LEIDSE GEOLOGISCHE MEDEDELINGEN, Deel 52, Aflevering 1, pp. 1 21, 1-7-1981

obtainedBasement evolution inbythe Northernthe HesperianLeidenMassif.researchA preliminarysurveygroupof results

BY

E. den Tex

Abstract

Historical notes onGalician geology, and on the work ofthe Leiden University petrology team in particular, are first provided. This is followed by

introduction the of mantle an to geology with emphasis on its crystalline basement and upper inliers.

Six lithotectonic units are distinguished: 1) the Variscan granitic rocks and migmatites. 2) the Palaeozoic supracrustal rocks and dismembered

meta-ophiolites, 3) the blastomylonitic graben between Malpica and Tuy, 4) the Lalin and Forcarey Units, 5) the Ordenes basin and its meso-

catazonal peripheral belt, 6) the predominantly mafic-ultramafic catazonal complex at Cabo .

in The supracrustal history of western Galicia late Precambrian and early Palaeozoic times, as inferred from neighbouring areas, is briefly

outlined and is with the tectonic and evolution of the mantle and lower crustal rocks contained in the compared igneous, metamorphic upper

basement which have sustained polymetamorphic complexes (1—4), high-pressure and high-temperature metamorphism under a flow-folding

the Variscan Several models for the of the basement in the northern Massif regime prior to orogeny. proposed development complexes Hesperian

are briefly discussed. It is considered most likely that an early Palaeozoic rift system caused by mantle plume diapirism, and accompanied by

deepseated thermal metamorphism, lower crustal recycling, updoming of the crust and incipient sea floor spreading, was closely followed by

Variscan low-pressure metamorphism, migmatization and granite emplacement under an intermittently compressive and dilatational tectonic

the regime. Finally, probability of a Precambrian orogenic crust in western Galicia is briefly explored.

Contents

1. Historical I notes 4.6. The catazonal central complex at Cabo Ortegal 14

2. introduction 2 Geological 5. Models for the development of the basement inliers in

W Galicia 14

3. Supracrustal history of NW 2 5.1. A Caledonian orogenic cycle 14

5.2. Variscan basement nappes of Penninic 16 style. ...

4. Lithotectonic 4 units 5.3. Suture zone of Variscan a collision-type orogen 17 4.1. The Variscan rocks and granitic migmatites. ... 4 5.4. Back-arc-basins of a Variscan island arc 18

4.2. The Palaeozoic rocks and dismembered supracrustal 5.5. Mantle plume rift system model IX

meta-ophiolites 5

4.3. The and 9 blastomylonitic polymetamorphicgraben Acknowledgements ]9

4.4. The Ordenes basin and its belt II peripheral ....

4.5. The Lalin and Forcarey Units 11 References 19

1. HISTORICAL NOTES gkuicophane-bearingsyenitic gneisses in the vicinity of .

He inferred the the activity ofan Archaean orogeny to explain Schulz the first (1835) was geologist to mention the presence nature and setting of these rocks. A porphyroid formationof

of a terrain' (read: Precambrian in infra-Cambrian known de "primitive basement) age. locally as 'Olio Sapo', was first Galicia in which he defined e.g. the 'formación de Lage'. This described by Sampelayo ( 1922). From 1929 onward extensive

primitive terrain was subdivided Ch. Barrois in contributions the by (1882) to geologyof Galicia were made by Dr. I.

eastern, and by J. McPherson (1881, in western Galicia Pondal. This eminent 1883) Parga geologist produced six map

to the formations: 1) and western scale comprise following granitic augen- sheets of Galicia on a of 1:50,000. a 1:200.000

gneisses. 2) rocks, chlorite- and talc-schists, and ofthe Province La green 3) map of Coruña.and a 1:500,000map of the micaschists of Villalba. McPherson distinguished garnet- NW Iberian Peninsula. He also (re-) defined the following and kin- rock units: Formación bearing gneisses amphibolites, granulites. eclogites, de Lage. Olio de Sapo, Complejo

zigites and serpentinites at Cabo Ortegal, and what he called Antiguo (ancient rock complex between Malpica and Tuy).

Esquistos de Ordenes (schists around Ordenes), Lopolito de

Rocas Básicas (lopolith of basic rocks around the Ordenes

* Prof. Dr. E. Den Tex, Geological Institute, Garenmarkt lb, basin), and the eastern granite and schist terrain.

Leiden, The Netherlands In 1955 the Department of Structural Geology in the State 2

University at Leiden commenced detailed mapping in the ancient complex under the direction of L. U. de Sitter, followed in 1957 by W. P. de Roever, with graduate students of the Petrology Department in that university, at Cabo

Ortegal. and on the peralkaline gneisses near Vigo. The present author succeeded de Roever in 1959 and took over the

Leiden. direction of the Galicianresearch group at Systematic mapping of western Galicia on a scale of 1:25.000 was initiated in that year. Geochronological work by the Z.W.O.

Laboratory for Isotope Geology at Amsterdam was initiated

N. A. in 1961 underthedirectionofH. Priem. Gravity surveys

of of key areas were carried out since 1968 by the Department

Geophysics and Hydrogeology in the State University at

Leiden directed by J. G. Hagedoorn. while structural and in geochemical investigations were occasionally performed collaboration with H. J. Zwart and C. J. L. Wilson of the

Department of Tectonics in the State University at Leiden, and with H. A. Das of the Energy Research Centre of the

Netherlands at Petten respectively.

Since 1955 over a hundred unpublished M. Sc. theses* and

of the Massif showing its division in ten published Ph. D. theses have appeared on areas or Fig. 1. Locality map Hesperian After al. zones. Bard et (1972). problems concerning western Galician geology. A close palaeogeographic

collaborationwith the Laboratorio Geológico de Lageof Dr.

Parga Pondal was maintained throughout. The mapping is reduced thicknesses of Lower Palaeozoic campaignwas terminatedin 1973and a geological synthesis by strongly se-

sheets of Galicia a and the complete absence of Palaeozoic now in preparation. Eight map western on quences, by Upper rocks in Galicia scale of 1:100.000 are being published by the Galician research supracrustal western (Fig. 2).

E-W group. An cross section on the same scale has been 3. SUPRACRUSTAL HISTORY NW SPAIN prepared for the 1977 Meetingat Göttingen ofthe studygroup OF

"Variscan Orogeny in Europe" within Working Group 9 of the

Inter-Union Geodynamics Project. In 1977 the Galician Comprehensive cross-sections through eastern Galicia, As- Julivert the Fifth Reunion on the Geology turias and Cantabriacompiled by Mattel 1968). et al. research group organized the of the western Iberian Peninsula with the mafic/ultramafic ( 1972)and van der Meer Mohr ( 1975) indicate presence of

extensive shallow in late Proterozoic and Cambrian rocks of western Galicia as main theme (Arps et al.. 1977). seas early

times, followed by the development first of an important westward the late 2. GEOLOGICAL INTRODUCTION clastic wedge on a dipping slope during Cambrian and early Ordovician. then by euxinic and turbi-

known ditic conditions and late A broad orogenic belt ofpredominantly Variscan age. during the middle Ordovician. and in as the Hesperian Massif, occupies the western perimeter of the terminated by the return of extensive shallow seas the

