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Paleozoic evolution of pre-Variscan terranes: From Gondwana to the Variscan collision

January 2005
Geological Society of America Special Papers 364

January 2005
364

Authors:

University of Lausanne

The well-known Variscan basement areas of Europe contain relic terranes with a pre-Variscan evolution testifying to their peri-Gondwanan origin (e.g., relics of Neoproterozoic volcanic arcs, and subsequent stages of accretionary wedges, backarc rifting, and spreading). The evolution of these terranes was guided by the diachronous subduction of the proto-Tethys oceanic ridge under different segments of the Gondwana margin. This subduction triggered the emplacement of magmatic bodies and the formation of backarc rifts, some of which became major oceanic realms (Rheic, paleo- Tethys). Consequently, the drifting of Avalonia was followed, after the Silurian and a short Ordovician orogenic event, by the drifting of Armorica and Alpine domains, accompanied by the opening of the paleo-Tethys. The slab rollback of the Rheic ocean is viewed as the major mechanism for the drifting of the European Variscan terranes. This, in turn, generated a large slab pull force responsible for the opening of major rift zones within the passive Eurasian margin. Therefore, the µrst Middle Devonian Variscan orogenic event is viewed as the result of a collision between terranes detached from Gondwana (grouped as the Hun superterrane) and terranes detached from Eurasia. Subsequently, the amalgamated terranes collided with Eurasia in a second Variscan orogenic event in Visean time, accompanied by large-scale lateral escape of major parts of the accreted margin. Final collision of Gondwana with Laurussia did not take place before Late Carboniferous time and was responsible for the Alleghanian orogeny.

Detailed plate tectonic evolution of pre-Variscan units preserved in European Variscan mountain chain (see text for explanation). AA, Austro-Alpine; Ab, Alboran; Ad, Adria–south Alpine; Al, Alborz; Am, Armorica; Ap, Apulia; Aq, Aquitaine; Ce, Cetic; Ch, Channel; cI, central Iberia; Ct, Cantabria; DH, Dinarides-Hellenides; Di, Dizi; Do, Dobrogea; gC, great Caucasus; Gi, Giessen; He, Helvetic; Hz, Harz; iA, intra-Alpine; Ib, northwestern Iberia allochthon; Is, Istanbul; Kb, Karaburun; KT, Karakum-Turan; Lg, Ligerian; Lz, lizard; MD, Moldadubian; Mg, Meguma; Mo, Moesia; Ms, Meseta; OM, Ossa- Morena; Or, Ordenes ophiolites; Pe, Penninic; Pp, Paphlagonian; RH, Rheno-Hercynian; Sk, Sakarya; SM, Serbo-Macedonian; sP, south Portuguese ; Sx, Saxo-Thuringian; tC, trans-Caucasus; Zo, Zonguldak.

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INTRODUCTION

Relics of the Variscan mountain chain are well known from

many places in Europe (e.g., Iberia, Armorica, Moesia, the

French Central Massif, the Saxo-Thuringian and Moldanubian

domains, and Alpine pre-Mesozoic basement areas; Fig. 1), and

modern reviews reveal their complex evolution since the De-

vonian (Franke, 1989, 1992; Dallmeyer and Martínez García,

1990; von Raumer and Neubauer, 1993, 1994; Keppie, 1994;

Dallmeyer et al., 1995; Matte, 1998; Arenas et al., 2000; Franke

et al., 2000). As consequences of Variscan and/or Alpine oro-

genic events, pre-Variscan elements in these areas mostly appear

as polymetamorphic domains. Geotectonic nomenclature and

zonation in these classical areas of Variscan evolution mirror the

main Variscan tectonic structures (e.g., Suess, 1909; Kossmat,

1927; Stille, 1951), and evidently cannot be valid for the de-

scription of pre-Variscan elements. Relics of distinct geological

periods from the Proterozoic to the Ordovician have been ob-

Geological Society of America

Special Paper 364

2002

Paleozoic evolution of pre-Variscan terranes:

From Gondwana to the Variscan collision

Gérard M. Stamp×i

Institut de Géologie et Paléontologie, Université de Lausanne, CH-1015 Lausanne, Switzerland

Jürgen F. von Raumer

Institut de Minéralogie et Pétrographie, Université de Fribourg, CH-1700 Fribourg, Switzerland

Gilles D. Borel

Institut de Géologie et Paléontologie, Université de Lausanne, CH-1015 Lausanne, Switzerland

ABSTRACT

The well-known Variscan basement areas of Europe contain relic terranes with a

pre-Variscan evolution testifying to their peri-Gondwanan origin (e.g., relics of Neo-

proterozoic volcanic arcs, and subsequent stages of accretionary wedges, backarc rift-

ing, and spreading). The evolution of these terranes was guided by the diachronous

subduction of the proto-Tethys oceanic ridge under different segments of the Gond-

wana margin. This subduction triggered the emplacement of magmatic bodies and the

formation of backarc rifts, some of which became major oceanic realms (Rheic, paleo-

Tethys). Consequently, the drifting of Avalonia was followed, after the Silurian and a

short Ordovician orogenic event, by the drifting of Armorica and Alpine domains, ac-

companied by the opening of the paleo-Tethys. The slab rollback of the Rheic ocean is

viewed as the major mechanism for the drifting of the European Variscan terranes.

This, in turn, generated a large slab pull force responsible for the opening of major

rift zones within the passive Eurasian margin. Therefore, the µrst Middle Devonian

Variscan orogenic event is viewed as the result of a collision between terranes detached

from Gondwana (grouped as the Hun superterrane) and terranes detached from

Eurasia. Subsequently, the amalgamated terranes collided with Eurasia in a second

Variscan orogenic event in Visean time, accompanied by large-scale lateral escape of

major parts of the accreted margin. Final collision of Gondwana with Laurussia did

not take place before Late Carboniferous time and was responsible for the Alleghan-

ian orogeny.

263

Stamp×i, G.M., von Raumer, J.F., and Borel, G.D., 2002, Paleozoic evolution of pre-Variscan terranes: From Gondwana to the Variscan collision, in Martínez

Catalán, J.R., Hatcher, R.D., Jr., Arenas, R., and Díaz García, F., eds., Variscan-Appalachian dynamics: The building of the late Paleozoic basement: Boulder, Col-

orado, Geological Society of America Special Paper 364, p. 263–280.

served in many of the basement units. The oldest elements were

considered to be part of a Late Proterozoic supercontinent (e.g.,

Hoffmann, 1991; Unrug, 1997) and may have been detached

from what is known as Gondwana or Laurentia-Baltica or

Siberia. Examples for the Gondwana origin were given by Zwart

and Dornsiepen (1978) and Ziegler (1984), and tectonic com-

plications occurring in such polyorogenic basement massifs

were illustrated by Hatcher (1983) for the Appalachians. It is the

aim of this contribution to discuss the plate tectonic evolution of

these European regions, from the Ordovician onward, in a larger

context of global palinspastic reconstructions.

REVIEW OF PRE-VARISCAN EVOLUTION

Pre-Variscan relics include, besides Cadomian-type base-

ment units, evidence for a sequence of late Precambrian to early

Paleozoic plate tectonic settings (e.g., successive stages of de-

velopment of oceanic crust, volcanic arcs, active margins, and

collision zones). Their corresponding evolution has to be dis-

cussed in the general framework of their peri-Gondwanan loca-

tion. Alpine basement areas (Stamp×i, 1996; von Raumer, 1998;

von Raumer and Stamp×i, 2000) as well as Avalonia have to be

included in the discussion.

In von Raumer et al. (2002) we tried to compare the early

Paleozoic plate tectonic evolution of Avalonia and of microcon-

tinents formerly situated at its lateral eastern continuation along

the Gondwana margin (e.g., Cadomia, and the Alpine terranes),

and we proposed a similar evolution of all these terranes until

the breakoff of Avalonia. Based on the presence of late Cado-

mian (550–520 Ma) granitoids, comparable Neoproterozoic to

Cambrian detrital sediments and volcanites, and Cambrian

oceanic crust, we suggested that initial stages of the Rheic ocean

should have been preserved in the microcontinents formerly lo-

cated in the eastern prolongation of Avalonia at the Gondwana

margin (Fig. 2). Using a model of continuous Gondwana-di-

rected subduction since the Neoproterozoic and comparing time

of rifting, breakoff, and emplacement of granitoids, we distin-

guished several steps of a plate tectonic evolution summarized

as follows.

1. A Neoproterozoic active margin setting with formation

of volcanic arcs is observed along the entire length of the future

microcontinents at the Gondwanan border (e.g., Fernández

Suárez et al., 2000; Schaltegger et al., 1997; Zulauf et al., 1999).

Granites of Neoproterozoic age (ca. 550 Ma), common in many

Gondwana-derived basement blocks, probably indicate slab

breakoff at the end of the Cadomian orogeny. Zircons in these

granites carry the evidence of peri-Gondwanan origin. Latest

Proterozoic to Early Cambrian sedimentary troughs developed

prior to the opening of the Rheic ocean, which resulted from

continued oblique subduction and rifting in a backarc situation.

2. The drift of Avalonia and the opening of the Rheic ocean

were enhanced after the subduction of the mid-oceanic ridge,

under Gondwana, of what we called the proto-Tethys ocean (the

former peri-Gondwanan ocean, Fig. 2). Large-scale magmatic

264 G.M. Stamp×i, J.F. von Raumer, and G.D. Borel

Figure 1. Present-day locations of ter-

ranes and blocks for western Europe.

