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Isotopic Geochronology of the Xianghongdian Alkaline Complex, Northern Margin of the Dabie Mountains, China
Author(s) -
Zhuliang YANG,
Weizhou SHEN,
Jialin SHEN,
Kuiyuan TAO,
Fanggui XIE
Publication year - 1999
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/j.1755-6724.1999.tb00849.x
Subject(s) - nepheline syenite , geochemistry , nepheline , geology , petrogenesis , hornblende , pegmatite , peralkaline rock , carbonatite , biotite , petrology , mantle (geology) , volcano , paleontology , quartz
To the north of the Qinling‐Dabie orogen there exists a Mesozoic (K 1 ) granite‐syenite belt called the Beihuaiyang granite‐syenite belt, in which the Xianghongdian alkaline complex outcrops in the Devonian Foziling schist and also intruded into the slightly earlier volcanic rocks. This alkaline complex is composed of syenite, alkaline syenite and nepheline syenite, but the nepheline syenite occurs inside the alkaline syenite in the pod‐like, irregular, lenticular or layered shape. Researches on the petrogenesis of the alkaline complex and the relationship between the alkaline syenite and the nepheline syenite must rely on precise isotopic ages. Previous researches have reported isotopic dating results merely by the 40 Ar/ 39 Ar method on hornblende and biotite separated from the alkaline syenite and nepheline syenite. In view of this, the authors have made fairly detailed isotopic geochronological studies of the alkaline syenite and nepheline syenite by using Rb‐Sr isochron for the whole rock and minerals, U‐Pb for single zircon separate and the 40 Ar/ 39 Ar method for hornblende and potash feldspar. The results of this research are completely different from those of previous researches and show that the nepheline syenite was formed far earlier than the alkaline syenite.