E xcursion to the Central Pyrenees, September 1959

BY

L.U. de Sitter and H.J. Zwart

Abstract

The of twelve is short of account a day excursion preceded by a general description

the Central Pyrenees, their stratigraphy and structure and the regional metamorphism.

The day by day description of the excursion follows the route which twice crosses the Paleozoic of the Pyrenees.

Contents

p.

Preface 2

Introduction 4

Stratigraphy 6

Cainbro-Ordovici.iii 6

Silurian 7

Devonian 8

Carboniferous 9 , ,. Pre-Hercynian Carboniferous- D „ t ., rost-rlercynian Carboniferous 9

Penno-Triassic 9

Post-Trias formations lü

Structure 10

Regional met imorplnsni and intrusive rocks 13

Ihr Excursion 17

References -is

I. of Central Plate Geological map the Pyrenees 1 : 200.000.

Plate II. Set of (i sections through the Central Pyrenees; for location see fig. 2. PREFACE

to In order show our foreign colleagues something of the results of our

work in the Central Pyrenees and with the hope to arrive at a better under-

standing of our problems by comparing their experience with ours, an excursion

was arranged lasting from the 15th to the 27th of September 1959. Starting in Seo de crossed the Urgel we Pyrenees northwards through Andorra into France, then westwards then the axial went south, entering zone by following

the Garonne river. We crossed the the axial zone again going southwards by

Valle de Aran and the Pallaresa valley and finally went back lo Viella by the

tunnel through the Maladeta massif.

We had the of the the whole pleasure seeing among participants during

or part of the excursion:

M. Bertraneu, B.R.G. G. M, Paris

Prof. Brindley, University of Dublin

Prof. Brinkmann, Bonn

Prof. Gill, Trinity College, Dublin

M. Guitard, B. R. G. G. M.. Paris

Prof. Hollingvvorth, University College, London Prof. Picard, Hebrew University, Jerusalem

Prof. Ecole des Mines, Paris Raguin, sup. Prof. Sutton, Imperial College, London

Mrs, Sutton—Watson, Imperial College, London Prof. R. Triimpy, Zurich

Prof. Wenk. Basel

and several french and dutch To several other young geologists. our regret French and Italian, colleagues. Spanish, were unfortunately prevented, some onl)

at last the moment, to attend our meeting. Leader General of the excursion was Prof. de Sitter, who also was responsible

for the explanation on all the non-crystalline rocks. Dr. Zwart was responsible the rocks the 2nd 6th and 8th and Prof. lor metamorphic seen on to day day

for the excursion the Marimaña 10th Brindley morning to granite on the day.

which intrusive mass he has been mapping iti 1958 and 1959.

Mr. Boschma from Leiden looked after our well in very efficiently being field the and in the villages where we passed the night.

Our excursion can be as to the Société regarded a sequence the excursion of géologique de France in the eastern Pyrenees i Bull. Soc. Géol. France. 6e sér. fase. 8. in the t. 8, 1958) September 1958. and we profited largely from ex- perience gathered there.

The excursion was mainly concerned with the structure of (he Pyrenees as a. Mountain chain and its metamorphic history. The stratigraphy of the Paleo/oic

received considerable attention but the lack oí torils in this highly cleaved region makes detailed knowledge unfortunately impossible.

As much of our detailed information about the 8000 km- which have been 3

the Central will or are being mapped in Pyrenees is, or be published, in separate and in 50.000 with of which three reports particular by 1 : maps explanation, have been published already (sheet 3. de Sitter-Zwart, 1959; sheet 4. Klein- smiede, 1960; sheet 5, Zandvliet. 1960). this account of the excursion will give only an introduction to the more important problems and a short description of the itinerary we followed. INTRODUCTION

staff members. Since 1948 a group of varying composition, students and lias been mapping the Central Pyrenees (Plate I). Various publications, mentioned in the reference list, have the other in seen light, reports are deposited our

files. In recent years special petrographical and structural studies have been undertaken principally by Dr. Zwart (1958a & b. 1959a & b).

Our studies have mostly been restricted to the Paleozoic, the younger sediments have been far constitue the boundaries only mapped as as they or

cover of the Paleozoic, and our structural analysis is mainly concerned with the

Hercynian structures, although the Alpine deformation had to be analysed in

far understand how much be subtracted from the so as to must present

configuration to arrive at the Hercynian structure. The result of this latter be study can formulated very briefly in the concept that the Tertiary struc-

ture is partly an outward extension to the north and south of the Hercynian

and of the structure, partly a morphogenetic arching combined with tilting whole mountain chain.

From a purely descriptive point of view the Pyrenean mountain chain con- of both sists an axial zone, some 50 km wide, of Paleozoic rocks flanked on

sides by"sub-Pyrenean" zones, consisting of Paleozoic cores with a Mesozoic-

Tertiary mantle. These internal zones are flanked again by Upper Cretaceous- northern internal the of Tertiary marginal troughs. Although the zone, zone the satellite massifs, is considerably broader (20 km) than its southern equivalent.

the —10 the whole is thus Xogueras zone (4 km), structure fundamentally sym-

metric and we can not talk about foreland and hinterland.

These two outwards from the axial internal and steps zone, zone marginal

not the centre trough, have a profound significance. The axial zone is only

of the Hercynian compression but has in its centre also the deepest and central

two zones are the part of the Paleozoic geocyncline. The internal the sites of Lowest Cretaceous of the Late Eocene thickest deposits as a precursory phase

Pyrenean phase of folding, mainly restricted to this zone. The marginal troughs

are filled with Upper Cretaceous, and Lower Tertiary sediments and its outer

borders sites of Miocene, of which have are the younger, phases folding, recently authoi been studied in great detail by Mangin, 1959. The conclusion of this of axial is that the most pronounced tectonic phase on the borders the zone the also Lower-Miocene must certainly be regarded as erroneous, as long as

discordant Pobla de Segur conglomerates, which are generally regarded as

for instance not to Oligocène (see Misch. 1934. and Hupé, 1954) are proven be Miocene.

ol Thus wc see that both the formation sedimentary basins and their sub-

deformations wander outwards from the since the in the sequent rentre unset Devonian. The Pyrenean mountain chain derives its fundamental symmetric block structure from its situation between two cratonic blocks, the Aquitanian

in the north and the Ebro block in the south, the basins encroach more and

blocks the the more on these during long history and folding phases follow for in the direction. them faithfully step step same 5

