FN Archimer Export Format
PT J
TI Mantle exhumation at magma-poor passive continental margins. Part I. 3D architecture and metasomatic evolution of a fossil exhumed mantle domain (Urdach Iherzolite, north-western Pyrenees, France)
BT 
AF LAGABRIELLE, Yves
   ASTI, Riccardo
   FOURCADE, Serge
   CORRE, Benjamin
   POUJOL, Marc
   UZEL, Jessica
   LABAUME, Pierre
   CLERC, Camille
   LAFAY, Romain
   PICAZO, Suzanne
   MAURY, Rene
AS 1:1;2:1;3:1;4:1;5:1;6:1;7:2;8:3;9:4;10:4;11:5;
FF 1:;2:;3:;4:;5:;6:;7:;8:;9:;10:;11:;
C1 Univ Rennes, CNRS, UMR Geosci Rennes 6118, Campus Beaulieu, F-35000 Rennes, France.
   Univ Montpellier, CNRS, Geosci Montpellier, F-34095 Montpellier, France.
   Univ Nouvelle Caledonie, LIVE, BPR4, F-98851 Noumea, France.
   Univ Lausanne, Inst Earth Sci, CH-1015 Lausanne, Switzerland.
   Inst Univ Europeen Mer, Univ Brest, CNRS, UMR Geosci Ocean 6538, Pl Nicolas Copernic, F-29280 Plouzane, France.
C2 UNIV RENNES, FRANCE
   UNIV MONTPELLIER, FRANCE
   UNIV NOUVELLE CALEDONIE, FRANCE
   UNIV LAUSANNE, SWITZERLAND
   UBO, FRANCE
UM LGO
IF 0.579
TC 23
UR https://archimer.ifremer.fr/doc/00637/74920/76106.pdf
   https://archimer.ifremer.fr/doc/00637/74920/76107.zip
LA English
DT Article
DE ;North Pyrenean Zone;Urdach;mantle exhumation;fluid-rock interactions;listvenites;greenschist facies;detachment faults;Late Cretaceous
AB In two companion papers, we report the detailed geological and mineralogical study of two emblematic serpentinized ultramafic bodies of the western North Pyrenean Zone (NPZ), the Urdach massif (this paper) and the Saraille massif (paper 2). The peridotites have been exhumed to lower crustal levels during the Cretaceous rifting period in the future NPZ. They are associated with Mesozoic pre-rift metamorphic sediments and small units of thinned Paleozoic basement that were deformed during the mantle exhumation event. Based on detailed geological cross-sections and microprobe mineralogical analyses, we describe the lithology of the two major extensional fault zones that accommodated: (i) the progressive exhumation of the lherzolites along the Cretaceous basin axis; (ii) the lateral extraction of the continental crust beneath the rift shoulders and; (iii) the decoupling of the pre-rift cover along the Upper Triassic (Keuper) evaporites and clays, allowing its gliding and conservation in the basin center. These two fault zones are the (lower) crust-mantle detachment and the (upper) cover decollement located respectively at the crust-mantle boundary and at the base of the detached pre-rift cover. The Urdach peridotites were exposed to the seafloor during the Late Albian and underwent local pervasive carbonation and crystallization of calcite in a network of orthogonal veins (ophicalcites). The carbonated serpentinized peridotites were partly covered by debris-flows carrying fragments of both the ultramafics and Paleozoic crustal rocks now forming the polymictic Urdach breccia. The mantle rocks are involved in a Pyrenean overturned fold together with thin units of crustal mylonites. Continent-derived and mantle-derived fluids that circulated along the Urdach crust-mantle detachment led to the crystallization of abundant metasomatic rocks containing quartz, calcite, Cr-rich chlorites, Cr-rich white micas and pyrite. Two samples of metasomatized material from the crust-mantle detachment yielded in situ zircon U/Pb ages of 112.9 +/- 1.6 Ma and 109.4 +/- 1.2 Ma, thus confirming the Late Albian age of the metasomatic event. The cover decollement is a 30-m thick fault zone which also includes metasomatic rocks of greenschist facies, such as serpentinecalcite association and listvenites, indicating large-scale fluid-rock interactions implying both ultramafic and continental material. The lowermost pre-rift cover is generally missing along the cover decollement due to tectonic disruption during mantle exhumation and continental crust elision. Locally, metasomatized and strongly tectonized Triassic remnants are found as witnesses of the sole at the base of the detached pre-rift cover. We also report the discovery of a spherulitic alkaline lava flow emplaced over the exhumed mantle. These data collectively allow to propose a reconstruction of the architecture and fluid-rock interaction history of the distal domain of the upper Cretaceous northern Iberia margin now inverted in the NPZ. 
PY 2019
PD JUN
SO Bsgf-earth Sciences Bulletin
SN 0037-9409
PU Edp Sciences S A
VL 190
IS 1
UT 000475766500001
DI 10.1051/bsgf/2019007
ID 74920
ER

EF