AA, Austroalpine; Ab, Alboran (Betic-

Rif-Calabria-Kabbilies-Sardinia); Ad,

Adria (Tuscan Paleozoic-Southern

Alps); Am, Armorica; Ap, Apulia; Aq,

Aquitaine (Montagne Noire-Pyrenees);

Ce, Cetic; Ch, Channel; cI, Central

Iberia; Ct, Cantabria-Asturia-Ebro; DH,

Dinarides-Hellenides; Gi, Giesen; He,

Helvetic; Hz, Harz; iA, intra-Alpine

(Tizia-Transdanubian-Bükk); Ib, al-

lochthonous units of northwestern Iberia;

Lg, Ligeria (Massif Central–South Bri-

tanny); Lz, Lizzard; MD, Moldanubian;

Ms, Meseta; OM, Ossa-Morena; Or, Or-

denes ophiolites; Pe, Penninic; RH,

Rheno-Hercynian; Si, Sicanian basin; sP,

south-Portuguese; Sx, Saxo-Thuringian.

SOUTH

OUTH

POLE

OLE

ERINDIA TERRANE

SM Lg

He MD

Mo Am

cI iA

Ib Ab

Ad Ts

SOUTH

POLE

DH Mn

AVALONIAN

VALONIAN

TERRANES

Mg sP

CADOMIAN TERRANE

AVAL ON IA N TERRANES

ERINDIA TERRANE

Lough Nafooey arc

Taconic arc

Figure 2. Location of pre-Variscan basement units at Gondwanan margin during Early Ordovician (490 Ma), modiµed from Stamp×i

(2000), showing early stages of Rheic ocean spreading. After short separation from Gondwana, Cadomia reaccreted to Gondwana in Mid-

dle Ordovician time. Thereafter Hun superterrane detached from Gondwana during opening of paleo-Tethys (dashed line along Gond-

wanan border). Avalonia: Is, Istanbul; Mg, Meguma; Mo, Moesia; sP, south Portuguese; Zo, Zonguldak. (Dean et al., 2000, proposed an

Avalonian origin for the Istanbul Paleozoic; see also Seston et al., 2000, and Winchester, 2002). Cadomia: AA, Austro-Alpine; Cm, Cado-

mia; He, Helvetic; Ib, allochthons from northwestern Iberia; Lg, Ligerian; MD, Moldanubian; Pe, Penninic; SM, Serbo-Macedonian; Sx,

Saxo-Thuringian. Serindia: Kb, Karaburun; KT, Karakum-Turan; nC, north China; Qi, Qilian; Tn, north Tarim. Gondwana: Ab, Albo-

ran; Ad, Adria; Al, Alborz; Am, Armorica; Ap, Apulia; Aq, Aquitaine; cA, central Afghanistan; cI, central Iberia; Cr, Carolina; Cs, Chor-

tis; Ct, Cantabria; DH, Dinarides-Hellenides; iA, intra-Alpine; LT, Lut-Tabas; Mn, Menderes; Ms, Meseta; OM, Ossa-Morena; Pr, Pamir;

Qs, south Qinling; SS, Sanandaj-Sirjan; Si, Sicanian basin; sT, south Tibet; Ta, Taurus; Ts, south Tarim; Yu, Yucatan.

pulses of granites and/or gabbros ca. 500 Ma indicate this in-

creased thermal activity (e.g., Abati et al., 1999). In the eastern

continuation of Avalonia, only embryonic stages of the Rheic

rifting may have existed (Fig. 2). Drifting was hampered by the

still-existing mid-oceanic ridge of the proto-Tethys, the colli-

sion of which with the detaching terranes triggered the con-

sumption of this embryonic eastern Rheic ocean. The amalga-

mation of volcanic arcs and continental ribbons with Gondwana

occurred in a short-lived orogenic pulse. The resulting cordillera

started to collapse during the Late Ordovician, leading to the

opening of the paleo-Tethys rift. The chemical evolution of

granitoids is the mirror of the general evolution from Cambrian-

Ordovician rifting, to Cambrian-Ordovician active margin, and

Ordovician amalgamation.

3. Mid-ocean ridge subduction during the Ordovician, in

the former eastern prolongation of Avalonia, triggered not only

the intrusion of many Ordovician granitoids, but also facilitated

the opening of paleo-Tethys and the Late Silurian drift of the

composite Hun superterrane (Stamp×i, 2000). There is little ev-

idence of this episode, neither sedimentation in a backarc setting

(e.g., Saxo-Thuringian domain; Linnemann and Buschmann,

1995), nor Late Ordovician–Early Silurian active margin settings

(e.g., Reischmann and Anthes, 1996) in many of the basement ar-

eas composing Cadomia (sensu lato; see following), except in the

Alpine areas (Stamp×i, 1996; von Raumer, 1998).

In the European pre-Variscan basement areas, hidden in the

Variscan and Alpine mountain chains, a striking comparability

of pre-Silurian evolutions shows that the pre-Variscan elements

had similar related locations along the Gondwana margin. Many

contain Cadomian basement with related evidence of Late Pro-

terozoic detrital sedimentation and volcanic-arc development,

relics of a Rheic ocean, Cambrian-Ordovician accretionary

wedges, evidence of an Ordovician orogenic event with related

granite intrusions, and subsequent volcanicity and sedimenta-

tion indicating the opening of paleo-Tethys. The occurrence of

active margin settings during the Early Silurian supports a

southward subduction of the Rheic and proto-Tethys oceans.

VARISCAN COMPLICATIONS—DISCUSSION

The pre-Variscan elements discussed herein have been in-

terpreted from a Gondwana point of view (von Raumer et al.,

2002), without regard to their post-Silurian evolution. Plate tec-

tonic reconstructions of the Variscan history depend on paleo-

magnetic data and models of Variscan evolution. Independent of

the model applied, the pre-Variscan elements mentioned herein

were strongly transformed during the Variscan collision, and

many of these relics appear today as polymetamorphic and

migmatized domains, wherein much information has been lost.

It is evident that size and contours of the many continental frag-

ments have changed considerably. Nonetheless, in our recon-

structions the original outlines are used to facilitate recognition

of well-known basement areas. Evidently, after the Silurian, the

Gondwana-derived continental blocks (Ziegler, 1984) started to

be involved in the global Variscan orogenic cycle. This is not the

place to discuss all the models currently available, and the reader

is referred to the references given in the introduction, and to the

new observations and data presented during the µeld trips at the

Fifteenth Basement Tectonics Meeting in A Coruña, Spain (Are-

nas et al., 2000; Gil Ibarguchi et al., 2000). In northwestern

Spain, large-scale nappes and their ramps and horses involved

all lithospheric levels, from the upper mantle to the upper crust,

thus redistributing the former lateral orogenic zonation. Com-

parable observations come from the mid-European Variscides

(Matte et al., 1990; Schulmann et al., 1991; Mingram, 1998;

Stipska et al., 1998). It is evident that a pre-Variscan orogenic

zonation has been involved in the Variscan collisional events

(e.g., Martinez Catalán et al., 1997; Arenas et al., 2000), and

relics of oceanic domains appear as fragments within large di-

vergent orogenic belts (Pin, 1990; Matte, 1991; Martinez Cata-

lan et al., 1999).

Although we do not discuss details about the Variscan meta-

morphic evolution, we add some new points of view concerning

the oceanic evolution. Such a discussion is needed in relation to

the different oceanic realms of the Variscan domain (e.g., Iape-

tus, Rheic, Galicia–Massif Central oceans) that have already

been identiµed. Although many occurrences of so-called am-

phibolites known from the Variscan mountain chain still need to

be geochemically characterized and dated, a comparative ap-

proach (von Raumer et al., 2002, and references therein) may

furnish additional arguments for comparing plate tectonic

events across continental fragments derived from Gondwana. In

the following summary of related arguments, based on the in-

ferred former peri-Gondwanan location, we assume, instead of

multioceanic models, the existence of one aborted Rheic ocean,

contemporaneous with the drift of Avalonia, in all basement

units derived from Gondwana (i.e., Cadomia sensu lato and the

Alpine terranes). This model includes the Pulo do Lobo, Gali-

cia, and Massif Central oceans (Robardet, 2000, and also local-

ities from the Bohemian massif; Crowley et al., 2000), and µts

the interpretation of the Cambrian events in northwestern Iberia

(Abati et al., 1999). Pieces of this suture zone, in the basement

assemblages of Cadomia (sensu lato) and the Alpine areas, were

accreted or obducted to the Gondwana margin in the Ordovi-

cian, whereas Avalonia underwent Ordovician-Silurian collision

with Laurentia-Baltica. The main point we develop is that the

continuation of subduction of the Rheic–proto-Tethys oceans

under the remaining peri-Gondwanan blocks triggered mag-

matic events (the subducting ridge being a heat source) and

backarc spreading (with the formation of sedimentary basins

and extrusion of volcanics) from the Middle Ordovician and,

µnally, the opening of paleo-Tethys, from the Silurian. There-

fore, this new proposal considers that the Variscan collision in

Europe took place between Gondwana-derived terranes and

Laurussia and not between Laurussia and Gondwana (Stamp×i

et al., 2000).

266 G.M. Stamp×i, J.F. von Raumer, and G.D. Borel

short

GENERAL PRINCIPLES

In North America and western Europe, Variscide collisional

processes are usually inferred to have ranged from the Early De-

vonian to the Late Carboniferous–Early Permian; and the

Tethyan cycle (opening of the Alpine Tethys–Central Atlantic

system) not to have started before Middle Triassic time. An ap-

parent lack of major tectonic events during the Permian and Tri-

assic is certainly responsible for the focus of attention on the Car-

boniferous history of the Variscides of Central Europe. However,

the Variscan domain extends over the entire Alpine area and even

further in the Dinarides and Hellenides. It also extends in time as

deformations become younger, possibly grading into the eo-

Cimmerian (Middle to Late Triassic) deformations, southward

and eastward. This assumption is based on the fact that the pa-

leo-Tethyan domain was not fully closed in southeastern Europe

before the Late Permian. This is shown by Early Permian to Mid-

dle Triassic fully pelagic sequences found in Sicily (Catalano et

al., 1988) and similar Carboniferous to Middle Triassic se-

quences in Crete (Krahl et al., 1986; Stamp×i et al., 2002), lo-

cated at the southern border of the Variscan domain. In the Hel-

lenides and farther east, the µnal closure of this oceanic realm

generally took place during the Carnian (S¸engör, 1984).