Iberian Peninsula (Fig. 1). Its northernextremity is situated in Silurian (van der Meer Mohr. 1975. and pers. comm., 1977)

in NW Western Galicia, the former kingdom Galicia Spain. (Fig. 3). Sedimentation gaps, locally accompanied by slight with the provinces and La Coruña and parts of of and Orense, constitutes the axial zone. It consists a flanked either side the geanticlinal ridge on by géosynclinal 2. of the NW Iberian Peninsula. After Carte Fig. Geological map troughs of eastern Galicia and SW Portugal, in which thick géologiquedu Nord Ouest de la Peninsule Ibériqueau 500.000 me. accumulations of Upper Proterozoic and Palaeozoic sedi- From Engels (1972). ments and volcanics have been preserved. An (infra-) Cam- Legend: 1—7: Variscan rocks, 1: gabbro. 2—3 calcalkaline graniteseries brian volcanodetrital molasse deposit forms an antiformal (2: postkinematic biotite granite. 3: interkinematic biotite grano- belt of between the NE géosynclinal and the axial outcrops diorite), 4—7 alkaline granite series (4: postkinematic two-mica Pondal zone in western Galicia and northernPortugal (Parga granites, 5: interkinematic two-mica granites, 6: inhomogeneous

et al., 1964; Parga & Vegas. 1971; Bard et al., 1972; Fontboté migmatic granites. 7: migmatites). 8—12: Upper Precambrian and Ordovician than & Julivert, 1974). It indicates substantial uplift and erosion of Lower Palaeozoic (meta-)sediments (8: younger 9: Armorican quartzite — and Silurian, Cambrian, Ordovician up to a Precambrian granitic crust in what was to become the axial Armorican quartzite inclusive (Spain), Complexo Xisto-grauvaquico The character ofthis zone ofthe Variscan orogen. geanticlinal ante-ordovicico (Portugal), 10: Upper Precambrian (fine-grained zone is further substantiated by its bimodal volcanic content. facies), 11: Upper Precambrian (Ollo de Sapo facies), 12: un- differentiated metasediments), 13: coarse-grained augengneiss, 14:

* consulted Precambrian metasediments and late Ordovician The M. Sc. theses ara written in Dutch. They may be at probably younger

metasediments. the National Museum of Geology and Mineralogy.Garenmarkt lb, orthogneiss (undifferentiated), 15: polymetamorphic

Leiden, be obtained in the of the 16: metabasic rocks (partly polymetamorphic). 17: ultramafic rocks or may photocopy at expense

applicant. (partly polymetamorphic). 3 4

Fig.3. Stratigraphiccross-section ofthe Lower Palaeozoic strata between Cabo de Peñas and the antiform of Barquero, just E ofthe Cabo Ortegal

Complex. From van der Meer Mohr (1975).

angular unconformities,predominantly monomictic conglo- phic basement inliers. Two are mono- or non-metamorphic.

the merates, and felsic volcanics, have been reported from The summary starts with the latter,placing more emphasis on

from the Upper Cambrianand the Ordovician/Siluriantransition basement inliers later on.

is zone. The letter hiatus widespread and may extend from the

Arenig to the lowermost Devonian. Near San Vitero, in the 4.1. The Variscan granitic rocks and migmatites

province of Zamora, it is terminated by polymictic conglo- In Galicia and northern Portugal two main types of Variscan

merate horizons containing deformedand metamorphic peb- granitic rocks have been recognized: 1 ) predominantly biotite-

bles derived from Lower Ordovician and older formations bearing calcalkaline granites and granodiorites with a

(Martinez Garcia, 1972; et al., it is subcalcic and two- Aldaya 1976). Although plagioclase (An ]ll40), 2) predominantly clear that deformation and penetrative regional metamor- mica-bearing alkaline granites carrying albiteor albite-oligo-

of intermediate in phism pressure must have occurred clase (An (Fig. type 0 20) 5). early Palaeozoic time (see also Capdevila, 1965; Aldaya et al., The first type is rarely associated with granitic migmatites,

Martinez of Caledonian veins and mineralizations kind. 1973), Garcia's implication a orog- pegmatites, quartz ore of any

In enic cycle in NW Spain is unwarranted, since evidence of Galicia its intrusion may be either inter- or post-kinematic large-scale compressive tectonics and uplift of a mountain in relation to the two main phases of Variscan deformation.

of that The inter-kinematic is with range age is lacking. In our opinion the early type locally associated leucocratic Palaeozoic of and with tourmaline-, geography NW Spain is rather reminiscentof a microgranites garnet-or beryl-bearing segment of continental crust with marine incursions owing to aplites.

taphrogenic movements like block-faulting and flexuring. The second main type of granite frequently grades into

The axial zone of the northern Hesperian Massifcontains granitic migmatites and is abundantly associated with numerous inliers of upper mantleand lower to middle crustal pegmatites, quartz veins and Sn-, W- and Li-mineralizations material in polyphase tectonic and poly-metamorphic facies (Ypma, 1966; Hensen. 1967; Hilgen, 1970). It is almost

the suggesting high pressures and temperaturesof formationand exclusively intcrkinematic, i.e. emplaced between first and subsequent rétrogradation. They are arranged in more or less second phase of Variscan deformation (Capdevila & Floor, linear belts tectonically juxtaposed with non- or monometa- 1970; Floor, 1970; Floor, Kisch & Oen Ing Soen, 1970;

morphic Upper Proterozoic and Palaeozoic sediments, vol- Capdevila, Corretge & Floor, 1973) (Fig. 6).

been canics, migmatites and granites (Fig. 4). Rb-Sr whole rock isochron ages have determined at

316 ± 10 Ma for the interkinematicalkaline and calcalkaline

4. LITHOTECTONIC UNITS granites, and at 297 ± 11 Ma for the post-second phase

calcalkaline granites (Priem et al.. 1970; van Calsteren et al.,

in Six lithotectonic units may be distinguished western Ga- 1979). licia, four ofwhich are polyphase tectonic and polymetamor- Variscan granitic rocks are distributed widely throughout 5

Fig. 4. Map showing the distribution of polymetamorphicbasement inliers. ofmolasse and flyschoid deposits of Upper Precambrian age, and of

Ordovico-Silurian orthogneisses set in probably Upper Precambrian metasediments. From Den Tex ( 1976). Data after Den Tex & Floor ( 1967) and

Bard et al. (1972).

the of where Ribeiro 1972; axial zone the northern Hesperian Massif, but they into NW Portugal A. (pers. comm., 1974)

basement from the the occur rarely within the polymetamorphic inliers has reported fossil ages ranging Cambrian to

mentioned below. A distinct preference for fundamental Silurian for the various formations involved. Similar but

rather less variable rock found in the central faults, such as the boundary faults of the blastomylonitic types are

graben is displayed by the interkinematiccalcalkalinegranites Galician schist area between Forcarey. Lalin. Carballinoand

(Den Tex. 1974),while the postkinematic granites frequently Avion. A low-pressure plurifacial metamorphism has affected

chlorite, biotite form composite bodies ofsubcircular or concentrical outcrop. these rocks giving rise to 1 & II, garnet,

staurolite,and andalusiteI & II in pelitic rock types. This took

4.2. The Palaeozoicsupracrustal rocks and dismembered meta- place mainly before the second tectonic phase in a strati-

the first ophiolites graphic sequence previously disturbed by and main

In of Variscan deformation Meerbeke westernmost Galicia (Fig. 7) the presence of Palaeozoic phase (Hilgen. 1971; van

supracrustal rocks is based on lithostratigraphic correlations et al., 1973; Aldaya et al., 1973; Minnigh, 1975).

only, no identifiable fossils having been found in them. Further to the NE anchi- to low-grade metamorphic

with Monometamorphic (semi-) pelitic schists quartzose or supracrustals ofOrdovician and Silurian ages have been iden-

feldspathic laminae, white and black quartzites, anthracite tified in the northwestern limb of the Barquero antiform

schists, amphibolites, calcsilicate rocks and iron-rich horizons (Matte, 1968).The sediments occurring here are rather similar

south in those found in the mentioned above, but occur mainly of the Ria de y Noya a to areas they are

submeridionalbelt near the Atlanticcoast. This beltcontinues interstratified with and overlain by arkoses. crinoidal lime- 6

5. Distribution of the and in the NW Iberian Peninsula. From Den Tex Data afterCarte Fig. map calcalkaline biotite granites granodiorites (1977).