The last of the whole is the which phase sequence morphogenetic phase occurred the end of the Miocene in the Pliocene. Two Miocene probably quite at or

or younger aplanation surfaces or peneplains have been preserved admirably in the central zone of the Pyrenees, only slightly remodeled by later glaciations. The

principal surface is found in the central zone a little above 2000 m altitude and

sides gradually drops to both thus forming a very broad and shallow arch. A surface 2400 alt. is less well The higher at roughly m preserved. base of this arch

is not the whole as quite horizontal, orogene has been tilted a block with a north dipping slope, with the result that the southern marginal trough, the Tremp

basin, is at a much higher altitude than its northern equivalent which is complcicU buried beneath younger sediments. Therefore we find the original post-Eocene folding phase conglomerates outcropping high above the river beds in the south and mostly deeply buried in the north. The age of the morphogenetic uplift has been revealed to us by a small outcrop of sediment, filling up an ancient gorge

in the granite and Paleozoic rock of the central zone, containing at its bottom

and The conglomerates at its top some lignites (see 9th day). pollen of the latter its Pontian 1957). give age roughly as (Jelgersma. STRATIGRAPHY

The details of the stratigraphy of the Paleozoic of the Central Pyrenees is known because fossil evidence is almost absent very insufficiently completely exept in the Silurian black shales.

There is a lower, neritic Cambro-Ordovician series below the Silurian and a

shale-limestone sequence of the Devonian above it, topped by the Lower Carboni-

ferous.

THE CAMBRO-ORDOVICIAN

The Cambro-Ordovician consists of a monotonous series of slates, sandy slates,

quartzites and microconglomerates of unknown thickness certainly exceeding 2000 in and less than 5000 One habitus probably m. gets the impression that a shaly

prevails in the west and south and a psammite character in north and east. Most

probably the deepest exposed rock is the limestone and black ferruginous slate out-

cropping in an antiform near Lladorre in the Cardos river, which could perhaps be identified as the "série de Canaveilles" of Cavet, 1951. If older sediments

their character is masked because mica- are present original they are replaced by

schists and augengneisses. Above it occurs a finely stratified series of thin slate and sandsone alternation of "schistes rubanés" character, overlain at its turn by

a thick slate-sandy slate-quartzite-microconglomerate sequence. It is only at the better top that recognizable horizons occur, coarse conglomerates, massive dolomite,

limestone and thin slightly calcareous fossiliferous slates. The latter have given Caradoc fauna and the a (Roussel. 1904. Dalloni, 1930, Cavet 1958) represents oldest fossiliferous horizon in the Pyrenees. Whether Cambrium is represented by of the lower série de Canaveilles has been some part series ( for instance, as

suggested by Cavet, or below a certain conglomerate as suggested by Destombes.

of Even Pre-Cambriani be in 1953) remains a matter conjecture. might present

the lower part of the section.

The of the of the Cambro-Ordovician is development top part very irregular. The thick massive dolomite-limestone series of Trimouns (Zwart 1954) and that of Bentaillou are not in the same position in relation to the Silurian for instance. first the being almost right below it, the second being separated from it by a few

hundred meters of sediments carrying a thin stratified calcareous layer (probably of the Caradoc an equivalent fossiliferous horizon) and a thick conglomerate. The

Bentaillou limestone can be followed eastwards to the north flank of the Auzal granite, but the conglomerate above it disappears in that direction. The limestone can most probably be correlated with the thick dolomite round the Marimaña granite, where it carries at its base a typical alternation of limestone and quartzite called "sandwich limestone". Sometimes it is a typical crinoid limestone. In the

bul western portion of our map this limestone horizon has disappeared, .1 ± 20 ra thick limestone occurs again at the base of the Silurian in the Bosost dome. It links up roughly with the Bentaillou limestone by its occurences north of the

Barrado: and in the Liât As all these limestones be valley region. are apt to mineralized, talc, in Trimouns. lead-zinc ores in Bentaillou. Liât and Bosost. it has 7

been referred limestone" 1869 The extension to as the "metalliferous (Mussy, —70). of this limestone/dolomite facies has been given by Zandvliet, 1960 (fig. 1). Coarse conglomerates occur both above and below it in the Bentaillou region and even as far south as Llavorsi one can observe two conglomerate horizons with

a calcareous layer with slates and sandstones between them. The pebbles consist almost of and well rounded. exclusively quartzite or quartz are not particularly the The matrix may be either sandy or shaly. Sometimes pebbles are tectonically flattened, sometimes they have preserved their original shape, but the matrix has folded and of Tor. Andorra been intensively flat tened. Near the village near the border, they are clearly of a fluviatile origin with sand lenses on the lee side of

a big pebble and sandy clay around it. Their rather monomict character and

their fluviatile that all the from the origin suggest pebbles are directly derived

Cambro-Ordovician itself. On of the massive limestone top occur occasionally limestone breccias in matrix. The facies ol the whole is neritic a shaly sequence and certainly not a flysch facies.

1. of Fig. Isopach map the Upper Ordovician massive limestone-dolomite. After Zandvliet, 1960.

THE SILURIAN

The Silurian is represented by its well known black shale facies characterized by graptolites and occasional beds of Orthoceras bearing black limestone. It is a typical euxenic facies with pyrite and a certain carbon content, very high alumina. low As silica and relatively high iron content. the iron occurs as an easily soluble sulfide, the rock always give rise to ferruginous springs. The graptolites, mainly Monograptus, have shown thai the Silurian is complete

the lower and niemhers. hut no to except perhaps extreme upper as single top bottom section has been analysed and this rock is always extremely tectoni/ed the evidence is rather incomplete. Rather and in in the north, the black shales black frequently, particular (any limestone beds with orthoceras and few a brachiopods. Very rarely a sandstone occurs within the black slates.

As the of the Ordovician has rather variable it would top a composition not be impossible that there exists a slight disconfonnity at the basis of the Silurian 8

the slates The top of Silurian has been chosen arbitrarily where the black are limestone calcareous the south the is formed covered either by or by slates. In top alternation of black slates and thin limestones intercalations. As by an long as

fossil evidence is lacking we are here at a loss where to draw a reasonable limit

between the Devonian and the Silurian.

In the region of Pia de Beret, between the Upper Pallaresa and [ñola rivers, black Most this is i lie typical slates are missing altogether. probably due, however, fault and the of the and to movements squeezing along top Ordovician not to facies change.