Stamp×i et al. (1991) and Stamp×i (1996) discussed this di-

achronous closure of the large paleo-Tethys ocean, insisting on

the development of backarc oceans or basins within the Per-

mian-Triassic Eurasian margin (Ziegler and Stamp×i, 2001) and

the closure of paleo-Tethys between terranes drifting away from

Eurasia (e.g., Pelagonia; Vavassis et al., 2000) and terranes drift-

ing away from Gondwana (the Cimmerian blocks of S¸engör,

1979; Stamp×i, 2000; Stamp×i et al., 2001a, 2001b).

Subsequently, the Atlantic-Alpine-Tethys system opened

north of this eo-Cimmerian collisional zone, which thereafter

was fully incorporated into the Alpine fold belt. This explains

why the end member of the Variscide orogeny, the eo-Cimmer-

ian event, is usually not taken into consideration by many. For

most of those who study the Hercynian, the southern part of

Variscan Europe (e.g., Spain, southern France) is usually re-

garded as stable Gondwana, which certainly it was in early Pa-

leozoic time, whereas it was part of Gondwana-derived terranes

accreted to Laurussia between the Late Devonian and Early Car-

boniferous. We formerly grouped these terranes as the Hun su-

perterrane (von Raumer et al., 1998; Stamp×i, 2000). In view of

their relatively independent kinematic evolution (Fig. 3), we

propose labeling its eastern components (Karakum-Turan,

Tarim, north China, south China, north Tibet, and Indochina) the

Asiatic Hunic terranes, whereas its western part is labeled the

European Hunic terranes and comprises three major blocks: Ar-

morica (sensu lato), Cantabria-Aquitaine-Ligeria-Moldanubia,

and Alboran–Adria–intra-Alpine–Cetic (Fig. 4).

The main outcome of this proposal is that the Variscan col-

lision must be polyphase and polymetamorphic. Initially it was

made of the accretion of major terranes along the European seg-

ment of the passive margin of Laurussia (Avalonia), correspon-

ding to the closure of the Rheic ocean in the Late Ordovician

(Fig. 3). Thereafter, Gondwana collided with Laurussia, includ-

ing previously accreted terranes, mainly along the Alleghanian

segment of Laurussia; this last event was diachronous and young-

ing eastward and corresponded to the closure of the paleo-Tethys.

This scheme implies that after the accretion of the European

Hunic terranes to Laurussia (Avalonia), the ocean located to the

south of them (paleo-Tethys) started subducting northward, the

Laurussian margin becoming an active margin. Subsequent sub-

duction of the mid-oceanic ridge of paleo-Tethys led, in Visean

time, to a Variscan cordillera stage.

HUN SUPERTERRANE

The European Hunic terranes include all continental frag-

ments accreted to Laurussia during the Variscan cycle and in-

ferred to have previously been in lateral continuity with Avalo-

nia along the Gondwana margin (Fig. 2). We place Armorica

(sensu lato) (Ossa-Morena, Central Iberia, Brittany, Saxo-

Thuringia) north of North Africa (Fig. 2) based on paleomag-

netic data (e.g., Torsvik and Eide, 1998; Torsvik et al., 1992) and

sedimentological and faunal data (e.g., Paris and Robardet,

1990; Robardet et al., 1994; Robardet, 1996). These data do not

show a major separation of Armorica from Gondwana before the

Early Devonian. We propose that all the other Hunic terranes

were in lateral continuity to Armorica (sensu lato), forming a

ribbon-like superterrane. Their drifting from Gondwana is de-

limited by paleomagnetic data from the eastern part of the Eu-

ropean Hunic terrane, like the Noric-Bosnian block (Schätz et

al., 1997) and the Bohemian block (Krs and Pruner, 1999).

The Asiatic Hunic terranes elements are represented by Tu-

ran and Pamir (the Kara-Kum–Tarim terrane of Khain, 1994;

Zonenshain et al., 1990), together with Tarim and north China,

which are inferred to have escaped from Gondwana in the Early

Devonian. This escape followed the accretion to the northern

parts of these regions of the Serindia terrane in the Late Sil-

urian–Early Devonian (Meng and Zhang, 1999; Yin and Nie,

1996), as well as the accretion of island arcs in Vietnam (Find-

ley, 1998) and east China (Hutchison, 1989) at the same time; a

similar development is also found along the Australian margin

(e.g., Foster and Gray, 2000).

Therefore, the Hun superterrane in Early Ordovician (Fig. 2)

to Early Silurian reconstructions is spread over a relatively large

paleolatitudinal area (from 60° south to the equator). Changes of

facies can be expected between Armorica and terranes in the Alps

(e.g., Carnic, Austroalpine, and intra-Alpine domains) located

within the tropical zone, which present a Silurian to Carbonifer-

ous stratigraphic evolution very similar to that of the Gondwanan

margin in Iran (Alborz) and Turkey (Taurus).

The prerift-synrift sequences of the Hun superterrane pres-

ent a uniform sedimentary evolution equal to that found on the

Gondwanan border. For example, in the Armorica (sensu lato)

Paleozoic evolution of pre-Variscan terranes 267

short

OUTH

POLE

OLE

320 Ma

MUG

SOUTH

OUTH

POLE

OLE

SOUTH

OUTH

POLE

OLE

MUG

Kh-Ma

340 Ma

SOUTH

OUTH

POLE

OLE

SOUTH

OUTH

POLE

OLE

360 Ma

SOUTH

OUTH

POLE

OLE

SOUTH

OUTH

POLE

OLE

380 Ma

Asiatic Hunic

European Hunic

Asiatic Hunic

European Hunic

SOUTH

OUTH

POLE

OLE

SOUTH

OUTH

POLE

OLE

SOUTH

OUTH

POLE

OLE

400 Ma

Asiatic Hunic

European Hunic

SOUTH

OUTH

POLE

OLE

SOUTH

OUTH

POLE

OLE

SOUTH

OUTH

POLE

OLE

420 Ma

SOUTH

OUTH

POLE

OLE

VALONIA

Figure 3. Drift history of Gondwana-derived basement areas

between Late Silurian and late Carboniferous. 420 Ma pro-

jection is centered on present-day lat 10N, long 25E; 400 Ma

and 380 Ma projections are centered on 10N, 20E; 360 Ma

projection is centered on 05N, 25E; 340 Ma projection is

centered on 10N, 25E; and 320 Ma projection is centered on

20N, 20E. These reconstructions were elaborated using

GMAP program (Torsvik and Smethurst, 1994, 1999). Ref-

erence paleopoles are from Baltica (Torsvik and Smethurst,

1994, 1999). Position of Gondwana is constructed from pa-

leomagnetic data (van der Voo, 1993; Klootwijk 1996) and

admissible wander path (e.g., Tait et al., 2000; Stamp×i and

Borel, 2001). Mug, Mugdozar ocean; Pp, Paphlagonian

ocean; KT, Karakum-Turan; Tm, Tarim; nC, north China;

sC, south China; nT, north Tibet (Qiantang); IC, Indochina

(Borneo included); KZ, Kazakhstan.

LEGEND

PaleoTethys

Laurussia

Gondwana

320 Ma

PaleoTethys

Laurussia

340 Ma

PaleoTethys

Laurussia

360 Ma

Paphlagonian

ocean

PaleoTethys

Rheic

Laurussia

380 Ma

PaleoTethys

Rheic ocean

Asiatic ocean

Gondwana

420 Ma

segment (Robardet et al., 1994), Late Ordovician clastics (in-

cluding minor volcanics) representing synrift formations are

capped by Ashgillian glacial marine deposits, related to an ice

cap that possibly developed on the nascent rift shoulders (e.g.,

Sardinia, Ghienne et al., 2000; Taurus, Monod et al., 2002).

Early Silurian marine sediments containing cherts represent a

southward deepening toward the rift zone and are dominated by

black graptolite shales. These anoxic Silurian deposits charac-

terize the widening of the rift zone, but also show that connec-

tions with major oceans were not yet realized. Silurian ×ood

basalts have been reported in many areas, and can be regarded

as contemporaneous with the onset of sea×oor spreading.

The postrift evolution of the European Hunic terranes dif-

fered greatly depending on their µnal position in relation to the

Rheic suture to the north or the paleo-Tethys suture to the south.

The present juxtaposition of terranes cannot be used readily to

understand their transformation during the Devonian and Car-

boniferous. Some terranes were deeply metamorphosed during

the Middle Devonian, others were affected later in Visean time

(340 Ma), and ×ysch development on some blocks did not start

before the late Carboniferous (310 Ma). Thus it is obvious that

some blocks were not involved in the µrst phase of metamor-

phism, which must have affected mainly the leading edge of the

superterrane, being related to the subduction and suturing of the

Rheic ocean. The European Hunic terranes were µnally accreted

individually to Laurussia, but not before the Visean, and were

accompanied by widespread metamorphism and development

of ×ysch. The former could be due to imbrication of the terranes

and crustal thickening processes, or also to the subduction of a

remnant mid-ocean ridge in the paleo-Tethys ocean (Fig. 3).

