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- Title
西秦岭造山带早中生代花岗岩成分多样性及形成机制.
- Authors
豆敬兆; 何 俊; 黄曦光; 陈福坤
- Abstract
The occurrence and compositional diversity of granitic pluton is determined by properties of source rocks and conditions of partial melting, and can be further modified by magmatic processes such as magma mixing, crystal fractionation and assimilation during the transfer. However, the role and relative importance of each process during pluton construction are still elusive. Several representative Early Mesozoic granitic plutons in the West Qinling orogen were chosen to illustrate how the magmatic processes control the compositional variation of granitic plutons. The S-type granites in the West Qinling orogen were derived from partial melting of metapelite and can be classified into two categories based on geochemical features, i.e., high Sr content, and low Rb/Sr ratio and REE content (Group A), and low Sr content, and high Rb/Sr ratio and REE content (Group B). Groups A and B might have been produced through fluid-present and fluid-absent incongruent melting of muscovite, respectively, which can well explain respective contrasting major and trace elemental characteristics, and zircon and monazite saturation temperatures. Three types of zircon were identified in the microgranular mafic enclaves(MMEs)from Mishuling pluton based on the morphology. They have consistent zircon U-Pb age but different trace elemental and Hf isotopic compositions. Type-3 zircon develops {100} prisms and has εHf(t)similar to these of zircon in the host granite. Hence type-3 zircon is interpreted as xenocryst captured from the host granitic magma. Type-1 and type-2 zircons are characterized by {100}+{110} and {110} prisms, respectively. They have relatively higher Th/U ratio and εHf(t)values than type-1 zircon, and may have crystallized from hybridized magmas with varying degrees of the mixing. The mafic endmember of the hybridized magma likely has mantle-derived affinity. Thus, the MMEs in Mishuling pluton record crust-mantle interaction. Zhongchuan pluton is comprised of five rock units from the periphery to the center, which mostly have indistinguishable zircon U-Pb ages. The peripheric porphyritic granodiorite is intruded by phenocryst-bearing (K-feldspar and quartz) medium-grained biotite monzogranite; medium-grained biotite monzogranite is crosscut by medium-grained two-mica tourmaline granite, which is inversely invaded by fine-grained biotite monzogranite in the center. Moreover, the correlations between contents of Rb and Ba, and contents of Rb and Sr for these rock units are not observed. Therefore, Zhongchuan pluton might have been formed by incremental assembly of at least five magma batches.
- Subjects
ZIRCON; MUSCOVITE; ROCK properties; IGNEOUS intrusions; MAGMAS; BIOTITE
- Publication
Journal of Earth Sciences & Environment, 2023, Vol 45, Issue 2, p227
- ISSN
1672-6561
- Publication type
Article
- DOI
10.19814/j.jese.2022.11041