The thickness is difficult to evaluate because the black slates arc invariably strongly tectonized. sometimes squeezed in thin strips, sometimes accumulated in

thick masses. Nevertheless it seems to be thicker in the north, perhaps 200 m.

than in the where 50 would be better centre in perhaps a guess.

THE DEVONIAN

The Devonian shows a variable facies, as well in a north-south direction very

as east-west, parallel to the mountain chain, but the variation is most pronounced

in a N-S cross section. We find in the Valle de Aran, the central portion of the axial zone, a completely different development as compared with the northern and southern sections which, at least for the upper part, are rather similar. The main diference lies in the development of the Upper Devonian, which in the north and south is characterized facies thickness, by a griotte sometimes of great which is in the completely missing the centre. In centre a curious quartzitic and grauwacke turbidite facies, which is unknown in the border regions, has developed above limestone-shale alternation. This turbidite is overlain a line a sequence by slate which could be correlated with similar slates grained green perhaps on top of the griotte occurring in the N\V. In the SW region, between the Esera and

Ribagorzana rivers an alternation of quartzites and dolomites occurs below the

from it slate horizon. fossils of the whole griotte separated by a Dating by sequence

in only possible in the extreme north, in the Arize massif principally, and possibly

well also on the southern border. The griottes often carry goniatites but seldom enough preserved for determination. Recently conodonts have given better results (Ziegler 1959).

The thickness of the Devonian is also variable. In the Salai area ¡i has very been 1400 but and in the Arize valued at in. further west only at 300—400 m

massif at 360-540 in. In the Llavorsi syncline it is only 330 m thick and in the

been Valle de Aran several ridges and basins have distinguished with greath varying thicknesses (Kleinsmiede. 1960).

no the There can be doubt that after the very regular sedimentation of

Devonian a Silurian, the represents period of much greater unrest.

The of the Devonian seems a of the top to be locally period emergence. In

north, in the Arize massif and elsewhere coarse monomict limestone conglomerates

have been found there surface and the upper limestones often show a karstic erosion (Ovtracht. 1956). Moreover the boundary with the Carboniferous is

variable. In the central syncline of the axial /one the Carboniferous rests probably

the basal limestones. In other sections, however, there is unbroken on an sequence

from Devonian to Carboniferous (Ziegler. 1959).

CARBONIFEROUS

The have subdivided in Carboniferous rocks to l>r .1 pre-Hercynian-folding

sequence and a post-Hercynian sequence. 9

The pre-Hercynian Carboniferous

Since Ziegler. 1959, has shown with conodonts, and Durand Delga, 1958

with tentaculites, that at least in some sections the Tournaisian is not missing, as

had been assumed until then, the evidence of the field geologist both in the of Montagne Noir and in the Pyrenees, who often have found evidence a gradual

transition from Devonian to Carboniferous, stands on much firmer ground.

The Carboniferous both in the south and in the north starts with a chert

horizon, carrying phosphate nodules. The chert is followed by shales and sand-

which in the north fauna of Visean stones, carry occasionally a goniatite Upper age. In the south these shales are characterized by single corals. Both the shales and sandstones are often micaceous.

Often the cherts are missing and are replaced by pebble beds or conglomerates in which well rounded chert dominate, quartz pebbles and angular pebbles and which other Bellver carry occasionally gneissic or crystalline rock pebbles ( district I. These beds in the in the north of conglomeratic occur Jueu syncline, west our

map and in the southern zone. Sometimes both the chert containing conglomerates

or breccias are present in one section ¡Salat valley). Thin limestones occur

occasionally in the shale-sandstone sequence. A different facies is developed in the central syncline of the Uppei Esera and find black micaceous sandstones and shales with Jueu valleys, «here we plant

fragments, sometimes of large dimension. This flora has been regarded as Lower

Westphalian by Zeiller (Roussel 1904).

The post-Hercynian Carboniferous

In the northern border zone of the Pyrenees it are the red Permo-Triassic rocks which cover unconfonnably the Hercynian folded Paleozoic, but in the southern border rocks zone there occur Upper-Carboniferous and perhaps Permian between the Permo-Triassic folded and the Hercynian sequence. In coal is known, situated between one outcrop near Aguiró a seam two

coarse conglomerates, which has delivered an Upper Westphalian flora (Dalloni.

1930). The is followed the volcanic upper conglomerate by sequence, mostly tufs,

which is common all along the southern border of the Pyrenees, and which carries

coal seams with a Stephanian flora. The same formation has also been reported

from Mouthoumet.

Arcalis in carbonaceous In one outcrop, opposits the Pallaresa valley, black flora and which is Permian shales have given a containing Walchia's regarded as (Dalloni. 1930).

The Stephanian is overlain everywhere by the Permo-Triassic, sometimes with

a slight unconformity.

The Stephanian volcanic formation shows abundant evidence of volcanic activity in the neighbourhood, bombs and lapilli for instance and has accordingly

a the carries water laterally strongly varying development. Towards top it fresh coal and the cherts, conglomerates, sandstone beds, black shale beds and seams at base find sometimes weathered we coarse conglomerates as at Aguiró or shally

surface deposits of the older rocks, cracks in the Devonian limestones filled up

with pebbles and similar rock types.

THE PERMO-TRIASSIC

The Permo-Triassit is developed in ils classical continental facies oi red cross-bedded sandstones, quartz-pebble conglomerates, breccias and red mudstone. 10

The Triassic follows with the typical muschelkalk. gray dolomite and cavernous

dolomite (anhydrite dolomite, cargneules) and the Kenper gypsiferous marls, pure salt, black small and bodies of basic rocks gypsum, shale, carrying large (ophite's) and folded slabs of muschelkalk.

THE POST-TRIAS FORMATIONS

Little attention has been the Mesozoic than Trias and paid by us to younger the where their threw the structural to Tertiary, except occurence special light on

development. We refer the reader to Castoras, 1933 for the northern bolder zone

and to Misch, 1934, for the southern border.

The most conspicious member is without doubt the thiek Urgonian limestone which forms chain of the fault a very pronounced hilltops along North-Pyrenean

In the south each of the north-south rivers has cut zone. running a deep canyon in these thick and strongly folded limestones. The maximum development of this north Lower Cretaceous sequence (Urgonian limestone and Aptian shales in the i

is restricted to narrow zones flanking the axial zone in the north and the Nogueras

zone in the south.

