江苏东海片麻状碱性花岗岩的地球化学及其构造指示意义

Translated title of the contribution: Geochemistry of gneissic alkaline granites in Donghai County, Jiangsu Province, and its tectonic significances

Jian Hu*, Jiansheng Qiu, Rucheng Wang, Shaoyong Jiang, Pei Ni, Jinhai Yu

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)

Abstract

The Donghai region is tectonically located in the southwestern margin of the Su-Lu Orogenic Belt. Several Neoproterozoic gneissic alkaline granite plutons, with typical mineral assemblages of quartz + K-feldspar + oligoclase-albite + aegirine (aegirine-augite)/arfvedsonite, were outcropped in this area. Chemically, these granites are characterized by rich in silicon (SiO2 = 73.43% - 77.38%), alkaline (K2O+Na2O = 8.19% - 9.53%), poor in calcium and magnesium, and high FeO*/(FeO* +MgO) ratios (=0.83-0-94). They also show enrichments of Ga, Y, Zr, Hf, and depletions of Sr, P, Ti, and display high 104XGa/Al ratios (=2.76 -5-15). Chondrite-normalized REE distribution patterns of them are right-inclined, with (La/Yb)N rarios of 2.08-17-89, and display moderate-strong europium depletions ((Eu=0.12-0.66). On the discrimination diagrams proposed by Whalen et al (1987) and Eby (1990), they are all plotted in the A-type granite field. Considering that the rocks have high values of agpacity index (=0.99-1.22) and low A/NKC ratios (=0.78 -0.93), thus they should be grouped into peralkaline A-type granites. These granites show lower Y/Nb and Y/Ta ratios, with values of 1.85-9.72 and 4.71-30.14 respectively, and display clearly depletions of Nb, Ta, Ti on the primitive mantle-normalized spidergrams, implying that they preserve some geochemical fingerprints of the foregoing arc magmatism. On the diagrams for subdivision of A-type granites proposed by Eby (1992), they fall in the A2 field, which was interpreted as a characteristic of post-collisional granites. Integration of mineral chemistry and whole-rock geochemistry with geodynamic considerations suggests that the Donghai gneissic alkaline granites were emplaced during the earliest extensional stage of orogenic collapse, rather than produced in syn-rift period. This understanding has important significances both in further revealing the Neoproterozoic tectonic evolutions of the Su-Lu Orogenic Belt and in profoundly probing the breakup mechanism of the Rodinian supercontinent.

Translated title of the contributionGeochemistry of gneissic alkaline granites in Donghai County, Jiangsu Province, and its tectonic significances
Original languageChinese
Pages (from-to)1877-1891
Number of pages15
JournalActa Geologica Sinica
Volume80
Issue number12
Publication statusPublished - 15 Dec 2006
Externally publishedYes

Keywords

  • Donghai
  • Geochemistry
  • Gneissic alkaline granite
  • Jiangsu
  • Neoproterozoic
  • Tectonic setting

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