We observed temperature variations over 10 months within a Kuroko ore (hydrothermal sulfide) cultivation apparatus installed atop a 50-m-deep borehole drilled in the Noho hydrothermal system in the mid-Okinawa Trough, southwestern Japan, for monitoring of hydrothermal fluids and in situ mineral precipitation experiments. Temperature and pressure in the apparatus fluctuated with the tidal period immediately after its installation. Initially, the average temperature was 75–76 °C and the amplitude of the semi-diurnal tidal temperature modulation was ~0.3 °C. Four months later, the amplitude of tidal temperature modulation had gradually increased to 4 °C in synchrony with an average temperature decrease to ~40 °C. Numerical modeling showed that both the increase in tidal amplitude and the decrease in average temperature were attributable to a gradual decrease in inflow to the apparatus, which promoted conductive cooling through the pipe wall. The reduced inflow was probably caused by clogging inside the apparatus, but we cannot rule out a natural cause, because the drilling would have significantly decreased the volume of hot fluid in the reservoir. The temperature fluctuation phase lagged the pressure fluctuation phase by ~150°. Assuming that the fluctuations originated from inflow from the reservoir, we conducted 2-D numerical hydrothermal modeling for a poroelastic medium. To generate the 150° phase lag, the permeability in the reservoir needed to exceed that in the ambient formation by ~3 orders of magnitude. The tidal variation phase can be a useful tool for assessing the hydrological state and response of a hydrothermal system.

Indian shield has a few Archean cratons and the Dharwar Craton is the largest among them. Based on lithology, age, and geochemical properties the DC is divided into the Western Dharwar Craton (WDC), Central Dharwar Craton (CDC), and Eastern Dharwar Craton (EDC). The WDC preserves the oldest fragments and consist of two generations of volcanosedimentary sequences, –older Sargur Group (>3.0 Ga), younger Dharwar Supergroup (<3.0 Ga)– and multiple generation of granitic rocks ranging from 3.3 to 2.5 Ga. Detailed structural and stratigraphic investigations of the volcano-sedimentary sequences in the WDC are carried out. Especially in the Chitradurga Schist Belt (CSB), Bababudan Schist Belt (BSB) and Shimoga Schist Belt (SSB). Margins of the schist belts which in contact with the basement gneiss are dominated by rift-related conglomerate. Moreover, the schist belts are dominated by sedimentary structures indicating shallow marine sequences and slump deformations. Six stages of deformation events were identified from the study area; among those two events (D2 and D3) were regional-scale deformations. D2 event represents reverse faults and upright folds while D3 event is a strike-slip sinistral fault. The boundaries between schist belt and basement gneiss are also dominated by D2 reverse faults. Most of the rock formation in the WDC is folded during D2 event and the intensity of the folding increases from the west to east. Tightly folded sequences are present in the CSB, that is the eastern margin of WDC. Unfolding of the layers show that the schist belts are narrow, short-lived basins typically resembling aborted-rift settings in the Phanerozoic. Folded layers seem to be sandwiched between reverse faults (D2) represents a fold-and-thrust belt. Results from structural and stratigraphic investigation in the WDC point to the role of failed rifts or half oceans in the Archean. The schist belts distributed at least in the WDC represent the basins formed in the multiple rifting events. These ‘incomplete oceanic’ sequences later amalgamated to each other during regional scale shortening event. The presence of failed rifts also support the absence of complete ophiolitic sequence in the DC.