@article{fdi:010094366,
  title = {{P}etrogenetic link between metasedimentary rocks, migmatites and granitoids in the {V}ariscan basement of the {P}ontgibaud area, {F}rench {M}assif {C}entral - implications for the crustal structure},
  author = {do {C}armo, {C}. {P}. and {V}anderhaeghe, {O}. and {L}aurent, {O}. and {B}erger, {J}. and {B}ellanger, {M}. and {L}eisen, {M}athieu and {C}hmeleff, {J}.},
  editor = {},
  language = {{ENG}},
  abstract = {{T}he architecture of the crust in the {F}rench {M}assif {C}entral ({FMC}) is described as a nappe stack composed, from top to bottom, of the {U}pper {G}neiss {U}nit ({UGU}), the {L}ower {G}neiss {U}nit ({LGU}), and the {P}ara-{A}utochthonous {U}nit ({PAU}), which are intruded by {C}arboniferous granitic plutons. {I}n the {P}ontgibaud region, the {U}pper {G}neiss {U}nit/{L}ower {G}neiss {U}nit ({UGU}/{LGU}) attribution and the relationship between metamorphic and magmatic rocks are uncertain. {T}his hinders both our understanding of the geodynamic processes that led to the construction of the {V}ariscan orogenic belt, and a precise assessment of the deep geothermal potential of this high-heat flow area. {O}ur field investigations document a metamorphic gradient with, from {S}outh to {N}orth, micaschists and paragneiss with a gently, dominantly southward-dipping foliation grading into migmatites that display a steeper foliation. {A} maximum late {E}diacaran deposition age of sedimentary protoliths is determined from {LA}-{ICPMS} {U}-{P}b dates of the youngest detrital zircon populations that range from 588.9 +/- 7.1 to 571.8 +/- 8.2 {M}a. {E}quilibrium phase diagrams calculated for selected samples document a metamorphic gradient from 2.3- 5.3 kbar, and 570 degrees-660 degrees {C}, characterizing a mid- to low pressure-high temperature event dated from 357.6 +/- 1.5 to 342.2 +/- 4.6 {M}a by {LA}-{ICP}-{MS} {U}-{P}b analyses of metamorphic monazite. {T}he contact between the metasedimentary rocks and migmatites is crosscut by peraluminous, cordierite-biotite-bearing {C}laveix and {G}elles granitic plutons dated at 338.0 +/- 7.3 {M}a and 323.3 +/- 9.7 {M}a, respectively by {U}-{P}b on zircon. {T}he distribution of {U}-{P}b dates and {L}u-{H}f isotopic compositions of detrital zircon in metamorphic rocks; the absence of {HP} mineral relics; the age of {HT} metamorphism of ca. 357-345 {M}a; and the lack of a major mylonitic tectonic contact, which would typify the base of {UGU}, collectively support that the exposed crust of the {P}ontgibaud area corresponds to {LGU} metamorphic rocks. {M}oreover, the mineralogy, bulk chemistry and zircon {L}u-{H}f isotopic composition of the granites and migmatites are consistent with an origin by partial melting of {LGU} metasedimentary rocks. {T}hese data show that the {P}ontgibaud area exposes a section along a {C}arboniferous {MP}-{LP}/{HT} metamorphic gradient from micaschists to migmatites. {G}enesis and extraction of a large volume of granitic magma require higher temperatures (>800 degrees {C}) that were not reached by the exposed rocks. {A}ccordingly, we propose that the local mid- and lower crustal levels are made of rocks with a similar protolith as those exposed at the surface, but affected by higher metamorphic grade and magma extraction.},
  keywords = {{F}rench {M}assif {C}entral ; {V}ariscan belt ; migmatites ; crustal structure ; metamorphism ; {FRANCE} ; {MASSIF} {CENTRAL}},
  booktitle = {},
  journal = {{BSGF} - {E}arth {S}ciences {B}ulletin},
  volume = {196},
  numero = {},
  pages = {13 [32 p.]},
  ISSN = {0037-9409},
  year = {2025},
  DOI = {10.1051/bsgf/2025004},
  URL = {https://www.documentation.ird.fr/hor/fdi:010094366},
}