TY - JOUR
KW - Barrovian metamorphism
KW - crustal thickening
KW - polyphase P–T path
KW - pseudosections
KW - Variscan Pyrenees
AU - Luc De Hoÿm de Marien
AU - Benjamin Le Bayon
AU - Pavel Pitra
AU - Jean Van Den Driessche
AU - Marc Poujol
AU - Florence Cagnard
AB - Abstract The Variscan metamorphism in the Pyrenees is dominantly of the low-pressure?high-temperature (LP-HT) type. The relics of an earlier, Barrovian-type metamorphism that could be related to orogenic crustal thickening are unclear and insufficiently constrained. A microstructural and petrological study of micaschists underlying an Ordovician augen orthogneiss in the core of the Canigou massif (Eastern Pyrenees, France) reveals the presence of two syntectonic metamorphic stages characterized by the crystallization of staurolite (M1) and andalusite (M2), respectively. Garnet is stable during the two metamorphic stages with a period of resorption between M1 and M2. The metamorphic assemblages M1 and M2 record similar peak temperatures of 580°C at different pressure conditions of 5.5 and 3 kbar, respectively. Using chemical zoning of garnet and calculated P?T pseudosections, a prograde P?T path is constrained with a peak pressure at  6.5 kbar and 550°C. This P?T path, syntectonic with respect to the first foliation S1, corresponds to a cold gradient (of  9°C/km), suggestive of crustal thickening. Resorption of garnet between M1 and M2 can be interpreted either in terms of a simple clockwise P?T path or a polymetamorphic two-stage evolution. We argue in favour of the latter, where the medium-pressure (Barrovian) metamorphism is followed by a period of significant erosion and crustal thinning leading to decompression and cooling. Subsequent advection of heat, probably from the mantle, leads to a new increase in temperature, coeval with the development of the main regional fabric S2. LA-ICP-MS U?Th?Pb dating of monazite yields a well-defined date at c. 300 Ma. Petrological evidence indicates that monazite crystallization took place close to the M1 peak pressure conditions. However, the similarity between this age and that of the extensive magmatic event well documented in the eastern Pyrenees suggests that it probably corresponds to the age of monazite recrystallization during the M2 LP-HT event.
BT - Journal of Metamorphic Geology
DA - 2019/08/01
N2 - Abstract The Variscan metamorphism in the Pyrenees is dominantly of the low-pressure?high-temperature (LP-HT) type. The relics of an earlier, Barrovian-type metamorphism that could be related to orogenic crustal thickening are unclear and insufficiently constrained. A microstructural and petrological study of micaschists underlying an Ordovician augen orthogneiss in the core of the Canigou massif (Eastern Pyrenees, France) reveals the presence of two syntectonic metamorphic stages characterized by the crystallization of staurolite (M1) and andalusite (M2), respectively. Garnet is stable during the two metamorphic stages with a period of resorption between M1 and M2. The metamorphic assemblages M1 and M2 record similar peak temperatures of 580°C at different pressure conditions of 5.5 and 3 kbar, respectively. Using chemical zoning of garnet and calculated P?T pseudosections, a prograde P?T path is constrained with a peak pressure at  6.5 kbar and 550°C. This P?T path, syntectonic with respect to the first foliation S1, corresponds to a cold gradient (of  9°C/km), suggestive of crustal thickening. Resorption of garnet between M1 and M2 can be interpreted either in terms of a simple clockwise P?T path or a polymetamorphic two-stage evolution. We argue in favour of the latter, where the medium-pressure (Barrovian) metamorphism is followed by a period of significant erosion and crustal thinning leading to decompression and cooling. Subsequent advection of heat, probably from the mantle, leads to a new increase in temperature, coeval with the development of the main regional fabric S2. LA-ICP-MS U?Th?Pb dating of monazite yields a well-defined date at c. 300 Ma. Petrological evidence indicates that monazite crystallization took place close to the M1 peak pressure conditions. However, the similarity between this age and that of the extensive magmatic event well documented in the eastern Pyrenees suggests that it probably corresponds to the age of monazite recrystallization during the M2 LP-HT event.
PY - 2019
SN - 0263-4929
SP - 863
EP - 888
T2 - Journal of Metamorphic Geology
TI - Two-stage Variscan metamorphism in the Canigou massif: Evidence for crustal thickening in the Pyrenees
UR - https://doi.org/10.1111/jmg.12487
VL - 37
ER -