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[Display omitted] • The Early Carboniferous clastic sediments in the North Lhasa Terrane was mainly from the Indian continent and partly from the Australian continent. • The North Lhasa Terrane may be located at the northern margin of the Indian- and Australian continent during the Early Carboniferous. • The reduction of Grenvillian detrital zircons in the Yongzhu Formation might be associated with the Early Carboniferous rifting process in the eastern Lhasa Block. The Lhasa Block was located at the northern margin of East Gondwana before it drifted away, but its exact paleogeographic location in the Late Paleozoic remains controversial. The Late Paleozoic strata in the Lhasa Block, especially the Lower Carboniferous, for which the rock assemblage and sedimentary age have been described but the in-depth research on provenance and tectonic environment are still lacking, may provide vital information about its paleogeographic location. This study presents a systematic field geological survey of the Lower Carboniferous Yongzhu Formation, along with U-Pb dating and Hf isotope analysis of detrital zircons. The detrital zircons U-Pb data revealed major age peaks at 530 and 980 Ma as well as several subordinate age peaks at 784, 890, 1160, 1514, 1690, 2480, and 2600 Ma. The Hf isotopes of the detrital zircons showed similarity with zircons from the Indian continent on the age peaks at 980 and 890 Ma and with those from the Australian continent on the age peaks at 1160 and 2600 Ma, which indicates mixed provenance for the Yongzhu Formation. From this study, we infer that the Lhasa Block might have been located at the northern margin of the Indian and Australian continents during the Early Carboniferous. The weaker age peak at 1160 Ma of the Lower Carboniferous compared to the Pre-Carboniferous and Upper Carboniferous-Lower Permian might be related to the opening of the Sumdo Paleo-Tethys Ocean. [ABSTRACT FROM AUTHOR]

We present geochemical and age data for coeval basalt and rhyolite in the Yinshan Block, western North China Craton, to study the origin of the ‘Daly Gap’ in this bimodal volcanic suite. SHRIMP zircon U-Pb dating for felsic rocks and bulk rock 40 Ar/ 39 Ar dating for mafic rocks yield their ages of 107–133 Ma. The basalts show elevated abundances of incompatible elements with [La/Sm] N  = 2.65–3.54 and enriched Sr-Nd-Hf isotopic signatures ( 87 Sr/ 86 Sr(t) = 0.7054–0.7084, 143 Nd/ 144 Nd(t) = 0.5119–0.5123, 176 Hf/ 177 Hf(t) = 0.2824–0.2826), consistent with their derivation from low degree melting of previously metasomatized lithospheric mantle. The rhyolites display similar enrichment in alkalis and other incompatible elements, but have obvious Nb-Ta depletion. Combined with their more enriched Nd-Hf isotopic compositions (ε Nd (t) = −12 to −18, ε Hf (t) = −2 to −14), these rhyolites are inferred to have been generated by mixing of the mantle-derived basaltic magma with felsic melts derived from lower continental crust anataxis induced by the basaltic magma. Furthermore, the extremely low Ba, Sr, Eu contents, high Rb/Sr ratios and unexpectedly high 87 Sr/ 86 Sr (0.7920–0.7159) in these felsic samples also suggests that their parental magma experienced protracted fractional crystallization of plagioclase (K-feldspar to a lesser extent) en route to the surface. This rock association and the unique geochemical characteristics of these volcanic rocks offer a new view on the petrogenesis of bimodal volcanism: the mafic rocks originated from partial melting of the ancient lithospheric mantle. Underplating of the basaltic magmas triggered melting of lower continental crust. The extensive fractional crystallization of the hybridized magma resulted in the highly fractionated rhyolites. This mechanism explains the “Daly Gap” exhibited in this rock association in a continental setting and also the observation that both the lithospheric mantle and crust in East China are thinner than that in West China. [ABSTRACT FROM AUTHOR]

• The newly discovered Middle Permian granite dikes are adakitic in composition. • The adakitic magma was generated by partial melting of subducted oceanic slab. • The granite dikes were related to the subduction of the Sumdo Paleo-Tethys Ocean. The Sumdo Paleo-Tethys Ocean was the southernmost part of the Paleo-Tethys Ocean, located on the Qinghai–Tibet Plateau. However, the evolution of the Sumdo Paleo-Tethys Ocean and the origin of eclogites in the Sumdo area of Tibet are still matters of debate. Here we report newly discovered adakitic granite dikes from the Sumdo area of the central Lhasa terrane. The rocks have high SiO 2 , Al 2 O 3 , and Sr contents, high Sr/Y and La/Yb ratios, enrichment in light rare-earth elements (REEs), and depletion in Y, Yb, Th, and heavy REEs. They are characterized by low 87Sr/86Sr (0.703678–0.704427) and high 143Nd/144Nd (0.512825–0.512904) ratios, and positive ε Nd (t) (+6.41 to +7.38) and ε Hf (t) (+13.8 to +15.7) values. Zircon U–Pb dating yielded ages of 269.1 ± 4.1 and 266.4 ± 2.0 Ma for the rocks. Our data indicate that the Sumdo adakitic granite dikes were derived from partial melting of subducted oceanic slab, with the magma being influenced by slab-derived fluids and slight interaction with peridotite in the mantle wedge during ascent. By combining our new geochemical data with results of previous studies, we infer a subduction event involving the Sumdo Paleo-Tethys Ocean during the middle Permian, which led to the formation of the Sumdo adakitic granite dikes and the Sumdo, Jilang, and Xindaduo eclogites. [ABSTRACT FROM AUTHOR]