In the northern zone the Cenomanian is unconformable on this Lower Creta-

and its coastal facies line coïncides with the fault ceous roughly North-Pyrenean

zone. This coastal facies is characterized by coarse conglomerates, arkoses with

calcareous matrix, slided blocks of older rocks and lime- a. big (granites Devonian

stone) and similar phenomena of Wild-Flysch character. In the south such un-

conformity is unknown.

During the Senonian and Eocene the depositional basin shifted further out-

wards.

The late Eocene, the next folding phase was It put a stop to sedimentation in the southern and the accumulation of marginal through originated enormous

of in the southern border of the conglomerate mostly oligocène age Pyrenees,

which can be studied particularly well near the little town of Pobla de Segur.

They were deposited there (in a strongly dissected landscape of Lower Cretaceous rocks.

with of the Central The next Tertiary formation met in the axial /une Pyrenees is small of Miocene sandstone and >le a outcrop Upper lignite, clays, coarse pel>l

in filled the between the Arties and beds preserved a up canyon on crest Aguamoix rivers in the Valle de Aran. The of this formation is covered 40 top by some m of moraine which forms of the of the 2000 part general glacial cover ± in apla-

nation surface. This latter surface ranging from 1850—2350 in altitude is well developed both on the French (platform of Aston) and Spanish side (Coma the the above mentioned dates Romadera) of central Pyrenees. As canyon probably form the first morphogenic uplift of this aplanation surface, this uplift apparently did before the end of middle Miocene. Remnants of and older not start a higher

the surface at 2400 2600 m altitude have been preserved in some places on Spanish side ( Montareno. for instance) (Zandvliet. 1960).

The present topography of the Pyrenees is largely pre-glarial. and the glacia- tions modified the relief Most only very slightly. glacial cirques are remarkably shallow and morainic material does not descend far in the valleys.

STRUCTURE

The Central Pyrenean area represented on the accompanying 1:200.000 map

Plate I) and sections | Plate Hi. contains principally the axial zone and the 11

adjoining north and south Pyrenean internal zones. Of the northern internal

zone it are mainly the satellite massifs of St. Barthélémy, Arize, Trois Seigneurs

and Castillon which are included. The southern internal zone has been called the

Nogueras zone by Misch. The axial zone is separated by the north Pyrenean fault

/(inc. running over Aston. Vicdessos. Aulus, Bordes and St. Béat, from the satellite almost massifs. In the south its border is marked by an straight line of Permo-

Triassic crossing the Segre, Pallaresa. Ribagorzana and Esera rivers, south of of Paleozoic which we find the narrow Nogueras zone consisting Upper masses

sin rounded by Triassic.

The structural of this lion be divided in three main history map set can episodes, the Hercynian orogenesis, the morphogenetic uplift and the Alpine orogenesis.

Fortunately the Hercynian and Alpine deformations can be separated ratlici well. The axial zone has suffered no Alpine deformation except along narrow its southern and and fault axial /ones on northern boundary along lines in the the massifs /one. Neither have northern Paleozoic satellite been strongly deformed in lime. The the has been deformed in the Alpine Nogueras zone on contrary Tertiary. The whole mountain chain is concerned in the morphogenetic upheaval, independent of its previous structural history. Nevertheless in detail it is often

difficult to assign a certain structural feature to one of the major orogeneses, in

particular in the northern and southern internal zones.

In a former de Sitter have called to the paper, 1956, we attention symmetry of the its and its Pyrenean orogene, centripetal development intercontinental character. The is situated between cratonic blocks, the orogene two Aquitanian block in the north and the block in the south. Its distinct Ebro development as a

structural unit dates with certainty from the beginning of the Devonian, as is true

for all European Hercynian orogenes. Since then it has developed outwards further and further, encroaching on the continental regions to the north and south, towards

its present stage with marginal troughs in the south (Cuenca de Tremp) and in the north. The and form Hercynian Alpine structures are not independent, they

here unit. the one Nevertheless the Tertiary structures are not quite parallel to The fault Hercynian unes. North-Pyrenean between Vicdessos and Castillon cuts obliquely through the E-VV Hercynian folds of the Salat basin.

The whole has distinct of Ilcrcynian structure as a a cleavage type folding,

strongest in the centre and showing transitions to the concentric type both towards the north (Arize massif. Estours) and the south (lower Ribagorzana-Baliera rivers).

fact This gives a strong support to the thesis that the present Pyrcnean chain is

also the Ilercynian chain and did nol extend much further north and south.

The cleavage and axial plane dip variation is not quite so symmetrical. It is

true that it is vertical in the Salat, slightly north dipping in the Valle de Aran and Upper Pallaresa and Cardos rivers, hut further south this dip decreases

regularly and becomes very flat indeed downstream of Llavorsi and elsewhere near the southern border of the axial zone. Towards the north, however, flattening of the axial plane cleavage with southern dip is not so pronounced, although in the Arize axial do massif and in the Kstours region of the axial zone the planes

dip towards the south, but some structures in the Lez river dip northwards.

The intensity of the stress cleavage in general is less in the Carboniferous than in the Cambro-Ordovician. and its is neither greatest development quite central, it is outside the metamorphic regions, higher in the south than in the north.

Another of the is demonstrated the asymmetry orogene by regional meta-

morphism, which in the Central Pyrenees is distinctly restricted to a northern zone 12

the and is particularly strong in satellite massifs of the northern internal zone. Whether the distribution of the intrusive in has tectonical back- masses general a

ground or not is difficult to ascertain, more in detail there certainly are significant

coïncidences between structural lines and the arrangement of plutons.

A look at the shows that there is one central anticlinorium map containing the Aston massif in the east and the I.ys-Caillouas massif in the west. It is flanked

in the south narrow the Llavorsi cast and centre. by a syncline. syncline in the

the .[neu syncline in the west. The central anticline the of the Ganaveilles" has in its centre outcrop "série de

near Lladore which continues eastward in the Hospitalct massif. South of this

massif we find the Tor-Ordino syncline in Andona and north of it an important

thrustfault. the Merens fault/one. dying out westward. North of tlic Aston clonic and north of the north-Pyrenean fault the four satellite massifs of Trois St. Castillon, Arize, .Seigneurs and Barthélémy, once unit, dome, with certainly forming a single one a strongly developed regional

metamorphism. They were separated from one another and probably from the

Aston massif also in late a which accentuated a Ilcrrynian phase, separation was by the Cretaceous phase of faulting along the North Pyrenean fault/one.

