Petrogeochemistry of Late Mesozoic alkali-rich potassium-high granitoid in western Zhejiang and its tectonic significance.
2008; Science Press; Linguagem: Inglês
ISSN
2095-8927
Autores Tópico(s)Geomechanics and Mining Engineering
ResumoThe western part of Zhejiang features a wide distribution of late Mesozoic intrusive rock,where a set of alkali-rich potassium-high granitoid is recognized in the contiguous area among Jiangshan,Longyou and Suichang.Preliminary studies show that the formerly defined I-type granitoid is instead aluminum base A-type granitic rock,and that it is stretched in band-shaped north-east direction under obvious controls of Jiangshan-Shaoxing fault zone and Zhedaikou-Xikou fault zone in space.This type of rock is composed of alkali feldspar-quartz syenite,quartz syenite porphyry,syenite quartz monzonite,monzonite,adamellite,granite,and granite porphyry,with alkali-rich potassium-high as its remarkable characteristics.Its Wright Alkalinity ratio (A.R)=2.14～5.76, excessive Alkali index (AKI value)=0.58～0.96 (average is 0.83),partial aluminous to peraluminous (A/NKC=0.93～1.30, average is 1.05),rich in rare earth elements (∑ REE=226.65×10~(-6)～429.18×10~(-6)) and relatively high (Zr+Nb+Ce+Y) values (282×10~(-6)～826×10~(-6),average is 482×10~(-6)),but depleted in Ba,Ta,Nb,P,Ti etc.It also completely falls into A-type granitoid area in the Na_2O-K_2O genetic type chart,which indicates that it possesses the characteristics of A-type granite rock.The Nd isotope model age of Hongong pluton and Muchen pluton varies between 1.2～1.6Ga,from which it can be deduced that it on the whole originates from the partial melting of crustal rocks.Integrated regional background,feature of tectonic passive location and geochemistry data suggest that this set of alkali-rich potassium-high granitoid is formed under a post-collisional tectonic setting,and is product of the important tectonic-magmatic event in early Cretaceous in this region.
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