Large parts of the Hun superterrane kept Gondwanan fau-

nal characteristics at least until Early Devonian time. The con-

clusion that a large ocean never separated Armorica and Gond-

wana (Robardet et al., 1990) could be explained by a connection

between Gondwana and the Hun superterrane throughout its

drifting history, being, in its westernmost sector, always at-

tached to South America (Fig. 3). However, these Gondwanan

faunal characteristics disappeared in Praguian time, when simi-

lar spore assemblages are found in North Africa and in the

Rheno-Hercynian domain (Paris and Robardet, 1990). This can

be explained if the Hun superterrane is viewed as a land bridge

Paleozoic evolution of pre-Variscan terranes 271

Figure 4. Detailed plate tectonic evolution of pre-Variscan units pre-

served in European Variscan mountain chain (see text for explanation).

AA, Austro-Alpine; Ab, Alboran; Ad, Adria–south Alpine; Al, Alborz;

Am, Armorica; Ap, Apulia; Aq, Aquitaine; Ce, Cetic; Ch, Channel; cI,

central Iberia; Ct, Cantabria; DH, Dinarides-Hellenides; Di, Dizi; Do,

Dobrogea; gC, great Caucasus; Gi, Giessen; He, Helvetic; Hz, Harz;

iA, intra-Alpine; Ib, northwestern Iberia allochthon; Is, Istanbul; Kb,

Karaburun; KT, Karakum-Turan; Lg, Ligerian; Lz, lizard; MD,

Moldadubian; Mg, Meguma; Mo, Moesia; Ms, Meseta; OM, Ossa-

Morena; Or, Ordenes ophiolites; Pe, Penninic; Pp, Paphlagonian; RH,

Rheno-Hercynian; Sk, Sakarya; SM, Serbo-Macedonian; sP, south Por-

tuguese; Sx, Saxo-Thuringian; tC, trans-Caucasus; Zo, Zonguldak.

between the two domains. This also supports the idea that the

collision of Armorica (sensu lato) with the Eurasian domain (or

Eurasian outliers) occurred ca. 380 Ma. An earlier collision (Sil-

urian) is not supported by these faunal data, or by the lack of Sil-

urian synorogenic deposits on the Eurasian (Avalonian) margin

(e.g., the Rheno-Hercynian domain) facing the Rheic ocean.

There seems to be a contradiction between the inference

that Armorica should have docked with Laurussia in Middle De-

vonian time and the µnal welding in Namurian time, after the

closure of the Rheno-Hercynian domain. To reconcile these dif-

ferent lines of evidence, we propose that Armorica collided in

Middle Devonian time with blocks detached from the Lauruss-

ian (Avalonian) margin during an Early Devonian rifting event.

The latter led to the opening of the Rheno-Hercynian basin in

the Emsian, within the southern passive margin of Laurussia.

The oceanic nature of this basin (the Rheno-Hercynian ocean)

is proven by the ophiolitic and pelagic remnants found in the

Lizard, Giessen, and Harz nappes.

There are other problems associated with the present juxta-

position of the different terranes. The Cantabrian-Aquitaine ter-

rane (Fig. 4) developed a ×ysch sequence only in Moscovian

time (ca. 310 Ma) and was µnally juxtaposed with high-grade

metamorphic nappes of the Galician zone, where the metamor-

phism is much older (Middle Devonian). The Ligerian-

Moldanubian cordillera, extending from southern Brittany to

central Europe, is also juxtaposed to areas to the north (Armor-

ica sensu lato) and to the south (Aquitaine terrane, comprising

the Montagne Noire and Pyrenees), where ×ysch development

only started at the earliest in the late Visean or Namurian. How-

ever, large parts of the cordillera were strongly metamorphosed

before that time. Relics of a major Middle Devonian metamor-

phic event are found in nearly all the metamorphic domains of

the Variscan orogen. This has been conventionally interpreted as

a collision involving major continents (i.e., Gondwana and Lau-

russia), but no syncollisional ×ysch has ever been described in

neighboring regions and Gondwana was never close enough to

Laurussia to generate a continent-continent collision (Tait et al.,

2000; Stamp×i and Borel, 2002).

Our model (Figs. 2 and 4A) places all the European Hunic

terrane segments in continuity with each other in order to avoid

these contradictions. The leading, northern border of the supert-

errane is regarded as an active margin, affected by metamor-

phism and plutonism, whereas its hinterland stayed away from

this tectonothermal activity and developed a passive margin sed-

imentary succession. This situation prevailed until the Late De-

vonian (Fig. 4C), when major transcurrent events displaced the

eastern segments westward and intraterrane collisions took

place. The latter were accompanied by widespread ×ysch de-

velopment and the building of a Visean cordillera, usually with

diverging boundaries around the major blocks, giving rise to

double-vergent cordilleras (e.g., Matte, 1991; Neubauer and

Handler, 2000). The Rheic suture would have been located along

the northern active margin of the superterrane, whereas the pa-

leo-Tethys suture should be located along the southern border of

the superterrane. However, in view of the major Carboniferous

lateral displacements and rotation (Edel, 2000, 2001), suture du-

plication took place and led to present-day multiocean models.

The present southernmost portion of the European Hunic

terrane (the Noric-Bosnian terrane of Frisch and Neubauer,

1989), comprising Alboran, Adria, the intra-Alpine domain

(Carnic and Julian Alps, Tizia, Apuseni, Transdanubian, and

Bükk units), and domains located in the Dinarides and Hel-

lenides, together with north Sardinia and part of the southern

Alps, was transported southwestward during the µnal Laurussia-

Gondwana collision in the late Carboniferous (Fig. 4E). It col-

lided with the Visean cordillera to form a double vergent orogen

(Neubauer and Handler, 2000), following the fast northward

drift of Gondwana (Fig. 3). Other metamorphic units found in

the Alps (e.g., Cetic terrane) represent part of the Visean

cordillera, possibly transported westward with the Noric-Bosn-

ian block. In this context the Penninic domain would have been

located formerly to the east of the Helvetic domain (Giorgis et

al., 1999). This late Carboniferous collisional event was re-

sponsible for the µnal tectonic conµguration of the Variscan oro-

gen. These southernmost Variscan units are also characterised

by the development of late Carboniferous magmatic arcs along

their southern margins, dominated by calc-alkaline intrusions

(Stamp×i, 1996, and references therein), extending from the

Alboran domain (e.g., Calabria with a transition from arc to rift

between 295 and 275 Ma; Acquafreda et al., 1994) to the Hel-

lenides (Vavassis et al., 2000) and possibly to the Pontides. The

magmatic arcs were replaced in Permian time by major rift

zones leading to the opening of backarc basins in Late Per-

mian–Triassic time (Stamp×i, 2000; Stamp×i et al., 2001a,

2001b; Ziegler and Stamp×i, 2001).

The Carboniferous lateral displacements and rotations im-

ply the presence of major transcurrent faults and the opening of

Gulf of California–type oceans within the European Hunic ter-

rane (Fig. 4D). It is obvious that high-pressure rocks character-

izing the Middle Devonian event had to reach the surface rela-

tively rapidly, and the transcurrent movements were locally

largely transtensive, creating intramountain basins, usually

starting in the Late Devonian and found in the middle of the

Ligerian-Moldanubian cordillera. Younger Carboniferous coal

basins are also widespread. In this context the Zone Houillère

(Cortesogno et al., 1993), extending over 100 km or more in the

Penninic domain (Fig. 4E), is regarded as a late Carboniferous

pull-apart basin along one of these major faults (Giorgis et al.,

1999). It was accompanied by late Carboniferous–Early Per-

mian granites and minor gabbros, also found elsewhere in the

Alps (e.g., Capuzzo and Bussy, 2000) and emplaced in a sce-

nario of cordillera construction and destruction, but in a general

context of a still active margin.

Pelagic sequences of the Chios-Karaburun domain in the

Aegean region (Stamp×i et al., 2002), juxtaposed with Variscan

metamorphic blocks (Pelagonia, Sakarya), could also be part of

such gulf-like deep basin and/or of the paleo-Tethys accre-

tionary prism (Kozur, 1997, 1998). Carboniferous to Permian

mid-ocean ridge basalt (MORB) found in the Tavas unit of the

Lycian nappe (Kozur, 1999; Kozur et al., 1998), and in eastern

Iran (Ruttner, 1993) could be related to such Gulf of Califor-

nia–type oceans and/or to the paleo-Tethys (Fig. 4D).

These Visean lateral displacements would also involve ma-

jor crustal thickening in transpressive areas and the buildup of

high reliefs, leading to a cordillera stage, which lasted as long

as a relatively buoyant part of the paleo-Tethyan slab was sub-

ducting under the Eurasian margin. The major geodynamic

event at that time was the subduction of the paleo-Tethys mid-

ocean ridge. Thereafter, from the Late Carboniferous onward,

the increasing age of the subducting paleo-Tethyan slab gener-

ated important slab rollback and general extension affected the

cordillera from the Early Permian.

MIDDLE DEVONIAN PHASE

The opening of the paleo-Tethys along the European Hunic

segment and westward is viewed as backarc spreading related to

Gondwana-directed (southward) subduction of the Rheic ocean

(Fig. 3). The principle governing the drifting of the European

Hunic terranes away from Gondwana is the roll-back toward

Laurussia of the Rheic slab after Ordovician subduction of its

mid-oceanic ridge. The strong pull force of the major subduct-

ing Rheic slab also triggered the opening of rifts in the subduct-

ing plate, leading to the opening of small oceanic basins (the

Rheno-Hercynian ocean). This could explain the early collision

(during the Devonian) of Gondwana-derived European Hunic

terranes with Laurussia-derived terranes, whereas major colli-

sion and closure of the Rheno-Hercynian basin only took place

in Late Carboniferous time. We review next the evolution of the

intervening elements, the Rheno-Hercynian basin, the European

Hunic active margin in Armorica, the Ligerian cordillera, the

composite Middle Devonian event, and the Appalachians.

