SUBDUCTION ZONE FLUID CRYSTALLIZATION PRODUCTS—THE PERSPECTIVE FROM JADEITITE RESEARCH
Jadeite crystal chemistry limits the chemical fingerprint; however, solid solution with Cpx containing Na, Ca, Mg, Fe2+, Fe3+ permits greater capacity for incorporation of minor elements and REE, as well as provides PT constraints. Minor mica and feldspar-like phases record conspicuous LILE signatures: Cs, Rb, NH4+, Ba, Sr, Pb or the lack thereof. Jadeitite from two contexts in Guatemala demonstrate somewhat different evolutions; however, the whole-rock minor-to-trace-element compositions track remarkably well with global seafloor sediment (GLOSS), including LILE and HFSE, although not generally for K and Pb. The apparent mobility of Zr, Hf, Ta, and Nb is perhaps unexpected. Late-stage crystallization products typically saturate with omphacite or phengite, suggesting both fluid composition and condition changes but are not correlated with advanced exhumation. Interactions with hosting ultramafic mélange are minimal until the latest-stage crystallization (e.g., little Ni or Cr) suggesting H2O is largely absorbed by serpentinization, which is supported by comparably light δ11B in both jadeitite mica and serpentinite antigorite.
Consequently, jadeitites and their related vein crystallizations offer a window into fluids exiting the subduction channel into brittle mantle wedge.