A smaller Cambro-Ordovician dome on both sides of the Garonne river has

been called the Bosost dome, a with structure a regional metamorphic centre

round this town.

Between and round these three main units, the central anticlinorium. the

satellite massifs dome and the Bosost dome, we find the Devonian in strongly

compressed form, mostly as vertical or north dipping isoclinal folds. There is a

pronounced difference in style of folding between that of (he Cambro-Ordovician

and that of the Devonian. The Devonian 'with Carboniferous) has been sheared

off its Cambro-Ordovician basement along the incompetent Silurian slates and forms isoclinal folds of some hundred meteis width, whereas its basement shows

besides folds small the some larger numerous and micro folds. The top of Ordovician is curved dome surface with the generally a gently in strong contrast

isoclinal folds of the Devonian is bedding planes. There can be no doubt that it the of the Silurian which extremely incompetent character caused this strong

disharmonie This is less well the folding. strong disharmony developed on southern border of the axial where the slates of the Ordovician sometimes /one. top are included in the Devonian folds I Schuhnan. 1 !).")<> and morning 2n,d day. fig. 7).

The axial plane of the long syncline of Llavorsi has a distinct northern dip

of 70—60°. On the it l<>oks isoclinal bul in some map a simple syncline good

in the northern Devonian flank for instance, one that outcrops, can see man) small folds the parallel accompany major structure as large sized parasitic folds. the Maladeta massif become Approaching both flanks more complicated and show

several serundary folds of Silurian and Devonian. The same is true at its eastern

end in and near Andorra, where whole of folds, with thrusts, a set secondary even There are exposed. even the upper Ordovician slates take part in this small scale folding of the Devonian.

South of of Llavorsi we find another large anticlinorium Cambro-Ordo- vician rocks, reaching from Seo de Urgel to the Noguera de Tor. where it plunges

down below the Devonian. In this structure the disharmonie folding along th<-

Silurian slates is beautifully exposed in the Tor valley (Fig. 14). South of this anticlinorium in the Pallaresa. Flamisell and Mañanet valleys, the Devonian

shows horizontal recumbent folds with Silurian in the (cues of the anticlines and

sometimes Lower-Carboniferous in its synclines. It has been proposed thai these 13

folds are duc to gliding tectonics, the Devonian mantle of the anticlinoriuin gliding

sheared First ol down, off from the apex. Two facts contradict this hypothesis.

that the still on the in the (NE of all Devonian is present apex Monseny ridge

Capdella) and occurs there also in recumbent folds. Secondly the cleavage planes

in the Cambro-Ordovician basement flatten also to an almost horizontal position

to folds near Rialp and thus are roughly parallel the axial planes of the Devonian

further south.

Furthei fold axial west in the Ribagorzana. Halliera and Esera valleys the hut north. planes are steeper, always dipping

REGIONAL METAMORPHISM AND INTRU SIVE ROCKS

The regional metamorphism in the Central Pyrenees is restricted to the northern half of the Mountain chain. South of the Llavorsi syncline no regionally

metamorphosed rocks occur. Generally the metamorphism has attacked only the Cambro-Ordovician, Inn occasionally Silurian and Lower Devonian participated monoclines in this process. The regional metamorphic rocks occur either as large

in the north Pyrenean massifs, or broad anticlines in the axial zone. hand be subdivided in several The regional metamorphism can, on one the other hand in Thus succeeding phases, and on areas with different rocktypes.

it that well time concerned in the of these rocks. appears space as as are study

This is the main reason that no two metamorphic areas are exactly similar, resembles several although the Aston-Hospitalet anticline in respects the Canigou finds massif, and the Agly its counterpart more or less in the Barthélémy massif. the differences in will be and then the Firstly space treated, chronological

succession of the metamorphism. although both subjects cannot be treated entirely

separated.

One of the most striking features of the north Pyrenean massifs and the

gneiss anticlines of the axial zone are the different types of gneiss occurring in both

The characteristic rock of the north massifs is a linear regions. most type Pyrenean which features direction garnet-augengneiss, of one of the most important is the

of lineation N-S, in contrast with ihe E-W strike of the Hercynian belt of the

Pyrenees. Garnet-augengneisses have been found in the Agly massif (lineation N 'M) E).

in the Barthélémy and Arize massifs, (lineation N-S), as relics in the Trois Seigneurs massif, and finally almost the whole of the Castillon massil is made of up these rocks (lineation also N-S). The mineralógica! composition of these with cordierite and gneisses quartz, plagioclase, potassium feldspar, biotite, garnet,

absence of muscovite, is typical for katazonal conditions, and in fact these are the only really katazonal rocks of the Pyrenees. The rather dry metamorphism is

of close the facies, and the of typical metamorphism to granulitc préseme hypei-

sthene is not uncommon. Real granulites have been described by Guitard from

the Agly massif. The only hydrous minerals are biotite and hornblende. calc- In the garnet-augengneiss numerous layers and lenses of amphibolitcs. silicate rocks and marbles with the of aluminium- occur, testifying, together presence minerals and cordierite. the of these excess as garnet to sedimentary origin gneisses. In the Arize and massifs these the Barthélémy, Castillon gneisses are deepest

and in the first thick succession other exposed rocks, two areas a ol rocktypes

succeeds these towards the gneisses top. overlain In the Agly massif the garnet-gneisses ,ue almost immediately In

mica-schists, which in their tum made into phyllites. 14

the massif In Barthélémy the garnet-gneisses can be subdivided in several based different relations between and deformation. Towards units, on crystallization

the into non-linear without but with top they change migmatites, garnet, muscovite of leucocratic and much fibrolite. The migmatites are covered by a layer gneiss,

which in its turn is overlain by mica-schists. Both contacts of the leucocratic

gneiss are sharp. The mica-schists change gradually into phyllites, which art-

overlain by the Silurian black slates. A similar kind of succession exists in the Arize

and Trois Seigneurs massifs, although there the amount of exposed garnet-gneiss

is small. In the Castillon massif, the original cover of the garnet-gneiss has dis-

appeared and the whole massif is made of the same kind of gneiss.

The most difficult problem in the north Pyrenean massifs is the explanation of the N-S lineations in the which fit in the garnet-gneisses, seems to badly regional

A solution the author that picture. originally proposed by junior they represent

an older basement, does not seem warranted, in view of the situation in the Agly

massif, and the gradual transitions of garnet-gneiss to overlying migmatites. An absolute determination age may settle the issue.