Rheno-Hercynian basin

The Rheno-Hercynian basin is characterized by important

volcanism from the Early Devonian (e.g., Walliser, 1981;

Ziegler, 1988) that extended through most of the Devonian

Period. Geochemical characterization of this volcanism (Floyd,

1995) has shown the purely ensialic extensional nature of this

basin, and the absence of any subduction-related signatures.

MORBs have been found in many places (Lizard, Giessen,

Harz) and point to sea×oor spreading, most likely starting in the

Emsian. From the Namurian onward, this basin became a ×ex-

ural basin in the foreland of the advancing Variscan nappes; the

sedimentary records do not show evidence of any tectonic event

before this.

The prerift sequence is locally composed of relatively com-

plete Ordovician to Silurian sequences (e.g., east of the Rhine;

Franke, 1995), or a Silurian sequence with a gap between the

Silurian and Devonian (e.g., Moravo-Silesian region; Dvorak,

1995). Therefore, there is no indication of any middle Paleozoic

272 G.M. Stamp×i, J.F. von Raumer, and G.D. Borel

(Caledonian) event in what we regard as the hinterland part, i.e.,

the southern passive margin of the Avalonia terranes, whereas

by contrast, in its front part (e.g., the present northern Variscan

foreland), the Ordovician-Silurian sequence is clearly deformed

due to the suturing of Avalonia to Baltica. The rift shoulder up-

lift occurred in the Early Devonian, marked by clastic input de-

rived from the south or by a so-called Caledonian unconformity

in the Rhenish Massif. Thereafter, sedimentation graded from

Early Devonian synrift deposits to Middle Devonian to early

Carboniferous pelagic deposits (Franke, 1995).

European Hunic active margin in Armorica (sensu lato)

The accretionary prism to the south of the Rheno-Hercyn-

ian ocean is composed of the Giessen-Harz nappes and the

northern Phyllite zone. The mid-German Crystalline High

played the role of backstop; it is characterized by volcanic-arc

activity in Silurian time (e.g., Reischmann and Anthes, 1996;

Anthes and Reischmann, 2001). Pelagic sediments, extending

from the Silurian to the Early Carboniferous, are found in

melange or slivers in the accretionary sequences together with

MORB and other basalts of intraplate afµnity (seamounts; e.g.,

Flick et al., 1988; Nesbor et al., 1993). The Lizard ophiolite of

Cornwall is considered to be a Devonian ophiolite; its emplace-

ment in the accretionary prism was dated as Famennian

(365–370 Ma) by Sandeman et al. (1995) and could correspond

to the collision of the Rheno-Hercynian mid-oceanic ridge with

the prism.

The Rheno-Hercynian prism evolved from an older accre-

tionary belt developed during the southward subduction of the

Rheic ocean in Silurian time. The Rheic prism incorporated a

detached Eurasian block, located south of the Rheno-Hercynian

ocean; detached from the already thinned Avalonian passive

margin, this block could have been easily subducted. Its under-

plating and the subduction of the buoyant young Rheno-Her-

cynian oceanic lithosphere provided the necessary condition for

Devonian high-pressure rocks to be exhumed. The absence of

pelagic material older than Emsian in the Giessen-Harz nappe

makes it difµcult to place the Rheic prism in this domain; there-

fore, the Rheic suture should be placed in the Northern Phyllite

zone (Franke, 2000). In the Wippra area of the Phyllite zone,

MORBs are supposed to be partly of Ordovician and Silurian

age (Meisl, 1995), thus representing the Rheic ocean ×oor. Or-

dovician and Silurian fauna are described in this zone, some

with tropical or even boreal afµnities, which can be taken as a

Rheic signature.

A Silurian high-pressure event, recorded in the Leon do-

main in northern Brittany (Le Corre et al., 1991), could be re-

garded as a western continuation of this Rheic suture. In Gali-

cia (Marcos et al., 2000; Arenas et al., 2000) high-pressure

metamorphism in the allochthonous nappe is in the range

390–380 Ma. This Middle Devonian metamorphic complex

comprises several types of Ordovician ophiolitic fragments

transformed into eclogites, protolith ages ranging from 490 to

460 Ma and therefore possibly pertaining to the Rheic ocean. It

also contains other ultramaµc rocks (e.g., in the middle of the

Ordenes complex) with younger ages (390–380 Ma) (Ordoñez

Casado, 1998; Díaz García et al., 1999; Pin et al., 2000), most

likely representing the extension of the Rheno-Hercynian ocean

in that region (Fig. 4B). Thus the Middle Devonian event would

have sutured the Rheic ocean and created a new accretionary

wedge, including ophiolites of the Rheno-Hercynian ocean. The

second metamorphic event in the Cabo Ortegal sequence, dated

as ca. 345–350 Ma (Ordoñez Casado, 1998), would correspond

to the subduction of the paleo-Tethyan mid-oceanic ridge and

the buildup of the Visean cordillera. Younger ages (330–345 Ma)

were found in more external domains in the Ossa-Morena zone

(Ordoñez Casado, 1998) and mark the µnal suturing of Armor-

ica (sensu lato) with the South Portuguese promontory. The

Beja-Acebuches ophiolitic complex, separating the Ossa-

Morena zone from the South Portuguese zone (Oliveira and

Quesada, 1998; Eguiluz et al., 2000), would then correspond

again to the Rheic suture. The Pulo do Lobo accretionary com-

plex, located in a more external position, comprises normal-

MORB remnants, unconformably overlain by Late Devonian

×ysch. Therefore, it can be regarded as the Rheic accretionary

prism, comprising a fragment of the Rheno-Hercynian ocean.

The Late Devonian–Carboniferous development of the

South Portuguese zone would be directly related to the onset of

paleo-Tethys northward subduction, after the Middle Devonian

event. The ×ysch of the South Portuguese zone was derived from

backarc type basic rocks that cannot be of Rheno-Hercynian ori-

gin, but could be paleo-Tethyan. Thereafter, there is a wide-

spread development of a volcanic-sedimentary complex (the

Pyrite Belt) of Late Famennian–Visean age and bimodal signa-

ture, where felsic volcanics predominate (Thiéblemont et al.,

1994). This belt may represent a forearc-type basin to the newly

established active margin of Laurussia. Such Late Devonian

basins, where extension predominates, are also known in the

Meseta and Meguma-Avalon domain (e.g., Piqué and Skehan,

1992). These basins characterize the subduction and rollback of

the nonbuoyant northern part of the paleo-Tethyan slab. As sub-

duction proceeded, the mid-ocean ridge µnally collided with the

margin, probably in Visean time, generating numerous granitic

intrusions and closing these basins. Oroclinal bending of the

cordillera then took place and deformed the originally linear fea-

tures of the active margin (Weill et al., 2001). Such an oroclinal

bending of a large terrane was recently proposed by Johnston

(2001) for the Great Alaskan Terrane (SAYBIA).

Ligerian cordillera

In our model, suturing of the Rheic ocean took place all

along the outer border of the western part of the European Hunic

terranes during a Middle Devonian accretionary phase (Fig. 4B).

We have already extended the situation described herein from Ar-

morica (sensu lato) to the Iberian allochthonous units of Galicia,

and we infer that it extended eastward to the Münchberg nappe

Paleozoic evolution of pre-Variscan terranes 273

and to the western Sudetes. However, this Middle Devonian

event also affected areas located south of the Armorica (sensu

lato) domain. The Middle Devonian eo-Variscan metamorphic

event affected the Massif Central and other northern European

Variscan units (Faure et al., 1997) and was accompanied by

Givetian-Frasnian high-pressure events dated as 380–370 Ma.

This event, affecting simultaneously areas now imbricated in the

entire Variscan orogen, could not be a major continent-continent

collision, because Gondwana was still far away to the south at

that time (e.g., Tait et al., 2000; Stamp×i and Borel, 2002), and

the Rheno-Hercynian ocean far from closing (Fig. 3). To avoid

multiplying the number of oceans and terranes, we infer that all

the areas affected by this Ligerian phase were formerly located

on the leading edge of the eastern part of the European Hunic ter-

ranes. An example of this is the Middle Devonian suture between

the Saxo-Thuringian and Tepla-Barrandian domains (Franke et

al., 1995), where the Saxo-Thuringian domain, being of clear Eu-

ropean Hunic afµnity, cannot represent a block detached from

Laurussia during the opening of the Rheno-Hercynian ocean.

However, the sedimentary sequences in the Saxo-Thuringian

basin did not record the Middle Devonian collisional event;

pelagic conditions predominate from Silurian to Early Carbonif-

erous time (Falk et al., 1995). Therefore, as is the case for many

other parts of this Middle Devonian Rheic suture, it must have

been laterally displaced, and the present relationship between the

two domains remains ambiguous.

The same reasoning could be applied to other potential

Rheic suture zones like the Moldanubian and the Massif Central

domains. It is not yet clear if the Moldanubian zone underwent

this Middle Devonian event (Vràna et al., 1995), but it seems that

the major cordillera-building processes affecting this zone oc-

curred in the Early Carboniferous, most likely due to intra-Hu-

nic collisional events. However, the high-pressure rocks dated as

Middle Silurian in Bavaria (427 ±5 Ma; von Quadt and Gebauer,

1993) point to an active margin setting of the Moldanubian zone

at that time (like the German Crystalline zone and the Leon do-

main), but not necessarily to collision. Therefore, the Moldanu-

bian domain could also represent the same leading accretionary

edge of the European Hunic terranes at that time and should have

been located eastward of the Sudetes in prolongation of the Ar-

morica (sensu lato) terrane (Fig. 4).

