humaOhiada

1

surica and the Massif Central to the Bohemian Massif (IberianCzech [IC] belt), and

century with interpretations of its origin varying from vertical tectonics fauna and paleolatitudes (Tait et al., 2000; Robardet, 2003), and these

Gondwana Research 17 (2010) 306316

Contents lists available at ScienceDirect

Gondwana

w.through geosynclinal theory to plate tectonics (Kossmat, 1927; Bardet al., 1980; Matte, 1986). Using the plate tectonic paradigm, vestiges ofPaleozoic oceans have been inferred from the presence of dismemberedophiolitic rocks, some metamorphosed at high pressures (HP) and lowto high temperatures, preserved as remnants along presumed sutures.

Several such sutures have been recognized with the Variscanorogen (Fig. 1a), each of which has been attributed to the closure of anocean. However, one belt in particular has had various interpretations.This belt (#4 in Fig 1a), which includes Siluro-Devonian high-pressure(HP) rocks, extends from the CordobaCoimbra Shear Zone to Galiciain Iberia, and then from Armorica and the Massif Central in France tothe Black Forest and Bohemian Massif of Germany and the Czech

rocks show no evidence of active tectonism (Shelley and Bossire,2000, 2002). Indeed, these relationships are inconsistent with theinterpretation of the belt as a simple suture zone.

In this paper, we re-examine the IC belt and propose a new modelfor its origin that, we believe, better accounts for these relationships.The model involves subduction erosion along the northern margin ofGondwana and the extrusion of subducted HP rocks derived from theRheic Ocean into the overriding (Gondwanan) plate.

2. BackgroundRepublic. The IberianCzech (IC) belt, as it isvariety of arc, oceanic and passive marginvariously been attributed to an oceanic sutudextrally displaced slice of the Rheic Ocean

Corresponding author. Tel.: +52 555 622 4290.E-mail address: duncan@servidor.unam.mx (J.D. Kep

1342-937X/$ see front matter 2009 International Adoi:10.1016/j.gr.2009.08.007een studied for almost a2002). However, a difculty with these models is the fact that rocks ofthe same age on either side of the IC belt preserve similar GondwananThe Variscan orogenic belt of Europe has bKeywords:Variscan orogenHigh pressureExtrusionGalicianMassif CentralMoldanubian

1. Introductiongenerally been interpreted to be either: (a) a suture of the Galician, South Brittany, Massif Central andMoldanubian ocean; (b) a nappe rooted to thenorth in theRheicOcean; or (c) the result of post-collisional strike-slip shufing of theGondwananmarginduringwhich a slice of theRheicOceanwas inserted into theGondwananmargin. We agree with a Rheic Ocean origin, but propose that the IC belt represents a pre-collisional part of theGondwanan continentaloceanic margin that was removed by subduction erosion, underwent HP metamorph-ism, and was then extruded into the overlying Gondwanan plate. This model explains: (i) the lack ofpaleolatitudinal and faunal differences across the IC belt, (ii) the juxtaposition of active margin tectonics withinsynchronous passive margin sequences, and (iii) the pre-collisional age of most of the HP metamorphism. Thecomplete rangeofHP rocks in the ICbelt, fromblueschist tohot eclogites, indicates that previous correlationswithB- and A-type subduction, respectively, cannot be sustained.

2009 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

2000, 2002), and an allochthonous nappe (Martnez Cataln et al.,Received in revised form 24 August 2009Accepted 26 August 2009Available online 9 September 2009includes arc and periarc rocks, MORB and supra-subduction ophiolites, and passive margin sequences. It hasReceived 11 May 2009 Shear Zone) through ArmorThe high-pressure IberianCzech belt in tupper (Gondwanan) plate?

J. Duncan Keppie a,, R. Damian Nance b, J. Brendan Ma Departamento de Geologa Regional, Instituto de Geologa, Universidad Nacional Autnob Department of Geological Sciences, 316 Clippinger Laboratories, Ohio University, Athens,c Department of Earth Sciences, St. Francis Xavier University, Antigonish, Nova Scotia, Cand Department of Geology, St. Mary's University, Halifax, Nova Scotia, Canada B3H 3C3e Department of Earth Sciences, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4J

a b s t r a c ta r t i c l e i n f o

Article history: A Siluro-Devonian, high-pres

j ourna l homepage: wwhere termed, includes aassemblages, and hasre (e.g. Matte, 2001), a(Shelley and Bossire,

pie).

ssociation for Gondwana Research.rphy c, Jaroslav Dostal d, James A. Braid e

de Mxico, 04510 Mxico D.F., Mexicoo 45701, USAB2G 2W5

e (HP) belt (the IberianCzech or IC belt) extends from Iberia (CordobaCoimbrae Variscan orogen: Extrusion into the

Research

e lsev ie r.com/ locate /grWithin the Variscan orogenic belt of Europe (Fig. 1a and b), vemajor and twominor Paleozoic sutures havebeen identied (McKerrowet al., 2000; Franke, 2000; Stampi and Borel, 2002). These suturesseparate the major continents of Laurentia, Baltica and Gondwana, aswell as a number of microcontinental blocks that include Avalonia,northern and southern Armorica, the latter synonymous with the Hunterrane, and the Cimmerian terranes (Stampi and Borel, 2002).According to Stampi and Borel (2002) and Murphy et al. (2009a) all

Published by Elsevier B.V. All rights reserved.

307J.D. Keppie et al. / Gondwana Research 17 (2010) 306316of these terranes are ribbon continents of Gondwanan origin, Avaloniaseparating from Gondwana in the Early Ordovician, Armorica/Hun inthe Late Silurian, and Cimmeria during the Middle Permian. In theirwake, oceans formed between Gondwana and the ribbon continents,the Rheic, Paleotethys and Neotethys oceans, respectively. The vemajor sutures include:

1. the Iapetus suture marking the closure of a CambrianOrdovician/mid-Silurian ocean between Laurentia and BalticaAvalonia,

2. the Tornquist (or trans-European) suture delineating a CambrianOrdovician ocean between Avalonia and Baltica,

3. the Rheic suture delineating an OrdovicianEarly Devonian(Emsian) ocean between Laurussia (Avalonia) and the Armorica/Hun terrane,

Fig. 1. Maps of the Variscan orogen in Europe: (a) Paleozoic sutures (modied after McKershowing locations of cross-section in Figs. 2 and 3.4. the CrdobaGalicianLigerianMassif CentralMoldanubian su-ture (here named the IberianCzech or IC belt) delineating anOrdovicianDevonian ocean between northern and southernArmorica/Hun, and

5. the Paleotethys suture delineating a Late SilurianLate Carbonifer-ous ocean between the Cimmerian terranes and Gondwana.

The two minor sutures are limited to the Bohemian Massif andinclude:

(a) the Rheno-Hercynian suture marking a short-lived MiddleDevonian ocean between Laurussia and Saxo-Thuringia, and

(b) the Saxo-Thuringian suture marking an OrdovicianEarlyDevonian ocean between Saxo-Thuringia and Tepla-Barrandia(northern Bohemia).

row et al., 2000, Fig. 1), and (b) Variscan zones (modied after Murphy et al., 2009b)

308 J.D. Keppie et al. / Gondwana Research 17 (2010) 306316This paper focuses on the IC belt (#4) and its potential connectionto the Rheic suture (#3). Several origins have been proposed for the ICbelt (Figs. 2 and 3) and include: (a) an oceanic suture (e.g. Matte,2001); (b) a dextrally strike-slipped slice of the Rheic Ocean (Shelleyand Bossire, 2000, 2002); and (c) an allochthonous nappe (MartnezCataln et al., 2002). These models are summarized below.

2.1. Oceanic suture

The traditional plate tectonic interpretation implies that theophiolitic and HP rocks of the IC belt were extruded along thesubduction channel and so dene a suture that marks the remnants ofan ocean. This ocean has been variously designated the Galician ocean(Fig. 2b: Simancas et al., 2002), the Ligerian or southern Brittanyocean (Matte, 2001), the Massif Central ocean (Fig. 3b: Matte, 1986),and the Moldanubian or Tepla ocean (Fig. 3d: Franke, 2000; Matteet al., 1990).

