Reaction enhanced channelised fluid-flux along midcrustal shear zone: An example from Mesoproterozoic Phulad Shear Zone, Rajasthan, India

Journal of Earth system science

Sadhana M Chatterjee1¹  Subhrajyoti Das1¹  Manideepa Roy Choudhury1¹ 

[1] Department of Geological Sciences, Jadavpur University, Kolkata 700 032, India$$

关键词: Channelised fluid-flux;    metasomatism;    calc-silicate rocks;    Mesoproterozoic;    Phulad Shear Zone;    reactioninduced permeability;   

DOI  :  

学科分类：天文学(综合)

来源: Indian Academy of Sciences

【 摘 要 】

Fluid infiltration at great depth during regional metamorphism plays a major role in mass transport and is responsible for significant rheological changes in the rock. Calc-silicate rocks of the Kajalbas area of Delhi Fold Belt, Rajasthan, are characterised by foliation parallel alternate bands of amphibolerich and clinopyroxene–plagioclase feldspar-rich layers of varying thicknesses (mm to decimetre thick). Textural relation suggests that the amphibole grains formed from clinopyroxene and plagioclase in the late phase of regional deformation. Algebraic analysis of the reaction textures and mineral compositions was performed with the computer program C-Space to obtain the balanced chemical reactions that led tothe formation of amphibole-rich bands. The computed balanced reaction is 70.74 Clinopyroxene + 27.23 Plagioclase + 22.018 H$_2$O+5.51K$^+$+1.00Mg2$^+$+ 27.15 Fe$^{2+}$ = 22.02 Amphibole + 67.86 SiO$_2$ aqueous +36.42 Ca$^{2+}$+ 8.98 Na$^+$. The constructed reaction suggests that aqueous fluid permeated the calc-silicate rock along mm to decimetre thick channels, metasomatized the clinopyroxene–plagioclase bearing rocks to form the amphibole-rich layers. The regional deformation presumably created the fluid channels thereby allowing the metasomatic fluid to enter the rock system. The above reaction has large negative volume change for solid phases indicating reaction-induced permeability. Thermodynamic calculations suggest that the fluid–rock interaction occurred at 665±05◦C and 6.6±0.25 kbar (corresponding to ∼20 km depth). Textural modeling integrating the textural features and balanced chemical reaction of the calc-silicate rocks of Mesoproterozoic Phulad Shear Zone thus indicate that extremely channelled fluid flow was reaction enhanced and caused major change in the rock rheology.

【 授权许可】

Unknown