Similarly, the Ligerian cordillera of central France (Que-

nardel et al., 1991), extending up to the South Armorican do-

main (Le Corre et al., 1991), represents a large part of this De-

vonian Rheic suture zone and would also have been located east

of the Sudetes. The metamorphism of the Massif Central was be-

tween 400 and 360 Ma, whereas poorly dated older high-pres-

sure events could be related to Silurian subduction of the Rheic

ocean. Lardeaux et al. (2001) proposed an oblique continent-arc

collision for this region, a scenario similar to our Figure 4B. The

high-pressure event of South Armorica (Champtoceaux com-

plex) is dated as ca. 360 Ma (Ballèvre et al., 2000), including

continent-derived protoliths of Early Ordovician age. These

units were exhumed in the Visean and largely imbricated by

thrusting and shearing during dextral movements in the Late

Carboniferous. We have here the juxtaposition of two different

domains, the Ligerian and Armorican, along a continental su-

ture. Subduction-related granitic activity in Armorica was

mainly Carboniferous and may correspond to the subduction of

paleo-Tethys after the Middle Devonian event.

Composite Middle Devonian event

As shown in Figures 3 and 4, the Middle Devonian event

would have been created in a different geodynamic context

along the northern border of the Hun superterrane. From Portu-

gal-Galicia to the Sudetes, this event corresponds to the con-

sumption of a Rheno-Hercynian intervening terrane and mid-

oceanic ridge by the Rheic accretionary prism. This situation

can be extrapolated eastward in view of a potential continuation

of the Rheno-Hercynian ocean toward the Black Sea and Cau-

casus. In northern Turkey, Kozur et al. (1999) and Kozur (1999)

found remnants of a Carboniferous to Permian pelagic domain

(Paphlagonia) formerly located just south of the Istanbul zone,

which shows a development very similar to the Rheno-Hercyn-

ian domain (Göncüoglu and Kozur, 1998; Kozur et al., 2000).

This Paphlagonian ocean could be extended eastward to the Dizi

area of the western Great Caucasus (Adamia and Kutelia, 1987).

The difference between the situation east and west of the Moe-

sian promontory is that the µnal closure of these eastern pelagic

realms did not take place before the Permian.

In the oriental part of the European Hunic terranes, we pro-

pose that the Ligerian-Moldanubian domain collided with an is-

land-arc system derived from the subduction of the Asiatic ocean

(Zonenshain et al., 1985), a time equivalent of the Rheic ocean.

It was a large ocean connected to Panthalassa and developed nu-

merous island arcs. It was proposed that the amalgamation of

such island arcs (the Kipchak arc system) gave birth to the Kaza-

khstan plate (S¸engör and Natl’in, 1996). In view of the conver-

gence between Gondwana and the future continents composing

Laurasia, a collision between an Asiatic island-arc system and the

European Hunic terranes was probably unavoidable. We tenta-

tively place domains such as the Sakarya zone of northern Turkey

and part of the trans-Caucasus in this western Kipchak island-arc

system. Elements of this arc would also be found in the Ligerian-

Moldanubian cordillera, but most of this cordillera would most

likely belong to the European Hunic terranes.

Appalachians and Meguma-Meseta dilemma

In the Appalachians the situation is less clear, although po-

tentially simpler. It is less clear because a large part of the hin-

terland was lost in the opening of the Atlantic Ocean; it is ap-

parently simpler because the mountain-building processes

there appear to be a continuum of deformation (Keppie, 1989;

Piqué and Skehan, 1992). Some correlations are proposed be-

tween, for example, the Meguma belt and the Ligerian

cordillera of central France (Rast and Skehan, 1993), which

274 G.M. Stamp×i, J.F. von Raumer, and G.D. Borel

would somewhat complicate the story. One of the problems to

discuss here is the concept of tectonic phases, and, more pre-

cisely, the Acadian. This concept can only be used if it is sup-

ported by a consistent plate tectonic scheme; otherwise it is

meaningless. The Acadian phase proper should be restricted to

the docking of Avalonia to Laurentia, a docking generally ac-

cepted to be µnished by Late Silurian time for east Avalonia but

later for west Avalonia (Early Devonian; Friend et al., 2000).

Therefore, younger events could correspond to the docking of

Hun-like terranes to Laurentia, followed by the onset of sub-

duction of paleo-Tethys under this continent. The docking of

such terranes to Laurentia would be more or less simultaneous

to the Middle Devonian event further west. Dallmeyer and

Keppie (1987) have shown that the Meguma terrane was af-

fected by an Early to Middle Devonian tectonometamorphic

event, which could conµrm the accretion of terranes at that

time. The Meguma terrane was later intruded by Late Devon-

ian granites, showing that subduction of paleo-Tethys under

North America had already started at that time. Was the

Meguma block accreted to North America in Middle Devonian

time (Hun origin), or was it already part of Avalonia and de-

tached from Avalonia and accreted again? These are main ques-

tions that are also relevant for the Moroccan Meseta, which is

often considered to be part of the Meguma terrane. The absence

of Silurian metamorphism in the Meguma and Meseta terranes

is not a proof of their separation from Avalonia, because only

the leading edge of Avalonia should have undergone such meta-

morphism. The leading northern edge of Meguma was affected

by the Acadian orogeny (slaty cleavage dated as 405 Ma; Kep-

pie, 1989), which would exclude a Hun origin, whereas its

southern border remained a passive margin attached, in that

case, to the Rheic ocean. Then it became an active margin, doc-

umented by Emsian deformation, extending southward to the

Carolina region, where a tectonometamorphic event was dated

as 340–360 Ma (Dallmeyer et al., 1986). A younger event, dated

as ca. 268–315 Ma, marked the µnal collision with Gondwana.

A magmatic arc development is also known in the Meseta

starting in the Tournaisian (Aouli granitoids, Oukemeni and

Bourne, 1993) and postcollisional granites were emplaced until

the Early Permian (Amenzou and Badra, 1996). However, the

Meseta (e.g., Piqué, 1989) is characterized on its southeastern

border by the development of a south-facing passive margin,

with a prominent Early Devonian rift shoulder in the Rehamna

region, passing to the southeast to Early to Middle Devonian

deep-water deposits, therefore representing potential northern

paleo-Tethyan marginal series characteristic of Hun-like ter-

ranes (see following). This margin was deformed during a Late

Devonian tectonometamorphic phase (Huon et al., 1993), fol-

lowed by the installation of an arc in Visean time, clearly mark-

ing the change from a passive to active margin setting. Late

Visean (ca. 325 Ma) wild-×ysch-type deposits, also present in

the High Atlas (Jenny, 1988), mark the onset of deformation dur-

ing the collision with Gondwana. Therefore, we can question the

Meguma-Meseta connection, the Meguma being of Avalonian

origin and the Meseta of Hun origin in our point of view. The

limit between the two terranes could be located just offshore

Morocco, west of the El Jadida escarpment, where low-grade

metamorphic rock have been drilled (Kreuser et al., 1984).

We propose extending the Hun superterrane to Ecuador in

order to include terranes, found now around the Gulf of Mexico

area, that were detached from Gondwana in the Paleozoic

(Dallmeyer, 1989; Keppie et al., 1996). Consequently, Hun-like

terranes must have collided with North America. Potential candi-

dates could be represented by the Carolina terrane (Horton et al.,

1989) and related blocks, apparently separated from Laurentia by

oceanic elements (Bel Air–Rising Sun terrane). Terranes impli-

cated in the Alleghanian-Ouachita orogen are other potential can-

didates, like the Sabine block (Keller and Hatcher, 1999), as well

as the Yucatan, Chortis, Mexican (Oaxaca, Arequipa-Antofalla),

and other Central American terranes (Keppie et al., 1996).

PALEO-TETHYS EVOLUTION

The paleo-Tethys is more or less completely ignored by

those who follow the classic Hercynian ideas; therefore it is im-

portant to present here the main lines of its geodynamic evolu-

tion. The opening of paleo-Tethys is relatively well deµned on

an Iranian transect (Alborz Range, north Iran; Stamp×i, 1978;

Stamp×i et al., 1991, 2001a, 2001b) representing the southern

Gondwanan margin of the eastern branch of the ocean. Late Or-

dovician to Early Devonian ×ood basalts, rift shoulder uplift in

the Silurian, followed by the onset of thermal subsidence in the

Devonian, point to a Late Ordovician–Silurian rifting phase.

Sea×oor spreading took place in the Late Silurian or Early De-

vonian and the rift shoulders were completely ×ooded in the

Late Devonian, following regional thermal subsidence of the

passive margin. From Late Devonian until Middle Triassic time

a carbonate-dominated passive margin developed. A similar

evolution is found in the Cimmerian part of Turkey (for details

see references in Stamp×i 1996; Göncüoglu and Kozur, 1998).

Toward the west, along the African domain, there are few

data concerning the detachment of the European Hunic terranes

from Gondwana. In the High Atlas of Morocco (e.g., Destombes,

1971), the Silurian unconformably overlies the Ordovician and

presents locally, at its top, a conglomeratic sequence; the over-

lying Emsian-Eifelian sequence is locally very condensed and

represented by open marine carbonates. This starvation event

represents the onset of important thermal subsidence, which can

be related to the drifting of either Armorica or the Meseta from

Africa. On the basis of current information, it is unclear whether

the opening took place simultaneously all along the Gondwana

margin. Our preference is that the opening was earlier along the

western branch of the ocean (Fig. 3). Farther west, along the

Gondwana border, a major Carboniferous sedimentary wedge

developed directly on the Precambrian basement along the Ama-

zonian craton in Ecuador (Litherland et al., 1994); the absence

of any sequence that could represent the early Paleozoic active

or passive margin of this craton allows the opening of paleo-

Paleozoic evolution of pre-Variscan terranes 275

Tethys to be extended to the northern part of South America (as

discussed herein about the Mexican terranes origin; Fig. 3).