2.2. Dextrally strike-slipped slice of the Rheic Ocean

Shelley and Bossire (2000, 2002) explained the incongruitybetween HP IC belts active in the Silurian through theMiddle Devonianin France and their contemporaneous passive margin neighbours(Keppie andDallmeyer, 1989) in terms of post-360 Madextral shufingof terranes (Fig. 2c). In the context of the Late DevonianCarboniferousend-run of Laurentia around northern Gondwana suggested bypaleomagnetic data (Dalziel, 1997), a N2000 km slice of the southernRheic Ocean is trapped between the autochthonous and allochthonousNWAfrican margin, but the origin of the HP rocks is unclear. A modernanalogue of this process may have occurred in western North Americawhere collision of the East Pacicmid-oceanic ridgewith the trench hasresulted in opening the Gulf of California. This has produced thefollowing west-to-east sequence: Pacic Ocean, Baja California (a sliceof the Mexican margin), Gulf of California (small ocean basin), and thecontinental margin of Mexico. Such a mechanism would allow forpreservation of two slices of theRheicOcean, one inboard (theGalicianMassif CentralMoldanubian suture analogous to the Gulf of California)between the northern and southern Hun terranes, and the other alongthe Rheic Ocean suture (equivalent to the Pacic Ocean). As this motionwould have involved pieces of the Gondwanan margin and is roughlyparallel to paleolatitude, there would be no faunal or paleomagneticdistinction between different elements of the Hun terrane.

However, this mechanism is inconsistent with several observations:(i) dated dextral motion along the IC belt post-dates, rather thanpredates, closure of the Rheic Ocean estimated to have occurred at ca.355 Ma (Franke, 2000; Matte, 2001; Shelley and Bossire, 2000;Winchester et al., 2002); (ii) a trapped sliver of the Rheic Oceanwould likely have undergone low-grade metamorphism, not theobserved HP metamorphism that is generally attributed to subduction(Maruyama et al., 1996; Ernst et al., 1997); (iii) the Variscan orogen andthe IC belt terminate against the linear, NWSE Tornquist line andBaltica (Fig. 1), which severely limits the amount of post-collisional,orogen-parallel, relative displacement between the southern andnorthern Hun terrane; and (iv) a mid-ocean ridgetrench collisionalong the southernmargin of the RheicOceanhas yet to bedocumented.

The HP IC belt could be a ca. 4000 km long piece of the Rheic suture(1000 km in both France and Iberia, to which must be added anadditional ca. 2000 km to include the correlative HP Moldanubianrocks of the southern Bohemian Massif) if one takes the reconstruc-tions of Shelley and Bossire (2002) as occurring after Avalonian/Huncollision. However, the Rheic suture between Avalonia and the Hunterranes, even though it is partly covered by younger strata, appears tobe relatively intact and continuous, and there is no evidence of a4000 km long, missing segment (Matte et al., 1990; Franke, 2000;Winchester et al., 2002; Stampi and Borel, 2002). Furthermore,

paleomagnetically constrained paleolatitudes for Laurentia andGondwana are compatible with both the end-run model of Dalziel(1997) and the orthogonal closing of the Rheic Ocean of Stampi andBorel (2002), and the latter model has limited dextral motionbetween Laurussia and Gondwana. In addition, faunas from both thenorthern and the southern Armorica/Hun terrane are indistinguish-able from those of NW African Gondwana throughout the Devonian(Robardet, 2003) (Fig. 1a), which is compatible with both end-runand orthogonal models.

2.3. Allochthonous nappe

Martnez Cataln et al. (2007) and Arenas et al. (2007) proposedthat Rheic Ocean allochthons in NW Iberia were thrust southwardsout of the Rheic suture over Gondwana and subsequently caught up inorogen-parallel dextral shear zones (Fig. 2d and e). This resulted intwo ophiolitic belts, the Rheic suture in the north and the IC belt ofdextrally sheared allochthons to the south. In this model, theophiolites of the IC belt originated in the Rheic Ocean, removing theneed for a separate ocean along the IC belt. This model suggests thatthe HP rocks of the IC belt were produced by subduction beneathAvalonia on the northern Rheic margin (Fig. 2d), and weresubsequently thrust over Iberia upon closure of the Rheic Ocean.However, the model cannot account for the presence of NW Africandetrital zircons in the upper units in the Galician (NW Iberia)allochthon (Fernndez-Surez et al., 2003).

An additional mechanism that may account for the presence of HPIC rocks between the northern and southern Hun terrane is that of theextrusion of subducted HP rocks into the upper plate abovesubduction zones (Figs. 2 and 3). Such a mechanism has beenproposed for the Paleozoic Acatln Complex of southern Mexico,where forearc and passive margin rocks were removed by subductionerosion, subducted to depths of 50 km to produce blueschist andeclogite, and then extruded into the upper plate (Keppie et al., 2008).It may also apply to various segments of the modern Andes (Keppieet al., in press). A similar scenario has been proposed for Mesozoic HProcks that have been obliquely extruded across the Triassic Stikinia/Quesnellia arc (Dostal et al., 2009). This mechanism has not beenassessed for its potential application to the HP IC belt in the Variscanorogen and forms the topic of this paper.

3. General distinctions between inter-plate and intra-plate HP rocks

HP rocks can be divided into blueschists (HPLT = high pressurelow temperature) and eclogites (HPHT = high pressurehightemperature) (Fig. 4). The eclogite stability eld has been subdividedinto cold and hot eclogite types at the quartzcoesite boundary (Liouet al., 2004) (Fig. 3). Hot eclogites are generally termed ultrahighpressure rocks (UHP), the stability eld of which is further subdividedat higher pressures by the graphitediamond transition (Liou et al.,2004). Thesemetamorphicelds have generally been linked to specictectonic settings (Ernst, 2009; Zhang et al., 2009): (i) blueschists areusually synonymous with inter-plate, B-type subduction and requirecold upper mantle geotherms that are only found today where anoceanic plate is thrust beneath an oceanic or continental plate, asituation characteristic of Pacic-type orogens; and (ii) hot UHPeclogites are synonymouswith A-type subductionwhere a continentalplate is thrust beneath another continental plate, a scenario typical ofcontinentcontinent collisional, Alpine-type orogens marking anoceanic suture (Maruyama et al., 1996; van Keken et al., 2002; Liouet al., 2004; Stern, 2005). Cold eclogites may result from either slowexhumation of blueschists or retrogression of hot eclogites, and somayform in either Pacic- or Alpine-type orogens. All of these HP facies areeither Neoproterozoic or Phanerozoic in age: blueschists are youngerthan 800 Ma and are associated with subduction mlanges, whereasUHP rocks are younger than 630 Ma and are generally found with

continental crust (Stern, 2005). Hence, blueschists are commonly

Fig. 2. Iberia: (a) cross-section showing interpretations presented in this paper (in italics); (b) Galician and Rheic Ocean model of Simancas et al. (2002); (c) post-collisional, strike-slip model of Shelley and Bossire (2002); and (d and e) allochthonous nappe followed by strike-slip displacement model of Martnez Cataln et al. (2007).

309J.D. Keppie et al. / Gondwana Research 17 (2010) 306316

Fig. 3. France and Bohemia: (a) cross-section across the Massif Central-Ardennes (after Matte, 1986) with interpretations presented in this paper (in italics); (b) Massif Central andRheic Ocean model of Matte (1986); (c) cross-section across the Bohemian Massif (after Franke, 2000) with interpretation presented in this paper (in italics); (d) Moldanubian andRheic Ocean model of Franke (2000); (e) extrusion along Moldanubian Ocean suture model of Medaris et al. (2006); and (e) post-collisional folding and extrusion model ofSchulmann et al. (2005).

310 J.D. Keppie et al. / Gondwana Research 17 (2010) 306316

process occurs along Pacic-type margins where oceanic lithosphere isbeing subducted beneath either a continental or an oceanic plate (Cliftand Vannucchi, 2004). Numerical experimental data suggest thatsubduction erosion occurs during episodes of at-slab subduction,which alternate with moderate-steep subduction during which accre-tionary prisms and arcs form (Keppie et al., in press). Several types ofsubduction erosion occur: (i) steady erosion involving gradual ablationof the upper plate (Von Huene et al., 2004; Keppie et al., in press);(ii) development of a convection cell in the forearcarc region of theupper plate, as a result ofwhichmaterial is removed from the baseof theforearc, subducted, and then extruded into the upper plate (Stckhertand Gerya, 2005; Gerya and Stckhert, 2006; Castro and Gerya, 2007);and (iii) unsteady erosion involving sudden removal of large blocks ofthe upper plate (Keppie et al., in press). All of these processes removesome or all of the forearc and arc, which are transferred to thesubducting plate. If the removed material is oceanic lithosphere, its

facilitated by extension. Numericalmodels show that the latter scenario

311J.D. Keppie et al. / Gondwana Research 17 (2010) 306316associated with ophiolites, subduction mlanges (accretionary com-plexes), tonalitetrondjhemitegranitoid belts, and volcanic arcs,whereas UHP rocks are generally found as eclogite and garnetperidotite lenses in continental lithologies, and coeval arc magmatismis absent (Liou et al., 2004). Extrusion of all HP rocks requires a thrustlower boundary and a normal fault upper boundary (Liou et al., 2004;

