Wagnerite-Ma5bc, a new polytype of Mg-2(PO4)(F,OH), from;granulite-facies paragneiss, Larsemann Hills, Prydz Bay, East Antarctica

doi:10.2113/gscanmin.41.2.393;PN Part 2

	Wagnerite-Ma5bc, a new polytype of Mg-2(PO4)(F,OH), from;granulite-facies paragneiss, Larsemann Hills, Prydz Bay, East Antarctica
	Ren, LD 4; Grew, ES ; Xiong, M ; Ma, ZS
刊名	CANADIAN MINERALOGIST
	2003
卷号	41 页码:393-411
关键词	wagnerite magniotriplite crystal structure polytype granulite facies Larsemann Hills Antarctica
ISSN号	0008-4476
DOI	10.2113/gscanmin.41.2.393;PN Part 2
英文摘要	Wagnerite-Ma5bc, anew polytype, occurs in paragneiss associated with banded cordierite-prismatine gneiss in the Larsemann Hills. East Antarctica. It forms anhedral to euhedral grains mostly 0.5-2 mm across, some with a tabular habit. Textures are consistent With a primary assemblage wagnerite-Ma5bc + plagioclase + apatite + magnetite + ilmenite-hematite that crystallized under granulite-facies conditions (750 - similar to860degreesC, 6-7 kbar). Also present are biotite, quartz, K-feldspar, minerals of the monazite and xenotime groups, corundum, hercynite, and sulfide. Electron-microprobe analyses give P2O5 41.39, SiO2 0.06, TiO2 0.88, FeO 4.16, MnO 0.09, MgO 44.54, CaO 0.09, F 6.87, H2O (calculated for OH + F = 1) 2.04, O=F -2.89, total 97.22 wt%, corresponding to (Mg1.88Fe0.10Ti0.02)(P0.99O4)(F0.61OH0.39). The space group is Ia. Lattice parameters: a 9.645(2), b 31.659(6), c 11.914(2) Angstrom, beta 108.26(3)degrees, V 3455(l) Angstrom(3) for Z = 40. The crystal structure has been solved by direct methods and refined to R-1 = 0.0413 for the independent 4521 reflections [I > 2sigma(l)] using MoKalpha radiation. The primary difference between the wagnerite-Ma5bc and wagnerite-Ma2bc (e.g., type locality) is ordering of the (F,OH) positions. F can occupy one of two positions, resulting in two distinct configurations along the a direction. In magniotriplite, the sequence of configurations in the b direction is disordered, whereas in wagnerite-Ma2bc, the sequence is ordered 121212... and in wagnerite-Ma5bc, 12112... Magniotriplite and the wagnerite polytypes do not overlap in composition: minerals richer in Fe and Mn (average ionic radius greater than or equal to0.76Angstrom)crystallize as the disordered minerals in the triplite group, whereas highly magnesian minerals (average ionic radius less than or equal to0.73 Angstrom or greater than or equal to86% of the Mg end member) crystallize as the ordered polytypes of wagnerite. Magniotriplite formed at moderate temperatures (e.g., amphibolite-facies conditions), whereas wagnerite-Ma2bc is found in rocks formed under a wide range of P-T conditions. Compositional or kinetic factors (or both), rather than P-T, could play the leading role in determining the extent of F order; possibly many M22+PO4F compounds originally crystallize in the disordered state, the Mabc polytype, and only magnesian varieties subsequently order on cooling, i.e., Mn2+ and Fe2+ inhibit ordering.
学科主题	变质岩岩石学
WOS关键词	CRYSTAL-STRUCTURE ; PHASE ; EXHUMATION ; TRIPLITE
WOS研究方向	Mineralogy
语种	英语
出版者	MINERALOGICAL ASSOC CANADA
WOS记录号	WOS:000183341600011
内容类型	期刊论文
源URL	[http://119.78.100.197/handle/2HKVOGP0/37582]
专题	中国地质科学院地质研究所
作者单位	1.Chinese Acad Geol Sci, Inst Geol, Beijing 100037, Peoples R China. 2.Univ Maine, Dept Geol Sci, Edward T Bryand Res Ctr 5790, Orono, ME 04469 USA. 3.China Univ Geosci, Beijing 100083, Peoples R China. 4.中国地质科学院地质研究所
推荐引用方式 GB/T 7714	Ren, LD,Grew, ES,Xiong, M,et al. Wagnerite-Ma5bc, a new polytype of Mg-2(PO4)(F,OH), from;granulite-facies paragneiss, Larsemann Hills, Prydz Bay, East Antarctica[J]. CANADIAN MINERALOGIST,2003,41:393-411.
APA	Ren, LD,Grew, ES,Xiong, M,&Ma, ZS.(2003).Wagnerite-Ma5bc, a new polytype of Mg-2(PO4)(F,OH), from;granulite-facies paragneiss, Larsemann Hills, Prydz Bay, East Antarctica.CANADIAN MINERALOGIST,41,393-411.
MLA	Ren, LD,et al."Wagnerite-Ma5bc, a new polytype of Mg-2(PO4)(F,OH), from;granulite-facies paragneiss, Larsemann Hills, Prydz Bay, East Antarctica".CANADIAN MINERALOGIST 41(2003):393-411.