Géol. du de Péninsule I. NO la Ibérique au 500.000 me. by Parga Pondal et al. (1967). 7

Distribution of the alkaline mica in the NW Iberian Peninsula. From Den Tex Data after 5. Fig. 6. map two granites (1977). same source as Fig. 8

Fig. 7. Distribution map of Ordovico-Silurian orthogneisses and early Palaeozoic mafic and ultramafic rocks in Western Galicia. From Den Tex

(1979).

and stones, coarse quartzites. (micro-) conglomerates, rhyo- coeval rock types but also of the polymetamorphic basement

litic tuffs indicating epicontinental deposition in a shallow rocks exposed in the adjoining Cabo Ortegal complex. The Moeche described sea, and eventually penecontemporaneous erosion. Their Group may be as a Wildflysch formation from rather than olistostrome fossil age may range Upper Llandovery (Matte, 1968) to or a melange an (Hsii, 1974;

Upper Wenlock (FernandezPompa et al., 1976). This assem- Martinez Garcia et al., 1975), suggesting deposition in a deep

is furrow localized between exhumed blage followed by a monotonous sequence of interstratified an basement complex and arkoses, graywackesand phyllites indicating rapid subsidence a continental platform, locally involving more or less coeval

Its and deposition in probably Upper Silurian times (Fernandez tectonization. depositional age ranges from the Upper

Pompa et al., 1976). The top of this sequence is formedby the Silurian to the Devonian according to lithostratigraphic and fossil evidence greenschistfacies volcano-sedimentary Moeche Group con- (van der Meer Mohr, 1975; Fernandez Pompa

rather with the sisting mainly of mafic metavolcanics, meta-keratophyres. et al., 1976). It compares well Upper Devonian

fla¿er-metagabbros and serpentinites with subordinate va- flysch reported by Ribeiro& Ribeiro (1974) from the vicinity

riegated (quartz-) phyllites, metacherts and crinoidal lime- of the polymetamorphic catazonal Bragança complex in NE stone-lenses. The Group also includes volcano-sedimentary Portugal. and tectonic breccias containing fragments not only of all Rock suites rather similarto the Moeche Group have been 9

Fig. 8. Geologicalsketch map of the blastomylonitic graben between Malpica and Tuy in W. Galicia, divided in three segments (northernmoston

From Guardia, left, southernmost on righthand side). Den Tex (1979). Data after Geological map of Western Galicia 1:100,000. sheets Vigo-La

Pontevedra, Finisterre- and Mugia-Carballo. publ. by the Research Group Galicia of the Dept. of Petrology. Mineralogy and

Crystallography, State University at Leiden.

reported from the eastern, southern and western perimeter of 4.3. The blastomylonitic andpolymetamorphic graben

the Ordenes basin peripheral belt near Mellid,Villa de Cruces, A zone of repeatedly tectonized, polymetamorphic but non-

Silleda and the Monte Castelo. Koning ( 1966) was the first to migmatic rocks trends parallel to the Variscan grain and to the

distinguish these monometamorphicgreenschist- and amphi- Atlantic coast of western Galicia over a distance of 150 km

bolitc-facies rocks from the polymetamorphic amphibolite- from Malpica in the north to Tuy on the Portugueseborder. It

and granulite-facies mafic and ultramafic rocks with which was first recognized as a pre-Variscan unit by Parga Pondal who the of they are frequently associated in the field. The conspicuous (1956) gave it name Ancient Complex on the

banding of the polymetamorphic peridotites is completely grounds of its abundant granitic gneisses and polymetamor-

absent in the monometamorphic serpentinites. The amphi- phic paragneisses. Den Tex (1961) and Den Tex & Floor

inferred in bolites and metagabbros have characteristic fabrics ranging (1967) the presence of a fossil graben structure the

from flaser- to laminartextures of highly variableorientation. Ancient Complex which they prefer to call the blastomylonitic and and This inference More or less massive metagabbros meta-porphyrite dykes polymetamorphic graben. was mainly

arc seen to cut across these foliated rocks and to enclose them. based on the abundance within the complex of high-level

Around the Ordenes basin peripheral belt the dominantrock granites, some of which are distinctly peralkaline, and on its and inward faults which types in the greenschistfacies terrain are serpentinites steeply dipping boundary may locally

flaser-amphibolites, whereas meta-volcanic greenschists do- have acted as channelways for the emplacement of early

minatearound the Cabo Ortegal complex. In both areas the Variscan granodiorites and biotite granites (Fig. 8). In recent the constituents of the evidence for the fossil prevailing rock types are comparablewith years graben has steadily accumu-

an ophiolite suite but they never occur in the sequence lated (cf. Floor. 1966; Arps, 1970). Its sedimentary and

required by recent definitions of the term ophiolite (Anon- volcanic content resembles Upper Proterozoic and possibly

dismembered or some Lower Palaeozoic in N ymous, 1972). They may qualify as non- strata eastern Galicia and

1973) in a tecto- sand- sequence ophiolites (Miyashiro, distinctly Portugal. They were mainly greywackes, (semi-)pelites,

nized and metamorphic state, i.e. as a metamorphic melange. stones, cherts, calcareous or dolomitic marls, and mafic lavas 10

or tuffs. A regional metamorphism in the high- to in-

termediate pressure facies series has first affected these rocks

giving rise to biotiteand garnet in the schists and paragneisses.

while the mafic rocks were converted to amphibolites which

In the northernmost of the may contain garnet. segment

with graben lenses eclogitic (type C) parageneses have been

found. All these metamorphic rocks were intruded by calcal-

kaline, subalkaline and peralkaline granites. The latter, con-

taining riebeckite. aegirine. lepidomelane and astrophyllite.

are distinctly concentrated in the southern halfof the graben.

Some of these granites have caused hornfelses to develop in

country rocks of non- or low-grade regional metamorphism.

Minor occurrences of gabbro and of hybrid rocks between

gabbroand granite occur in the southernmost segment of the

graben, while a basic dyke swarm is seen to intrude the sub-

and calcalkalinebut not the a peralkaline granites, suggesting 9. Fig. Rb/Sr whole-rock data plots near Vigo in the blastomylonitic

time interval between their and a significant emplacement graben. From van Calsteren et al. (1979).

link between felsic genetic the basic and magmas (Floor,

1966).

Rb/Sr isochrons of granitic gneisses (Priem et al.. 1970; van morphology of their zircon crystals supports the contention

Calsteren al., from the indicate a middle that these were et 1979) graben to gneisses emplaced as high-levej magmatie

late their first Ordovician age for crystallization (Fig. 9). The granites (Arps, 1970).

10. and ofthe southern of the Ordenes drawn Fig. Simplified geological Bouguer anomaly map portion complex. Isogals at 5 mGal intervals.

Stippled areas are outcrops of mafic and ultramafic rocks (heavy unit). From Keasberry et al. (1976). 11

the Variscan this During ensuing orogeny assemblage of and their immediate context contain globuliths (Berthelsen.

rocks was first isoclinally foldedor flattened on subhorizontal 1970) of more or less hybridized garnet-bearing gabbro or

N -Strending axes, and metamorphosed ( but not migmatized) diorite (Hubregtse, 1973a). Subsequent blockfaulting in this in the facies has cordierite-amphibolite (Winkler, 1967). Later area juxtaposed high- and low-level portions of these

refolded on subvertical N S axial and which have they were trending planes gneissose locally garnetiferous granites may

and partially retrograded in the greenschist facies. In this been formed by anatexis of lower crustal material under the

the rocks first thermal action of the process granitic developed a blastomylonitic spinel-lherzolite bodies and their pyro-

texture and a foliation, marked by biotite + garnet or xenitic and gabbroic products of partial melting. A com-

riebeckite ± aegirine. which was subsequently folded and parison between the peripheral Ordenes belt and the fossil under recrystallized low-grade amphibolite or greenschist- graben reveals that both have been subject to a pre-Variscan

facies conditions. Rare intrusions of postkinematic biotite regional metamorphism. In the Ordenes belt this metamor-

granite constitutethe terminationof the Variscan cycle within phism is of the high- rather than the intermediate-pressure the structure. A model is and it associated with graben multi-stage graben con- type, is clearly upper mantle rock sidered most attractive: After a pre-Variscan stage of sub- complexes. A gravity survey by Keasberry et al. (1976) over sidence and intrusion magmatic the graben was compressed the southern and southeastern segments of the peripheral belt and it subsided metamorphosed. Subsequently again whereby suggests the subsurface presence of three high-density rock mineralized the d -3 veins of interkinematic Variscan bodies =2.89 quartz (av. gem ) causing positive Bouguer anom-

suite offset. granite were Such a sequence of events is alies of amplitudes: 25 mGal (E of Santiago), 15 mGal (at with the concentration within the of compatible graben the Mellid) and 10 mGal (near Sobrado) (Fig. 10). Depending on

