Metamorphic Evolution of Porphyroblastic Eclogite in Qinglongshan of Donghai of Northern Jiangsu Province
详细信息
- 责任者：Yan Rong (State Key Laboratory of Lithospheric Evolution ; Institute of Geology and Geophysics ; Chinese Academy of Sciences ; Beijing 100029 ; China) ; Yang Jianjun
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(5)
- 关键词：榴辉岩 ; eclogite ; 变质作用 ; metamorphism ; 苏鲁造山带 ; Su-Lu Orogenic Belt
- 页码：p.1621-1633
- 图表：illus., 6 tables, 41 refs.
- 分类号：0802
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
Part eclogites in Qinglongshan are characterized by epidote,kyanite and talc porphyroblast,but their peak metamorphic mineral assemblages are composed of fine-grained garnet + omphacite + phengite + coesite + rutile + epidote in matrix. The minerals in the peak assembkage show shape preferred orientation defining the rock foliation. The peak assemblage defined by garnet compositional isopleths in the calculated phase diagram is garnet + omphacite + phengite + kyanite + rutile + coesite + lawsonite + talc,inconsistent with the petrographic observation. The discrepancy probably resulted from the assumption of pure water to be the ultrahigh-pressure ( UHP) fluid phase. The randomly oriented porphyroblasts overprint the rock foliation,implying that they crystallized later than the peak assemblage under a weak shear stress field. Both petrography and phase diagram modelling demonstrate a crystallization sequence of kyanite-epidote-talc. The mode of epidote increases dramatically resulting in the formation of porphyroblasts at < 2GPa. The coesite pseudomorphs in the epidote porphyroblasts do not necessarily imply that they crystallized in the stability field of coesite. Rapid decrease in P-T was more likely the cuase of inclusion of the UHP assemblage in the epidote porphyroblasts. The P-T path defined by the mineral assemblages is typically the hair-pin type. Hydrous minerals were present in all the assemblages at different metamorphic stages,their amounts increased during retrogression,implying continuous ingress of fluids into the rock.
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