The migmatites of the north Pyrenean massifs are feldspathized mica-schists,

and also in the of the axial At the occur gneiss areas zone. many places typical banded due continued converted into migmatites are. to recrystallization. quartz- dioritic rocks, often with cordierite and sillimanite. Especially in the Trois Seigneurs massif this process was important, and there it was accompanied by strong mobili- zation and rheomorphism resulting in complete disorientation and flowing around of inclusions of amphibolite, calc-silicate rocks and marbles, which originally formed

continuous horizons. The has taken in the stratigraphie same process place

Barthélémy massif, but on a smaller scale. The variable metamorphic front, in tliis case the biotite isograd, sliows a with the Silurian. In the of the massif position regard to eastern part Barthélémy

biotite-schists reach as high as the Silurian, and the thickness of these schists few hundred Towards the the sinks off. amounts to only a metres. west isograd

together with an increased thickness of the mica-schists. This trend can be followed

in the Arize massif, where several thousands of metres of phyllites. covering a

thick series of mica-schists, lie below the Silurian black slates.

The characterized In regional metamorphic anticlines of the axial zone arc the absence of garnct-augengneisscs, and instead leucocratic augengneisses form

the core of these anticlines. These augengneisses differ in several respects from

the garnet-augengneisses. The lineations, due to elongation of minerals, are E-W

and to mine- parallel the trend of the fold axes of the low grade Paleozoic. The

ralógica] composition is different, garnet is absent, and biotite and muscovite are besides and inter- present both feldspars and quartz. The contact with overhing calated mica-schists is and the absence of always sharp, any typical sedimentary

relict as amphibolites, marbles or quartzites in the gneisses renders a determination

of the original, premetamorphic rocks difficult. There is choice oui of three

different possibilities,

1 intruded ( I they are pre- or syntectonically granites.

(2) they are isochemically metamorphosed sediments, i<>r example arkoses. 3) I they are melasomatie pelites or semipelites.

It is till to make a definite choice between the three up now, not possible

possibilities. There are arguments pro and con all three of them. For an igneous origin pleads the homogeneity of the gneisses and their sharp contacts with the rocks. This does the enclosing not explain, however, why augen-gneisses ate always 15

bound to a certain degree of metamorphism, unless it should be a synkinematic contact metamorphism, making mica-schists as contact rocks. This, at least, could

explain, why such a gneissified granite does not occur in lower grade rocks, but

it does not clarify the question why such a granite is always restricted to Cambro-

Ordovician rocks, and never has reached Devonian or Carboniferous rocks, which both have been intruded by the late tectonic instrusive biotite-granodiorites.

Furthermore it does not explain the metamorphism in the satellite massifs, in

which such gneisses hardly occur. Guitard An isochemically metamorphosed arkose series, as advocated by ( 1958) is field absence of such sediment not supported by evidence, as complete any outside the metamorphic areas and the lack of transitions between augengneiss and which would be when series would be micaschiste, expected a pelite-arkose

since there is little that the end- metamorphosed, reason to assume only pure

members, pelite, or arkose existed and no intermediate sediment, yielding for with do example a gneiss aluminium silicates. Such gneisses, however, not exist.

For for the these reasons 1 am in favour of a metasomatic origin augengneisses. the rocks Cambro-Ordovician rocks. original being normal, pelitic or semipelitic This is especially supported by the situation in the Hospitalet massif, where the

upper boundary of the gneiss is oblique with regard to the stratigraphie limits. A sedimentary origin of these augengneisses is further supported by zircon studies, recently carried out by G. W. Verspyck. In of the the any metamorphic region Pyrenees gneisses or migmatites are overlain by a series of mica-schists, in which at least three metamorph ic zones can be low with médium distinguished: a grade chlorite zone sericite-chlorite-phyllites, a biotite with grade /one biotite-muscovite-schists, and a higher grade andalusite-zone,

containing biotite. muscovite. andalusite. stanrolite and cordierite, the three alumi- nium-silicates stable Sillimanite fibrolite usually occurring in a assemblage. or

occurs as a fourth aluminium silicate, but it is always associated with granitization. and is largely a melasomatir mineral, usually replacing biotite. It is not indicative

for katazonal circumstances, and is in most rocks of the Pyrenees a mesozonal

mineral. Somewhere in or below the andalusite zone gneisses, migmatites or

for the first time. granites appear

With regard to the historical development of the metamorphism, it can be

slated thai liiere is a close correlation between different kinds of deformation and

decline of the size and the nature of metamorphism. Roughly speaking there is a of orientation of minerals, intensity folding, accompanied by a decreasing ending

in up unoriented post-kinematic crystallization.

We characterized formation of distinguish an early synkinematic phase, by

and late-kinematic with schistosity strongly oriented crystallization, a phase, cross-

folds in NW-SE and NE-SW direction, with weak orientation of new minerals, and a post-kinematic phase, not accompanied by movements in the metamorphic

regions. There are several, probably more or less local complications to this scheme:

for example an isoclinal folding phase with X-S axes, earlier than the crossfolding has been rallier important in the Bosost dome. ic mica-schists and During tlic early s\ nkii .cniat phase linear augengneisses been all oriented in E-W bave produced in which minerals are elongated or direction. is in and has low There The schistosity plane outcrops usually dips. is doubt that this of is with the no phase metainorphism contemporaneous cleavage

folding in the low grade Paleozoic sediments. All large structures, as the Cambro- Ordovician dome of the Pallaresa, the Llavorsi-syncline and the Aston-Hospitalet

gneiss anticline date from this folding period. In slates and mica-schists a new 16

the made small folds, si/c déformation, cross-folding has not usually exceeding .1 few and of a metres, is often accompanied by a fracture cleavage which in slates

is always post-crystalline. In mica-schists micas may grow in the fracture cleavage

and thus produce a coarse second schistosity, which as a rule ran immediately he identified under Minerals like andalusite and cordierite the microscope. grow

usually unoriented. and only occasionally in the foldaxes of the cross folds. The

direction of cross folding is mostly NW-SE. hut a second set at right angles to

the first one, occurs also at some places.