Ordovico-Silurian with their high-level granites, polyphase the density contrast chosen these bodies may reach depths deformation and mctamorphism, and with the generally between 4 and 11 km. Zones of progressive metamorphism lower of Variscan and absence of grade metamorphism (biotite. garnet, staurolite, kyanite) can be identified in semi- migmatites within the graben as compared to the rocks pelites belonging to the Ordenes schists at the inner fringe of outside. the peripheral belt roughly parallel to the outlines of the

It certainly represents the outcrop of the highest level central complexes N E ofSantiago and SE of Arzua. The high-

the basement inliers in western Galicia. and well with among pre-Variscan level orthogneisses of Mellid Sobrado compare

those of the fossil graben, while the adjoining,high-grade

4.4. The and its Ordenes basin peripheral belt garnetiferous augengneisses fit the deepseated context of

A to grossly structure, open-ended the north is mantle so basin-shaped lower crustal and upper materials characteristic of centred on the township of Ordenes in the Province of La the peripheral Ordenes belt in general. A Rb/Sr whole rock

It is with isochron of six Coruña. filled predominantly marinemetasediments granitic augengneisses near Mellid reveals a

(the Ordenes schists of Pondal. Parga 1956) and metabasic Silurian age (409 ± 26 Ma) for their crystallization (van rocks of similarlithology as those encountered in the blasto- Calsteren et al., 1979). The 50 Ma difference with granitic

Its mylonitic graben. constituent strata have repeatedly been gneisses of Ordovician age in the blastomylonitic graben folded and have been intruded, especially towards the per- might be due to slower cooling and crystallization of the closure, calcalkaline and subalkaline ipheral by high-level deeper seated garnet-bearing gneisses near Mellid or to a

association reminiscent of the granites, an highly blastomylo- younger intrusion age. nitic and polymetamorphic graben although the configu- ration is different. To the W. S and E the basin is surrounded 4.5. The Lalín and Forcarey Units by or less inward belt a more dipping peripheral consisting Structurally and Iithologically the Lalin Unit is a small size

of lower crustal and the predominantly upper mantle materials. replica of Ordenes basin. Hilgen (1971 ) defined the Lalin To the E. SE and W from Sobrado via Mellid to Ledesma and Unit as a basin structure, open-ended to the N, where it is from Bazar to N of Carballo, it is mixed accompanied by a separated from the Ordenes basin peripheral belt by an

of W zone mainly mafic metavolcanics. keratophyres. serpen- intermediatezone of E trending metabasic and metapelitic tinites and metasediments in greenschistfacies. The peripheral rocks similarin composition to those of the Lalin Unit and the belt is made of individual basin up essentially centralcomplexes of Ordenes proper, and by a slice of the Palaeozoic such the (Balli, 1965) and quasi-circular plan as Agualada volcano-sedimentary formation (Moeche Group cf. § 4.2).

Castriz/Bazar complexes ( Warnaars. 1967), the complex east The Lalin Unit contains polymetamorphic meta-graywackes of Zuuren, the Mellid Santiago (van 1969), complex (Hub- (with two generationsof garnet), garnetiferous amphibolites. 1973a, b) and the Sobrado and regtse, Teijeiro complex (Keas- orthogneisses closely resembling those of the blastomylo-

et al.. 1976; 1979). Some of these nitic The bcrry Kuijper. complexes graben. amphibolites are intimately interstratified Mellid) subhorizontal slices of with the and (e.g. incorporate spincl-lher- meta-graywacke concentrated in a belt along the

zolite with (garnet-) pyroxenite veins, while nearly all of them southern perimeter of the Unit, but unlike the Ordenes basin

contain to bodies or zones of metagabbro, and mafic felsic peripheral belt it contains no ultramafic rocks and lacks

granulite. amphibolite or The Mel- evidence of high-pressure paragneiss. granulite- or eclogite-facies metamorphic con- lid and also characterized Sobrado/Teijeirocomplexes are by ditions (Fig. 11). Gravity surveys have shown that the Lalin the of bodies of and the does presence large augen- orthogneiss, Unit not coincide with an appreciable Bouguer gravity blastomylonitic border zones of which grade into felsic and anomaly (Keasberry et al., 1976)(Fig. 10). The unit has been intermediate and that show evidence granulites paragneisses thrust over monometamorphic Lower Palaeozoic sediments

of been to fusion. The of having subject partial granitic gneisses the central Galician schist belt to the south. The contact is 12

sketch of the Lalín Unit and From al. Fig. 11. Geological map surrounding areas. Arps et (1977). Fig. 12. Geological sketch map and cross-sections of the Cabo Ortegal complex (relief 2.5 times exaggerated). From van Calsteren (1977a). 14

situated white horizon that shows evidence of in a quartzite depending on the density contrast chosen. The SW contact

and SE mylonitization. The Variscan isograds pass undisturbed from surface dips steeply inward the contact gently out-

the schist belt through the tectonic contact into the Lalin Unit ward. The three-dimensional model preferred by van Over-

indicating that its emplacement occurred before the main meercn is a tilted mushroom-shaped dome or a tilted mono-

phase of Variscan metamorphism. It is folded by the second cline overturned to the SW (Fig. 15). Van Calsteren (1978)

phase of Variscan deformationand intruded by late-Variscan studied the geochronologyand geochemistry ofsuitable rocks Lalin whole granites. The Forcarey Unit lies south of the Unit and is and minerals from the complex. He found a Rb Sr rock

Meerbekc 1973; of Ma for the lherzolitesand 354 17 Ma for similar to it in many respects (van et al., age 487 ± 122 ±

the Minnigh. 1975: J. D. Hilgen, pers. coram., 1979). the mafic granulites, while eclogite plots do not allow a

linear correlation on the Nicolaysen diagram. K-Ar mineral

4.6. central from the catazonal rocks show in the The catazonal complex at Cabo Ortegal ages a peak frequency Around Cabo Ortegal the largest of the central complexes of histogram at 390 Ma (Fig. 16). This indicates that the lower is crustal and upper mantle rocks in western Galicia well Iherzolitewhole rock systems closed first ( in Cambro-Silurian exposed by the Atlantic Ocean and the Bay of Biscay, and times) followed by the constituent minerals of lherzolitesand their rias. The terrestrial outcrop of 20 x 30 km is semi- their immediate country rocks, while the thermal event elliptical with the long axis trending NNE. It is likely to extend terminatedwith the closure ofthe hornblendegranulites at the northward below sealevel. The complex has been studied in end of the Devonian.

detail its The distribution of and elements led great as regards petrology, mineralogy, chemistry major trace van and geochronology (Den Tex & Vogel. 1962; Vogel. 1967; Calsteren to distinguish between continental quartz-nor-

Maaskant. 1970; Den Tex et al., 1972; van Calsteren 1977a, b, mative tholeiites. as represented by mafic granulites and