Fig. 4. Pressuretemperature paths for the highest pressure units in the IC belt:CordobaCoimbra shear zone (after Dallmeyer and Tucker, 1993; Ordoez-Casado,1998; Moita et al., 2005; Pereira and Apraiz, 2006), Malpica-Tui (after Santos Zaldueguiet al., 1995; Rodrguez et al., 2003; Llana-Fnez et al., 2002); Galicia (after Peucat et al.,1990; Dallmeyer and Gil Ibarguchi, 1990; Dallmeyer et al., 1991; Dallmeyer et al., 1997;Daz Garca et al., 1999; Pin et al., 2002), Baie d'Audierne (after Lucks et al., 2002), Ile deGroix (after Bosse et al., 2005 and references therein), Massif Central (after Lardeauxet al., 2001 and references therein), Moldanubuan (after Schulmann et al., 2005;Medaris et al., 2006, and references therein).Santosh et al., 2009).These HP and UHP rocks are generally inferred to have been

extruded up the subduction channel and so are taken to mark thevestiges of an ocean basin (e.g. Ernst et al., 1997; Warren et al., 2008).However, numerical modeling has recently shown that HP rocks canalso be extruded into the upper plate (Stckhert and Gerya, 2005;Gerya and Stckhert, 2006; Castro and Gerya, 2007; Keppie et al., inpress). In this model, material may be removed from the upper plateby subduction erosion, transferred to the subducting plate, and thenreturned to the upper plate by underplating, following which it isextruded into the upper plate (Keppie et al., in press).

This process has been used to account for Paleozoic HP rocks in theAcatln Complex of southern Mexico (Keppie et al., 2008), where itoccurred in a Pacic-type orogen with an association of bothblueschists and cold eclogites extruded into the upper plate.Geochemical and geochronological data from the Acatln Complexindicate that much of the HP continental lithologies were derivedfrom the rift-passive margin sequence of the upper plate with minorupper plate arc and MORB oceanic rocks (Keppie et al., 2008).Extrusion of these HP rocks into the upper plate means that the rockson either side of them are similar and the HP rocks do not mark anoceanic suture as is generally assumed (e.g. Ortega-Gutirrez, 1981).

In view of this new model, it is important to have criteria fordistinguishing HP rocks extruded along the subduction channel fromthose extruded into the upper plate, i.e. inter- versus intra-plateextrusion. In general, the two models share many of the samecharacteristics of Pacic- and Alpine-type orogens, however, there area few criteria that can distinguish between them.

One criterion involves the identication of material removed fromthe upper plate by subduction erosion. A modern example of thistakes ca. 1520 my to complete (c.f. Camacho et al., 2005), startingwithnear-surface material that is rst subducted to ca. 70 km synchronouswith 400600 km of lower plate subduction and then returned to thesurface by extrusion. Thus, the following criteria can be used to identifyextrusion of HP rocks into the upper plate following subduction erosion(Table 1): (i) a missing forearcarc is typical of the rst stage of thesubduction erosion/extrusion cycle; (ii) geochemical and geochrono-logical data may allow correlation of the geological record of the HPprotoliths with units in the upper plate; (iii) extrusion of the HPlithologies into the upper platemeans that the rocks oneither side of theHPbelt are similar, rather than representing distinct terranes; (iv) giventhe ca. 1520 my time frame for the subduction erosion/extrusion cycle,the subducting ocean needs to be at least 400600 km wide (andprobably much wider given that subduction erosion alternates withsubduction accretion; Clift and Vannucchi, 2004) and so likely separatesterranes with distinct terrestrial and shallow marine fauna, and, if theocean is roughly parallel to latitude, distinct paleomagnetic signatures;(v) subduction erosion occurs before closure of the ocean by (micro)continentcontinent collision; and (vi) episodes of subduction erosionmay be accompanied by an increase in the light/heavy rare earth ratio inassociated arc volcanic rocks (Kay et al., 2005).

4. Application to Variscan orogen

In this section, the criteria listed in Table 1 are applied to the majorVariscan sutures lying south of those of the Iapetus and the Tornquist

Table 1Distinctions between inter- and intra-plate extruded HP rocks.

Inter-plate HP rocks(Pacic and collision-type)

Intra-plate HP rocks

Extruded HP slice is bounded by thrust below and listric normal aboveExtrusion along subduction channel Extrusion into upper platePacic-type: pre-collisional extrusion Pre-collisional extrusionCollision-type: syn-collisional extrusion

HP belt separates distinct terranes Rocks similar across HP beltHP belt separates distinct faunal provinces Fauna similar across HP beltPaleomagnetic distinction possible No paleomagnetic distinction(U)HP rocks mainly from subducting plate (U)HP of both plates: upperN lowerCollision-type: passive margin+cont. basement

Upper: passive marginarc/periarc

Pacic-type: ophiolite+OIB+accretionary cx

Lower: ophiolite+OIBconversion toeclogite atdepthsN70 kmwould encourage it to sinkdeepinto themantle.However, if the removedmaterial is continental crust orinterleaved slices of continental and oceanic crust, its buoyancy resistsdeep subduction, and much of it is returned to the surface by extrusioneither along the subduction channel or into the upper plate, the latter

312 J.D. Keppie et al. / Gondwana Research 17 (2010) 306316oceans (#35 in Fig. 1a). Faunal and paleomagnetic paleolatitudinaldistinctions are clear for theRheic andPaleotethys sutures (#3 and#5 inFig. 1a: McKerrow et al., 2000; Tait et al., 2000), however theseparameters are absent for the hypothesized Rheno-Hercynian (#a),Saxo-Thuringian (#b) and IC (#4) sutures. Indeed, the lack of faunal andpaleomagnetic distinctions across the latter lines led Tait et al. (1997) tointroduce the term, Armorican Terrane Assemblage, for Bohemia, Saxo-Thuringia, Franconia, Iberia and Armorica (Tait et al., 1997). Thisassemblage is consistent with a recent plate tectonic synthesis byStampi and Borel (2002), who coined the term Hun terrane toencompass the Armorican Terrane Assemblage, and suggested that themain oceans were IapetusTornquist, Rheic, and Paleotethys with littleor noevidence for theRheno-Hercynian, Saxo-Thuringianand ICoceans.The Gondwanan lithostratigraphy and faunal afnities of the Armori-can/Hun terrane throughout the late Paleozoic suggest that it representsthe margin of northwest Africa (Robardet, 2003). The history of theRheic Ocean is inferred to span the Ordovician (Arenig)Late Devonian(Famennian) (ca. 480360 Ma) with subduction starting during theLlandoverian and culminating in collision between the Armorican/Hunterrane and Avalonia in the Late Devonian at ca. 360 Ma (McKerrow etal., 2000; Stampi and Borel, 2002), with small remnants surviving intothe Carboniferous (Azor et al., 2008). The demise of the Rheic Ocean ledto the initiation of subduction along the northernmargin of Paleotethysduring the LateDevonian (ca. 360 Ma) andwas followedduring the LateCarboniferous (ca. 320 Ma) by LaurussiaGondwana collision (Stampiand Borel, 2002).

4.1. The IberianCzech (IC) belt

The high-pressure (HP) ophiolitic and associated rocks lying alongthe IC belt (#4 in Fig. 1a) are generally interpreted to mark a suture ofan OrdovicianSilurian ocean that closed during the Devonian (e.g.Franke, 2000; Matte, 1986), implying that the HP rocks have beingextruded back up the subduction channel. The earliest structuralfabrics associated with extrusion have generally been stronglyoverprinted by later Variscan deformation making it difcult toascertain the nature of the original extrusional contacts bounding theHP rocks. However this overprinting is a complexity that is commonto both inter-plate and intra-plate extrusion zone models (Table 1).

4.1.1. IberiaIn northwestern Spain, HP rocks of the IC belt occur as several

allochthonous slices (Galician/Tras-os-Montes allochthons) that havebeen thrust over passive margin units of the Central Iberian terrane(Fig. 1b) (Arenas et al., 2007; Martnez Cataln et al., 2007). Thestructural stack comprises the following units: (i) Somosas mlangealong the sole thrust; (ii) basal unit consisting of rocks of theOrdovician (480460 Ma) rifted NW African margin that underwentlowhigh grade metamorphism dated at 380370 Ma; (iii) Lowerophiolitic allochthon composed of ca. 500 Ma oceanic rocks thatrecord HP/LT through amphibolite to greenschist facies metamor-phism with cooling through ca. 400 C by 3637 Ma; (iv) Upperophiolitic allochthon made up of ca. 395 Ma supra-subduction zoneoceanic rocks that underwent HP cold eclogitic metamorphism at ca.391376 Ma and cooled through ca. 550 C by 390376 Ma (Fig. 4);and (v) Upper slices composed of b480 Ma igneous and metasedi-mentary rocks that underwent HP/HT-intermediate pressurelow-grademetamorphism at ca. 400380 Ma. The lower parts of the nappepile have inverted metamorphic gradients and thrusts, whereas theupper parts record a right-way-up-metamorphic gradient withdetachment faults (Arenas et al., 2007; Martnez Cataln et al.,2007), a pattern typical of extrusion (Ernst et al., 1997; Keppie et al.,2008). The earliest post-collisional thrusting verges towards the east(Martnez Cataln et al., 2007), and was followed by Permian bending

of originally NS trending structures that accentuated the Iberianoroclinal arc (Kollmeier et al., 2000; Weil et al., 2000; Gutirrez-Alonso et al., 2003, 2008).

