Abstract. The roles of subsurface groundwater flow in the hydrological cycle within the alpine area characterized by permafrost and/or seasonal frost are poorly known. We studied the role of permafrost in controlling groundwater flow and the hydrological connections between glaciers in high mountain and river in the low plain with hydraulic head, temperature, geochemical, and isotopic data. The study area was a catchment in the headwater region of the Heihe River in the northeastern Qinghai-Tibet Plateau. The groundwater in the high mountains mainly occurs as suprapermafrost groundwater, and in the moraine and fluvio-glacial deposits on the planation surfaces of higher hills suprapermafrost, intrapermafrost, and subpermafrost groundwater co-occur. Glacier and snow-meltwater are transported from the high mountains to the plain through stream channels, slope surfaces, and supra- and subpermafrost aquifers. Groundwater in the Quaternary aquifer under the piedmont plain is recharged by the lateral inflow from permafrost groundwaters and the infiltration of streams, and is discharged as baseflow to the stream in the north. Groundwater maintained stream flow over the cold season and significantly contributed to the stream flow during the rainy season. 3H and 14C data indicated that the age of supra- and sub-permafrost groundwater, and groundwater in Quaternary aquifer of seasonal frost zone, ranges from 30–60 years. Two proposed mechanisms contribute to seasonal variation of the aquifer water-conduction capacity: (1) surface drainage through the stream channel during the high-flow period, and (2) subsurface drainage to an artesian aquifer confined by stream icing and seasonal frost during the cold season.

The redox evolution of Archean upper mantle impacted mantle melting and the nature of chemical equilibrium between mantle, ocean and atmosphere of the early Earth. Yet, the origin of these variations in redox remain controversial. Here we show that a global compilation of ∼3.8-2.5 Ga basalts can be subdivided into group B-1, showing modern mid-ocean ridge basalt-like features ((Nb/La)PM ≥ 0.75), and B-2, which are similar to contemporary island arc-related basalts ((Nb/La)PM < 0.75). Our V-Ti redox proxy indicates a more reducing upper mantle, and the results of both ambient and modified mantle obtained from B-1 and B-2 samples, respectively, exhibit a ∼1.0 log unit increase in their temporal evolution for most cratons. Increases in mantle oxygen fugacity are coincident with the changes in basalt Th/Nb ratios and Nd isotope ratios, indicating that crustal recycling played a crucial role, and this likely occurred either via plate subduction or lithospheric drips.

Constraining thickness and geothermal gradient of Archean continental crust are crucial to understanding geodynamic regimes of the early Earth. Archean crust-sourced tonalitic–trondhjemitic–granodioritic gneisses are ideal lithologies for reconstructing the thermal state of early continental crust. Integrating experimental results with petrochemical data from the Eastern Block of the North China Craton allows us to establish temporal–spatial variations in thickness, geothermal gradient and basal heat flow across the block, which we relate to cooling mantle potential temperature and resultant changing geodynamic regimes from vertical tectonics in the late Mesoarchean (~2.9 Ga) to plate tectonics with hot subduction in the early to late Neoarchean (~2.7–2.5 Ga). Here, we show the transition to a plate tectonic regime plays an important role in the rapid cooling of the mantle, and thickening and strengthening of the lithosphere, which in turn prompted stabilization of the cratonic lithosphere at the end of the Archean.

The conversion of Archean tectonic regimes from mantle plume to plate tectonic and the mechanism of subduction initiation are two crucial issues in the current Earth sciences. A typical komatiite‐tholeiite sequence consisting of ~2,850–2,800‐Ma komatiites and ~2,780–2,710‐Ma basaltic and andesitic to dacitic volcanic rocks is well preserved in the Archean Western Shandong terrane of the eastern North China Craton. These volcanic rocks were derived from the partial melting of a depleted mantle source with subsequent fractional crystallization, a metasomatized subarc mantle wedge, and a descending oceanic slab. Structural and kinematic observations suggest that the Qixingtai‐Yanlinguan‐Panchegou granite‐greenstone belt experienced ~2.85–2.80‐Ga extensional deformation (D1) by upwelling of a mantle plume and NE‐SW‐oriented shortening (D2) during ~2.78–2.71 Ga. The petrogenesis of the Mesoarchean to early Neoarchean metamorphosed volcanic rock series and regional deformation indicate that a plume‐induced self‐sustaining intraoceanic arc system with SW‐dipping subduction polarity operated ~2.8 Ga, followed by the evolution from initial to mature subduction. An increasing pull caused by the descending slab generated gravitational instability in the surrounding oceanic lithosphere and formation of a new initial subduction zone adjacent to the preexisting arc system. Similar to the process in the Western Shandong terrane, plume activity generally culminated in subduction events in many other Archean greenstone belts, revealing that plume‐arc interaction may have been a crucial mechanism for global Archean tectonic regime conversion from mantle plume to initial plate subduction in the crust of the early Earth.

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