Iherzolite 1978: van Calsteren et al.. 1979) as well as its stratigraphy, eclogites from the context, and olivine-normative

and mantle structure geophysics (Engels. 1972: Martinez Garcia et tholeiites of oceanic island or plume type, as repre- al., 1975; van der Meer Mohr. 1975; van Overmeeren. 1975). sented by the early Palaeozoic gabbros. pyroxenites and

rocks make of its from the Iherzolite Mafic and ultramafic up about 75"„ amphibolites derived by partial melting. surface area (Fig. 12). The core consists of spinel-lherzolite Van Calsteren (1977a. b) developed a two-stage melting with spinelfree webstcrite. wehrlite. (garnet-) pyroxenite and model for the Cabo Ortegal ultramafics on the basis of their pargasite phlogopite-bearing layers and veins. Their mine- chondrite-normalizedLa'Sm and K Rb ratios:

chemical data reflect mantle I A melt fraction from mantle ralogical and an upper origin as ) spinel-lherzolite a deep plume.

garnet- or aluminous pyroxene-pyrolite producing small 2) A pargasite-peridotite residual fraction yielding partial amounts of picritic or pyroxenitic liquid and leaving a spinel- melts of pyroxenite. pargasitite. phlogopite-roek and gabbro. of lherzolite as solid residue during its rise through the upper His mantle plume model for the basement inliers the N W mantle into the lower crust (Maaskant, 1970). Subsequently Iberian peninsula as a whole will be discussed in paragraph the ultramafic core has suffered the same tectonic and 5.5.

metamorphic history as the mafic and felsic granulites. eclogites. amphibolites and garnet-kyanite-biotite gneisses of 5 MODELS FOR THE DEVELOPMENT OF THE its immediatecontext (Fig. 13). Further out to the E. Sand W BASEMENT INLIERS IN W GALICIA the catazonal complex is surrounded by low-grade metamor- phic. locally ferruginous, slates, quartzites. cherts, and lime- In recent several have been madeto the Meer years attempts explain stones of Siluro-Devonian age (van der Mohr. 1975; development of the western Galician basement inliers. These Martinez Garcia et al., 1975) intermingled with greenschist- models will be discussed and evaluated in the following facies variolites. keratophyres. serpentinites and volcanic- group

sequence: breccias or melanges containing catazonal fragments (Arpset al., 1977). These peripheral associations indicate that the catazonal complex became exposed in Siluro-Devonian time, 5.1. A Caledonian orogenic cycle shedding debris around itself along with incipient seafloor Ferragne (1972), Martinez Garcia (1973) and Aldaya et al. spreading in the immediate vicinity. Engels (1972) demon- ( 1973) picked up a threadleft by Staub ( 1926) and Carrington strated polyphase deformation of the complex. It started in da Costa (1952) who inferred the activity of a Caledonian pre-Variscan times with N S trending fold axes in eclogites. orogenic cycle in the Hesperian Massif. In the context of this followed folds E N-S model by recumbent on W and axes in all the meso- to catazonal complexes and their partial catazonal rocks and the development of peripheral blastomy- envelopes of early Palaeozoic metasediments. metavolcanics lonite zones. During the Variscan orogeny the complex was and scrpentinites may be interpreted as Caledonian basement refolded on steep NNE trending axial planes. Its catazonal inliers imbricated with early Palaeozoic ophiolites and as-

sociated marine sediments. The evidence for core was locally retrogradedto greenschistfacies assemblages, a Caledonian accompanied by chevron folding and upthrusting into orogenic cycle to have occurred here is summarized in §3 and juxtaposition with the low-grade seafloor associations of 4. However, little evidence has so far been produced for the

P T Siluro-Devonian age. presence of "Caledonian' age (1) high low metamor-

JK gravity survey was carried out by van Overmeeren ( 1975). phism. (2) thrusting and compressive folding, (3)calcalkaline found A positive Bougueranomaly of 38 mGal amplitude was or potassic volcanism. (4) large-scale uplift, and (5) molasse- centred on the complex (Fig. 14). This suggests the presence of type erosion and deposition. I am thereforeinclined to adhere a high-density body reaching dephts between 3 and 6 km to Stille's (1927) and Lotze's (1945) view that the NW Iberian 15

13. of the Cabo in the Al-P.P. = Fig. Evolutionary path Ortegal peridotite pyrolite PT-diagram. aluminous pyroxene pyrolite. S-P.P. =

After Maaskant spinel pyroxene pyrolite. (1970). 16

Fig. 14. Maps ofthe Bouguer anomalies and metamorphic facies (inset) in the Cabo Ortegal area. After van Overmeeren (1975) and Engels (1972).

Fig. 15. Gravity model of the Cabo Ortegal complex. A tilted mushroom-shaped dome of dense material obliquely cut by the erosion surface. From van Overmeeren (1975).

has not been affected extensive peninsula by a complete orogenic cycle gravity nappe. On the other hand Ries and Shack- of Caledonian age. leton (op. cit.) maintain that all of the NW Iberianbasement

inliers are remnants of a Variscan thrust-plate rooted to the

5.2. Variscan basement Penninic style West, either in the nappes of blastomylonitic graben, or in the Porto-

Anthonioz 1969) and Ries & Shackleton 1971 advanced NW ( ( ) the Viseu-Guarda Zone of Portugal, or even further W. in the idea that basement inliers represent the klippen of eroded the Atlantic Ocean. Both views based are essentially on the basement produced the nappes by Variscan orogeny. The tectonic superposition of the high-grade polymetamorphic and Morais-Lagoa Bragança-Vinhais complexes in NE Por- basement complexes on low-grade monometamorphic sedi-

were inferred slid down tugal by Anthonioz(op. cit.) to have ments and volcanics of middle early to Palaeozoic age. from the Mid-Galician Cordillera the SW of to as parts an separated by more or less gently inward dipping blastomylo- 17

Fig. 16. Rb/Sr plot of whole rocks (with error bars), two edenites (crosses, with low Rb, Sr ratios), and two phlogopites (crosses, with high Rb/Sr

ratios) from Iherzolites in the Cabo Ortegal complex. Isochron 1 is calculated using all six whole-rock points. The reference line is obtained by omittingone slightly deviatingpoint (the sample with the lowest Rb/Srratio). Isochrons 2 and 3 are calculated from two whole-rock s and separated

phlogopites and edenites, respectively. Between brackets the K-Ar dates of the minerals are given.

tectonic Moreover, it is where the homeland of nitic soles, thrust planes and melanges. Synformal difficult to see such a

inverted structures and locally metamorphic zones in the nappe could have been situated.

of the basement complexes are also quoted in support

model. But the evidence Variscan nappe following negative

may be adduced: 1) the blastomylonitic soles are of pre- 5.3. Suture zone ofa Variscan collision-type orogen

and the In the wake of the of tectonics almost Variscan age (cf. § 4.4 4.6). 2) contact planes, though bandwagon plate anj

the internal dipping inward, do so at angles up to 80°. 3) tract of country containing mafic volcanics has lately been

structures are both synformal and antiformal but always proclaimed a suture zone of continentalcollision. As a result

the network of'suture zones' has ramified bilaterally or radially symmetrical in a statistical sense. 4) the considerably and

main phase Variscan fold axes are deflected around the continents are being split into ever smaller 'microcontinents'.

basement trend, the inliers. 5) positive Bouguer anomalies of up to 38 The Hesperian Massifhas been no exception to this

of the Galician-Castilian mGal amplitude are centred on some complexes zone having been cited e.g. as a suture

indicating deeply rooted rock masses of high density, 6) the zone between a North American/northern European con-

abnormally iron-rich facies ('lie-dc-vin') of the Silurian phyl- tinent and a northern Spanish microcontinent by Riding

and of lites surrounding certain catazonal complexes (Moráis and ( 1974). as a leading edge an Iberian microcontinentby

Bragança. cf. Ribciro. 1974) imply in situ erosion of the (ultra-1 Badham & Halls ( 1975). Some ofthe objections made against

mafic rocks concerned in a shallow Silurian sea, 7) the model 5.1 are equally valid v.a. v. 5.3, such as absence of high

postulated root zones are composed of more superficial rock P-low T metamorphism and of fully developed ophiolites of

Variscan volcanism of that is types (orthogneisses, paragneisses. amphibolites, etc.) than age. Calcalkaline age also absent

the presumed klippen (ultramafics,eclogites, granulites. etc.). in the NW Hesperian Massif, although chemically somewhat

The sense of movement in the basement inliersis radially or similarPermo-Carboniferousplutonism is widespread in that

bilaterally outward, which is incompatible with the movement area (cf. §4.1), accompanied by thrusting and compressive

In the evidence for obducted subducted picture that operates in thrust-plates or gravity-nappes. folding. summary or 18

oceanic lithosphère in the Variscan orogen of N W Spain is too

tenuous to be seriously considered.