Current models suggest that the Galician/Tras-os-Montes alloch-thons originated either in the Galician Ocean (Fig. 2b: Simancas et al.,2002), or in the Rheic Ocean (Fig. 2d: Arenas et al., 2007; MartnezCataln et al., 2007), before being subjected to post-collisional, dextralstrike-slip displacements along the Variscan orogen (Fig. 2c and e:Shelley and Bossire, 2002; Simancas et al., 2002; Martnez Catalnet al., 2007; Simancas et al., 2009). In the Galician Ocean model, theorigin of the Galician/Tras-os-Montes allochthons is attributed toclosure of a small ocean basin on the Gondwananmargin between theOssa Morena and Central Iberian zones preserved as the CrdobaCoimbra Shear Zone (Simancas et al., 2002, 2009). On the other hand,in the Rheic Ocean model, the Lower units represent the Gondwananpassive margin, the ophiolitic units were derived from the RheicOcean, and the Upper units were deposited along the trailing marginof Avalonia on the northern border of the Rheic Ocean. Closure of theRheic Ocean, attributed to north-dipping subduction beneath Avalo-nia, led to extrusion along the subduction channel and obduction ofthe Galician/Tras-os-Montes allochthons over African Gondwana.

The latter model, however, is inconsistent with detrital zircon datafrom the Upper slices of the Galicia/Tras-os-Montes allochthons(Fernndez-Surez et al., 2003), which record only 480610 Ma,ca. 2 Ga and ca. 2.5 Ga ages typical of NW Africa, and contain no ca.1 Ga zircons typical of Avalonia (Keppie et al., 2003). Thus, theophiolitic rocks appear to be bounded both below and above byGondwanan rocks suggesting they were extruded into the NWAfricanGondwanan margin along an intra-plate extrusion zone before beingthrust eastwards over the Central Iberian part of Gondwana.

If this is the case, the root zone for the extruded rocks may be thesinistral, WNW-trending CrdobaCoimbra Shear Zone that alsoexposesHP rocks (Fig. 2a), a conclusion consistentwith that of Simancaset al. (2009). This shear zone was superimposed on an inheritedPrecambrian boundary between the Central Iberian Zone (autochtho-nous Gondwana), and the Neoproterozoic OssaMorena Zone consistingof a Neoproterozoic arc overlain by Lower Paleozoic, Gondwananpassivemargin rocks (Quesada, 1990; Pereira et al., 2007). Cold eclogitefacies metamorphism at 7.59.5 kb and 650750 C appears to haveoccurred during the Early Carboniferous (340370 Ma) associated withsinistral deformation and exhumation along the shear zone (Fig. 4)(Pereira et al., 2008).

This scenario begs another question: which ocean was beingsubducted beneath Iberia? The only candidate appears to be the RheicOcean, a remnant of which may be preserved along the northernmargin of the South Portuguese Zone. The South Portuguese andCentral Iberian zones are separated by a structurally complex zoneinterpreted to be an accretionary prism (Pulo de Lobo) (Braid et al.,this volume) (Fig. 2a). The South Portuguese Zone consists of UpperDevonian clastics rocks that are inferred to rest on an Avalonianbasement (De la Rosa et al., 2002). The complex between the SouthPortuguese and the Ossa Morena zones consists of (i) pre-LateDevonian, low-grade schists andMORB basalts (Pulo de Lobo), (ii) theca. 330340 Ma Beja Acebuches ophiolite (Azor et al., 2008) that wasmetamorphosed at amphibolite facies and cooled through ca. 550 Cby ca. 340 Ma (Dallmeyer et al., 1993), and (iii) the MouraCubito HPeclogites, alkalic and oceanic basalts, marbles and gneisses (Simancaset al., 2009). These rocks were deformed by oblique sinistral, SW-vergent thrusting during the Carboniferous. A positive gravityanomaly and seismic data indicate the presence of a dense, highlyreective layer in the middle crust beneath the Ossa Morena Zone(Fig. 2a) that appears to correlate with similar features in the uppercrust of the South Portuguese Zone (IGN, 1976; Palomeras et al.,2008). This layer is here interpreted as Rheic Ocean mac crustunderplating the Ossa Morena Zone that was extruded up along theCordobaCoimbra Shear Zone and thrust eastwards over the Central

Iberian Zone as the Galician/Tras-os-Montes allochthons (Fig. 2a).

313J.D. Keppie et al. / Gondwana Research 17 (2010) 3063164.1.2. ArmoricaMost authors connect the CrdobaCoimbra Shear Zone with the

composite Armorican shear zone (=South Brittany suture) across adextral NW-trending fault (Fig. 1b). The HP complex in the Armoricanshear zone consists of four HP belts ranging from blueschist tohot eclogite (Figs. 1b and 4) (Ile de Groix/Vendee blueschist andeclogite, Champtoceaux hot eclogite and granulite, Lanvaux prehnitepumpellyite, and Leon eclogite), in which the HP metamorphism hasbeen dated at ca. 365 Ma in Ile de Groix (Bosse et al., 2005), N360 Main Champtoceaux (Ballvre et al., 1994; Bosse et al., 1999; Lucks et al.,2002), and ca. 380 Ma in Leon (Peucat, 1986). The HP belts alternatewith fault-bounded blocks consisting of (Cambrian)OrdovicianUpper Devonian stable shelf sequences (Shelley and Bossire, 2000).Stratigraphy and faunal provinciality indicate that the stable faultblocks represent parts of the NW African Gondwanan margin(Robardet, 2003). The intense post-355 Ma dextral shearing undoubt-edly caused some shufing of these units, including reversing thepolarity of depositional environments from the proximal Gondwanansedimentation in central and northern Brittany to the distal sedimentsof southwestern France (Southern terrane) adjacent to the HP rocks(Shelley and Bossire, 2000), and produced ower structures (Matte,2001; Cartier et al., 2001). However, the pre-collisional HP metamor-phism is similar to that in Iberia, suggesting that the HP rocksrepresent extruded and overthrust portions of the subductioncomplex. Their presence within similar Gondwanan blocks with noindication of Avalonian remnants (only Gondwanan detrital zirconhave been reported from northern Brittany: Fernndez-Surez et al.,2002) also suggests that these rocks were extruded into the upperplate, i.e. the NW African margin of Gondwana.

4.1.3. Massif CentralTheMassif Central is made up of a stack of nappes (Fig. 3a: Lardeaux

et al., 2001; Matte, 1986; Matte, 2001) that include (from bottom totop): (i) Gondwanan passive margin rocks overlain by late Paleozoicforedeep deposits; (ii) a Carboniferousmigmatitic granitegneiss domecomplex structurally overlain by a Stephanian listric basin; (iii) apolydeformed gneiss comprising metasedimentary rocks, Ordovicianorthogneisses, amphibolites, metarhyolites (leptynites) with lenticularrelicts of mac and felsic granulites, coesite-bearing eclogites, andgarnet- and spinel-bearing peridotites; (iv) Devonian bimodal volcanicrocks, siltstones and reefal limestones with Gondwanan fauna intrudedby gabbro deformed under greenschist facies conditions; and (v) smallremnants of eclogitic gneiss intruded by Carboniferous granitoidsoverlain by Visean sediments (Lardeaux et al., 2001). Peak UHPmetamorphism occurred during the latest SilurianEarly Devonian(420400 Ma) and was followed by exhumation to 30 km during theLate Devonian (380360 Ma) (Fig. 4; Lardeaux et al., 2001). Eclogiticprotoliths include rocks of oceanic, arc and back-arc tectonic settings(Matte, 2001; Lardeauxet al., 2001). Existingmodels generally infer thatthe oceanic and HP rocks mark the Massif Central oceanic suture(Fig. 3b: Lardeaux et al., 2001; Matte, 1986; Matte, 1998; Matte, 2001).However, the presence of Gondwanan rocks on either side of the HProcks, the supra-subduction origin of some of the rocks, and the 420400 Maage of peakmetamorphism all favour pre-collisional subductionand extrusion of both lower and upper plates (Fig. 3a). The nappestructure of themassif suggests that it is analogous to the Galician/Tras-os-Montes allochthons. Extrusion of the HP rocks associatedwith NNESSW stretching was apparently followed by Carboniferous kinematicreversal on the bounding faults and overprinted by dextral transpres-sional structures (Lardeaux et al., 2001).

