Timing of the final closure of the Paleo-Asian Ocean in the Alxa Terrane

constraints from geochronology and geochemistry of Late Carboniferous to Permian gabbros and diorites

Qian Liu, Guochun Zhao*, Yigui Han, Paul R. Eizenhöfer, Yanlin Zhu, Wenzhu Hou, Xiaoran Zhang

*Corresponding author for this work

Research output: Contribution to journalArticle

40 Citations (Scopus)

Abstract

Connecting the North China Craton to the east and the Tarim Craton to the west, the Alxa Terrane is a key place in investigating the timing of the final closure of the Paleo-Asian Ocean (PAO). New LA-ICPMS zircon U–Pb dating results reveal ca. 300–268 Ma gabbros and diorites in the Bayan Nuru area in the eastern part of the Alxa Terrane. The ~ 300 Ma gabbros show plagioclase accumulations with anorthite compositions, arc-like geochemical affinities with relative enrichment in large ionic lithophile elements and depletion in high field strength elements (e.g., Ti, Nb and Ta), as well as negative εHf(t) and εNd(t) values and high initial 87Sr/86Sr ratios. These features indicate a magma source of an enriched lithospheric mantle metasomatized by high fluid activities. In comparison, the 280–268 Ma gabbros and diorites also have arc-like geochemical affinities but show increasingly evolved isotope compositions, implying more sediment inputs. Compiled zircon εHf(t) and whole-rock εNd(t) values of the magmatic rocks in the Alxa Terrane decrease from the Late Carboniferous to the Early Permian, and increase from the Middle Permian to the Triassic. The significantly large variation in zircon εHf(t) and whole-rock εNd(t) values at ca. 280–265 Ma likely reflects a tectonic switch from a subduction setting to a post-collisional setting, corresponding to the timing of the final closure of the PAO in the Alxa Terrane. Thus, the PAO progressively closed from west to east along the northern margin of the Tarim Craton, the Alxa Terrane, and then the northern margin of the North China Craton during Late Carboniferous to Middle Triassic time.

Original languageEnglish
Pages (from-to)19-30
Number of pages12
JournalLithos
Volume274-275
DOIs
Publication statusPublished - 2017
Externally publishedYes

Keywords

  • Late Paleozoic
  • Zircon U–Pb–Hf isotopes
  • Whole-rock geochemistry
  • Alxa Terrane
  • Paleo-Asian Ocean

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