In gneiesses and migmatites this phase takes a quite different aspect. The

folds become much more disharmonie and their direction less regular. The style of deformation This mobilization is very plastic. is in the field, without exception the of smaller the accompanied by occurrence or larger granitic patches. Under it that all these rocks have heen microscope appears subjected In a re< rystalli/ation.

completely obliterating the earlier' augengneiss-texturc. even in those rocks, which

in die field an- siill augengneiss. Field evidence leaves little doubt that diese

granite patches are made by recrystallization of the original gneiss, probably

without much introduction oí material, water. Therefore new except granitization mobilization and are closely linked, and apparently are interrelated. The conclusion that deformation granitization and plastic in the gneisses arc contemporaneous with in slates and schists warranted distribution in the cross folding is by the field: in schists weak strong cross folding near granitized gneisses: or no cross

folding in not recrystallized augengneisses. Further evidence is furnished by peg- matite sills, genetically belonging to the metainorphism, which are cross folded with schists. together enclosing In general granitization has continued in post- kinematic time, resulting in unoriented. crosscutting granites and pegmatites.

showing no structural influence on adjacent rocks or inclusions. The occurrence of fibrolite in of the and and in some granites pegmatites the surrounding schists,

is related the and is to the result of aluminium to granitization, my opinion metasomatism, originating from the schists which have been granitized.

The whole of the Aston massif has been subjected to this mobilization and

and in resemble Sederholm's classical granitization, any respect they migmatite areas. The eastern part of the Hospitaiel massif has been preserved in its earrj between the synkinematic state and a comparison gneisses <>f both ateas is extremel) useful.

the the be Although during early synkinematic phase Pyrenees can divided in northern later the satellite massifs, southern two /oik's, a one, forming and a

one. the axial characterized bv and future /one. respectively garnet-augengneisses leucocratic difference augen-gneisses, this holds no longer good for late- and post- of kinematic time, because the same kinds migmatite. accompanied by mobilization,

occur in both zones.

The of of intrusive biotite-granodiorites the Central Pyrenees are all the diapiric The their be the type. date of emplacement can established with regard to different

folding phases, and with the aid of porphyroblasts in the contact rocks. It appeared that rocks with late K-W Folds of cleavage have been hornfelsized, clearly indicating

Relations a later age for the contact metamorphism. of andalusite porphyroblasts

with the slate in aureoles, also indicate surrounding contact metamorphie a post- reached kinematic origin. The same conclusion had airead) been by the occurrence of the granodiorites in regional metamorphie terrain, as for example in the Trois

ot Seigneurs massif. There mica-schists with a late static phase musí ovit i/atiou have cleark of thus been remctamot phoscd near the contact the granodiorite. later than the last of the testifying to an age phase regional inetamorphism. 17

rule the As a biotite-granodiorites occur outside regional metamorphic areas, Carboniferous. smaller show and intruded all Paleozoic strata up to the The stocks around a certain structural influence on theii host rocks, refolding them différent thrown who axes. Much new light on this problem has heen by J. Brindley. mapped

the Marimaña and Tredos stock in great detail. The larger bodies, like the

Maladeta Auzat the and their and batholiths, are. on map, clearly discordant, structural influence the sediments is far less than could be on adjacent expected by their enormous volume. It is suggested that these large bodies rose to higher levels along vertical faults, uplifting the covering sediments, which have been eroded away.

THE EXCURSION

The excursion started from the southern border of the axial zone and went

north of Seo de Andorra and descended the by way Urgel, passed through Ariége river, then went west to the Garonne river and crossed the axial /one again going

Fig. 2. Excursion route.

south the Pallaresa river. by way of The Nogueras zone and the unconformable rover of Stephanian, Trias and Tertiary were studied the first day south of Seo de Truel and the lasi days betweet] Pobla t\v Segur and Pont de Suerl (fig. 2). 18

Program

1st day From Seo de Urgél to Tahús-Castells and back

2nd day — morning — Rio Fontanedo

afternoon El Serrât (Andorra)

— 3rd day morning — Val d'Inclés

— afternoon Hospitalet - Ax les Thermes - Tarascón

Itli day morning Basal gneisses of the St. Barthélémy massif

5th day — Aston valley

- (Stli day 1st party Trois Seigneurs massif - St. Béat

2nd party - Estours. Salât valley - St. Béai

7th day — Col de Menté - Viella

}ith day — morning — Jueu valley-

- - afternoon folded pegmatites of Rio Barrados

9th day — Moncasan —• Aguamoix

10th day -- morning - Marimafia granite (Prof. Brindlev)

afternoon — Salardu - Sort

11th clay morning — Sort-Lladorre

afternoon - Sort-Pobla de Segur-Pont de Suert

12th day morning Stephanian and Triassie of Malpas

afternoon Rio de Tor section

1st day. From Seo de Urgél to Tahús-Castells

Seo de the the road between hills, Leaving Urgel, quite near town, passes two both of Ordovician schists. these hills flnviatile consisting Against a coarse conglo- merate-sandstone series has been deposited, which occupies a small basin wesl the of Segre river. Its age is supposed to be Pontian-Plaisantian (Chevalier. 1909:

Boissevain 19341, the the basins the river in the same age as higher up Segre Bellver The formation lies region. unconformbly on and against the schists and is certainly nol separated from it by faults as Boissevain suggests. The road follows the river and runs on quaternary alluvium. A little beyond the village of 1'la

de San Tirs the road cuts into the red sandstone and mudstone of the Trias,

which show here a regular dip of some 40° south. On the other side of the river,

to the west below the Trias, one can sec the remnants of a small excavation for

coal of the which is of this 500 a seam Stephanian. exploited east village m high in the flora mountains. The of Pia de San Tirs, collected on both sides of the

Segre valley contains several Pecopteridae and gives a Stephanian age (l)alloni.

[930, p. 97—100). The Trias of Hostalets shows a succession of red quartz conglomerate at the base, followed by thick red mudstones and red fine grained crossbedded sandstone. We take the the rivet, and the road Novés bridge across leading to de Segre and

first these beds and then into the pass through enter gypsiferous Keuper containing marbles with limestone and occasional gypsum, gypsiferous some dolomite and cellular dolomites.

A little further the of upstreams near village Belpuy we pass again through the red beds of the Triassic and then into the Devonian limestones. The contact

Trias-Devonian is not a normal contact, but a fault.