4.1.4. Bohemian MassifIn the Bohemian Massif, HP Moldanubian rocks are bounded to the

north by the Tepla-Barrandian and Saxo-Thuringian zones, whichconsist of Neoproterozoic Pan-African basement unconformably over-

lain byPaleozoic rocks containingGondwanan fauna (Franke, 2000) anddetrital zircon populations (Linnemann et al., 2007). The southernmargin ofMoldanubia is thrust over Brunia (Fig. 3c), which probably layalong themargin of Baltica during the Lower Paleozoic (Nowrocki et al.,2004). Moldanubia itself consists of a nappe of the HP Gfhl Unit thrustover the lower grade Drosendorf Unit, which consists of paragneissesandorthogneisseswith rare eclogite lenses. The eclogitemineralogy andgeochemistry in theHPnappe indicate tholeiitic,MORB, and arc or back-arc protoliths that were subjected to 1540 kb pressures (50140 kmdepth) and 8501000 C temperatures (Fig. 4: Schulmann et al., 2005;Medaris et al., 2006, and references therein). Associated garnetperidotites probably represent sub-continental mantle originating atdepths of 115210 km (3360 kb) under temperatures of 10001200 C, and are distinct from spinel peridotites derived fromsuboceanic asthenospheric mantle from depths of 6077 km (1722 kb) at 10301200 C (Medaris et al., 2006). Enveloping metasedi-mentary rocksmay representpassivemargin and forearc sediments thathave been subjected to pressures of at least 3040 kb (105140 kmdepth) (Fig. 4: Schulmann et al., 2005). Geochronological data indicateOrdovician protolith ages for the metasedimentary rocks and eclogites,peak metamorphism in the peridotites at 370350 Ma, and emplace-ment into continental crust during the Early Carboniferous (345323 Ma) followed by rapid exhumation to 70 km (351338 Ma) andcooling through ca. 550C by ca. 335 Ma (Schulmann et al., 2005;Medaris et al., 2006, and references therein). Carboniferous deformationinvolved channel ow and mushroom-shaped folding, and dextraltranspression (Fig. 3e) (Schulmann et al., 2005).

Traditional models suggest that the HP rocks represent theMoldanubian oceanic suture between the Tepla-Barrandian Zone andMoldanubia (Fig. 3d: Franke, 2000). Such amodel is consistentwith theproposal ofMedaris et al. (2006)whoproposed that the sub-continentalperidotites formed above the subducting Moldanubian oceanic plate,and that both were subsequently extruded up the subduction channel(Fig. 3e). (Schulmann et al., 2005) also suggested an extrusion model,this time above a subducting Rheic oceanic plate, but only for thecontinental crust (Drosendorf and Gfhl units) and during theCarboniferous (Fig. 3f). Although it is difcult to distinguish betweenthese twomodels, correlationwith theMassif Central is consistentwiththe latter one. However, continued extrusion may have accompaniedsubduction of the Tethys Ocean (Stampi and Borel, 2002).

5. Conclusions

Iberia appears to provide a template for the whole length of the ICHP belt, probably because it is less penetratively deformed bycollisional Variscan structures and wrench tectonics compared toother regions within the Variscan orogen (Fig. 5). A remnant of theRheic Ocean is preserved in the South Portuguese Zone that may betraced beneath the Ossa Morena Zone as a dense mid-crustal layer,part of which appears to have been extruded up the CordobaCoimbraShear Zone and thrust over the Central Iberian Zone as the Galician/Tras-os-Montes allochthons. The variation in the age of peak HPmetamorphism from ca. 390 Ma in the Galician/Tras-os-Montesallochthons to ca. 360 Ma in the CordobaCoimbra Shear Zone andca. 340 Ma in the Pulo de Lobo is explicable in terms of the ongoingdynamic process of subduction erosion, underplating and extrusionthat appears to have been active for a period of 3550 my along thesouthern margin of the Rheic Ocean (Fig. 5).

Amodel invokingextrusionofHP rocks into theupper (Gondwanan)plate represented by the IberianCzech (IC) belt explains severalenigmatic features:

(i) the lack of paleomagnetically-dened paleolatitudal separationacross the IC HP belt: different declinations suggests blockrotations (Tait et al., 1997, 2000);

(ii) the Gondwanan afnity of Devonian fauna on either side of the

IC HP belt (Robardet, 2003);

314 J.D. Keppie et al. / Gondwana Research 17 (2010) 306316(iii) the juxtaposition of active margin tectonics within synchro-nous passive margin sequences (Shelley and Bossire, 2000,2002);

(iv) the presence of similar detrital zircon populations of Gondwa-nan provenance on either side of the IC HP belt (e.g. Fernndez-Surez et al., 2003); and

(v) the pre-collisional age of most of the HP metamorphism.

On the other hand, several features of previous models also appearto apply, namely:

(a) the HP rocks represent subducted oceanic rocks, but ratherthan being part of the GalicianSouth BrittanyMassif CentralMoldanubian ocean (Matte, 1986, 2001; Matte et al., 1990;Matte, 1998; Franke, 2000; Matte, 2001; Medaris et al., 2006),they represent fragments of the Rheic Ocean (c.f. Arenas et al.,2007; Martnez Cataln et al., 2007);

(b) the pre-collisional extrusion of the HP rocks into the upper(NW African Gondwanan) plate was followed by post-

Fig. 5. Tectonic model for the southern margin of the Rheic Ocean: (a) Ordovician and SilurRheic Ocean beneath Gondwanawith the development of an arc complex that was removed bGondwanan plate along the IC belt; and (c) Carboniferous Laurussia (Avalonia)Gondwanathe Gondwanan margin and strike-slip displacements along the Variscan orogen (sinistralcollisional overthrusting eastwards in Iberia and southwardsin the Massif Central and Bohemia, but rather than originatingin the Rheic Ocean (Matte, 1986;Matte, 2001;Martnez Catalnet al., 2007), the HP rocks root in the extrusion zone; and

(c) post-collisional, strike-slip motions have been superimposedalong orogen-parallel shear zones and have disrupted theorderly sequence of tectonic settings (Shelley and Bossire,2000, 2002), however, the magnitude of relative motions isconstrained by the Tornquist Line against which the EW shearzones abut.

Theprotolithsof theHP rocks varywidely fromoceanic (?subductingplate) to supra-subduction zone units from arc, forearc, back-arc andpassive margin settings. This variation suggests that a combination oflower and upper plates were subducted and then extruded into theupper plate. Thus, the oceanic MORB and arc rocks may have formed inthe Rheic Ocean fringing the Gondwanan margin, whereas thecontinental arc and passive margin rocks were probably removed

ian development of a rift-passive Gondwanan margin; (b) Devonian subduction of they subduction erosion followed by underplating and extrusion of HP rocks into the uppercollision closing most of the Rheic Ocean and resulting in thrusting of the HP rocks overin Iberia and dextral in Armorica, Massif Central and Bohemian Massif).

315J.D. Keppie et al. / Gondwana Research 17 (2010) 306316from the southern margin of the Rheic Ocean by subduction erosion.This scenario is supported by the general absence of Silurian andDevonian arcs along the southern Rheic Ocean margin, which are hereinferred to have been removed by subduction erosion and incorporatedin the extruded HP rocks.

It is notable that all types of HP assemblages blueschists, coldeclogite and hot eclogite occur along the IC belt and all formed beforeterminal continentcontinent collision. As a consequence, previouscorrelations of blueschists and hot eclogites with B- and A-typesubduction, respectively, can no longer be sustained. This conclusionis consistent with numerical modeling, which shows that blueschistsand eclogites merely reect the depth and residence time to which therocks were subducted before being extruded (e.g.Stckhert and Gerya,2005; Gerya and Stckhert, 2006; Keppie et al., in press).

Acknowledgements

We thank Dr. James Lee and an anonymous reviewer for theirconstructive comments on the rst draft of the paper. We would like toacknowledge a Papiit grant IN103003 andaCONACyTgrant (CB-2005-1:24894) to JDK, anNSFgrant (EAR0308105) andanOhioUniversity 1804Award to RDN, a NSERC Discovery grants to JBM and JD, and an NSERCPost-Graduate Scholarship to JAB.

