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SHRIMP dating of the Permo-Carboniferous Jinshajiang ophiolite, southwestern China Geochronological constraints for the evolution of Paleo-Tethys [查看] PingJian、DunyiLiu、XiaomengSun

SHRIMP U–Pb zircon dating of gabbro, anorthosite, trondhjemite and granodiorite from the Jinshajiang ophiolitic me´ lange of southwestern China provides geochronological constraints on the evolution of Paleo-Tethys. The ophiolitic me ´ lange is exposed for about 130 km along the Jinshajiang River where numerous blocks of serpentinite, ultramafic cumulate, gabbro, sheeted dikes, pillow lavas and radiolarian chert are set in a greenschist matrix. A cumulate gabbro-anorthosite association and an amphibole gabbro have ages of 338 ± 6 Ma, 329 ± 7 Ma and 320 ± 10 Ma, respectively, which constrain the time of formation of oceanic crust. An ophiolitic isotropic gabbro dated at 282–285 Ma has the same age as a trondhjemite vein (285 ± 6 Ma) cutting the gabbro. These ages probably reflect a late phase of sea-floor spreading above an intra-oceanic subduction zone. At the southern end of thenJinshajiang belt, a granitoid batholith(268 ± 6 Ma), a gabbro massif (264 ± 4 Ma), and a granodiorite (adakite) intrusion (263 ± 6 Ma) in the ophiolitic me´ lange constitute a Permian intra-oceanic plutonic arc complex. A trondhjemite dike intruded serpentinite in the me´ lange at 238 ± 10 Ma and postdates the arc evolution of the Jinshajiang segment of Paleo-Tethys.