Geochemisty and Petrogenesis of the Early Cretaceous Shangcheng and Daquandian Granites in the North Dabie Mountains
详细信息
- 责任者：Gao Xinyu (Key Laboratory of Marginal Sea Geology ; South China Sea Institute of Oceanology ; Chinese Academy of Sciences ; Guangzhou 510301 ; China) ; Zhao Taiping
- 刊名：Geochimica
- 出版年：2013
- 卷期：42(4)
- 关键词：花岗岩 ; granite ; 大别山 ; Dabie Mountains
- 页码：p.307-339
- 图表：illus., 3 tables, 146 refs.
- 分类号：0801
- issnNo：ISSN0379-1726
- isbnNo：CN44-1398/P
摘要
The Shangcheng and Daquandian granites are located to the north of the metamorphic core complex in the West Dabie Mountains.The Shangcheng granite mainly consists of porphyry bitotite monzogranite with LA-ICP-MS zircon U-Pb ages of(137±2)-(141±2) Ma and the Daquandian granite mainly consists of monzogranite with LA-ICP-MS zircon U-Pb ages of(118±1) Ma,respectively.The granitic rocks are metaluminous to weak peraluminous,high-K calc-alkaline I-type granite,enriched in silica(SiO 2 = 67.18%-76.83%),potassium(K2O = 3.12%-4.66%),aluminum(Al 2 O 3 = 12.92%-15.93%,ACNK = 0.91-1.11) and depleted in MgO(0.42%-1.08%).The rocks are enriched in LREE and depleted in HREE((La/Yb) N = 5.03-77.6).The Shangcheng granite is relatively enrichend in Sr(546-1005 μg/g),Ba(585-2069 μg/g),Sr/Y(72.0-122) and depleted in Y(6.05-9.15 μg/g),Yb(0.45-0.84 μg/g),Nb,Ta and Ti,with high Sr/Y(72.0-122),indicative of a deep origin with garnet and rutile residual.The slightly negative Eu anomalies(δEu = 0.78-0.92) suggest a small amount of plagioclase as residual phase in the source.The Daquandian granite is depleted in Sr(27.7-859 μg/g),Ba(118-2598 μg/g),Y(5.00-22.9 μg/g),Yb(0.38-2.42 μg/g),with low and Sr/Y(2.51-77.5) and negative Eu anomalies(δEu = 0.43~0.84),suggesting garnet and plagiochase as residual phase in the source.Zircons from Shangcheng granite gave negative ε Hf(t) values of -30.2 to -15.6 with two-stage Hf model ages of 2173 to 3079 Ma.Zircons from Daquandian granite gave negative ε Hf(t) values of -23.2 to -16.7 with two-stage Hf model ages of 2227 to 2628 Ma.The two granites have Hf model ages as old as Paleoarchean to Archean,which cannot be derived from partial melting of North Dabie orthogneisses alone,but require involvement of more ancient Archean crust in their source region.Thus,their source represents a mixture of crustal rocks between North Dabie gneiss and the Archean Kongling complex in the northern part of the South China Block.In combination with previous studies,the Shangcheng granite is suggested to be formed by partial melting of the thickened lower crust heated by mantle derived magma at the onset of lithospheric thinning.The parental magmas of Daquandian granite were formed by partial melting of crustal materials heated by mantle-derived magma under extensional circumstances.Evolution from Shangcheng granite to Daquandian granite indicates the progress of the lithosphere thinning and the transformation of tectonic regime to an extensional setting.
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