A New Interpretation of Centimetre-scale Variations in the Progress of Infiltration-driven Metamorphic Reactions: Case Study of Carbonated Metaperidotite, Val d'Efra, Central Alps, Switzerland期刊界 All Journals 搜尽天下杂志传播学术成果专业期刊搜索期刊信息化学术搜索

A New Interpretation of Centimetre-scale Variations in the Progress of Infiltration-driven Metamorphic Reactions: Case Study of Carbonated Metaperidotite, Val d'Efra, Central Alps, Switzerland

Authors:	FERRY, JOHN M. RUMBLE, DOUGLAS, III WING, BOSWELL A. PENNISTON-DORLAND, SARAH C.

Affiliation:	¹ DEPARTMENT OF EARTH AND PLANETARY SCIENCES, JOHNS HOPKINS UNIVERSITY, BALTIMORE, MD 21218, USA ² GEOPHYSICAL LABORATORY, CARNEGIE INSTITUTION OF WASHINGTON, 5251 BROAD BRANCH ROAD, NW, WASHINGTON, DC 20015, USA ³ EARTH SYSTEM SCIENCE INTERDISCIPLINARY CENTER, UNIVERSITY OF MARYLAND, COLLEGE PARK, MD 20742, USA

Abstract:	Progress ( ${xi}$ ) of the infiltration-driven reaction, 4olivine +5CO₂ + H₂O = talc + 5magnesite, that occurred during Barrovianregional metamorphism, varies at the cm-scale by a factor of3·5 within an ${approx}$ 3 m³ volume of rock. Mineral and stableisotope compositions record that X_CO₂, ${delta}$ ¹⁸O_fluid, and ${delta}$ ¹³C_fluidwere uniform within error of measurement in the same rock volume.The conventional interpretation of small-scale variations in ${xi}$ in terms of channelized fluid flow cannot explain the uniformityin fluid composition. Small-scale variations in ${xi}$ resulted insteadbecause (a) reactant olivine was a solid solution, (b) initiallythere were small-scale variations in the amount and compositionof olivine, and (c) fluid composition was completely homogenizedover the same scale by diffusiondispersion during infiltrationand subsequent reaction. Assuming isochemical reaction, spatialvariations in ${xi}$ image variations in the (Mg + Fe)/Si of the parentrock rather than the geometry of metamorphic fluid flow. Ifinfiltration-driven reactions involve minerals fixed in composition,on the other hand, spatial variations in ${xi}$ do directly imagefluid flow paths. The geometry of fluid flow can never be determinedfrom geochemical tracers over a distance smaller than the oneover which fluid composition is completely homogenized by diffusiondispersion. KEY WORDS: Alpine Barrovian metamorphism; diffusion; metamorphic fluid composition; metamorphic fluid flow; reaction progress

Keywords:	: Alpine Barrovian metamorphism diffusion metamorphic fluid composition metamorphic fluid flow reaction progress
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