关键词: 泥盆纪弧后盆地, 古生代岩浆弧, 拉萨－澳大利亚联系, 岩石圈结构, 拉萨地体, 西藏高原

Abstract:

        The history of breakup, drift, subduction, and collision of the Lhasa Terrane during the Paleozoic remains poorly
understood because of the scarcity of data. This paper reviews the Mesozoic lithospheric architecture and explores the origin
and Paleozoic evolution of the Lhasa Terrane on the basis of geological and geochemical data currently available. Abundant
zircon Hf isotope and whole-rock Nd isotope data of silicic rocks indicate that the southern and northern Lhasa subterranes

are dominated by juvenile crust with possible Precambrian crystalline basement locally preserved, while the central Lhasa subterrane
is a microcontinental ribbon with ancient basement rocks as old as Archean. Over 3000 U-Pb ages of detrital zircons from Late
Neoproterozoic-Paleozoic strata define an age peak of ca. 1170 Ma for the Lhasa Terrane and identical age peaks of ca. 950 Ma
for the Amdo, Southern Qiangtang, and Tethyan Himalaya. Thus the most plausible explanation for the origin of the Lhasa Terrane
is that it came from the northern Australia. The ca. 492 Ma bimodal metavolcanic rocks identified in the central Lhasa subterrane
were likely developed in an active continental margin representing a part of a magmatic arc paleogeographically located in the
northern Australian continent and may be a result of slab break-off of the subducting proto-Tethyan oceanic lithosphere. The Late
Devonian to Early Carboniferous gneissic granitoids in both the southern margin of the Lhasa Terrane and Southern Qiangtang are
S-type granitoids with significant contributions from mantle-derived materials. These rocks may have been emplaced in a back-arc
setting that ultimately evolved to what is known as the Songdo Tethyan Ocean. The Lhasa-northern Australia collision at the end of
the Middle Permian may have triggered the southward subduction of the Bangong-Nujiang oceanic lithosphere, imposing a critical
role on the subsequent tectonomagmatic evolution of the Lhasa Terrane during the Mesozoic.

Key words: Devonian back-arc basin, Paleozoic magmatic arc, Lhasa-Australian connection, lithospheric architecture, Lhasa
Terrane, Tibetan Plateau