loading page

Two-Stage Mafic-Felsic Magma Interactions and Related Magma Chamber Processes in the Arc Setting: An Example from the Enclave-Bearing Calc-alkaline Plutons, Chinese Altai
  • +2
  • Xing Cui,
  • Min Sun,
  • Guochun Zhao,
  • Yunying Zhang,
  • Jinlong Yao
Xing Cui
University of Hong Kong
Author Profile
Min Sun
University of Hong Kong

Corresponding Author:minsun@hku.hk

Author Profile
Guochun Zhao
Department of Earth Sciences, the University of Hong Kong
Author Profile
Yunying Zhang
University of HongKong
Author Profile
Jinlong Yao
Northwest University
Author Profile


A systematic dataset of petrography, mineralogy, geochronology, and geochemistry is reported for the enclave-bearing calc-alkaline I-type granitoids from the Chinese Altai, Central Asian Orogenic Belt (CAOB). Zircon U–Pb dating and geochemical data indicate that the MME and granitoids formed coevally at ~395 Ma in a subduction setting. Geochemical modelling and hybrid testing suggest that the granitoid parental magma was formed by mixing between a mafic and a felsic endmember that can be identified by isotopic compositions. The mafic rocks have (87Sr/86Sr)i of 0.7048 – 0.7062, εNd(t) of -0.5 – +2.6, and zircon εHf(t) of +2.3 – +5.4, while the host granitoids have similar Sr isotopic compositions ((87Sr/86Sr)i = 0.7054 – 0.7064), but generally lower whole-rock εNd(t) and zircon εHf(t) values (-2.2 – +0.4 and +0.6 – +4.6, respectively). The sharp decrease of An values from cores to rims (e.g., from ca. 80 to 40) of plagioclase phenocrysts points to polybaric crystallization accompanied by degassing, which is supported by the pressure and water content estimations based on amphibole compositions. Petrographic evidence and plagioclase in-situ Sr isotopic compositions ((87Sr/86Sr)i = 0.7053 - 0.7071) confirm the interaction of two isotopically different magmas during the mineral crystallization. A model for the formation of the enclave-bearing calc-alkaline plutons in an arc setting is presented: in-depth mantle and crustal melting and efficient magma mixing controlled the principal chemical compositions of the granitoid intrusions, while the later decompression-dominated crystallization, magma mingling and limited mixing in the higher crustal level finally determined the texture, mineral composition, and enclave morphology.
Dec 2021Published in Geochemistry, Geophysics, Geosystems volume 22 issue 12. 10.1029/2021GC009939