References

Arenas, R., Martnez Cataln, JR., Snchez Martnez, S., Daz Garcia, F., Abati, J.,Fernndez-Surez, J., Andonaegui, P., Gmez-Barreiro, J., 2007. Paleozoic ophiolitesin the Variscan suture of Galicia (northwest Spain): distribution, characteristics,and meaning. In: Hatcher Jr., R.D., Carlson, M.P., McBride, J.H., Martnez Cataln, J.R.(Eds.), 4-D Framework of Continental Crust: Geological Society of America Memoir200, pp. 425444. doi:10.1130/2007.1200(22).

Azor, A., Rubatto, D., Simancas, J.F., Gonzlez Lodeiro, F., Martnez Poyatos, D., MartnParra, L.M., Matas, J., 2008. Rheic Ocean ophiolitic remnants in southern Iberiaquestioned by SHRIMP UPb zircon ages on the Beja-Acebuches amphibolites.Tectonics 27, TC5006. doi:10.1029/2008TC002306.

Ballvre, M., Marchand, J., Godard, G., Goujou, J.C., Christian, J., Wyns, R., 1994. Eo-Hercynian events in the Armorican massif. In: Keppie, J.D. (Ed.), Pre-MesozoicGeology in France. Berlin, Springer-Verlag, pp. 183194.

Bard, J.P., Burg, J.P., Matte, P., Ribeiro, A., 1980. La chaine hercynienne d'Europeoccidentale en termes de tectonique des plaques. In: Cogne, J., Slansky, M. (Eds.),Geologie de l'Europe - du Precambrien aux bassins sdimentaires post-hercyniens.26th International Geological Congress, Colloquium C6, Villeneave, pp. 234246.

Bosse, V., Ballvre, M., Fraud, G., de Jong, K., Peucat, J.J., Ruffet, G., 1999. Geochronologicalconstraints on the timing and rate of exhumation of eclogite-facies rocks from theChamptoceaux nappe (Armorican Massif, France). Abstract of Proceedings, Meta-morphic Studies Group (Geological Society of London and Mineralogical Society ofGreat Britain) conference on Exhumation of Metamorphic Terranes, Rennes, 31August2 September, 1999, 8.

Bosse, V., Fraud, G., Ballvrec, M., Peucat, J.-J., Corsini, M., 2005. RbSr and 40Ar/39Arages in blueschists from the Ile de Groix (Armorican Massif, France): implicationsfor closure mechanisms in isotopic systems. Chemical Geology 220, 2145.

Camacho, A., Lee, J.K.W., Hensen, B.J., Braun, J., 2005. Short-lived orogenic cycles and theeclogitization of cold crust by spasmodic hot uids. Nature 435, 11911996.

Cartier, C., Faure, M., Lardeux, H., 2001. The Hercynian orogeny in the South ArmoricanMassif (Saint-Georges-sur-Loire Unit, Ligerian Domain, France): rifting andwelding of continental stripes. Terra Nova 13, 143149.

Castro, A., Gerya, T.V., 2007. Magmatic implications of mantle wedge plumes:experimental study. Lithos 79, 229250.

Clift, P.D., Vannucchi, P., 2004. Controls on tectonic accretion versus erosion in subductionzones: implications for the origin and recycling of the continental crust. Review ofGeophysics 42 (2), RG2001. doi:10.1029/2003RG000127.

Dallmeyer, R.D., Gil Ibarguchi, J.I., 1990. Age of amphibolitic metamorphism in theophiolitic unit of the Morais allochthon (Portugal): implications for early Hercynianorogenesis in the Iberian Massif. Geological Society [London] Journal 147, 873878.

Dallmeyer, R.D., Ribeiro, A., Marques, F., 1991. Polyphase Variscan emplacement of exoticterranes (Morais and BraganaMassifs) onto Iberian successions: evidence from 40Ar/39Ar mineral ages. Lithos 27, 133144. doi:10.1016/0024-4937(91)90025-G.

Dallmeyer, R.D., Tucker, R.D., 1993. UPb zircon age for the Lagoa augen gneiss, MoraisComplex, Portugal: tectonic implications. Geological Society [London] Journal 150,405410.

Dallmeyer, R.D., Fonseca, P., Quesada, C., Ribeiro, A., 1993. 40Ar/39Ar mineral age con-straints for the tectonothermal evolution of a Variscan suture in southwest Iberia.Tectonophysics 222, 177194. doi:10.1016/0040-1951(93)90048-O.

Dallmeyer, R.D., Martnez Cataln, J.R., Arenas, R., Gil Ibarguchi, J.I., Gutirrez-Alonso, G.,Farias, P., Aller, J., Bastida, F., 1997.DiachronousVariscan tectonothermal activity in theNW IberianMassif: evidence from 40Ar/39Ar dating of regional fabrics. Tectonophysics277, 307337. doi:10.1016/S0040-951(97)00035-8.

Dalziel, I.W.D., 1997. NeoproterozoicPaleozoic geography and tectonics: review,hypothesis and environmental speculation. Geological Society of America Bulletin109, 1642. doi:10.1130/0016-7606(1997) 109b0016:ONPGATN2.3.CO;2.

De la Rosa, J.D., Jenner, G.A., Castro, A., 2002. A study of inherited zircons in granitoidrocks from the South Portuguese and Ossa-Morena Zones, Iberian Massif: supportfor the exotic origin of the South Portuguese Zone. Tectonophysics 352, 245256.

Daz Garca, F., Arenas, R., Martnez Cataln, J.R., Gonzlez del Tnago, J., Dunning, G.R.,1999. Tectonic evolution of the Caren Ophiolite (northwest Spain): a remnant ofoceanic lithosphere in the Variscan belt. Journal of Geology 107, 587605.doi:10.1086/314368.

Dostal, J., Keppie, J.D., Ferri, F., 2009. Geochemistry of Triassic Takla Group in Quesnelliaconrms correlation with Stikinia, Canadian Cordillera: a single arc terraneduplicated by strike-slip, oroclinal bending, or split by extrusion of high-pressureCache Creek rocks? In: Murphy, J.B., Keppie, J.D., and Hynes, A. (Eds.), Modern andAncient Orogens. Geological Society of London, Special Publication, 327, 7187.doi:10.1144/SP327.5.

Ernst, W.G., 2009. Subduction-zone metamorphism, calc-alkaline magmatism, and conver-gent-margin crustal evolution. Gondwana Research. doi:10.1016/j.gr.2009.05.010.

Ernst, W.G., Maruyama, S., Wallis, S., 1997. Buoyancy-driven, rapid exhumation ofultrahigh-pressure metamrophosed continental crust. Proceedings of the NationalAcademy of Science 94, 95329537.

Fernndez-Surez, F., Gutirrez Alonso, G., Jeffries, T.E., 2002. The importance of along-margin terrane transport in northern Gondwana: insights from detrital zirconparentage in Neoproterozoic rocks from Iberia and Brittany. Earth and PlanetaryScience Letters 204, 7588.

Fernndez-Surez, J., Daz Garca, F., Jeffries, T.E., Arenas, R., Abati, J., 2003. Constraintson the provenance of the uppermost allochthonous terrane of the NW IberianMassif: inferences from detrital zircon UPb ages. Terra Nova 15, 138144.

Franke,W., 2000. Themid-European segment of theVariscides: tectonostratigraphic units,terrane boundaries and plate tectonic evolution. In: Franke, W., Haak, V., Onken, O.,Tanner, D. (Eds.), Orogenic Processes: Quantication and Modelling in the VariscanBelt, vol. 179. Geological Society of London Special Publication, pp. 3561.

Gerya, T.V., Stckhert, B., 2006. Two dimensional numerical modeling of tectonic andmetamorphic histories at active continental margins. International Journal of EarthScience 95, 250274.

Gutirrez-Alonso, G., Fernndez-Surez, J., Jeffries, T.E., Jenner, J.E., Tubrett, M.N., Cox,R., Jackson, S.E., 2003. Terrane accretion and dispersal in the Northern Gondwanamargin: an Early Paleozoic analogue of a long-lived active margin. Tectonophysics365, 221232. doi:10.1016/S0040-1951(03)00023-4.

Gutirrez-Alonso, G., Murphy, J.B., Fernndez-Surez, J., Hamilton, M., 2008. A Devonianage for the El Castillo Volcanic rocks (Salamanca, Central Iberian Zone): implicationsfor rifting along the northern Gondwanamargin and the evolution of the Rheic ocean.Tectonophysics 461, 157165.

IGN., 1976. Mapa de Espaa de Anomala de Bouguer, 1:1000000, Instituto GeogrcoNacional, Madrid.

