Late Cretaceous (100-89Ma) magnesian charnockites with adakitic affinities in the Milin area, Eastern Gangdese: partial melting of subducted oceanic crust and implications for crustal growth in Southern Tibet

Lin Ma, Qiang Wang*, Derek A. Wyman, Zheng-Xiang Li, Zi Qi Jiang, Jin Hui Yang, Guo Ning Gou, Hai Feng Guo

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

107 Citations (Scopus)

Abstract

Rapid Mesozoic-Early Cenozoic crustal growth in the Gangdese area, southern Tibet, has commonly been attributed to pre-collisional and syn-collisional underplating of mantle-derived magmas. Here, we report on adakitic magnesian charnockites (i.e., hypersthene-bearing diorites and granodiorites) near Milin, in eastern Gangdese, that provide new insights into the crustal growth process of the region. Zircon U-Pb analyses of seven charnockite samples indicate that they were generated in the Late Cretaceous (100-89Ma). They exhibit variable SiO2 (53.9 to 65.7wt.%) contents, high Na2O/K2O (1.6 to 14.4) and Sr/Y (27.2 to 138.7) ratios, low Y (6.5 to 18.5ppm), heavy rare earth element (e.g., Yb=0.6 to 1.6ppm) and Th (0.20-2.39ppm) contents and Th/La (0.02-0.23) ratios, with relatively high Mg# (46 to 56) and MgO (2.0 to 4.5wt.%) values. They are characterized isotopically by high and slightly variable εNd(t) (+2.4 to +4.0) and εHf(t) (+10.1 to +15.8) values with relatively low and consistent (87Sr/86Sr)i (0.7042 to 0.7043) ratios. Their pyroxenes have high crystallization temperatures (876 to 949°C). The Milin charnockites were most probably produced by partial melting of subducted Neo-Tethyan oceanic crust that was followed by adakitic melt-mantle interaction, minor crustal assimilation and fractional crystallization of amphibole+plagioclase. The upwelling asthenosphere, triggered by the roll-back of subducted Neo-Tethyan oceanic lithosphere, provided the heat for slab melting. Therefore, we suggest that, in addition to pre-collisional and syn-collisional underplating of mantle-derived magmas, the recycling of subducted oceanic crust has also played an important role in continental crustal growth in southern Tibet.

Original languageEnglish
Pages (from-to)315-332
Number of pages18
JournalLithos
Volume175-176
DOIs
Publication statusPublished - 15 Aug 2013
Externally publishedYes

Keywords

  • adakitic charnockite
  • crust growth
  • gangdese batholith
  • roll-back
  • slab melting
  • Tibet

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