scholarly journals Two-step obduction of the Porvenir serpentinites: A cryptic Devonian suture in SW Iberian Massif (Ossa-Morena Complex)

2021 ◽  
Author(s):  
Rubén Díez Fernández ◽  
Jerónimo Matas ◽  
Ricardo Arenas ◽  
Luis Miguel Martín-Parra ◽  
Sonia Sánchez Martínez ◽  
...  
Keyword(s):  
Continental Crust ◽  
Upper Mantle ◽  
Suture Zone ◽  
Lower Plate ◽  
Late Devonian ◽  
Iberian Massif ◽  
Step Process ◽  
Nw Iberia ◽  
Thrust System ◽  
Tectonic Slice

ABSTRACT The Porvenir serpentinites are an ∼600-m-thick body of meta-peridotites exposed in SW Iberia (Variscan Orogen). The serpentinites occur as a horse within a Carboniferous, out-of-sequence thrust system (Espiel thrust). This thrust juxtaposes the serpentinites and peri-Gondwanan strata onto younger peri-Gondwanan strata, with the serpentinites occupying an intermediate position. Reconstruction of the pre-Espiel thrust structure results in a vertical juxtaposition of terranes: Cambrian strata below, Porvenir serpentinites in the middle, and the strata at the footwall to the Espiel thrust culminating the tectonic pile. The reconstructed tectonic pile accounts for yet another major thrusting event, since a section of upper mantle (Porvenir serpentinites) was sandwiched between two tectonic slices of continental crust (a suture zone sensu lato). The primary lower plate to the suture is now overlying the upper plate due to the Espiel thrust. Lochkovian strata in the upper plate and the Devonian, NE-verging folds in the lower plate suggest SW-directed accretion of the lower plate during the Devonian, i.e., Laurussia-directed underthrusting for the closure of a Devonian intra-Gondwana basin. Obduction of the Porvenir serpentinites was a two-step process: one connected to the development of a Devonian suture zone, and another related to out-of-sequence thrusting that cut the suture zone and brought upward a tectonic slice of upper mantle rocks hosted in that suture. The primary Laurussia-dipping geometry inferred for this partially obducted suture zone fits the geometry, kinematics, and timing of the Late Devonian suture zone exposed in NW Iberia and may represent the continuation of such suture into SW Iberia.

scholarly journals Tectonostratigraphy of the Mérida Massif reveals a new suture zone exposure in SW Iberia

2020 ◽  
Author(s):  
Rubén Díez Fernández ◽  
Ricardo Arenas ◽  
Esther Rojo-Pérez ◽  
Sonia Sánchez Martínez ◽  
José Manuel Fuenlabrada
Keyword(s):  
Continental Crust ◽  
Root Zone ◽  
Suture Zone ◽  
Variscan Orogeny ◽  
Continental Lithosphere ◽  
Iberian Massif ◽  
Isotopic Data ◽  
Structural Position ◽  
Cadomian Orogeny ◽  
Paleozoic Rocks

Abstract. Dividing a crystalline basement into tectonostratigraphic units, along with the recognition of the nature of their boundaries (primary vs. tectonic), are essential steps to identify major tectonic slices involved in orogeny. The Neoproterozoic and Paleozoic rocks of the Mérida Massif (SW Iberia) have been grouped into five tectonostratigraphic units according to their structural position, continental or oceanic crust affinity, and equivalent tectonometamorphic evolution. Each unit is separated from the rest ones by either crustal-scale thrusts and/or extensional detachments. The lowermost unit (Magdalena Gneisses; lower plate) has continental crust affinity, and rest below a variably strained and metamorphosed mafic-ultramafic ensemble, referred to as the Mérida Ophiolite (suture zone). The Neoproterozoic Montemolín Formation of the Serie Negra Group constitutes a unit with continental crust affinity (Upper Schist-Metagranitoid Unit; upper plate) located on top of the Mérida Ophiolite. A carbonate-rich succession (Carija Unit) occupies the uppermost structural position. Structural and isotopic data suggest that the suture zone depicted by the Mérida Ophiolite and the tectonic piling and main foliation of the Neoproterozoic and Cambrian units were formed during the Cadomian Orogeny. Superimposed shortening during the late Paleozoic formed a train of upright to NE-verging folds and thrusts that affected the Cadomian suture zone and juxtaposed it onto Ordovician strata (fifth tectonostratigraphic unit) during the Variscan Orogeny. Cenozoic contraction during the Alpine Orogeny formed SW-directed thrusts in an intraplate setting. The Mérida Ophiolite represents a new Cadomian suture zone exposure of the Iberian Massif, but its root zone is yet to be identified. This suture zone exposure seems to share a far-travelled nature with other Cadomian and Variscan suture zone exposures in Iberia, making the latter a piece of continental lithosphere built at the expense of allochthonous terranes transferred inland from peri-Gondwana onto mainland Gondwana, both during the Neoproterozoic-Cambrian and the Devonian-Carboniferous.

