TY - JOUR

T1 - A flower-like glomerophyric diorite porphyry from Central China

T2 - Constraints on the unusual texture

AU - Zhu, Yu Xiang

AU - Wang, Lian Xun

AU - Ma, Chang Qian

AU - Zhang, Chao

N1 - Funding Information: This study is financially supported by the National Natural Science Foundation of China (No. 41530211 , 41502046 ) and Geological Survey Project of China ( DD20160030 ). The Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan) ( CUGCJ1711 ) is also acknowledged for partial financially support. Haochen Duan, Qihui Xiong, Yuchen Liu, Lian Cai and Yanqing Li are acknowledged for their help during field sampling and laboratory analysis. Special thanks to Prof. Shanrong Zhao, Dr. Chang Xu, Dr. Bin Xia, Prof. Nengsong Chen and Prof. Paul Robinson for their helpful suggestion on sample identification and manuscript preparation. We appreciate the constructive comments from Prof. Michael D. Higgins and another anonymous reviewer as well as Editor Nelson Eby.

PY - 2018/10

Y1 - 2018/10

N2 - An unusual texture with plagioclase phenocrysts clustered as flower-like glomerocrysts has been discovered in the Wulong diorite porphyry at the southern margin of North China Craton. The rock consists mainly of plagioclase and amphibole, with the former as dominant phenocryst. Two groups of the plagioclase phenocrysts have been distinguished: flower-like glomerocrysts (FG-type) and single isolated phenocrysts (SP-type). Chemical compositions of both FG- and SP-type plagioclases are similar in anorthite contents (An35–45) which are slightly higher than the matrix (An25–35). Calculation of the plagioclase crystallization time based on Crystal Size Distribution (CSD) program shows that the FG-type crystals have been formed within a longer timescale (226–2782 years) than the SP-type crystals (98–1910 years). The concave down CSDs and lack of small crystals for FG-type plagioclases suggest that coarsening may have been involved. In contrast, a concave-up CSD within the size of 3–10 mm plagioclase, indicating that a rejuvenation kinetic process after coarsening. A possible formation history for the unusual flower-like plagioclase glomerocrysts was proposed as follows. (1) Initial nucleation and growth of single crystals in a confined environment. (2) Ascent of early crystals with magma upwelling and radial coarsening at the roof layer of magma chamber. (3) Remobilization of dense crystal mush and final emplacement at shallow level of crust. (4) Rapid cooling and extensive nucleation and growth of matrix. (5) Post-magmatic alteration and metamorphism. It is likely that the morphologic diversity of plagioclase glomerocrysts are largely influenced by variation of undercooling degrees. The second step is the most important for the formation of the flower-like glomerophyric texture which requires an environments of relatively low undercooling degree.

AB - An unusual texture with plagioclase phenocrysts clustered as flower-like glomerocrysts has been discovered in the Wulong diorite porphyry at the southern margin of North China Craton. The rock consists mainly of plagioclase and amphibole, with the former as dominant phenocryst. Two groups of the plagioclase phenocrysts have been distinguished: flower-like glomerocrysts (FG-type) and single isolated phenocrysts (SP-type). Chemical compositions of both FG- and SP-type plagioclases are similar in anorthite contents (An35–45) which are slightly higher than the matrix (An25–35). Calculation of the plagioclase crystallization time based on Crystal Size Distribution (CSD) program shows that the FG-type crystals have been formed within a longer timescale (226–2782 years) than the SP-type crystals (98–1910 years). The concave down CSDs and lack of small crystals for FG-type plagioclases suggest that coarsening may have been involved. In contrast, a concave-up CSD within the size of 3–10 mm plagioclase, indicating that a rejuvenation kinetic process after coarsening. A possible formation history for the unusual flower-like plagioclase glomerocrysts was proposed as follows. (1) Initial nucleation and growth of single crystals in a confined environment. (2) Ascent of early crystals with magma upwelling and radial coarsening at the roof layer of magma chamber. (3) Remobilization of dense crystal mush and final emplacement at shallow level of crust. (4) Rapid cooling and extensive nucleation and growth of matrix. (5) Post-magmatic alteration and metamorphism. It is likely that the morphologic diversity of plagioclase glomerocrysts are largely influenced by variation of undercooling degrees. The second step is the most important for the formation of the flower-like glomerophyric texture which requires an environments of relatively low undercooling degree.

KW - Crystal size distribution

KW - Diorite porphyry

KW - Flower-like

KW - North China craton

KW - Plagioclase glomerocryst

KW - Wulong

UR - http://www.scopus.com/inward/record.url?scp=85051394193&partnerID=8YFLogxK

U2 - 10.1016/j.lithos.2018.07.031

DO - 10.1016/j.lithos.2018.07.031

M3 - Article

AN - SCOPUS:85051394193

VL - 318-319

SP - 1

EP - 13

JO - LITHOS

JF - LITHOS

SN - 0024-4937

ER -