5.4. Back-arc-basins of a Variscan island arc

Bardetal. (1973(and Ribeiro( 1974) presented more sophisti-

cated models of for the a collision-type orogen Hesperian

Massifas a whole. In their perspective the Galician-Castilian

zone(including Mid-GaliciaandTrás-os-MontesinPortugal)

was once a back-arc-basin that developed behind an island

remnants arc, of which are situated in the Ossa-Morena zone

of the SW Iberian Peninsula. An oceanic plate, subducted

from the SW underneath the Iberian continent, is invoked to

the explain presence ofthe presumed island arc at the collision

front in the Ossa-Morena zone. A back-arc-basin is then

supposed to have formed owing to mantle diapirism from the

subducted oceanic lithosphère, and later to have closed by

collision and subduction of island-arc and continentalcrust

from the SW and the NE respectively, accompanied bycrustal

this model fit the diapirism. Although appears to observed

distension tectonics in the Mid-Galician Trás-os-Montes

zone, admitting mantle diapirism and incipient seafloor in euxinic basin, it spreading an encounters grave objections

where time-spacc-rock relations are involved. Firstly, the

presumed back-arc-basin in the Mid-GalicianTras-os-Mon-

tes region is situated some 500 km NNE of the postulated

and trench outer island arc and shows early Palaeozoic

(Ordovico-Silurian) mantle-crust diapirism and incipient Fig. 17. Diagram illustrating the rift system model for the early

Palaeozoic of seafloor spreading. Assuming a dip of 30-45° for the sub- geological evolution Western Galicia.

ductedplate, a depthof300 500 km should have been reached

by its lowermost tip. During subduction to these depths,

glaucophane-schist or eclogue facies metamorphism should the site of long-lived epeirogenic movements and bimodal have occurred followed calcalkaline and vol- by potassic magmatic activities from the late Precamhrian right up to the

canism with Cu-Zn-Pb mineralizationas characteristic Variscan In it along orogcnic climax. a general way was mainly

features of 1972 a mature island arc (Stanton. and pers. uplift that this zone had then suffered but subordinate

However and comm., 1977). only pumpellyite- greenschist subsidence, concentrated in grabcn-like structures, was an

facies of later Palaeozoic Devono-Carbo- essential These to metamorphism age ( corollary. observations led the concept of a

niferous) is found in the Ossa-Morena zone accompanied by rifted basement dome, deformed, metamorphosed and grani-

spilite-keratophyre volcanism and tized the Variscan Tex. non-ophiolitic pyrite-jas- by orogeny (Den 1977. 1979; van

Belt pei-manganese mineralization in the so-called Pyrite of Calsteren & Den Tex. 1978). The occurrence of dismembered

the SW Iberian Peninsula. These features could reflect volcánica a mcta-ophiolites. and melanges of Siluro-Devonian

of cugeosynclinal setting or an incipient stage island arc age. closely associated with some of thecatazonalcomplexes, formation (Schermerhorn. 1975a. b). For the of only western was interpreted as evidence incipient seafloor spreading

of portion of the Hesperian Massif the model a fully de- upon drifting asunder ofthe continental crust along preferred island and veloped arc back-arc-basin is therefore rejected. branches of the rift system (Fig. 17).

The results of and geochronological. geochcmical geo- 5.5. Mantle model plume—rift system physical work on the catazonal complexes at Cabo Ortegal

Within the at rifl- Galician research group Leiden continental and in the peripheral belt of the Ordenes basin led van and mantle plume models have been under discussion during Calsteren (1977a, b. 1978: van Calsteren el al.. 1979) to the last decade. Den Tex Recently (1977), van Calsteren assume the presence of an early Palaeozoic mantle plume

(1977a. b. 1978; van Calsteren et al.. 1979) and van Calsteren beneath the continentalcrust ofthe N W Hesperian Massif(cf.

& Den Tex (1978) these models in detail. í¡ 4.5). The Iherzolitc Cabo developed more spinel-pargasite at Ortegal was

In 1961 the author ventured the idea that the to melt from present shown by him be a possible fraction a pyrolitic ancient of Pondal (1956) is a fossil complex Parga graben (cf. parent material in the deep mantle, and to be a probable

4.3). It was then believed to be Prccambrian residual ofits S an essentially counterpart own mafic associates at a later stage feature, but work (Priem et al.. of in second-order isotope-geochronological partial melting a diapiric body (Fig. 18). Calsteren al.. 1979) has since shown that the 1966.1970; van et According to van Calsteren the mantle plume and its diapiric accompanying epeirogenic granites and associated basic dyke off-shoots caused not only the inferred doming, rifting and

of In of swarms are early Palaeozoic (Ordovico-Silurian) age. the thinning the continental crust, but also the two phases of

of the of light supracrustal history adjoining areas (cf. i; 3) it granulite facies metamorphism as well as the granitic anatexis became clear that Mid-Galiciaand Tras-os-Montes had been and palingenesis that occurred concomitantly with the latter 19

phase. In this part of the model, mass movement of hot rock

and is both the mechanical and the magma used to explain

thermalevents that are recorded in the early Palaeozoic rocks

and structures concerned. Its relation to the later Palaeozoic

features of the Variscan orogeny proper cannot yet be

resolved, but the virtualoverlap of radiometric dates from the

Variscan granites and the granulites around the mantleplume

diapir at Cabo Ortegal is suggestive of a fairly close link (van

Calstcren. 1977a). The presence of a lower continentalcrust,

that was crystalline before the Cambro-Ordovician onset of

mantlediapirism, is implicit in the model outlined above (see

also!}4.5). Results ofradiometric dating on zircons from some

of the crustal rocks in Galicia confirm the assumption of a

Precambrian orogenic basement to the Northern Hesperian

Massif (Kuijper. 1979).

ACKNOWLEDGEMENTS

I am indebted to all members,past and present, of the working

in group Galicia in the State University at Leiden, and

particular to C. E. S. Arps, J. M. A. Buiskool Toxopeus.

P. W. C. vanCalsteren, P. Floor. J. D. Hilgcn. E. J. Keasberry, and H. Koning, R. P. Kuijper. L. D. Minnigh G. van dcr Fig. 18. Diagram illustratingthe mantle plume model for the early Wegen, for personal communications, stimulating dis- Palaeozoic geological evolution of Galicia. From van Calsteren

of the (1977a). cussions and critical reading manuscript.

REFERENCES

terrains Asturies Aldaya. F.. Arribas. A., Gonzalez-Lodeiro, F.. Iglesias. M.. Martin- Barrois, Ch.. 1882. Recherches sur les anciens des et

ez-Catalan. J. R. & Marlinez Garcia, E.. 1973. Presencia ele una de la Galice. Mém. Soc. Géol. du Nord. Lille, 2. Mém. 1. 630 t. pp. el nueva fase de deformación probablemente pre-hercinica en Berthelsen. A.. 1970. Globulith a new type of intrusive structure

the noroeste y centro de la peninsula ibérica (Galicia central. Zamora > exemplified by metabasic bodies in Moss area. SE Norway

Salamanca. 29 48. Salamanca). Stud. Geol. 6, pp. Norges Geol. Underspk.. 266, pp. 70 85.

