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Crustal growth event in the Cathaysia Block at 2.5 Ga: evidence from chronology and geochemistry of captured zircons in Jurassic acidic dykes

journal contribution
posted on 2023-05-21, 12:36 authored by Li, SL, Lai, JQ, Xiao, WZ, Belousova, EA, Rushmer, T, Lejun ZhangLejun Zhang, Ou, Q, Liu, CY

Six acidic dykes were discovered surrounding the Laiziling pluton, Xianghualing area, in the western Cathaysia Block, South China. A number of captured zircons are found in two of these acidic dykes. By detailed U-Pb dating, Lu-Hf isotopes and trace-element analysis, we find that these zircons have ages clustered at c. 2.5 Ga. Two acidic dyke samples yielded upper intersection point U-206/Pb-238 ages of 2505 +/- 42 Ma and 2533 +/- 22 Ma, and weighted mean Pb-207/Pb-206 ages of 2500 +/- 30 Ma and 2535 +/- 16 Ma. The majority of these zircons have high (Sm/La)(N), Th/U and low Ce/Ce* ratios, indicating a magmatic origin, but some grains were altered by later hydrothermal fluid. Additionally, the magmatic zircons have high Y, U, heavy rare earth element, Nb and Ta contents, indicating that their host rocks were mainly mafic rocks or trondhjemite-tonalite-granodiorite rock series. Equally, their moderate Y, Yb, Th, Gd and Er contents also indicate that a mafic source formed in a continental volcanic-arc environment. These zircons have positive epsilon(Hf)(t) values (2.5-6.9) close to zircons from the depleted mantle, with T-DM (2565-2741 Ma) and T-DM2 (2608-2864 Ma) ages close to their formation ages, indicating that these zircons originated directly from depleted mantle magma, or juvenile crust derived from the depleted mantle in a very short period. We therefore infer that the Cathaysia Block experienced a crustal growth event at c. 2.5 Ga.

History

Publication title

Geological Magazine

Volume

158

Issue

4

Pagination

567-582

ISSN

0016-7568

Department/School

School of Natural Sciences

Publisher

Cambridge University Press

Place of publication

United Kingdom

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Copyright 2020 The Authors

Repository Status

  • Restricted

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Expanding knowledge in the health sciences

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