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.

Cretaceous granites are widespread in the North Dabie orogen, Central China, but their emplacement sequence and mechanism are poorly known. The Tiantangzhai Complex in the North Dabie Complex is the largest Cretaceous granitic suite consisting of six individual intrusions. In this study, zircon U–Pb ages are used to constrain the crystallization and protolith ages of these intrusions. The Shigujian granite is a syn-tectonic intrusion with an age of 141 Ma. This granite was emplaced under a compressional regime. Oscillatory rims of zircons have yielded two peaks at 137±1 Ma and 125±1 Ma. The 137±1 Ma peak represents the beginning of orogenic extension and tectonic collapse, whereas the 125±1 Ma peak represents widespread granitic magmatism. Zircon cores have yielded concordant ages between 812 and 804 Ma, which indicate a crystallization age for the protolith. The Tiantangzhai granites show relatively high Sr contents and high La/Yb and Sr/Y ratios. The Shigujian granite has positive Eu anomalies resulting from partial melting of a plagioclase-rich source in an over-thickened crust. Correspondingly, in situ Lu–Hf analyses from zircons yield high negative εHf(t) values from −24.8 to −26.6, with two-stage Hf model ages from 2748±34 to 2864±40 Ma, suggesting that the magmas were dominantly derived from partial melting of middle to lower crustal rocks. The Dabie orogen underwent pervasive NW–SE extension at the beginning of the early Cretaceous associated with subduction of the Palaeo-Pacific plate beneath eastern China.