RT Journal Article
T1 A peri-Gondwanan arc in NW Iberia. II: Assessment of the intra-arc tectonothermalevolution through U–Pb SHRIMP dating of mafic dykes
A1 Díaz García, Florentino
A1 Sánchez Martínez, Sonia
A1 Castiñeiras García, Pedro
A1 Fuenlabrada Pérez, José Manuel
A1 Arenas Martín, Ricardo
AB The arc-derived upper units of the Órdenes Complex, NW Iberia, are emplaced above the Variscan suture andcontain a low-grade metasedimentary uppermost section, with a maximum depositional age of 510–530 Ma,intruded by a number of mafic dykes. Three deformational events affect the metasedimentary section. Theyoungest deformation event (D3) is of undifferentiated Variscan age and consists of metre- to decametre-scale,close upright folds with axes plunging gently towards N20°E. The most important D2 structure is a regional S2foliation axial planar of minor foldswith dextral asymmetry. The presence of a stretching lineation parallel to theD2 fold axes is related to a top-to-the-north sense of shearing in a context of regional extension. The oldestmeterscaleD1 folds are developed in suitable greywacke–pelite alternations and consist of tight folds with chevron andsimilarmorphologies, axes plunging gently toward N20°E, and a continuous S1 axial planar foliation. The essentialcharacteristic of the D1 deformation event is depicted by a set of west-vergent folds with reverse limbs less than2 kmin wavelength, that are affected in their lower part by the generalised presence of the regional S2 foliation.The age of D2 and D1 structures is notwell constrained. The diabase dykes intruding the low-grade turbidites cutthe D1 folds and their field relationships suggest that they were emplaced at the end of the D2 shearing eventand prior to the upright D3 Variscan folds. Zircon grains obtained from one of the diabase dykes were analysedfor U–Pb at the SHRIMP-RG facility at Stanford University. An age of c. 510 Ma, based on the analysis of 31individual zircon grains, is interpreted to date the crystallization of the Ares dyke. The tectonic and magmaticevolution of the top turbiditic series of the Órdenes Complex is tentatively related to the dynamics of a peri-Gondwanan arc developed during active subduction beneath Gondwana and suggests: (1) accretion beneath thearc during west-vergent (present coordinates) nappe development (D1); (2) extension of the arc during top-tothe-north shearing (D2); and (3) final intrusion of the diabasic dykes into an intra-arc turbiditic series. Thisevolution spans the end of volcanic arc activity and the onset of the opening of the Rheic Ocean.
PB Elsevier Science B. V., Amsterdam
SN 1342-937X
YR 2009
FD 2009
LK https://hdl.handle.net/20.500.14352/49777
UL https://hdl.handle.net/20.500.14352/49777
LA eng
DS Docta Complutense
RD 22 abr 2025