RT Journal Article
T1 Diachronous Variscan tectonothermal activity in the NW IberianMassif: Evidence from 40Ar/39Ar dating of regional fabrics
A1 Dallmeyer, R. David
A1 Martínez Catalán, José Ramón
A1 Arenas Martín, Ricardo
A1 Gil Ibarguchi, José Ignacio
A1 Gutiérrez Alonso, Gabriel
A1 Farias Arquer, Pedro
A1 Bastida Ibáñez, Fernando
A1 Aller, Jesús(1956-)
AB Multigrain concentrates of hornblende and muscovite together with whole-rock slate/phyllite samples have been dated(27 analyses) using 40Ar/39Ar incremental-release methods along a systematic traverse across the various lithotectonicstructural elements which comprise northwestern sectors of the Variscan Iberian Massif. Hornblende concentrates fromamphibolites in the allochthonous Ordenes Complex yield plateau isotope-correlation ages of 425 Ma and 377 Ma.Muscovite concentrates and whole-rock slate/phyllite from this and the Cabo Ortega1 Complex yield plateau ages whichrange from 367 Ma to 295 Ma. Analyses of similar material from the relative autochthon yield plateau ages between 359Ma and 275 Ma. Muscovite concentrates from three late- to post-kinematic granitic stocks yield plateau ages between 309Ma and 274 Ma.At least seven of the 4oAr/39Ar analyses from metamorphic rocks record variable thermal rejuvenation of intracrystallineargon systems associated with emplacement of proximal granitic stocks. The remaining analyses may be used to constrainthe local age of various Variscan tectonothermal events. The oldest fabric ages are recorded in allochthonous units whereasthe youngest fabric ages occur along the boundary between internal and external zones. Middle Devonian ages are recordedin the allochthon and suggest a chronological continuity with deformational events in the relative autochthon, whereVariscan deformation initiated in the Upper Devonian and diachronously prograded eastward. The first deformationalevents recorded in the limit within the internal and external zones occurred ca. 20-25 Ma later (lower Namurian).Variscan deformation systematically prograded diachronously eastward across the orogen as new crustal material wasadded along the front of the developing erogenic wedge. However, the entire orogen remained tectonically active withdifferent structural features forming at different times and at different places. An average propagation rate of ca. 5 km/m.y.is suggested by consideration of a 20-25 Ma difference in correlative fabric ages and present separations.
PB Elsevier, B.V.
SN 0040-1951
YR 1997
FD 1997
LK https://hdl.handle.net/20.500.14352/57754
UL https://hdl.handle.net/20.500.14352/57754
LA eng
DS Docta Complutense
RD 20 abr 2025