& Aldaya. F\, Carls, P.. Martinez Garcia, E. . J.-L.. 1976. Calsteren, P. W. C. van. 1977a. A mantle-plume model interpretation

Nouvelles précisions sur la série de San Vitcro (Zamora. Nord- for the Paleozoic geology of Galicia with emphasis on the Cabe

C. R. Acad. Sci. Paris. 881 883. Proc. ouest de l'Espagne). 283D, pp. Ortegal area (NW Spain). Kon. Ned. Akad. Wct.(B) 80. pp.

168. Anonymous. 1972. Penrose field conference on ophiolites. Geotimes. 156

17/12, pp. 24-25. . 1977b. Geochronological. geochemical and geophysical investi-

des Anthonioz, P. M.. 1969. Etude pétrographique et structurale gations in the high-grade mafic-ultramafic complex at Cabo

régions de Moráis et Bragança(NE Portugal). Thèse, Université de Ortegal and other pre-existing elements in the Hercynian basement

of Galicia Lcidse Geol. Poitiers, 311 pp. (NW Spain). Meded . 51. pp. 57-61.

Arps, C. E. S.. 1970. Petrology of a part of the Western Galician . 1978. Geochemistry of the polymetamorphic mafic-ultramafic

basement between the Rio Gallas and the Ria de Arosa (NW complex at Cabo Ortegal (NW Spain). Lithos, 11. pp. 61-72.

Leidse Geol. 1978. rift Spain) with emphasis on zircon investigations. & Den Tex. E.. An early Paleozoic continental system in

Adv. Paleorift Meded.. 46. pp. 57 155. Galicia (NW Spain). NATO Study on systems,

('alsteren. P. W. C. J. R. P. & DenTex, E.. Oslo. 1977. Reidcl Publ. Co.. Dordrecht Boston. 8 van.Hilgcn, D., Kuijper. pp. (Abstr.

1977. Mafic and related complexes in Galicia: an excursion guide. 1977).

Leidse Geol. Meded.. 51. pp. 63-94. . Boelrijk. N. A. I. M.. Hcbeda. E. H.. Priem. H. N. A., Den Tex, E.,

Badham. J. P. N. & Halls. C., 1975. Microplale tectonics, oblique Verdurmen. E. A. Th. & Verschure, R. H.. 1979. lsotopic datingof

collisions, and evolution of the mal'ic-ultramafic Hercynian orogenic systems older elements (including the Cabo Ortegal

3 376. Geology. 7. pp. 373 complex) in the Hercynianorogenof NW Spain: Manifestations of

Balli. C'hem. G. M.. 1965. Orogenesi creinica e metallogcncsi Delia regione de a presumed early Paleozoic mantle-plume. Geol., 24. pp.

Carballo-Santa Comba (La Coruña. Spagna NO) con particolarc 35 56.

riferimento al giacimentowolframifero di Santa Comba. Diss. no. C'apdevila. R.. 1965. Sur la géologie du Précambrien et du Pa-

3677 E.T.H. Zurich. 197 pp. lèozoique dans la région de Lugo et la question des plissements

Bard. Ph. & Ribeiro. 1972. Le Inst. J-P.. Capdcvila. R.. Matte. A.. assyntiques et sardes en Espagne. Notas y Com. Geol. Min

Serv. Précambrien de la meseta ibérique. Notes & Mém. Géol. España. 80. pp. 157 174.

Rabat. 236. 315-335. & P.. 1970. Les différents de leur Maroc. pp. Floor, types granites hercyniens et

1973. Geolectonic model for the Iberian Vanscan distribution dans le nord de Geol. Min.. -, -,-&-, Orogcn ouest l'Espagne. Bol. y

Nature 241, 50-52. 215-225. Phys. Sci., pp. 81/2-3, pp. 20

. Corretge. G. & Floor, P.. 1973. Les graniloides varisques de la rOrdovïcien-Silurien. Bull. Soc. Géol. Miner. Bretagne. IV.

Meseta Bull. Soc. Géol. Fr.. 15. 209-228. 7. ibérique. pp. pp. 1

Da Costa. Os E. J.. Calsteren, P. W. C. & R. P.. 1976 Carrington J.. 1952. movimentos caledónicos e pre- Keasbcrry. van Kuijper.

Bol. Paleozoic mantle in liminares hercinicos naPeninsula Ibérica. Soc. Geol. Portugal. Early diapirism Galicia. Tectonophys., 31. pp

10. pp. I 12. T61-65.

1961. results in 1966. Den Tex. E.. Some preliminary of'penological work Koning, H.. Les types de roches basiques ci ultrabasiques qu'on

Galicia (NW Spain). Leidse Geol. Meded., 26. pp. 75 91. rencontre dans la partie occidentale de la Galice (Espagne). Leidse

1974. The its Geol. Meded.. 36. 235 242. . polycyclic lithosphère:an attempt to assess orogenic pp.

Cent, de la Soc. Géol. des domaines R. P.. 1979. L'-Pb and the memory. Belgique. Géologie Kuijper. systematica petrogenetic evolution

cristallins. 145 181. of inlracru-slal Liège, pp. rocks in the Paleozoic basement ol' Western Galicia

1977. sonrôle dans l'évolution de la Chaîne nr. . Lesoclepolycycliqueet (NW Spain). Vcrhand. 5, ZWO Laboratorium voor Isolopen-

Int. Varisque en Galice occidentale (Espagne du NW). Colloque geologie. Amsterdam. 101 pp.

C. N. R. S. 243: La Chaîne no. Varisque d'Europe Moyenne et Lotze. F.. 1945. Einige Problème der Iberischen Meseta. Geotekton-

Occidentale. Rennes 26 Sept.-Oct. 1974. (Abstr.) and Proc. 1977. ische 6. 12. Forsch., pp. I 67-78. pp. Maaskant. P.. 1970. Chemical petrology ofpolymctamorphie ultra- 1979. A continental rift in NW . prc-Variscan system Spain. Krysta- maficrocks from Galicia, NW Spain. LeidseGeol. Meded..45. pp. linikum. 14. 19 31. pp. 237-325.

& Vogel, D. E.. 1962. A "Granulitgebirge"al Cabo Ortegal. Geol. Macpherson. J.. 1X81. Apuntes petrográficos de Galicia. Ann. Soc Rundschau. 52, 95-111. pp. Hist. Esp. Nat.. 10. pp. 49 87 & Floor, P.. 1967. A blastomylonitic and polymetamorphic 'Gra- . 1883. Sucesión estraligrafica de los terrenos arcaicos de España in Western Galicia (NW A la ben' Spain). Etages Tectoniques. Soc. Hist. Ann. Esp. Nat.. 12. pp. 341 378.