The northern Hunic margin of the paleo-Tethys ocean is well

represented in the middle part of the European Hunic terranes in

the Carnic Alps (Schönlaub and Histon, 1999: Laufer et al., 2001),

Tuscany, Sardinia, and the Alboran fragments (cf. Stamp×i,

1996); it is also characterized by a Late Ordovician–Early Silurian

clastic and often volcanic synrift sequence (Silurian ×ood basalts

are also known in Sardinia and the Rif; Piqué, 1989). Rift-related

thermal uplift, erosion, and tilting took place in Silurian time and

are often (wrongly) related to the Taconic event (Tollmann, 1985).

Open marine conditions started in the Silurian, being represented

by a graptolites facies; a more general ×ooding took place in the

Early Devonian and marked the onset of widespread thermal sub-

sidence related to sea×oor spreading.

The Saxo-Thuringian domain was part of the northern mar-

gin of paleo-Tethys before the lateral displacement of the

Moldanubian zone to the south of it. Its autochthonous sequence

(Falk et al., 1995) is marked by basin deepening in Silurian time,

accompanied by lavas and tuffs in the Ludlow representing the

synrift event, whereas pelagic Gedinnian to Givetian sediments

represent the drift sequence.

On the northern margin, the Visean usually marks the onset

of widespread ×ysch deposition, often accompanied by volcanic

activity. We regard this major change as marking the general ag-

gregation of the different terranes to Eurasia to form the Variscan

cordillera; it also marks the onset of paleo-Tethys subduction

and the transformation of the margin from passive to active, the

×ysch troughs usually representing forearc basins. Accretionary

sequences related to this subduction are little known, most likely

because important subduction erosion took place during the

cordillera stage, as observed now along the South American ac-

tive margin. Potential paleo-Tethyan accretionary sequences are

located in the southern part of the Variscan orogen, and in all

cases were metamorphosed and intruded by subsequent Late

Carboniferous granites; in addition, they were usually involved

in eo-Cimmerian and Alpine deformation. However, pelagic De-

vonian-Carboniferous to Early Triassic pelagic sediments of pa-

leo-Tethyan origin are found in Sicily, the Dinarides, Hel-

lenides, and Turkey (Karaburun) (Stamp×i et al., 2002).

CONCLUSIONS

Deciphering the evolution of former circum-Gondwana ter-

ranes is a feasible enterprise; similar geological evolutions are

found in these terranes. The explanation of the present com-

plexity should not be sought in complex plate tectonic scenarios

involving numerous oceanic realms; on the contrary, and in view

of the similarities, a simple model is preferable. A single terrane

model is also proposed for the accretion of all the Alaskan ter-

ranes (Johnston, 2001).

We propose continuous southward subduction of oceanic

realms under the Gondwanan border, starting in the Late Neo-

proterozoic,which triggered the detachment of three main ter-

ranes. First Avalonia in the Early Ordovician, then the European

Hunic terranes in the Late Silurian, promptly followed by the

eastern Hunic terranes in the Early Devonian.

The accretion of these terranes to Laurussia was complex.

Whereas the Avalonia superterrane had a relatively simple evo-

lution with a classical collision of an active and passive margin,

a more complex scenario is necessary to explain the Variscan

collage. In order to take into account similarities in the different

parts of the European Hunic terranes, we propose that areas af-

fected by the Middle Devonian high-pressure phase were lo-

cated on the leading accretionary edge of these terranes, whereas

areas not affected by this major eo-Variscan event were located

on the paleo-Tethys margin of the terrane. This Middle Devon-

ian eo-Variscan event is inferred to be related to accretion of

buoyant material derived from Laurussia and subduction of a

peri-Laurussian ocean, whereas farther east the event is related

to collision with an island-arc system.

To explain the subsequent large-scale mixture of active and

passive margins, important lateral displacements and rotations

must be invoked: most who study Hercynian ideas would agree

with this proposition (e.g., Matte et al., 1990; Edel, 2000,

2001), but the majority would place these translations in a con-

text of continent-continent collision. We propose that these

took place during the displacement of terranes along a still-ac-

tive margin, the translations being accompanied by transten-

sional and tranpressional events leading to the opening of Gulf

of California–type oceans and in other places to the buildup of

cordilleras.

During the growth of the late Carboniferous cordillera, two

types of geological evolution developed. The westward one is

toward a continent-continent collision where the accreted ter-

ranes got squeezed between Laurussia and Gondwana (this is

the prevailing scenario for the Alleghanian regions), whereas

eastward, subduction continued with a general rollback of the

paleo-Tethyan slab. This, in turn, generated the opening of nu-

merous backarc basins and oceans, starting in the Early Permian

and lasting until the Middle Triassic closure of the paleo-Tethys

oceanic domain.

Postcollisional Permian-Carboniferous granites, for exam-

ple found in Morocco (e.g., Amenzou and Badra, 1996), should

be related to slab detachment when major crustal attenuation

through generalized extension is not documented. In other west-

ern European regions, postcollisional Permian-Carboniferous

granites should be related to slab detachment and/or the collapse

of the cordillera, but not to postcollisional processes, the µnal

collision being far distant in time and space. The µnal closure of

paleo-Tethys from Sicily to the Caucasus took place during the

eo-Cimmerian cycle, and the closure of backarc oceans issued

from the paleo-Tethys slab rollback took place only in Creta-

ceous time (Stamp×i et al., 2001b).

We hope that our provocative suggestions will trigger a new

round of discussion for the coming years; more µeld data should

be gathered for a better approach of Variscan history, and pale-

oreconstructions on a larger scale should be included.

276 G.M. Stamp×i, J.F. von Raumer, and G.D. Borel

ACKNOWLEDGMENTS

We thank the conveners of the Basement Tectonics 15 Galicia

2000 congress (R. Arenas, Madrid; F. Diaz Garcia, Oviedo; J.R.

Martinez-Catalan, Salamanca) for providing an ideal environ-

ment for stimulating discussion, encouraging us to publish this

paper, and for encouraging remarks. We also thank J. Mosar,

with whom these reconstructions were initiated, and H. Kozur

for sharing key information on Paleozoic paleogeography. Our

warm thanks to Dave Gee (Uppsala) for his engaged criticism

and a readable English version, and we thank an anonymous re-

viewer for constructive suggestions.

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280 G.M. Stamp×i, J.F. von Raumer, and G.D. Borel

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The distribution of Gondwana-derived terranes in the Early Paleozoic

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October 2012

Gérard Maurice Stampfli · Jürgen F. von Raumer · Gilles D. Borel

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Jan 2024
ISL ARC

The XV mafic‐ultramafic intrusion is located in the western part of the Posht‐e‐Badam Block (PBB) within the Central Iranian Micro‐Continent (CIMC). Petrographically, the intrusion is composed of gabbro and pyroxenite. Apatite U–Pb dating has established the crystallization age of this intrusion to be 363 ± 67 Ma. The XV intrusive rocks are tholeiitic to slightly calc‐alkaline in nature and are characterized by an enrichment of large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to high field strength elements (HFSE) and Heavy Rare Earth Elements (HREE), respectively. The major oxide elements display continuous trends relative to SiO 2 . The ⁸⁷ Sr/ ⁸⁶ Sr(i) ratios range from 0.7045 to 0.7056, and the εNd(i) values range from 2.63 to 3.30. In addition, the ²⁰⁶ Pb/ ²⁰⁴ Pb, ²⁰⁷ Pb/ ²⁰⁴ Pb, and ²⁰⁸ Pb/ ²⁰⁴ Pb ratios exhibit a narrow range, varying from 18.68 to 18.70, 15.67 to 15.71, and 38.84 to 38.99, respectively. The geochemical and isotopic characteristics suggest that the parental magma was derived from a Sub‐ Continental Lithospheric Mantle (SCLM) that was modified by oceanic slab‐derived components. The locations of the XV intrusive rocks in εNd(i) versus TDM (Ga) and Nb/La versus discrimination diagrams further support this conclusion. Fractional crystallization is identified as the dominant process influencing the formation of distinct lithological units within the XV intrusive rocks. Our newly presented isotopic and geochronological data, when considered in the regional context, suggest that the XV intrusive rocks were formed in an extensional tectonic setting. In this scenario, upwelling from the asthenospheric mantle induced heating, leading to the melting of previously subduction‐modified SCLM. Comparative analysis with previously published ages indicates that extensional magmatism in the PBB continued into the Middle Paleozoic.

The Ivrea-Verbano Zone lherzolites: Refractory or refertilized mantle? Both!

Conference Paper

Dec 2023

Dualism of intraplate and subduction-related volcanism in the Palaeozoic of the Rhenish Massif (Central Europe) and its plate tectonic relevance

Preprint

Full-text available

Jun 2024

H.-D. Nesbor

Palaeozoic volcanic rocks are widely distributed within the sedimentary rock sequence of the Rhenish Massif. A total of 185 new geochemical analyses of these have been evaluated, allowing a distinction based on indicative trace elements and rare earth elements between intraplate volcanism and subduction-related volcanism. The latter began in the Silurian and continued through the entire Devonian and likely into the early Carboniferous. The trigger for the volcanic activities was the subduction of the Rheic Ocean northward beneath the southern margin of Avalonia. A magmatic arc had developed above the subduction zone, where explosive eruptions occurred throughout the entire timespan. To the north the Rhenohercynian back-arc basin opened from the Lower Devonian onwards, whereby Avalonia was spited into a northern and a southern part. As a result of the increasing rifting of the thinned continental crust of the southern Avalonian shelf area, intense bimodal intraplate volcanism began in the Givetian, parallel to the subduction-related volcanism, persisting until the early Frasnian. The first volcanic cycle ended, after a long interruption in the deeper Upper Devonian, with the eruption of primitive basaltic magma in the highest Famennian. Due to the retreat of the subduction zone (roll back), Southern Avalonia migrated increasingly southward with simultaneous expansion of the back-arc basin. A new volcanic cycle began in the Early Carboniferous, which is characterized by an evolution from tholeiitic to alkaline basaltic magma. The products of both volcanic cycles occupy large areas in the Lahn-Dill region, the Kellerwald, and the Waldeck region. Subvolcanic intrusions and feeder dykes in the Northern Taunus and Sauerland evidence the widespread distribution of volcanism beyond the present-day limits imposed by erosion.

