Upper Mesozoic tectonic evolution of the Meso-Tethys Ocean. Geochronological and geochemical constraints from central Tibetan Plateau ophiolites and magmatic arc rocks

Ophiolites and magmatic arc rocks can provide key constraints on tectonic and geodynamic reconstructions of collisional zones, involving continental assembly and fragmentation through time. With the aim to better define the regional geodynamic evolution of central Tibetan Plateau, in this contribution we report new whole-rock chemical and zircon SHRIMP U-Pb age data from ophiolites and associated magmatic arc rocks of the Meso-Tethys oceanic realm. Lower Cretaceous oceanic crust is indicated by MORB-like pillow basalts (132.9 +/- 1.4 Ma) from the Dongqiao ophiolite and sheeted dikes (116.8 +/- 1.4 Ma) from the Yunzhug ophiolite. Their geochemical fingerprints are compatible with a DMM-like source, slightly modified by slab-derived metasomatic components, demonstrating a back-arc paleo-tectonic setting of formation. Magmatic arc rocks from the northern and central Lhasa sub-terranes and southern Qiangtang terrane include I-type granitoids from the Asa (155.5 +/- 1.0 Ma), Jiarebu Tso (136.1 +/- 1.3 Ma), and Dongqiao (107.5 +/- 0.9 Ma) areas. These rocks are all compatible with an origin in subduction to post-collisional settings, involving both lower crustal and mantle-derived components. The adakite-like andesites of Wuru Tso (114.1 +/- 1.2 Ma) and the andesites of Tangra Yumco (116.1 +/- 1.4 Ma) both indicate derivation from subduction-related sources. Specifically, the Wuru Tso andesites originated from the partial melting of an oceanic slab contaminated by enriched mantle, without continental crust contribution, whereas the Tangra Yumco andesites were derived from a subduction-modified mantle source. When framed in the regional scenario, the new temporal and geochemical constraints presented in this study suggest a new Mesozoic geodynamic evolution for the Meso-Tethyan Ocean that includes: (a) co-existence of two retreating subduction systems with opposite polarities (northward and southward) at similar to 155 Ma; (b) back-arc extension in the upper-plate domains during similar to 136-132 Ma; (c) slab break-off at similar to 117-114 Ma; and (d) collision and post-collisional tectonics in the Lhasa-Qiangtang starting at similar to 107 Ma.