Baconnièrc, Neuchatel. pp. 169 178 Martinez Garcia. E.. 1972. El Silúrico de San Vitero (Zamora) J. P. & D. F... 1972. -, Engels, Vogel, A high-pressure intermediate Comparación con series vecinas e importancia orogenica. Acta facies series in the Prccambrian at Cabo Ortegal temperature 7. 104 108. geoL Hisp.. pp. (Northwest 24th Spain). Int. Geol. Congress Montreal. Sect. 2. pp. . 1973. Deformación y metamorfismo en lazonadeSanabria. Sludia 64- 73. Salamanca. 5, Geológica. pp. 7 106. Engels. J. P.. 1972. The cata/onal polymetamorphic rocks at Cabo . Fernandez Pompa. F.. Arce. M.. Fernandez Marinez. F . Fernan- (NW Spain). A structural and petrofabric study l.eidse Ortegal dez Tomas. J. & Monteserin. V.. 1975. Nuevos datos para la 133. Geol. Meded.. 48. pp. 83 interpretación del complejo básico de Cabo Ortegal (Galicia. Fernandez F.. Monteserin V. & Peinado Pompa. Lopez. Moreno, M.. Noroeste de Tecniterrae. España). 7. pp. 8 12. 1976. Mapa Memoria de la Hoya núm. Geológico y explicativa 7 Matte. Ph.. 1968. La structure de la virgation hercynienne de Gaine (0603) Cedeira. Publ. del IGME. 1-73. pp. Géol. 44. 157 280. (Espagne). Alpine. pp. A., 1972. Le Précambrien le de la Province Ferragne, et Paléozoique Meer Mohr. C. G. 1975. The van der, Palaeozoic strata near Moeche de l'Orense (Nord-Ouest de l'Espagne) Stratigraphie-Teclonique- in Galicia. NW Leidse Geol. Spain. Meded.. 49. pp. 487^97. Thèse Mélamorphisme. Univ. Bordeaux 1. 249 pp. Meerbeke. G. L. E. van. Hilgen. J. D. & Floor. P.. 1973 Preliminar) Hoor. 1966. P.. Petrology of an aegirine-riebeckite-gneiss bearing results of the investigation of'the central Galician schist area (Prov. of the Massif: part Hesperian theGaliñeiroand surroundingareas. of Orense and Pontevedra. NW-Spain). Leidse Geol. Meded.. 49. Leidse Geol. Meded.. 36. 204. Vigo. Spain. pp. I pp. Î3 37.

. 1970. Session de travail consacrée a la subdivision des roches L. 1975. Tectonic and Minnigh. D., pétrographieaspects of an area granitiques hercyniennes dans le Nord-Ouest péninsulaire. Bol. SW of the Lalin Unit (Prov. Orense and Pontevedra. NW Spain). Geol. Min.. 81/2-3, 245 248. y pp. Leidse Geol. Meded.. 49. pp. 499 504. Kisch. H. J.&Oen 1970. , IngSoen. Essai de corrélation de quelques Miyashiro. A.. 1973. Metamorphism and metamorphic belts. Allen Nord granites hercyniens de la Galice et du de Portugal. Bol. Geol. and 95. Unwin. London, p. y Min.. 81 2-3. 242 244. pp. R. A. A Overmeeren. van. 1975. gravity investigationofthecatazonal

Kontbotè. J. M. & Julivert. M.. 1974. The Precambrian in the Iberian rock Cabo 2b, complex at Ortegal (NW Spain). Tectonophys.. pp. Peninsula. In: Précambrien des Zones Mobiles de l'Europe. Conf. 293 307.

Liblice 1972. Prague, 175 188. pp. J. R. & R.. 1971. Problems and discussion Parga. Vegas. on Hensen. B. J.. 1967. Mineralogy and of lithium petrography some tin. Precambrian Series of the Hcsperic Massif (Western Iberian

and beryllium bearing albite-pegmatites near Doade. Galicia. Peninsula). Geol. Rundschau. 61. pp. 44 69 Leidse Spain. Geol. Meded.. 39. pp. 249 259. Nota Parga Pondal. I.. 1956. explication del mapa geológico de la

Hilgcn.J D., 1970. Algunas observaciones sobre el granito porfiroide parte NO. de la Provincia de La Cortina, leidse Geol Meded.. 21.

deFontao su mineralizacion metalífera. Bol. Geol. Min. y y 31. pp. pp. 467 484. 199-210. . Matte. P. & Capdevila. R.. 1964. Introduction à la géologie de

1971. The Lalín Unit: a new structural element the . in Hercynian l'Ollo de Sapo' formation porphyroide antésilurienne du Nord-

orogen of Galicia (NW Spain). Proc. Kon. Ned. Akad. Wet.. (B) ouest de l'Espagne. Not. & Com. Inst. Geol. y Min. de España. 74. 1-10. pp. 76. 119-154. pp. Hsii. K. J., 1974. Melanges and their distinction from ohstostromes Priem. H. N. A., Boelrijk. N A. I. M.. Verschure. R. H . Hebeda. E.

In: Modern and Ancient Soc. Econ H & Floor. P.. 1966. Géosynclinal sedimentation. Isotopic evidence for Upper Cambrian or Pal. & Min. Spec. Publ.. 19. 321-333. pp. Lower Ordovician granite emplacement in the Vigo area, north- J. J. Hubregtse. M. W., 1973a. of the Mellid area, a Geol. & 45. 36 40. Petrology western Spain. Mijnb.. pp.

Precambnan polymetamorphic rock complex. Galicia. NW & Verdurmen, E. Th.. acid Spain. ... A. 1970. Dating events of L,eidse Geol. Meded.. 49. 9-31. pp. plutonism through the Paleozoic of the Western Iberian Peninsula

1973b. Distribution of elements in basic facies 274. . some granulite Eclog. Geol. Helv.. 63. pp. 255

rocks. Verh. Kon. Ned. Akad. Wet. Amsterdam. 68 27/1, pp. Ribeiro, A., 1974. Contribution à l'étude tectonique de Trás-os- Julivert. M.. Marcos. A. & J.. 1972. L'évolution Montes oriental. Scrv. Geol. de Mem.. 24. 168. Truyols. Portugal. pp. I du Nord-Ouest paléogéographique de l'Espagne pendant Ribeiro. L. R. & Ribeiro. A.. 1974. Signification paléogéographique 21

R. L.. 1972. Ore Petrology. McGraw Hill, New York, et tectonique de la présence de galets de roches métamorphiques Stanton, pp

du Tras-os-Montes 652-654. dans un flysch d'âge dévonien supérieur

R. Gedanken Tektonik oriental (Nord-Est du Portugal). C. Acad. Sci. Paris, 278, pp. Staub. R.. 1926. zur Spaniens. Vierteljahres-

3161-3163. schrift. Naturf. Ges. Zurich. 70. pp. 196-260.

Riding, R.. 1974. Model of the Hercynian fold belt. Earth & Plan. Sci Stille. H.. 1927. Uber West-Mediterrane Gebirgszusammenhànge

Letters. 24, 125-135. Abh. Ges. Wiss. Göttingen. Math.-phys. Klasse N.F.. 12. 3 pp. pp.

Ries. A. C. & Shackleton, R. M., 1971. Catazonal complexes of Vogel. D. E., 1967. Petrology ofan eclogite- and pyrigarnite-bearing

rock at Cabo NW North-West Spain and North Portugal, remnants of a Hercynian polymetamorphic complex Ortegal. Spain.

Leidse Geol. Meded.. 40. 121-213. thrust plate. Nature Phys. Sci.. 234. pp. 65-68. pp.

Sampelayo. P. H., 1922. Criaderos de hierro de España, Hierros de Warnaars. F. W.. 1967. Petrography of a peridotite-. amphibolite-

terrain NW of de Galicia, t. I. Mem. Inst. Geol. España, t. IV. 483 pp.. pp. 47-48. and gabbro-bearing polyorogenic Santiago

Schermerhorn. L. J. G.. 1975a. Spilites, regional metamorphism and Compostela (Spain). PhD. thesis. State Univ. at Leiden, 280 pp.

of rocks subduction in the Iberian pyrite belt: some comments. Geol. & Winkler. H. G. F.. 1967. Pedogenesis metamorphic (2nd

54. 23-35. éd.). Springer- Berlin. 237 Mijnb., pp. Verlag, pp. mineralización metalífera 1975b. Pumpellyite-facies metamorphism in the Spanish pyrite Ypma, P. J. M.. 1966. Sumario de la y su

belt. I, 71 86. en Galicia occidental Leidse Geol. Meded.. 36. Pétrologie. pp. genesis (España).

del Reino de Galicia 279 291. Schulz. G.. 1835. Descripción geognóstica pp.

A. 1969. of Gráficas Reunidas S.A., Madrid. 176 pp. Zuuren. van, Structural petrology an area near Santiago

de Compostela (NW Spain). Leidse Geol. Meded.. 45. pp. 1-71.