• 标题：The passive margin of northern Gondwana during Early Paleozoic:Evidence from the central Tibet Plateau
• 关键词：Gondwana,Passive margin,Tibet Plateau,Early Paleozoic,
• 作者：Yiming Liu, Sanzhong Li,M.Santosh,Shengyao Yu, Yuhua Wang, Runhua Guo,Linshan Xu, Jie Zhou, Zaizheng Zhou

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 The centralesouth domain of the Tibet Plateau represents an important part of the northern segment of Gondwana during the early Paleozoic. Here we present zircon UePb, LueHf isotope, and wholeerock geochemical data from a suite of early Paleozoic magmatic rocks from the central Tibet Plateau, with a view to gain insights into the nature and geotectonic evolution of the northern margin of Gondwana. Zircon grains in four granitic rocks yielded ages of 532496 Ma with negative εHf(t) values (13.7 to 0.6). Zircon grains in metaebasalt and mafific gneiss yielded ages of 512 ± 5 Ma and 496 ± 6 Ma, respectively. Geochemically, the granitic rocks belong to higheK calcealkaline and shoshonitic Setype granite suite, with the protolith derived from the partial melting of ancient crustal components. The mafific gneiss and metaebasalt geochemically resemble OIB (Oceanic Island Basalt) and EeMORB (Enriched MideOcean Ridge Basalt), respectively. They were derived from low degree (~5e10%) partial melting of an enriched mantle (garnet and spinel lherzolite) that was contaminated by upper crustal components. The parental magmas experienced orthopyroxeneedominated fractional crystallization. Sedimentological features of the CambrianeOrdovician formations indicate that the depositional cycle transformed from marine regression to transgression leading to the formation of parallel/angular unconformities between the Cambrian and Ordovician strata. The hiatus associated with these unconformities are coupled with the peak of the early Paleozoic magmatism in Tibet Plateau, indicating a tectonic control. We conclude that the CambrianeOrdovician magmatic suite and sedimentary rocks formed in an extensional setting, and we correlate this with the postepeak stage of the PaneAfrican orogeny. The postecollision setting associated with delamination, orogenic collapse or lithospheric extension along the northern margin of Gondwana, can account for the CambrianeOrdovician magmatism and sedimentation, rather than oceanic subduction along the external margin. We thus infer a passive margin setting for the northern Gondwana during the Early Paleozoic.