Detrital signatures of the Ghomaride Culm cycle (Rif Cordillera, N Morocco): New constraints for the northern Gondwana plate tectonics

Article

Full-text available

May 2024

Genesis of the Lakhshak orogenic Au–Sb deposit, SE Iran: insights from geology, microthermometry and stable isotope geochemistry

Preprint

Full-text available

Mar 2024

The Lakhshak Au–Sb deposit in the SE Iran, is closely associated with Eocene calc–schist and quartz schist rocks intruded by Oligocene dikes and mylonitic granitoid. The main mineralization is characterized by a NE–SW shear zone structure and hydrothermal alterations have mainly developed in the contact zones of granitoid and calc–schist units. Quartz veins and veinlets are associated with Au and Sb–bearing minerals consisting of pyrite, arsenopyrite, stibnite, pyrrhotite, chalcopyrite, sphalerite, gold and electrum. The ore genesis, metallogenic processes, and the origin of ore fluids in the Lakhshak deposit are unknown, hence we report for the first time the geological, petrographic, microthermometry of fluid inclusions, Raman spectroscopy and sulfur and oxygen isotopes studies. In this study, four types of fluid inclusion assemblages were recognized in the mineralized quartz veins. The results of fluid inclusion microthermometric measurments yield homogenization temperatures of two–phase LV (type III) and ternary carbonic–aqueous phase (LCO 2 + LH 2 O + VCO 2 ; type IV) fluid inclusions vary between 200 to 280°C and 300 to 330°C, whereas their salinity range from 9 to 11% and 8 to 13% wt. % NaCl, respectively. This implies that gold precipitation is derived from low–temperature and low–salinity ore fluids. The calculated δ ¹⁸ O fluid values of quartz vary from 7.5 to 9.8‰, implying that the ore fluids may have a metamorphic origin that reacted repeatedly with the volcanic rocks along the conduits as well as the granitoid units adjacent to the ores and subsequently experienced sporadic equilibrium in oxygen fractionation during formation. Therefore, due to the significant oxygen isotopic exchange in the fluid–rock reaction, the metamorphic fluids show the isotopic properties of specific fluids of magmatic origin. Moreover, the δ ³⁴ S values of pyrite (3.0 to 4.1‰) and stibnite (–0.9 to 0.8‰) from the main satge of mineralization show a magmatic origin for sulfur. Accordingly, it is suggested that the mixing and dilution of metamorphic fluids with meteoric water plausibly had a substantial effect on the evolution of ore–forming system at Lakhshak, similar to orogenic gold deposits worldwide.

Tracking cycles of Phanerozoic opening and closing of ocean basins using detrital rutile and zircon geochronology and geochemistry

Article

Full-text available

Feb 2024
GEOLOGY

Sedimentary basins provide a deep time archive of tectonic and Earth-surface processes that can be leveraged by detrital mineral U-Pb dating and geochemistry to track paleogeography, magmatism, and crustal evolution. Zircon preserves the long-term (billions of years) record of supercontinent cycles; however, it is biased toward preserving felsic crustal records. Detrital rutile complements the detrital zircon record by providing constraints on the time and temperature of rifting and mafic magmatism, metamorphism, exhumation of the middle and lower crust, subduction, and amagmatic orogenesis. We use detrital zircon U-Pb and detrital rutile U-Pb geochronology and trace element analysis of Permian to Eocene siliciclastic rocks in the southern Pyrenees to capture supercontinent cycles of ocean basins opening and closing. Detrital rutile age spectra show peaks at ca. 100 Ma associated with rifting and hyperextension in the Pyrenean realm, 200 Ma associated with the Central Atlantic Magmatic Province, and 330 Ma, 375 Ma, and 400 Ma associated with subduction and Rheic Ocean crust formation. Zr-in-rutile thermometry and rutile Cr-Nb systematics provide further insight into metamorphic facies (peak metamorphic temperatures) and source rock lithology (mafic versus felsic affinity). Detrital zircon age spectra have peaks at ca. 300 Ma, 450 Ma, and 600 Ma associated with major orogenic events and felsic magmatism, and Th/U ratios provide information on relative zircon formation temperatures. Comparison of these independent records shows that detrital rutile reflects rifting, magma-poor orogenesis, and oceanic lithospheric processes, while detrital zircon detects continental lithospheric processes. Integrated detrital zircon and rutile data sets archive past geological events across multiple Wilson cycles.

Constraining reducing conditions in the Prague Basin during the late Silurian Lau/Kozlowskii extinction event

Article

Jan 2024

The Silurian was marked by repeated extinctions, carbon cycle volatility, and significant intervals of climatic change. The most notable of these events were the Ludfordian Lau/Kozlowskii extinction and associated Mid-Ludfordian Lau carbon isotope excursion, both of which have been linked to a period of global cooling and expanded reducing conditions in the global oceans. Here we present new data that characterize marine paleoredox conditions of the Prague Basin, a peri-Gondwanan terrane. This study utilizes iodine-to-calcium ratios to assess local redox conditions in a shallow water carbonate succession and iron speciation and redox-sensitive trace element concentrations to assess local redox conditions of a deeper water sequence. Consistently low values of I/Ca in the shallow water section suggest either persistent local low oxygen conditions or possibly diagenetic overprinting. Iron speciation data suggest that bottom water redox conditions in the deeper shelf setting were consistently anoxic with possible intermittent euxinia. Concentrations of redox-sensitive trace elements consistently higher than upper continental crust values also indicate persistent reducing conditions in the deeper part of the basin. These local redox proxy data from the Prague Basin, including trends in new pyrite sulfur isotope (δ ³⁴ S pyr ) data, are consistent with findings that expansion of anoxic and/or euxinic oceanic conditions occurred. These data, derived from a mid-paleolatitude marine setting, fill an important gap in our current global dataset from this interval of the late Silurian. Thematic collection: This article is part of the Chemical Evolution of the Mid-Paleozoic Earth System and Biotic Response collection available at: https://www.lyellcollection.org/topic/collections/chemical-evolution-of-the-mid-paleozoic-earth-system Supplementary material: https://doi.org/10.6084/m9.figshare.c.7008107

Wilson cycles of the Zagros fold and thrust belt: A comprehensive review

Article

Jan 2024

Phanerozoic structures and events

Article

Jan 1992

Wolfgang Franke

Petrography and K-Ar dating of the Mazagan granodiorite, Deep Sea Drilling Project Leg 79, Holes 544A and 547B.

Article

Jan 1984

Gneissic granodiorite was recovered by drilling at the base of the Mazagan escarpment, 100 km W of Casablanca, Morocco, at 4000 m water depth. Coarse, predeformative muscovite yielded dates of approx 515 Ma, fine-grained muscovite approx 455 Ma, biotite approx 360 and 335 Ma, and feldspar approx 315 Ma. These dates are tentatively correlated with the microscopic results. We assume a minimum age of middle Cambrian for the granodiorite, an Ordovician deformation and mylonitization, and a Late Carboniferous overprint under upper greenschist facies conditions. -Authors

Das mitteleuropäische variszische Grundgebirge im Bilde des gesamteuropäischen

Article

Jan 1951

H. Stille

Geological evolution of Middle Pontide area (Northern Turkey) and eastward continuation of the Meliata-Hallstatt Ocean

Article

Oct 1999

The Marianske-Lazne complex, remnants of a subducted early Paleozoic seaway: Basement Tectonics

Conference Paper

Jul 2000

Genesis of the south-Iberian pyrite belt in a palaeoaccretionary prism? Petrological arguments

Article

Jan 1994

The South-Iberian pyrite belt was emplaced during an episode of extensional tectonics of Upper Famenian to Visean age, subsequent to a major episode of accretion of oceanic exotic terranes, in the southern part of the Iberian Variscan orogen. It shows the association of calc-alkaline acidic rocks and tholeiitic basalts. The magmatism is bimodal but with a large predominance of acidic products. Three successive acidic volcanic episodes are described. Similar rocks are described in plutonic complexes intruding palaeo-accretionary prisms, e.g. the Shimanto belt (SW Japan) or the accretionary prism of Alaska. Some samples with high Zr contents are comparable to the granites of the British Volcanic Tertiary Province. In agreement with recent models for the geodynamic evolution of the South-Iberian Variscan orogen, it is proposed that the Pyrite belt was emplaced over an accretionary prism, subsequent to its deformation, metamorphism and partial melting. -from English summary

Die cadomische Diskordanz im Saxothuringikum (oberkambrisch-tremadocische overlap-Sequenzen)

Article

Jan 1995

The Palaeozoic evolution of the Alps

Article

Jan 1994

The paper attempts to reconstruct the puzzle of pre-Mesozoic basement areas in the Alps, and to present the geological history from Proterozoic to Permian times, including Proterozoic to Early Palaeozoic rifting history, by stepwise crustal shortening and the final collision during the Late Variscan. -Authors

Age constraints on the Cadomian evolution of the Tepl?? Barrandian unit (Bohemian Massif) through electron microprobe dating of metamorphic monazite

Article

Jan 1999

The geosynclinal development of the Rheinische Schiefergebirge (Rhenohercynian Zone of the Variscides, Germany)

Article

Jan 1981

O.H. Walliser

Paleozoic evolution of pre-Variscan terranes: From Gondwana to the Variscan collision

Abstract and Figures

Supplementary resource (1)

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