Abstract High-pressure metamorphism and ophiolite emplacement (Songshugou ophiolite) attended suturing of the Yangtze craton to Rodinia during the c. 1.0 Ga Grenvillian orogeny. The Qinling microcontinent then rifted from the Yangtze craton at c. 750 Ma. The Erlangping intraoceanic arc formed in the Early Ordovician, was emplaced onto the Qinling microcontinent in the OrdoviciaN–Silurian, and then both units were accreted to the Sino-Korea craton before being stitched together by the c. 400 Ma AndeaN–Style Qinling arc. Subsequent subduction beneath the Qinling-Sino-Korean plate created a Devonian-Triassic accretionary wedge that includes eclogites, and formed a coeval volcano-plutonic arc that stretches from the Longmen Shan to Korea. In the Late Permian-Early Triassic, the northern edge of the South China Block was subducted to >150 km depth, creating the diamond- and coesite-bearing eclogites of the Dabie and Sulu areas. Exhumation from the mantle by lithosphere-scale extension occurred between 245 and 195 Ma during clockwise rotation of the craton. The Yangtze-Sino-Korea suture locally lies tens of km north of the exhumed UHP–HP part of the South China Block, implying perhaps that the very tip of the South China Block was not subducted, or that the UHP–HP rocks rose as a wedge that peeled the upper crust of the unsubducted South China Block from the lower crust. The Tan–Lu fault is an Early Cretaceous to Cenozoic feature. The apparent offset of the Dabie and Sulu UHP terranes by the Tan–Lu fault is a result of this Cretaceous to Cenozoic faulting combined with post-collisional extension north of Dabie.

The blueschist-greenschist facies transition for a model basaltic system Na 2 O-CaO-MgO-Al2O 3 -SiO2-H 2 O is defined by a univariant reaction: 6 clinozoisite + 25 glaucophane + 7 quartz + 14 H 2 O = 6 tremolite + 9 chlorite + 50 albite; for the Fe 2 O 3 -saturated basaltic system, by a discontinuous one: 4 epidote + 5 Mg-riebeckite + chlorite + 7 quartz = 7 hematite (magnetite) + 4 tremolite + 10 albite + 7 H 2 O. These two reactions were experimentally investigated to determine the nature of the blueschist-greenschist transition. The results have located the first reaction at 350 ± 10°C, 7.8 ± 0.2 Kb and 450 ± 10°C, 8.2 ± 0.4 Kb. Reconnaissance experiments for the second reaction indicate that the minimum pressure for the occurrence of epidote + Mg-riebeckite + chlorite + quartz is about 4 Kb at 300°C for f O2 defined by the hematite-magnetite buffer. The presently determined P-T location for the blueschist-greenschist transition in the Fe-free basaltic system is about 3 Kb lower than the minimum pressure limit of glaucophane of Carman and Gilbert (1983), but is compatible with the revised stability field of jadeite + quartz determined by Holland (1980). Introduction of Fe 3+ into the model basaltic system significantly lowers the minimum pressure limit for occurrence of the buffered assemblage sodic amphibole + epidote + actinolite + chlorite + albite + quartz, and the participating phases gradually increase their Fe 3+ /Al ratio with decreasing pressure. Isopleths of sodic amphibole composition in the buffered assemblage in terms of X G1 are delineated and the effect of Fe 2+ and temperature on the isopleths are discussed. The Al 2 O 3 content of sodic amphibole coexisting with epidote + actinolite + chlorite + albite + quartz decreases systematically with decreasing pressure and hence can be used as a geobarometer. Pressure estimates for metabasites at Ward Creek of the Franciscan terrane, the Mikabu greenstones of the Sanbagawa belt, the Otago schists of Lake Wakitipu, New Zealand, and the blueschists at Ouegoa, New Caledonia, based on the proposed glaucophane geobarometry, are in agreement with those derived from sodic pyroxene geobarometry.