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Retrograde P‐T‐t path for the Voltri Massif eclogites (Ligurian Alps, Italy): some tectonic implications
Author(s) -
MESSIGA B.,
SCAMBELLURI M.
Publication year - 1991
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.1525-1314.1991.tb00506.x
Subject(s) - geology , glaucophane , eclogite , amphibole , geochemistry , metamorphic rock , albite , lawsonite , massif , overprinting , plagioclase , blueschist , sill , paragenesis , greenschist , petrology , tectonics , paleontology , quartz , subduction
The retrograde P‐T trajectory of the eclogitic Fe‐Ti‐gabbros from the Ligurian Alps is constrained by the appearance of mineral parageneses post‐dating the Na‐clinopyroxene + garnet eclogitic assemblage and indicating the following sequence of metamorphic events: (1) amphibolitic stage— edenite/katophorite + plagioclase (An 33–43 ) + oxides in symplectitic aggregates; (2) glaucophanic stage— a porphyroblastic glaucophanic amphibole has overgrown the symplectite, winchite also occurs as thin rims around glaucophane and both amphiboles are, sometimes, armoured by atoll garnets; (3) albite‐amphibolite stage—barroisite/katophorite + albite + epidote + oxides ± chlorite overprint the glaucophanic stage minerals; (4) greenschist stage—represented by actinolite + albite + epidote + oxide paragenesis. The metamorphic evolution is complex and the decompression path, on a P–T diagram, is significantly different from those defined in the literature for the Voltri eclogites. The main features inferred from the P–T path are the following: (1) the pressure climax does not match the thermal climax, the maximum temperature conditions are in fact achieved during the early stage of uplift; (2) a decrease in temperature, suggested by the appearance of glaucophane after the amphibolitic symplectite; (3) successive uplift, probably accompanied by an increase in temperature. The complexity of the P‐T path drawn for the Voltri eclogites can be explained with a mechanism of successive underthrusts propagating from the innermost to the outermost sector of the Ligurian Alps.