Common metamorphic P-T-t history of metabasite and metapelite in the Danba Barrovian sequence (SW China): Implications for the Mesozoic tectono-thermal evolution of the eastern Tibetan Plateau

The Mesozoic tectono-thermal evolution of the eastern Tibetan Plateau, SW China, recorded by metamorphic rocks commonly has been investigated using ubiquitous metapelite that characterizes Barrovian sequences. This study examined the metamorphic histories of both the metabasite slivers or lenses and the host metapelite in the Danba dome (eastern Tibetan Plateau, SW China). The metabasite is dominantly composed of amphibole + plagioclase + quartz + ilmenite ± garnet ± biotite ± titanite, with varied bulk-rock compositions. The peak metamorphic pressure-temperature (P-T) conditions (∼5.4−7.8 kbar/∼650−690 °C) of the metabasite and metapelite from the sillimanite zone are almost identical. Zircon U-Pb dating yielded peak metamorphic ages of ca. 192 Ma for the migmatite zone and ca. 188−176 Ma for the sillimanite zone, whereas cooling ages of ca. 169−159 Ma were recorded by most rocks. Combined with the temperatures obtained by Ti-in-zircon thermometry, a relatively slow cooling rate of ∼4.7 °C/m.y. was determined. Zircon ages are consistent for immediately adjacent metabasite and metapelite, and the monazite ages of one metapelite without metamorphic zircon growth also overlap the zircon ages of the neighboring metabasite. These results indicate that the metabasite and metapelite in the Danba dome shared a common metamorphic history. However, the diachronicity of peak metamorphism may imply differential burial of rocks in the Danba dome, that is, earlier burial in the northern part (migmatite zone in the metamorphic core) than in the southern part. The younger age tails (after ca. 160 Ma, particularly in the southern part of the Danba dome) may result from later disturbances related to episodic (ca. 149−148 Ma, ca. 139 Ma, and ca. 128 Ma) thermal activations in the eastern Tibetan Plateau. Our data, combined with published data, indicate that the Danba dome and the Longmenshan Thrust Belt in the eastern Tibetan Plateau experienced common Mesozoic tectono-thermal evolution since the Late Triassic−Early Jurassic amphibolite-facies metamorphism.