Characteristics of Porphyritic Granitic Gneiss in Taili Area, Western Liaoning Province and Their Geological Significance
详细信息
- 责任者：Li Jian (East China Mineral Exploration and Development Bureau ; Nanjing 210007 ; China) ; Zhang Xia
- 刊名：Geological Journal of China Universities
- 出版年：2013
- 卷期：19(2)
- 关键词：花岗质片麻岩 ; granitic gneiss ; 辽宁 ; Liaoning Province
- 页码：p.259-273
- 图表：illus., 3 tables, 46 refs.
- 分类号：0802
- issnNo：ISSN1006-7493
- isbnNo：CN32-1440/P
摘要
The characteristics,formation,and evolution of the porphyritic granitic gneiss in Taili area of western Liaoning Province was studied in detail based on petrology,geochemistry and zircon U-Pb dating.This study provides new petrological evidence for investigating the geological evolution of the North China Craton.The granitoid rocks are mainly composed of granitic gneiss,porphyritic granitic gneiss,and biotite adamellite in the study area.The porphyritic granitic gneiss intruded into and was formed later than granitic gneiss.The porphyritic texture is well-developed with different amount of alkali feldspar and quartz depending on the distance relative to the deformation zone.Phenocrysts are much bigger in the areas far away from the deformation zone,while the porphyritic granitic gneiss with eye-like structures has been highly deformed and mylonitized in the deformaltion zone.The SiO 2 and K 2 O contents of the porphyritic granitic gneiss range from 67.54% to 75.64% and from 2.89% to 4.67%,respectively.It is enriched in light rare earth elements as well as in Ba and Sr;while depleted in heavy rare earth elements Ti,Nb,Ta and P.Chondrite-normalized REE distribution patterns of granitic rocks show weak negative Eu anomalies.Therefore we speculate that the residual phase of the source has more garnets.Geochronological studies have shown that zircons,which are characterized by growth bands and high Th/U ratios(0.28~1.20),are attributed to magmatic origin.The LA-ICP-MS zircon U-Pb weighted average ages of two samples are(224.6±2.5) Ma and(216.44±0.50) Ma,respectively.In conclusion,we find that the protolith of porphyritic granitic gneiss belongs to I-type granite with source rocks of meso-basic volcanic rocks from the lower crust,and was formed in the late Triassic as evidenced by lithospheric thinning of the North China Craton in the Mesozoic.
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