We report the trace element budget of multiphase solid inclusions (MSI) representative for supercritical fluids formed during progressive UHP phengite and allanite breakdown at P from 3.0 to 4.0 GPa and T from 700 to 860°C in a clay-rich meta-sandstone. In situ LA-ICP-MS analyses have been performed on primary MSI within prograde-peak coarse-grained kyanite from a kyanite quartzite (Donghai, south Sulu, China). Studied MSI consist of paragonite+muscovite+anhydrite+K-Na-hydrous sulphate+fluid and are representative for an alkali-alumino-silicate aqueous solution, released during deep subduction. All MSI are enriched in LILE and REE and depleted in HFSE with varying fractionation patterns. A progressive increase in LREE, Sr, and Th is observed in MSI. Strong enrichments in Rb and Pb occur in MSI with low LREE, and strong enrichments in Ba within MSI with intermediate LREE. These distinct trace element fractionations in the MSI are interpreted as due to complete dissolution of phengite, associated with, and followed by, progressive dissolution of accessory allanite during prograde-to-peak metamorphism. The geochemical signature of supercritical fluids generated by partial dissolution of phengite in presence of allanite shows a trace element fractionation (e.g., high Ba/La and low La/YbN ratios) compatible with that of aqueous fluids at high pressures. Subduction fluids formed by allanite dissolution following phengite exhaustion acquire a melt-like trace element fractionation pattern (e.g., low Ba/Th, and high Th/Rb ratios). The gradual and selective incompatible trace element enrichment in aqueous fluids released by metasediments during deep subduction can result in distinct metasomatic signatures in relatively small portions, close to each others, of the overlying mantle wedge, with relevant consequences on the geochemical signature of magmas.
Ferrando, S., Frezzotti, M., & Petrelli, M. (2016). Birth of subduction components preserved in fluid inclusions. Intervento presentato a: American Geophysical Union, Fall General Assembly 2016, San Francisco, USA.
|Citazione:||Ferrando, S., Frezzotti, M., & Petrelli, M. (2016). Birth of subduction components preserved in fluid inclusions. Intervento presentato a: American Geophysical Union, Fall General Assembly 2016, San Francisco, USA.|
|Carattere della pubblicazione:||Scientifica|
|Presenza di un coautore afferente ad Istituzioni straniere:||No|
|Titolo:||Birth of subduction components preserved in fluid inclusions|
|Autori:||Ferrando, S; Frezzotti, M; Petrelli, M|
FREZZOTTI, MARIA LUCE (Corresponding)
|Data di pubblicazione:||2016|
|Nome del convegno:||American Geophysical Union, Fall General Assembly 2016|
|Appare nelle tipologie:||02 - Intervento a convegno|