Theoretical inversion of the fossil hydrothermal systems with oxygen isotopes of constituent minerals partially re-equilibrated with externally infiltrated fluids,Earth and Environmental Science Transactions of the Royal Society of Edinburgh

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Theoretical inversion of the fossil hydrothermal systems with oxygen isotopes of constituent minerals partially re-equilibrated with externally infiltrated fluids
Earth and Environmental Science Transactions of the Royal Society of Edinburgh ( IF 0.9 ) Pub Date : 2021-06-30 , DOI: 10.1017/s1755691021000244
Chun-Sheng WEI , Zi-Fu ZHAO

While the external infiltration of water has been identified from modern geothermal and/or fossil hydrothermal systems through stable isotopes, the physicochemical boundary conditions like the initial oxygen isotopes of water

$( {{\rm \delta }^{ 18}{\rm O}_{\rm W}^{\rm i} } ) $

and rock as well as alteration temperature were implicitly presumed or empirically estimated by the conventional forward modelling. In terms of a novel procedure proposed to deal with partial re-equilibration of oxygen isotopes between constituent minerals and water, the externally infiltrated meteoric and magmatic water are theoretically inverted from the early Cretaceous post-collisional granitoid and intruded Triassic gneissic country rock across the Dabie orogen in central-eastern China. The meteoric water with a

$ {{\rm \delta }^{ 18}{\rm O}_{\rm W}^{\rm i} } $

value of −11.01 ‰ was externally infiltrated with a granitoid and thermodynamically re-equilibrated with rock-forming minerals at 140°C with a minimum water/rock (W/R)o ratio around 1.10 for an open system. The lifetime of this meteoric hydrothermal system is kinetically constrained less than 0.7 million years (Myr) via modelling of surface reaction oxygen exchange. A gneissic country rock, however, was externally infiltrated by a magmatic water with

$ {{\rm \delta }^{ 18}{\rm O}_{\rm W}^{\rm i} } $

value of 4.21 ‰ at 340°C with a (W/R)o ratio of 1.23, and this magmatic hydrothermal system could last no more than 12 thousand years (Kyr) to rapidly re-equilibrate with rock-forming minerals. Nevertheless, the external infiltration of water can be theoretically inverted with oxygen isotopes of re-equilibrated rock-forming minerals, and the ancient hydrothermal systems driven by magmatism or metamorphism within continental orogens worldwide can be reliably quantified.

更新日期：2021-06-30

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