Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
A model for granite evolution based on non‑equilibrium magmaseparation: evidence from the Gharib and Qattar fluorite‑bearing granites, Eastern Desert, Egypt
Geologiska institutionen, Lunds universitet.
Department of Geology, Assiut University, Assiut, Egypt.
Department of Geology, Assiut University, Assiut, Egypt.
Swedish Museum of Natural History, Department of Geology.
Show others and affiliations
2019 (English)In: International journal of earth sciences, ISSN 1437-3254, E-ISSN 1437-3262, Vol. 108, no 4, p. 1201-1232Article in journal (Refereed) Published
Abstract [en]

We present 77 new granite whole-rock analyses from the Qattar and Gharib areas, Eastern Desert, Egypt. Both areas includea “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 elementsas 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 slopewith 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 diffusionrates 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 fo rtheir high frequency in the Eastern Desert.

Place, publisher, year, edition, pages
Springer, 2019. Vol. 108, no 4, p. 1201-1232
Keywords [en]
Buoyancy · Fluorite · Complex ions · Principal component analysis · Magma separation · Diapir · Granite ·
National Category
Geochemistry
Research subject
The changing Earth
Identifiers
URN: urn:nbn:se:nrm:diva-3366OAI: oai:DiVA.org:nrm-3366DiVA, id: diva2:1368618
Available from: 2019-11-07 Created: 2019-11-07 Last updated: 2019-11-08Bibliographically approved

Open Access in DiVA

fulltext(3032 kB)1 downloads
File information
File name FULLTEXT01.pdfFile size 3032 kBChecksum SHA-512
d444f6941c01bda11fe10042d56fbe4fe115d38a8c885e528a7160aa18751f53776bf95bc1648d265711268745b7b8550d457c1c06e6a25466ed117496558c1b
Type fulltextMimetype application/pdf

Other links

https://link.springer.com/article/10.1007%2Fs00531-019-01701-1

Search in DiVA

By author/editor
Persson, Per-Olof
By organisation
Department of Geology
In the same journal
International journal of earth sciences
Geochemistry

Search outside of DiVA

GoogleGoogle Scholar
Total: 1 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

urn-nbn

Altmetric score

urn-nbn
Total: 4 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf