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Petrology of phlogopite‐sapphirine‐bearing Al‐Mg granulites from Ihouhaouene, In Ouzzal, Hoggar, Algeria: an example of phlogopite stability at high temperature
Author(s) -
MOURI H.,
GUIRAUD M.,
HENSEN B. J.
Publication year - 1996
Publication title -
journal of metamorphic geology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.639
H-Index - 114
eISSN - 1525-1314
pISSN - 0263-4929
DOI - 10.1111/j.1525-1314.1996.00045.x
Subject(s) - phlogopite , geology , granulite , cordierite , geochemistry , sillimanite , quartz , metamorphism , mantle (geology) , biotite , materials science , paleontology , facies , ceramic , structural basin , composite material
Al‐Mg granulites, with cordierite, garnet, sapphirine, orthopyroxene, sillimanite, spinel, phlogopite, K‐feldspar, plagioclase and variable quartz from Ihouhaouene (In Ouzzal, Algeria), display a range of decompression textures involving the breakdown of orthopyroxene and sillimanite, and of garnet. The succession of parageneses suggests that the P–T–t evolution corresponds to decompression with cooling from peak conditions of about 950°C and 10 kbar. This decompression path is obtained from the paragenetic analysis in the FMAS system. However, according to current KFMASH grids, this P–T–t evolution should take place outside the stability field of phlogopite+quartz; yet this assemblage is probably stable during most of the P‐T evolution, notably during peak metamorphism. This discrepancy is interpreted as the effect of the high content of F in phlogopite which should shift its stability limit towards higher temperature. The consequences of this shift on the phase relationships in the KFeMASH system are investigated and it is concluded that a topological inversion could exist in the F‐bearing system.