Kay, S.M., Godoy, E., Kurtz, A., 2005. Episodic arc migration, crustal thickening, subductionerosion, and magmatism in the south-central Andes. GSA Bulletin 117 (1/2), 6788.doi:10.1130/B25431.1.

Keppie, D.F., Currie, C.A., Warren, C., 2009. Subduction erosion modes: comparing niteelement numerical models with the geological record. Earth and Planetary ScienceLetters 287, 241254.

Keppie, J.D., Dallmeyer, R.D., 1989. Tectonic map of Pre-Mesozoic terranes in Circum-Atlantic Phanerozoic Orogens. International Geological Correlation Programme:Project #233: Terranes in Circum-Atlantic Paleozoic Orogens.

Keppie, J.D., Nance, R.D., Murphy, J.B., Dostal, J., 2003. Tethyan, Mediterranean, andPacic analogues for the NeoproterozoicPaleozoic birth and development of peri-Gondwanan terranes and their transfer to Laurentia and Laurussia. Tectonophysics365, 195220.

Keppie, J.D., Dostal, J., Murphy, J.B., Nance, R.D., 2008. Synthesis and tectonicinterpretation of the westernmost Paleozoic Variscan orogen in southern Mexico:from rifted Rheic margin to active Pacic margin. Tectonophysics 461, 277290.

Kollmeier, J.M., van der Pluijm, B.A., van der Voo, R., 2000. Analysis of Variscandynamics, early bending of the CantabriaAturias Arc, northern Spain. Earth andPlanetary Science Letters 181, 203216.

Kossmat, F., 1927. Gliederung des varistischen gebirgsbaues. Abhandlungen desSchsischen Geologischen Landesamtes 1, 139.

Lardeaux, J.M., Ledru, P., Daniel, I., Duchene, S., 2001. The Variscan FrenchMassif Centrala new addition to the ultrahigh pressure metamorphic club: exhumation processesand geodynamic consequences. Tectonophysics 332, 143167.

Linnemann, U., Gerdes, A., Drost, K., Buschmann, B., 2007. The continuum betweenCadomian orogenesis and opening of the Rheic Ocean: constraints from LA-ICP-MSUPb zircon dating and analysis of plate-tectonic setting (Saxo-Thuringian zone,northeastern Bohemian Massif, Germany). In: Linnemann, U., Nance, R.D., Kraft, P.,Zulauf, G. (Eds.), The Evolution of the Rheic Ocean: From AvalonianCadomianActive Margin to AlleghenianVariscan Collision, vol. 423. Geological Society ofAmerica Special Paper, pp. 6196. doi:10.1130/2007.2423(03).

Liou, J.G., Tsujimori, T., Zhang, R.Y., Katayama, I., Maruyama, S., 2004. Global UHPmetamorphism and continental subduction/collision: the Himalayan model.International Geology Review 46, 127.

Llana-Fnez, S., Marcos, A., 2002. Structural record during exhumation and emplacementof high-pressurelow-to intermediate-temperature rocks in the Malpica-Tui unit(Variscan belt of Iberia). In: Martnez Cataln, J.R., Hatcher Jr., R.D., Arenas, R., DazGarca, F. (Eds.), VariscanAppalachian Dynamics: the Building of the Late PaleozoicBasement: Geological Society of America Special Paper, vol. 364, pp. 125142.

Lucks, H., Schulz, B., Audren, C., Triboulet, C., 2002. Variscan pressuretemperatureevolution of garnet pyrozenites and amphibolites in the Baied'Audiernemetamorphicseries, Brittany (France). In: Martnez Cataln, J.R., Hatcher Jr., R.D., Arenas, R., DazGarca, F. (Eds.), VariscanAppalachian Dynamics: the Building of the Late PaleozoicBasement: Geological Society of America Special Paper, vol. 364, pp. 89103.

Pin, C., Paquette, J.L., Santos Zalduegui, J.F., Gil Ibarguchi, J.I., 2002. In: Martnez Cataln,J.R., Hatcher Jr., R.D., Arenas, R., Daz Garca, F. (Eds.), Early Devonian Suprasubduc-tion-zone Ophiolite Related to Incipient Collisional Processes in the WesternVariscan Belt: the Sierra de Caren Unit, rdenes Complex, Galicia. VariscanAppalachian Dynamics: The Building of the Late Paleozoic Basement, vol. 364.Geological Society of America Special Paper, pp. 5771.

Quesada, C., 1990. Precambrian terranes in the Iberian Variscan foldbelt. In: Strachan, R.A.,Taylor, G.K. (Eds.), Avalonian and Cadomian Geology of the North Atlantic. Glasgow,Blackie and Son, pp. 109133.

Robardet, M., 2003. The Armorica microplate: fact or ction? Critical review of the

316 J.D. Keppie et al. / Gondwana Research 17 (2010) 306316Cuadra, P., Gmez Barreiro, J., and Rubio Pascual, F. 2002, Thrust and detachmentsystems in the Ordenes Complex (northwestern Spain): Implications for theVariscan-Appalachian geodynamics. In: Martnez Cataln, J.R., Hatcher Jr, R.D.,Arenas, R., Daz Garca, F. (Eds.), Variscan-Appalachian Dynamics: The Building ofthe Late Paleozoic Basement. Geological Society of America Special Paper vol. 364,pp. 163182.

Martnez Cataln, J.R., Arenas, R., Daz Garca, F., Gmez-Barreiro, J., Gonzlez Cuadra, P.,Abati, J., Castieiras, P., Fernndez-Surez, J., Snchez Martnez, S., Andonaegui, P.,Gonzlez Clavijo, E., Dez Montes, A., Rubio Pascual, F.J., Valle Aguado, B., 2007. Spaceand time in the tectonic evolution of the northwestern IberianMassif: implications forthe comprehensionof theVariscanbelt. In:Hatcher Jr., R.D., Carlson,M.P.,McBride, J.H.,Martnez Cataln, J.R. (Eds.), 4-D Framework of Continental Crust: Geological Societyof America Memoir 200. doi:10.1130/2007.1200(21).

Maruyama, S., Liou, J.G., Terabayashi, M., 1996. Blueschists and eclogites of the world,and their exhumation. International Geology Review 38, 485594.

Matte, P., 1986. Tectonic and plate tectonic model for the Variscan belt of Europe.Tectonophysics 126, 329374.

Matte, P., 1998. Continental subduction and exhumation of HP rocks in Paleozoicorogenic belts: Uralides and Variscides GFF, 120, pp. 209222.

Matte, P., 2001. The Variscan collage and orogeny (480290 Ma) and the tectonicdenition of the Armorica microplate: a review. Terra Nova 13, 122128.

Matte, P., Maluski, H., Rajlich, P., Franke, W., 1990. Terrane boundaries of the Bohemianmassif: result of large-scale Variscan shearing. Tectonophysics 177, 151170.

McKerrow,W.S.,MacNiocaill, C., Ahlberg, P.E., Clayton,G., Cleal, C.J., Eagar,R.M.C., 2000. TheLate Paleozoic relations between Gondwana and Laurussia. In: Franke, W., Haak, V.,Onken, O., Tanner, D. (Eds.), Orogenic Processes: Quantication and Modelling in theVariscan Belt, vol. 179. Geological Society of London Special Publication, pp. 920.

Medaris, L.G., Beard, B.L., Jelnek, E., 2006. Mantle-derived, UHP garnet pyroxenite andeclogite in the Moldanubian Gfhl nappe, Bohemian Massif: a geochemical review,new PT determinations, and tectonic interpretation. International Geology Review48, 765777.

Moita, P., Munh, J., Fonseca, P., Pedro, J., Tassinari, C., Arajo, A., Palcios, T., 2005.Phase-equilibria and geochronology of the OssaMorena eclogites. Actas do VIIICongresso de Geoqumica dos Pases de Lngua Portuguesa 2, 463466.

Murphy, J.B., Nance, R.D., Cawood, P.A., 2009a. Contrasting modes of supercontinentformation and the conundrum of Pangea. Gondwana Research 15, 408420.

Murphy, J.B., Gutirrez-Alonso, G., Nance, R.D., Fernandez-Suarez, J., Keppie, J.D.,Quesada, C., Dostal., J., Braid, J.A. 2009b. Rheic Ocean mac complexes: overviewand synthesis. In: Murphy, J.B., Keppie, J.D., Hynes, A. (Eds.), Ancient Orogens andModern Analogues. Geological Society of London, Special Publication vol. 327, pp.343369. doi:10.1144/SP327.15.

Nowrocki, J., Zylinska, A., Bula, Z., Grabowski, J., Krzyiwiec, P., Poprawi, P., 2004. EarlyCambrian location and afnities of the Brunovistulian terrane (Central Europe) inthe light of palaeomagnetic data. Journal of the Geological Society of London 161,513522.

