International audienceDuring the Late Palaeozoic Variscan Orogeny, Cambro-Ordovician and/or Neoproterozoic metasedimentary rocks of the Albera Massif (Eastern Pyrenees) were subject to low-pressure/hightemperature (LPHT) regional metamorphism, with the development of a sequence of prograde metamorphic zones (chlorite-muscovite, biotite, andalusite-cordierite, sillimanite and migmatite). LPHT metamorphism and magmatism occurred in a broadly compressional tectonic regime, which started with a phase of southward thrusting (D1) and ended with a wrench-dominated dextral transpressional event (D2). D1 occurred under prograde metamorphic conditions. D2 started before the P–T metamorphic climax and continued during and after the metamorphic peak, and was associated with igneous activity. P–T estimates show that rocks from the biotite-in isograd reached peak-metamorphic conditions of 2.5 kbar, 400 C; rocks in the low-grade part of the andalusite-cordierite zone reached peak metamorphic conditions of 2.8 kbar, 535 C; rocks located at the transition between andalusitecordierite zone and the sillimanite zone reached peak metamorphic conditions of 3.3 kbar, 625 C; rocks located at the beginning of the anatectic domain reached peak metamorphic conditions of 3.5 kbar, 655 C; and rocks located at the bottom of the metamorphic series of the massif reached peak metamorphic conditions of 4.5 kbar, 730 C. A clockwise P–T trajectory is inferred using a combination of reaction microstructures with appropriate P–T peudosections. It is proposed that heat from asthenospheric material that rose to shallow mantle levels provided the ultimate heat source for the LPHT metamorphism and extensive lower crustal melting, generating various types of granitoid magmas. This thermal pulse occurred during an episode of transpression, and is interpreted to reflect breakoff of the underlying, downwarped mantle lithosphere during the final stages of oblique continental collision

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The cooling history of Hercynian calc-alkalic, post-kinematic plutonic intrusions of the Montnegre massif (NE Spain) has been determined by 40 Ar/ 39 Ar analysis of two hornblendes, four biotites and eight K-feldspars (Kfs). The hornblendes have 40 Ar/ 39 Ar total fusion ages of 291±3 Ma and define the magmatic cooling of the basic and oldest structural intrusions. The biotites from the acid and intermediate rocks have 40 Ar/ 39 Ar plateau ages of 285±3 Ma, which date cooling of the intrusions through argon closure in biotite. The 40 Ar/ 39 Ar ages of the K-feldspars vary widely, ranging from 276-191 Ma. A correlation between K-feldspar 40 Ar/ 39 Ar total fusion age and several other features such as structural state, microstructures indicated by obliquity and, to some degree, optically visible perthites, is consistent with post-crystallisation partial argon loss in the K-feldspars. The δD values of the biotites also correlate with age and chlorite contents, but this is not so for the δ 18 O values of either feldspar or quartz. We infer that most microtextural changes occurred during cooling of the batholith, but a possibly Mesozoic, late disturbing hydrothermal event of weak intensity and with only minor fluid circulation must have occurred. This event provoked significant argon loss in the most structurally complex K-feldspars and is recorded in the hydrogen, but not oxygen, isotope data.

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