Open AccessEffect of finite deformation and deformation rate on partial melting and crystallization in metapelites
Author(s) -
Misra Santanu,
Burg JeanPierre,
Mainprice David
Publication year - 2011
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2010jb007865
Subject(s) - partial melting , crystallization , strain rate , materials science , deformation (meteorology) , shear rate , simple shear , geology , shear stress , mineralogy , rheology , thermodynamics , composite material , mantle (geology) , geochemistry , physics
Strain and strain rate partitioning in partially molten rocks are two of the important mechanisms that govern the process of coupling and/or decoupling of the partially molten lithosphere. Consequently, the proportion of partial melt and crystals and their network in partially molten rocks influence the degree of the partitioning along with the bulk rheology of the system. This study explores the possible role of finite strain and strain rate on the rate and volume of partial melting and crystallization in a metapelitic system undergoing deformation. Cylinders of synthetic quartz‐muscovite aggregate (7:3 volume ratio) were deformed in torsion at 750°C, 300 MPa and constant shear strain rate ( = 3 × 10 −4 s −1 ) for finite shear strains ( γ ) 1–15. The deformed samples were studied along the longitudinal tangential (LT) and axial (LA) sections to obtain the data along a range of strain rates for a given finite strain and vice versa. The results showed that deformation plays an important role on the kinetics of partial melting and crystallization. With increasing strain rate, amount and rate of crystallization comprise the volumetrically dominant process compared to partial melting at a given finite strain. In contrast, when the strain rate is constant, partial melting is the dominant process over crystallization up to moderate strain ( γ < 5). The dominant process reverses at higher strain, and the system shows more crystallization than partial melting. Application of the experimental data to geological systems implies that for metapelites a significant amount (∼20%) of partial melt can generate at high strain rate and moderate strain ( γ ∼ 7), but at high strain ( γ = 15) the system is melt depleted. Under such conditions, decoupling should take place in brittle‐ductile mode. On the other hand, rocks undergoing deformation with low strain rates and strain ( γ < 3) contain more than 25% partial melt, which can act as a major decoupling agent by localizing ductile shear zones.