Ordoez-Casado, B., 1998. Geochronological studies of the Pre-Mesozoic basement ofthe Iberian Massif: the Ossa Morena Zone and Allochthonous complexes within theCentral Iberian Zone. PhD Thesis, ETH(12.940), Zurich.

Ortega-Gutirrez, F., 1981. Metamorphic belts of southern Mxico and their tectonicsignicance. Geosica Internacional 20 (3), 177202.

Palomeras, I., Carbonell, R., Flecha, I., Simancas, J.F., Ayarza, P.,Mata, J.,MartnezPoyatos, D.,Azor, A., Gonzalez Lodeiro, F., Prez Estan, A., 2008. Constraints on the Lithosphereacross the Variscan Orogen of SW Iberia from dense wide-angle seismic reectiondata. Journal of Geophysical Research. doi:10.1029/2007JB005564.

Pereira, M.F., Apraiz, A., 2006. High Pressure Mac Granulites in the CoimbraCordbaShear Zone (Campo Maior Unit, Northeast Alentejo): Metamorphic and Geother-mobarometric Characterization. VII Congresso Nacional de Geologia, Estremoz,Portugal.

Pereira, M.F., Silva, J.B., Chichorro, M., Moita, P., Santos, J.F., Apraiz, A., Ribeiro, C., 2007.Crustal growth and deformational processes in the northern Gondwana margin:Constraints from the Evora Massif (Ossa-Morena zone, southwest Iberia, Portugal).Geological Society of America Special Paper 423, 333358. doi:10.1130/2007.2423(16).

Pereira, M.F., Apraiz, A., Silva, J.B., Chichorro, M., 2008. Tectonothermal analysis of high-temperature mylonitization in the CoimbraCrdoba shear zone (SW IberianMassif, Ouguela tectonic unit, Portugal): evidence of intra-continental transcurrenttransport. Tectonophysics 461, 378394. doi:10.1016/j.tecto.2007.11.042.

Peucat, J.J., 1986. Behaviour of RbSr whole rock and UPb zircon systems duringpartial melting as shown in migmatitic gneisses from the St Malo Massif, NEBrittany, France. Journal of the Geological Society of London 143, 875885.

Peucat, J.J., Bernard-Grifths, J., Gil Ibarguchi, J.I., Dallmeyer, R.D., Menot, R.P., Cornichet,J., Iglesias Ponce de Len, M., 1990. Geochemical and geochronological cross sectionof the deep Variscan crust: the Cabo Ortegal high-pressure nappe (northwesternSpain). Tectonophysics 177, 263292. doi:10.1016/0040-1951(90)90285-G.concept and contradictory palaeobiogeographical data. Palaeogeography, Palaeo-climatology, Palaeoecology 195 (2003), 125148.

Rodrguez, J., Cosca, M.A., Gil Ibarguchi, J.I., Dallmeyer, R.D., 2003. Strain partitioningand preservation of 40Ar/39Ar ages during Variscan exhumation of a subductedcrust (Malpica-Tui complex, NW Spain). Lithos 70, 111139. doi:10.1016/S0024-4937(03)00095-1.

Santos Zalduegui, J.F., Schrer,U., Gil Ibarguchi, J.I., 1995. Isotopeconstraints on the age andorigin ofmagmatism andmetamorphism in theMalpica-Tuy allochthon, Galicia, NW-Spain. Chemical Geology 121, 91103. doi:10.1016/0009-2541(94)00123-P.

Santosh, M., Maruyama, S., Sato, K., 2009. Anatomy of a Cambrian suture in Gondwana:Pacic-type orogeny in southern India? Gondwana Research 16, 321341.

Schulmann, K., Krner, A., Hegner, E., Wendt, I., Konopsek, J., Lexa, O., tpsk, P., 2005.Chronological constraints on the pre-orogenic history, burial, and exhumation ofdeep-seated rocks along the eastern margin of the Variscan orogen, BohemianMassif, Czech Republic. American Journal of Science 305, 407448.

Shelley,D., Bossire,G., 2000. Anewmodel for theHercynianorogenofGondwananFranceand Iberia. Journal of Structural Geology 22, 757776. doi:10.1016/S0191-8141(00)00007-9.

Shelley, D., Bossire, G., 2002. Megadisplacements and the Hercynian orogen ofGondwanan France and Iberia. In: Martnez Cataln, J.R., Hatcher Jr., R.D., Arenas, R.,Daz Garca, F. (Eds.), VariscanAppalachian Dynamics: the Building of the LatePaleozoicBasement, vol. 364.Geological Society of America Special Paper, pp. 209222.

Simancas, F., Gonzlez Lodeiro, F., Expsito Ramos, I., Azor, A., Martnez Poyatos, D.,2002. In: Martnez Cataln, J.R., Hatcher Jr., R.D., Arenas, R., Daz Garca, F. (Eds.),Opposite Subduction Polarities Connected by Transform Faults in the Iberian MassifandWestern European Variscides. VariscanAppalachian Dynamics: the building ofthe late Paleozoic basement: Boulder, Colorado, vol. 364. Geological Society ofAmerica Special Paper, pp. 253262.

Simancas, J.F., Azor, A., Martnez-Poyatos, D., Abdelfatah Tahiri, A., El Hadi, H., Gonzlez-Lodeiro, F., Prez-Estan, A., Carbonell, R., 2009. Tectonic relationships of South-west Iberia with the allochthons of Northwest Iberia and the Moroccan Variscides.Compte Rendu Geosciences, 341, #1.

Stampi, G.M., Borel, G., 2002. A plate tectonic model for the Paleozoic and Mesozoic.Earth and Planetary Sciences Letters 196, 1733.

Stern, R.J., 2005. Evidence from ophiolites, blueschists, and ultrahigh-pressuremetamorphic terranes that the modern episode of subduction tectonics began inNeoproterozoic time. Geology 33, 557560.

Stckhert, B., Gerya, T.V., 2005. Pre-collisional high pressure metamorphism and nappetectonics at active continental margins: a numerical simulation. Terra Nova 17,102110.

Tait, J., Bachtadse, V., Franke,W., Soffel, H., 1997. Geodynamic evolution of the EuropeanVariscan fold belt. Geologische Rundschau 86, 585598.

Tait, J., Schtz, M., Bachtadse, V., Soffel, H., 2000. Paleomagnetism and Paleozoicpaleogeography of Gondwana and European terranes. In: Franke, W., Haak, V.,Onken, O., Tanner, D. (Eds.), Orogenic Processes: Quantication and Modelling in theVariscan Belt, vol. 179. Geological Society of London Special Publication, pp. 2134.

Von Huene, R., Ranero, C.R., Vannucchi, P., 2004. Generic model of subduction erosion.Geology 32, 913916.

van Keken, P.E., Kiefer, B., Peacock, S.M., 2002. High-resolution models of subductionzones: implications for mineral dehydration reactions and the transport of waterinto the deepmantle. Geochemistry, Geophysics, Geosystems 3, 1056. doi:10.1029/2001GC000256.

Warren, C.J., Beaumont, C., Jamieson, R.A., 2008. Modelling tectonic styles and ultra-highpressure (UHP) rock exhumation during the transition from oceanic subduction tocontinental collision. Earth and Planetary Science Letters 267, 129145.

Weil, A.B., van der Voo, R., van der Pluijm, B.A., Pars, J.M., 2000. The formation o fanorocline bymultiphase deformation: a paleomagnetic investigation of the CantabriaAstruias Arc (Northern Spain). Journal of Structural Geology 22, 735756.

Winchester, J.A., Pharaoh, T.C., Verniers, J., 2002. Palaeozoic amalgamation of CentralEurope: an introduction and synthesis of new results from recent geological andgeophysical investigations. In: Winchester, J.A., Pharaoh, T.C., Verniers, J. (Eds.),Palaeozoic Amalgamation of Central Europe, vol. 201. Geological Society [London]Special Publication, pp. 118.

Zhang, R.Y., Liou, J.G., Ernst, W.G., 2009. The DabieSulu continental collision zone: acomprehensive review. Gondwana Research 16, 126.Martnez Cataln, J.R., Daz Garca, F., Arenas, R., Abati, J., Castieiras, P., Gonzlez

The high-pressure IberianCzech belt in the Variscan orogen: Extrusion into the upper (Gondwana.....IntroductionBackgroundOceanic sutureDextrally strike-slipped slice of the Rheic OceanAllochthonous nappe

General distinctions between inter-plate and intra-plate HP rocksApplication to Variscan orogenThe IberianCzech (IC) beltIberiaArmoricaMassif CentralBohemian Massif

ConclusionsAcknowledgementsReferences