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Durham University

Department of Earth Sciences

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Publication details for Professor Yaoling Niu

Zhu, D.C., Mo, X.X., Niu, Yaoling, Zhao, Z.D., Wang, L.Q., Liu, Y.S. & Wu, F.Y. (2009). Geochemical investigation of Early Cretaceous igneous rocks along an east-west traverse throughout the central Lhasa Terrane, Tibet. Chemical Geology 268: 298-312.

Author(s) from Durham

Abstract

Bulk-rock major and trace element, Sr–Nd isotope, zircon U–Pb and Hf-isotope data are reported for
Early Cretaceous igneous rocks sampled along an east–west traverse through the central Lhasa subterrane
(E80°00′–E89°) in southern Tibet. These results offer new insights into the pre-Cenozoic geology and
tectonomagmatic evolution of the Lhasa Terrane, and provide boundary conditions for the origin and evolution
of the Tibetan Plateau. Our new data, together with data from the literature indicate that the Early Cretaceous
magmatismin the central Lhasa subterrane lasted for a long period (~143–102 Ma) with a magmatic flare-up at
~110 Ma. The latter is accompanied by mafic magmatism in this terrane. The silicic rocks are metaluminous to
peraluminous, and enriched in Rb, Th, and U, and depleted in Ba, Nb, Ta, Sr, P, and Ti, with varying initial 87Sr/86Sr
(0.7073–0.7209), negative εNd(t) (.13.7 to .4.6), and negative to positive zircon εHf(t). The andesitic and
dioritic enclaves are characterized by initial 87Sr/86Sr of 0.7088–0.7148, εNd(t) of.9.9 to.7.8, and zircon εHf(t)
of.9.5 to.0.2, similar to those of the 110±3 Ma silicic rocks. The bulk-rock Sr and Nd isotopic data and zircon
εHf(t) values indicate an increased contribution of a mantle component in the generation of the Early Cretaceous
igneous rocks in the central Lhasa subterrane at ~110 Ma. Available bulk-rock Nd- and zircon Hf-isotope data
indicate that the crust of the central Lhasa subterrane, at least its oldest elements, was emplaced during the
Archean. This further indicates that the central Lhasa subterrane with ancient basementmust have been a microcontinental
block (i.e., the Lhasa micro-continental block) extending in an east–west direction for >700 km
(E82°–E89°)with a width of ~100 km. The contemporaneous presence of S-type (more crustal source) and I-type
(significant mantle input) melts of the Early Cretaceous igneous rocks in this subterrane are interpreted as the
consequences of varying extents of interactions between the existing continental crust and mantle-derivedmelts
(including crustal anatexis). We suggest that the mantle-derived melts resulted from southward subduction of
the Bangong–Nujiang Ocean seafloor in a syncollisional setting related to the Lhasa–Qiangtang collision, and that
the magmatic flare-up with strong mantle input at ~110 Mawas genetically associatedwith the slab break-off of
this subducting seafloor.