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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., Pan, G.T. & Wu, F.Y. (2009). Zircon U-Pb dating and in-situ Hf isotopic analysis of Permian peraluminous granite in the Lhasa terrane, southern Tibet: Implications for Permian collisional orogeny and paleogeography. Tectonophysics 469(1-4): 48-60.

Author(s) from Durham

Abstract

The Lhasa terrane has long been interpreted as a simple tectonic block rifted from Gondwana
during the late Paleozoic and then drifted northward before finally amalgamating with the
Qiangtang terrane during the Early Cretaceous. In this paper we document Permian
peraluminous granites near Pikang in the southern margin of the central Lhasa terrane, close to
the recently documented Songdo eclogite of Permian age. Zircon SHRIMP and LA-ICPMS U-Pb
dating for a Pikang granite sample gives an identical crystallization age of about 263 Ma and a
wide age range of inherited zircons (283–2141 Ma). In situ Hf isotopic analyses for 20 zircons of
263 Ma yielded εHf(t) values of –4.5 to +1.9. The Pikang granites have high A/CNK values (≥
1.08) and high normative corundum (1.3–2.0%), indicative of peraluminous S-type granite. They
are characterized by moderately negative Eu anomalies (Eu/Eu* = 0.48–0.61), and strongly
negative Ba, Nb, Sr, P and Ti anomalies. The granites have high εNd(t) values (.6.4 to .6.0) and
low initial 87Sr/86Sr ratios (0.7082–0.7096) relative to melts derived from mature continental
crust. These rocks are interpreted to have been generated by mixing between mantle melts and
their induced melting of mature crustal materials. We interpret the Pikang peraluminous granite
magmatism, the regional angular unconformity between the Middle and the Upper Permian and
the eclogite of the same metamorphic age (~262 Ma) from the same geotectonic location to
represent different products of a common event in time and space. We tentatively term this
common event as syncollisional orogeny, i.e., “the Permian Gangdese Orogeny”. We further
hypothesize that the orogeny may be genetically associated with the collision between the Lhasa
terrane and the northern margin of Australia, following the closure of the Paleo-Tethyan Ocean
south of the Lhasa terrane.