[1] Nominally anhydrous minerals in 46 peridotite xenoliths hosted by Cenozoic basalts from five localities (Fangshan, Penglai, Qixia, Changle, and Hebi) of the eastern part of the North China Craton (NCC) have been investigated by Fourier transform infrared spectrometry (FTIR). The water contents (H 2 O wt %) of clinopyroxene (cpx), orthopyroxene (opx), and olivine (ol) range from 27 to 223 ppm, 8 to 94 ppm, and ∼0 ppm, respectively. On the basis of (1) the homogenous H 2 O content within single pyroxene grains and (2) the equilibrium partitioning of H 2 O between cpx and opx, it is suggested that the pyroxenes largely preserve the H 2 O content of their mantle source, although possible H loss during xenolith ascent cannot be excluded for ol. The recalculated whole-rock H 2 O contents, using mineral modes and assuming a partition coefficient of 10 for water between cpx and ol, range from 6 to 56 ppm (average of 23 ± 13 ppm). In combination with previously reported data, the recalculated whole-rock water contents of peridotite xenoliths (105 samples from 9 localities) hosted by Cenozoic basalts from the eastern part of the NCC range from 6 to 85 ppm (average of 25 ± 18 ppm). The Cenozoic lithospheric mantle of the eastern part of the NCC is therefore characterized by a low water content compared to continental lithospheric mantle worldwide represented by typical cratonic and off-cratonic peridotites (normally 40-180 ppm, with average values of 119 ± 54 ppm and 78 ± 45, respectively) and to oceanic mantle values (>50 ppm) inferred from MORB and OIB. Peridotite xenoliths have low-to-moderate spinel Fe 3+ /SFe (0.02-0.34) and whole rock DFMQ values (from −4.2 to 2.2, normally between −2.5 and 1.5), which are not correlated with pyroxene H 2 O contents. Therefore, the low water contents cannot have resulted from oxidation of the mantle xenoliths and may have been caused instead by heating from an upwelling asthenosphere flow that acted in concert with NCC lithospheric thinning during the late Mesozoic to early Cenozoic. If so, the present eastern NCC lithospheric mantle represents essentially relict ancient lithospheric mantle after the thinning event, rather than newly accreted and cooled asthenospheric mantle.

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A structural, petrological and geochronological (U-Th-Pb of zircon and monazite) study reveals that the lower crust sequences of the Variscan high-grade basement cropping out between Solenzara and Porto Vecchio, south-east Corsica (France) have been tectonically juxtaposed along with middle crustal rocks during the extrusion of the orogenic root of the Variscan chain. We propose that a system of hightemperature, orogen-parallel shear zones that developed under a transpressive dextral tectonic regime caused the exhumation of the entire sequence. This tectonic complex is thus made up of rocks having undergone different P-T conditions (eclogite-?, high-pressure granulite facies and amphibolite facies) at different times, reflecting the progressive foreland migration of the orogenic front. The Solenzara granulites were derived from burial of continental crust to high-pressure (1.8-1.4 GPa) and high-to ultrahigh-temperature conditions (900-1000°C) during the Variscan convergence: U-Pb ELA-ICPMS zircon dating constrained the timing of this metamorphism at c. 360 Ma. The gneisses cropping out at Porto Vecchio are middle crustal-level rocks that reached their peak temperature conditions (700-750°C at <1.0 GPa) at c. 340 Ma. The diachronism of the metamorphic events, the foliation patterns and their geometry suggest that the granulites were exhumed to middle crustal levels through channel flow tectonics under continuous compression. The amphibolite facies gneisses of Porto Vecchio and the granulites of Solenzara were accreted through the development of a major dextral mylonitic zone forming under amphibolite facies conditions: in situ monazite isotope dating (ELA-ICPMS) revealed that this deformation occurred at c. 320 Ma and was accompanied by the emplacement of syntectonic high-K melts. A final HTLP static overprint, constrained at 312-308 Ma by monazite U-Th-Pb isotope dating, is related to the emplacement of the igneous products of the Sardinia-Corsica batholith and marks the transition from the Variscan orogenic event to the Permian extension.

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