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Early Jurassic plutonic rocks from the Central Lhasa block that range from gabbro to granite yield similar 206Pb/238U ages ranging from 187.6 Ma to 196.0 Ma. Gabbros and diorites are characterized by similar radiogenic 87Sr/86Sr(t) ratios that range from 0.7053 to 0.7060, unradiogenic ε Nd (t) values ranging from −4.2 to −2.5 and ε Hf (t) values ranging from −8.8 to −2.8. Compared with the intermediate to mafic rocks, the granites have much higher 87Sr/86Sr(t) ratios, from 0.7102 to 0.7127, and lower ε Nd (t) values, from −8.7 to −7.5, and ε Hf (t) values from −11.9 to −7.5. Elemental and isotopic data suggest that the gabbros were derived from a melt-modified subarc mantle, diorites represent derivatives produced by hornblende fractional crystallization of gabbros, and granites were generated by the melting of ancient crustal basement rocks. Combined with literature data, these results suggest that the Central Lhasa block, as well as parts of the Southern and Northern Lhasa blocks, also contains ancient crystalline basement rocks. • Gabbros, diorites and granites from the central Lhasa yield similar ages from 187.6 Ma to 196.0 Ma. • The gabbros were derived from a melt-modified sub-arc mantle. • The diorites represent the differentiation product from the parental gabbroic magma. • The granites were generated by melting of ancient crustal basement rocks. • Parts of the Southern and Northern Lhasa also contain ancient crystalline basement rocks. [ABSTRACT FROM AUTHOR]

The timing of collision between the Lhasa and Qiangtang blocks is crucial to understanding the plate tectonics of the Tibetan Plateau. Here we track block movements through a sedimentological study of the Lower Cretaceous nonmarine Duoni Formation, which widespreadly crops out in the central segment of the Bangong-Nujiang Suture Zone and unconformably overlies the Jurassic accretionary complex. The >500-m-thick Duoni Formation was initially deposited in the lacustrine and deltaic environments adjacent to the shoreline, which then evolved into a continental highland-related fluvial and alluvial environment. Palaeocurrent data indicate a northward source for the lower portion and a southward source for the upper portion of the Duoni Formation. Contents of quartzite clasts of the conglomerates increase upward, and lithology of sandstones also changes from greywacke to subarkose to quartz arenite upward. Detrital modal of sandstones (Qt 34 F 6 L 60 , Qm 18 F 6 Lt 76 , and Qp 21 Lvm 27 Lsm 53) of the Duoni Formation supports the transition from a mixed to a recycled orogenic source through time. Zircon U Pb dating of interbedded andesite layers in the Duoni Formation indicates a depositional age at ca. 113 Ma. These results demonstrate that the Lower Cretaceous Duoni Formation of the Baingoin basin developed in a foreland basin in the processes of the collision between the Lhasa and Qiangtang blocks. • The Lower Cretaceous (~113 Ma) Duoni Formation comprised a series of shallow lake, fluvial and alluvial strata. • The nonmarine Duoni Formation in Baingoin basin recorded a foreland basin in response to the Lhasa-Qiangtang collision. • The Lhasa-Qiangtang collision occurred in the Early Cretaceous in central Tibet. [ABSTRACT FROM AUTHOR]

The Xigatze fore-arc basin, one of the well-preserved fore-arc basins worldwide, consists of interesting nearly E-W trending dike swarms of basaltic to granitic compositions. Mid-Miocene more felsic dikes to the responses of fore-arc lithosphere provide important records to the post-collisional processes. Miocene (~15–11 Ma, zircon U Pb ages) high Sr/Y magmatic rocks from the Xigatze area in this study are characterized by (1) rich in Na as compared with K contents (Na 2 O/K 2 O = 1.75–5.62) and high Al 2 O 3 content (> 16 wt%); (2) high Sr but low Y contents, thus high Sr/Y (>81.0) ratios, resembling those of adakites; (3) enrichment in LREE and depletion in HREE with weakly negative or no Eu anomalies (Eu/Eu⁎ = 0.80–1.02); (4) small range in 87Sr/86Sr(t) (0.705080–0.706031) and ε Nd (t) (−3.1 − +0.4) values, indicating that the Xigatze Miocene magmatic rocks are derived from partial melting of juvenile lower crust with minor contributions from the ancient crust in the Lhasa terrane; (5) thickened crust with a crustal thickness of ~52–69 km estimated from (La/Yb) N values. As compared with those in the Gangdese high Sr/Y suite, the Xigatze ones have lower SiO 2 and K 2 O contents, but higher Na 2 O/K 2 O, Sr/Y, and K/Rb ratios, the higher Sr/Y and K/Rb ratios implying a weaker effect by amphibole either as a residual in the source or as a fractionation phase during the magma ascent than that in the Gangdese suite. • The dioritic to granitic dikes in Xigatze fore-arc basin are formed at ~15–11 Ma. • These Miocene dikes show high Sr/Y and La/Yb ratios with adakitic affinity. • They are derived from partial melting of juvenile mafic lower crust. • The southern Tibet experienced crustal thinning from ~19–17 Ma to ~15–11 Ma. [ABSTRACT FROM AUTHOR]