Discovery of an Indosinian Granite: Luoguyan Pluton in Northwestern Fujian Province, South China, and Its Petrogenesis and Tectonic Significance
详细信息
- 责任者：Xiang Tingfu (State Key Laboratory for Mineral Deposits Research ; School of Earth Sciences and Engineering ; Nanjing University ; Nanjing 210093 ; China) ; Sun Tao
- 刊名：Geological Journal of China Universities
- 出版年：2013
- 卷期：19(2)
- 关键词：I型花岗岩 ; I-type granite ; 福建 ; Fujian Province
- 页码：p.274-292
- 图表：illus., 6 tables, 99 refs.
- 分类号：0801
- issnNo：ISSN1006-7493
- isbnNo：CN32-1440/P
摘要
In this paper,the Luoguyan pluton in the northwestern inland area of Fujian Province was selected as an example for a detailed geochronological,whole rock geochemical,and Sr-Nd-Hf isotopic geochemical study in order to elucidate its petrogenesis.LA-ICP-MS U-Pb zircon ages of two samples(LGY02 and LGY10) from the Luoguyan pluton are(227.1± 2.6) Ma(LGY02) and(234.4±1.5) Ma(LGY10),indicating that this pluton was generated in the Indosinian stage.Chemically,this pluton is metaluminous(most of the A/CNK values are lower than 1.0),and shows high contents of silica(SiO 2 >74%) and alkalies(K 2 O+Na 2 O =8.57%~9.22%,K 2 O/Na 2 O>1.4),low abundance of calcium,magnesium,and iron.The rocks display low total REE contents(∑REE=116.72×10-6 ~236.53×10-6) and low contents of Zr+Ce+Nb+Y(< 350×10-6) with strongly negative Eu anomalies(δEu=0.17~0.37),and are enriched in Rb,Nd,Th,U,Hf,depeted in Ba,Nb,Sr,Zr,Ti.Overall,our integrated mineralogical and geochemical features suggest that the Luoguyan granites are highly fractionated I-type granites.Isotopically,samples show high and variable initial 87 Sr/ 86 Sr ratios(0.7078~0.7130),yet low and constant ε Nd(t)(-12.17~-10.70),corresponding to two stage model age of the 1.87~2.00 Ga.However,their zircon Hf isotopes show large variations,with ε Hf(t) values varying between-13.0~-6.8,corresponding to two stage model age of 1.69~2.08 Ga.Combining with the discovery of the Indosinian Yangfang syenite located in Pucheng-Wuping fault zone and the Xiamao diabase originated from the enriched mantle,we suggest that the Luoguyuan pluton was derived from a mixed magma which mingled with an enriched mantle-derived component similar to the Xiamao diabase with a crustal felsic component derived from the partial melting of basement Mayuan metamorphic rocks,during which the tectonic setting was an extension environment,and then experienced a high degree of differentiation during crystallization.