Protracted garnet growth in high‐P eclogite: constraints from multiple geochronology and P–T pseudosection

摘要: Understanding convergent margin processes requires determination of the onset and termination subduction, duration subduction-zone metamorphism, subduction zone polarity. Garnet growth intracrystalline zonation can be used to constrain timing, kinetics tectonometamorphic processes. An eclogite from Huwan shear in Hong'an orogen was investigated with combined pseudosection analysis multiple geochronologies. The illustrates that garnet is continuous along an early near-isothermal trajectory followed by a near-isobaric heating path 1.9 GPa/500 °C 2.4 GPa/575 °C subsequent decompression. 40Ar/39Ar dating amphibole inclusion yielded age 310 ± 5 Ma, which consistent U–Pb 305 ± 3 Ma for metamorphic zircon within uncertainty. core rim material produced Lu–Hf ages 296.9 ± 3.8 256.9 ± 3.9 Ma respectively; latter its Sm–Nd 254.3 ± 4.6 Ma same aliquots. Similarly, limited c. 257 Ma were obtained rims inclusions. These interpreted bracket period difference up 40 Ma best explained protracted growth. We propose rocks represent detachment part downgoing slab remained free significant compression/decompression or heating/cooling close channel, most likely underplating mantle wedge, long time. incorporated into following channel due successive entry buoyant materials, exhumed at some time later than 254 Ma. increasing observations garnet growth long-lived various orogens worldwide demand more sophisticated geodynamic models.