Variscan Suture Zone and Suspect Terranes in the NW Iberian Massif: Allochthonous Complexes of the Galicia-Trás os Montes Zone (NW Iberia)

2019 ◽  
pp. 99-130 ◽  
Author(s):  
J. R. Martínez Catalán ◽  
J. Gómez Barreiro ◽  
Í. Dias da Silva ◽  
M. Chichorro ◽  
A. López-Carmona ◽  
...  
Keyword(s):  
Suture Zone ◽  
Iberian Massif ◽  
Nw Iberia

Rift inheritance controls the switch from thin- to thick-skinned thrusting and basal décollement re-localization at the subduction-to-collision transition

2021 ◽  
Author(s):  
Stefano Tavani ◽  
Pablo Granado ◽  
Amerigo Corradetti ◽  
Giovanni Camanni ◽  
Gianluca Vignaroli ◽  
...  
Keyword(s):  
Sedimentary Cover ◽  
Complete Removal ◽  
Lower Plate ◽  
Accretionary Wedge ◽  
Convergent Margins ◽  
Middle Crust ◽  
Rifted Margins ◽  
Thrust System ◽  
Structural Levels ◽  
Rifted Margin

In accretionary convergent margins, the subduction interface is formed by a lower plate décollement above which sediments are scraped off and incorporated into the accretionary wedge. During subduction, the basal décollement is typically located within or at the base of the sedimentary pile. However, the transition to collision implies the accretion of the lower plate continental crust and deformation of its inherited rifted margin architecture. During this stage, the basal décollement may remain confined to shallow structural levels as during subduction or re-localize into the lower plate middle-lower crust. Modes and timing of such re-localization are still poorly understood. We present cases from the Zagros, Apennines, Oman, and Taiwan belts, all of which involve a former rifted margin and point to a marked influence of inherited rift-related structures on the décollement re-localization. A deep décollement level occurs in the outer sectors of all of these belts, i.e., in the zone involving the proximal domain of pre-orogenic rift systems. Older—and shallower—décollement levels are preserved in the upper and inner zones of the tectonic pile, which include the base of the sedimentary cover of the distal portions of the former rifted margins. We propose that thinning of the ductile middle crust in the necking domains during rifting, and its complete removal in the hyperextended domains, hampered the development of deep-seated décollements during the inception of shortening. Progressive orogenic involvement of the proximal rift domains, where the ductile middle crust was preserved upon rifting, favors its reactivation as a décollement in the frontal portion of the thrust system. Such décollement eventually links to the main subduction interface, favoring underplating and the upward motion of internal metamorphic units, leading to their final emplacement onto the previously developed tectonic stack.

Restoration of the Caledonian Baltoscandian margin from balanced cross-sections: the problem of excess continental crust

1987 ◽  
Vol 78 (3) ◽  
pp. 197-217 ◽  
Author(s):  
R. A. Gayer ◽  
A. H. N. Rice ◽  
D. Roberts ◽  
C. Townsend ◽  
A. Welbon
Keyword(s):  
Continental Crust ◽  
Cross Section ◽  
Continental Margin ◽  
Cross Sections ◽  
Branch Line ◽  
Norwegian Coast ◽  
Thrust Sheets ◽  
Thrust System ◽  
Basement Ridge ◽  
The Baltic

ABSTRACTConsideration of six balanced cross-sections through parts of the Finnmark Caledonides, N Norway indicates that shortening varies between 25% and 75%. A restored long cross-section across the width of the orogen, constructed with the aid of a branch line map, demonstrates a foreland propagating thrust system, with earlier formed more internal metamorphic nappes thrust SE 330 km under ductile conditions and then carried piggyback ESE a further 296 km on later brittle thrust sheets. Total shortening is 78·7% with a translation of the most internal thrust sheet of 626 km.The restored section suggests that: (1) the rate of propagation of deformation from hinterland to foreland is c. 2·27 cm y−1; (2) incorporation of basement into the nappes resulted from inversion of extensional faults formed during Iapetus rifting; (3) during rifting a Finnmark basement ridge separated a 220 km wide southeasterly Gaissa basin from the passive Iapetus continental margin which was at least 423 km wide; (4) the Finnmark Caledonides resulted from a continent-microcontinent collision which obducted continental crust at least 600 km across the Baltic margin; and (5) the Caledonian Baltoscandian margin prior to Iapetus suturing extended at least 400 km W of the Norwegian coast. On a Bullard reconstruction this overlaps with Laurentian rocks in Greenland. The excess continental crust is accounted for by shortening of the Baltoscandian margin during collision.

The structure of a major suture zone in the SW Iberian Massif: the Ossa-Morena/Central Iberian contact

2001 ◽  
Vol 332 (1-2) ◽  
pp. 295-308 ◽  
Author(s):  
J.F. Simancas ◽  
D.Martı́nez Poyatos ◽  
I. Expósito ◽  
A. Azor ◽  
F.González Lodeiro
Keyword(s):  
Suture Zone ◽  
Iberian Massif
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