinized host is generally parallel with the MUT structures.…”

“…Lei et al, 2016) and/or protracted Zrn crystallization over several Ma (e.g. Flores et al, 2013;Meng et al, 2016). The latter process is visible in the trace element maps (Figure 7) that clearly F I G U R E 1 3 Schematic reconstruction of the evolution of the jadeitite body (not to scale).…”

“…The spread of clinopyroxene analyses along the omphacite solid solution reflects the importance of the jadeite substitution CaMg ↔ NaAl VI between diopside CaMgSi 2 O 6 and jadeite NaAlSi 2 O 6 end-members. The average of the whole-rock jadeitite compositions for the Pus'yerka locality (data from Meng et al, 2016) plots almost along the Jd-Di joint. The white jadeite-rich part of sample PU2 also exhibits a composition close to this average value.…”