• journal_title：Geology
• Contributor：Amlan Banerjee ; Shrema Bhattacharya ; K. Sajeev ; M. Santosh
• Publisher：Geological Society of America
• Date：2013-07-01
• Format：text/html
• Language：en
• Identifier：10.1130/G34129.1
• journal_abbrev：Geology
• issn：0091-7613
• volume：41
• issue：7
• firstpage：743
• section：Articles

Charnockite is considered to be generated either through the dehydration of granitic magma by CO₂ purging or by solid-state dehydration through CO₂ metasomatism during granulite facies metamorphism. To understand the extent of dehydration, CO₂ migration is quantitatively modeled in silicate melt and metasomatic fluid as a function of temperature, H₂O wt%, pressure, basal CO₂ flux and dynamic viscosity. Numerical simulations show that CO₂ advection through porous and permeable high-grade metamorphic rocks can generate dehydrated patches close to the CO₂ flow path, as illustrated by the occurrences of “incipient charnockites.” CO₂ reaction-front velocity constrained by field observations is 0.69 km/m.y., a reasonable value, which matches well with other studies. On the other hand, temperature, rate of cooling, and basal CO₂ flux are the critical parameters affecting CO₂ diffusion through a silicate melt. CO₂ diffusion through silicate melt can only occur at temperature greater than 840 °C and during slow cooling (≤3.7 × 10⁻⁵ °C/yr), features that are typical of magma emplacement in the lower crust. Stalling of CO₂ fluxing at ∼840 °C explains why some deep-level plutons contain both hydrous and anhydrous (charnockitic) mineral assemblages. CO₂ diffusion through silicate melt is virtually insensitive to pressure. Addition of CO₂ basal flux facilitates episodic dehydrated melt migration by generating fracture pathways.