The northeast Cathaysia area is characterized by an archetypical, transpressional system with widespread strike‐slip shear zones whose geometries, kinematics, and ages are critical for deciphering the Phanerozoic tectonic evolution of South China. We present new structural, geochronological and thermochronological data from the shear zones in the east Wuyishan and Chencai domains, which record two phases of deformation. The first phase corresponds to sinistral oblique shearing along arrays of NNE oriented, steep‐dipping zones under amphibolite facies conditions. The sinistral oblique shearing commenced at ~451 Ma, concurrently with regional NW/SE directed thrust shearing and folding; the coexistence of sinistral and thrust structures indicates NW‐SE transpressive shortening deformation. Dating by 40Ar/39Ar shows that such deformation terminated before 400 Ma and was followed by cooling through ~450–350°C at ~400–370 Ma. Our results, merged with published data, aid in tracing an Early Paleozoic orogen that extends through the Jiangnan domain into the northeast Cathaysia, with the southeast Yangtze acting as a foreland belt. The synorogenic shortening was interpreted as resulting from underthrusting of the Cathaysia beneath the east Yangtze. The second phase involved dextral oblique shearing associated with NNE‐SSW transpression under greenschist to amphibolite facies conditions at 245–228 Ma, which was followed by postkinematic magmatism and cooling at ~221–200 Ma. In the Cathaysia, similar Middle Triassic dextral shear zones were widespread and operated with approximately east striking thrusts as mutually complementary structures; their kinematic coupling can be explained by a contractional termination model. Geodynamically, we attributed Middle Triassic dextral transpression to the collisions of South China with North China and Indochina.

The Columbia River Basalt Group (CRBG) is the world’s youngest continental flood basalt province, presumably sourced from the deep-seated plume that currently resides underneath Yellowstone National Park in the northwestern United States. The earliest-erupted basalts from this province aid in understanding and modeling plume impingement and the subsequent evolution of basaltic volcanism. We explore the Picture Gorge Basalt (PGB) formation of the CRBG, and discuss the location and geochemical significance in a temporal context of early CRBG magmatism. We report new ARGUS-VI multicollector 40Ar/39Ar incremental heating ages from known PGB localities and additional outcrops that we can geochemically classify as PGB. These 40Ar/39Ar ages range between 17.23 ± 0.04 Ma and 16.06 ± 0.14 Ma, indicating that PGB erupted earlier and for longer than other CRBG main-phase units. These ages illustrate that volcanism initiated over a broad area in the center of the province, and the geochemistry of these early lavas reflects a mantle source that is distinct both spatially and temporally. Combining ages with the strongest arc-like (but depleted) geochemical signal of PGB among CRBG units indicates that the shallowest metasomatized backarc-like mantle was tapped first and concurrently, with later units (Steens and Imnaha Basalts) showing increased influence of a plume-like source.

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