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DOI	10.1007/s00531-019-01701-1
	A model for granite evolution based on non-equilibrium magma separation: evidence from the Gharib and Qattar fluorite-bearing granites; Eastern Desert; Egypt
	Lindh A.; Abu El-Rus M.A.; Mohamed M.A.-M.; Persson P.-O.; Scherstén A.
发表日期	2019
ISSN	14373254
起始页码	1201
结束页码	1232
卷号	108 期号:4
英文摘要	We present 77 new granite whole-rock analyses from the Qattar and Gharib areas, Eastern Desert, Egypt. Both areas include a “normal” granite and either a hypersolvus (Gharib) or an almost plagioclase-free granite (Qattar) enriched in fluorite. According to earlier results, F influences element distribution in granitic melts forming complexes with specific elements as Nb, Ta, Ga, Hf, Th, Zn, Sn, whereas F excludes Ba and Sr. We use principal component analyses to split the granite into chemical groups allowing an unbiased study of the inter-group element distribution. This adds the heavy REEs and Y to the earlier lists of elements with an affinity for F. The light REEs show a decreasing affinity with decreasing atomic mass; fluorine separates Sm from Nd, whereas Zr follows La. Opposite to some, but in accordance with other earlier results, the ratio Nb/Ta is higher in the fluorite-enriched than in the other granite. Weak tetrad effects are present. Zircon in the hypersolvus granite is high in common lead. We suggest F to be instrumental for separating Pb2+ from Pb4+. Two hypotheses may explain the occurrence of the two contrasting granites: they have either different sources, or they are co-magmatic, but the magma was split into two discrete types. We apply the second hypothesis as our working hypothesis. The liquidus has a gentler slope with pressure than the diapir requiring crystallisation to be most important in the lower part of the magma chamber. Our hypothesis suggests that globules of magma, enriched in volatile components, form during crystallisation due to slow diffusion rates in the crystallizing magma. Elements accompanying F are distributed into this magma batch, which has a lowered density and viscosity than the rest of the magma due to its increased contents of volatile components. A mushroom-formed diapir rises, forming the hypersolvus (or almost plagioclase-free) granite. Due to an edge effect, it is concentrated close to the wall of the magma chamber. The size and form of the outcropping granite depend on the intersection of the diapir with the erosion surface. Fluorine only makes it possible to follow the process. The model may be generalised to explain the diversification of non-F enriched granite, since the buoyancy of a magma batch several thousand m3 in size has a much larger impact on the system than the small negative buoyancy of crystals or small crystal aggregates. A-type granite classified merely from its trace element content may form from separated F-enriched magma batches. This may be the reason for their high frequency in the Eastern Desert. © 2019, The Author(s).
英文关键词	Buoyancy; Common lead; Complex ions; Diapir; Eastern Desert; Egypt; Fluorite; Granite; Magma separation; Principal component analysis
语种	英语
scopus关键词	buoyancy; diapir; fluorite; granite; ion; lead; magma chamber; principal component analysis; trace element; Eastern Desert; Egypt; Basidiomycota
来源期刊	International Journal of Earth Sciences
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/147844
作者单位	Department of Geology, Lund University, Sölvegatan 12, Lund, 223 62, Sweden; Department of Geology, Assiut University, Assiut, 71516, Egypt; Museum of Natural History, Box 50 007, Stockholm, 104 05, Sweden; 14 rue de la garde, Bourcefranc-le-Chapus, 17560, France
推荐引用方式 GB/T 7714	Lindh A.,Abu El-Rus M.A.,Mohamed M.A.-M.,et al. A model for granite evolution based on non-equilibrium magma separation: evidence from the Gharib and Qattar fluorite-bearing granites; Eastern Desert; Egypt[J],2019,108(4).
APA	Lindh A.,Abu El-Rus M.A.,Mohamed M.A.-M.,Persson P.-O.,&Scherstén A..(2019).A model for granite evolution based on non-equilibrium magma separation: evidence from the Gharib and Qattar fluorite-bearing granites; Eastern Desert; Egypt.International Journal of Earth Sciences,108(4).
MLA	Lindh A.,et al."A model for granite evolution based on non-equilibrium magma separation: evidence from the Gharib and Qattar fluorite-bearing granites; Eastern Desert; Egypt".International Journal of Earth Sciences 108.4(2019).