Geochemical Transactions is ready to receive manuscripts on all aspects of geochemistry. The official journal of the Geochemistry Division of the American Chemical Society.

During the ongoing uplift and expansion of the southeastern margin of the Tibetan Plateau, the front edge of the Sichuan‐Yunnan rhombic block (SYB) has experienced intense tectonic activity and frequent seismicity. In this study, the fluid geochemistry in the primary active faults at the front edge of the SYB was investigated, with the aim of understanding the tectonic activity and intersection relationship between the Xiaojiang fault (XJF) and the Red River fault (RRF). Thermal spring water and gases exhibit a coupled spatial distribution relationship; relatively high ion concentrations and ³He/⁴He ratios (Rc/Ra ratios of 0.21 to 0.62Ra) are observed along the RRF, Qujiang fault (QJF), and Shiping‐Jianshui fault (SJF). Multidisciplinary research results have indicated that mantle‐derived intrusion has been detected in the crust beneath the QJF and SJF. The current tectonic activity in the front edge of the SYB remains intense, with compressive stresses shifting toward the western side of the XJF and accumulating on the QJF and SJF. This has led to the development of fractures, enhancing the water–rock interaction and deep‐derived gas degassing along the faults. The unmixing characteristics of fluids at the intersection area of these two faults suggest the absence of conduits for fluid migration between the faults. Owing to the lower gas ³He/⁴He ratios, lower shear strain rates, stable reservoir temperature field, and extremely low historical seismicity in the Indo‐Chinese block, it is speculated that the current movement of the XJF may not cut through the RRF and continue southward.

The concentrations, isotope ratios, and fluxes of CH₄and CO₂from mud volcanoes measured during a field survey on the southern margin of the Junggar Basin are reported. The origins and outputs of CH₄and CO₂from the four mud volcanoes are assessed, and the relationship between the characteristics of degassing and regional tectonics is discussed. The geochemical data indicate that thermogenic gases derived from the hydrocarbon reservoirs beneath anticlines could be the main source of the CH₄emitted from the mud volcanoes and that hydrocarbon degradation by microbes and carbonate decomposition could be the primary contributors to CO₂emissions from the soil in and around the mud volcanoes. Microseepage was the main mode of release for CH₄and CO₂from the mud volcanoes. The total CH₄output from the mud volcanoes was 147.83 ton/year, comparable to that from mud volcanoes elsewhere. The total output of CO₂from the mud volcanoes was 603.96 ton/year, which suggests that more attention should be paid to CO₂from mud volcanoes. The CH₄and CO₂outputs from the mud volcanoes, and from the Xihu fold in the four anticlines, decreased from south to north. This observation is consistent with the intensity of regional tectonic activity, which weakens from south to north. The results suggest that regional compression is the major triggering mechanism for CH₄and CO₂emissions from the mud volcanoes.