South of the Rio de la Guardia 300 and we sec the imposing m high steep northern front of the Sierra de Prada. consisting of Mesozoic limestones with

dark Dogger dolomite at its base and Triassic in the valley and thick massive 19

limestone of wall. This Urgonian forming most the steep abrupt boundary between

the Paleozoic rocks with or without a Trias cover and the Mesozoic limestones

is typical for the whole southern border of the Central Pyrenees. The south-

Pyrenean north-south rivers cut deep canyons through this Mesozoic limestone

"defilados", and the excellent on zone, exposures the canyon walls show that the iimestones often folded almost in vertical folds. are isoclinally This boundary between Mesozoic and Paleozoic is in flexure the principal a steep or fault, and

deep erosion along that line as in the Guardia river, which we are following now,

is often due to the presence of soft gypsum along the fault line.

The road exposures are in rather massive gray limestones of the lower half

3. Two sections of in north of Rio Fig. Upper Devonian-Carboniferous, both Nogueras zone

de la Guardia valley. To the left complete section, right lower part Carboniferous missing.

After Mellema. 20

Devonian with of the section, occasionally an outcrop of black Silurian slates.

the road north de Castellas. it Where turns following the Arroyo soon inters a with both sides red and white Devonian limestones. canyon on Upper griotte When the road climb the mountain with it starts to up hairpin curves has entered already in Carboniferous shales.

The first the second southern of stop on hairpin gives us a good exposure

the contact Carboniferous/Devonian. The gray and white Devonian griotte lime-

stone is followed by a quartz-chert conglomerate, where the pebbles are floating

in a shale matrix without touching each other. The conglomerate contains

occasional gneiss pebbles (fig. 3). the of the road the Trias Higher up beyond village Espahent enters cover, but the is well dominant contact Trias-Devonian nowhere exposed. From a point,

just below the Trias a quarry in beautiful red "griotte" limestone with many

one has a view to the east on the wall of the goniatites, good opposite canyon

San Quirico Mountain. The structure, which dips steeply northwards and is

thought to be Hercynian, consists of a repetition, by thrusting, of the same upper sheet of red and white griotte with in the core probably some fold repetition.

The northern slope is roughly the Carboniferous-Devonian contact of the south

flank of an E-W syncline. N-S The Trias wedge has a (rend and its western boundary is a thrust as

he seen in road This N-S strike is feature. can a exposure. evidently an Tertiary

Some 3 km beyond the Trias-Devonian fault contact we find again a very good road exposure of the Devonian-Carboniferous contact. The gray griotte its several limestone contains near top chert hivers. Then shales alternate with

thin sandstones until the first conglomerate is found some 200 m above this contad

(fig. 4). It is supposed that the series below the conglomerate and above the Devonian in this section is missing in the first section and contains the Lower

Carboniferous.

The village of La Guardia is situated on an isolated Mesozoic limestone rock of about 1 km diameter surrounded on all sides by gypsiferous Triassic with small

bodies. A walk to the north the to where ophite along ridge brings us point view we have a good westwards, on a cross section of the most southern longi-

tudinal structure of the .Nogueras zone, an overthrusted anticline in the Devonian.

well thrust movement very exposed in the small Arroyo west of La Guardia. The

is northwards and is of because on the we find an Tertiary age, ridge exposure

in of the same thrustplanc showing a block of Dogger dolomite invoked die

thrusting (fig. 4).

From La (marcha the load descends little into the broad between a valley La Guardia and Tahus, forming the watershed between the Segrc and the Pallaies.i river. This with the gentle hilly country presents a strong contrast deep canyon

have left and remnant ol an older erosion we just represents a cycle preserved

at this altitude of 1400 1500 m.

the road to Tahus road shows the Along a exposure oligocène conglomerate Cactaceous which much unconformably on limestone, we will see on a grander scale on the 1 lth day. of When the road turns north to the village of Castells it cuts the gypsum Trias ih' again and enters the Carboniferous and the Devonian griotte. Walking

one the Devonian the upstreams passes through an excellent section of and into fossiliferous Silurian, which is very with graptolites, orthoceras and brachiopods.

further we Its top shows an alternation of black shale and limestone, down are in the typical black staining shales of the Silurian. 21

4. Fig. Tertiary thrusting in Nogueras zone west of Guardia.

After Mellema.

Fig. 5. Folding and thrusting in Llavorsi syncline in Andorra, Rio Fontenado. After Dessauvagie. 22

2nd day. Morning: Rio Fontaneda

The main road northwards towards Andorra stays in the Ordovician schists

until the frontier. road km 8 of nearly A exposure near gives a good example the thick the of the Ordovician. Near the of conglomerate near top village Santa the river and follow small road the mountains. Julia one can cross a up this road there of the Silurian and further Along are good exposures Devonian,

on the road follows the southern slope of the Rio Fontaneda and enters the

Ordovician shales. On the an admirable view of two opposite slope one gets

narrow bands of black Silurian slates with between them a band of Devonian

Devonian of limestone and on top Ordovician shales. The band of is the core isoclinal towards the an syncline, plunging east.

On of the the Devonian is top Ordovician again exposed, apparently thrusted

over the Ordovician (fig. 5). Near the frontier ridge the road crosses the Devonian

and in the syncline some exposures one can sec Strongly developed cleavage planes crossing the faintly preserved bedding. view From the frontier ridge a very good westwards shows the complicated

structure of the southern flank of the Llavorsi syncline consisting of several syn-

clines with Devonian cores with anticlines with Silurian alternating cores, appa- rently sheared of from their Ordovician substratum.

2nd day. Afternoon: El Se rrat

From Santa Julia the excursion drove to the city of Andorra, passing the

Andorra granodiorite, and then in the direction of El Serrat in the Valira del

Norte. First we passed the northern limb of the Llavorsi syncline, then the Cambro- Ordovician anticline near la Massana, and the Devonian of the Tor syncline near Before Serrât Silurian Ordino. reaching EI we passed a very large outcrop of

schists. El Serrât is situated on the Cambro-Ordovician meta-scclinicnts which

form the cover of the Hospitalet gneiss anticline. The limestone of the Canaveilles

series crosses the river a few hundred metres south of El Senat. The Silurian

somewhat further south lies here in abnormal tectonic position.

Both and the El Serrat-schists show structurally petrographically a complex

which in is twofold. The first of history, principle phase folding was cleavage

folding with east-west direction. The grade of metamorphism was low; producing

phyllites or muscovite-schists. The second folding phase was of different character, both predominantly concentric and with fold axes in NW-SE direction. Between

folding periods the grade of metamorphism rose to that of the andalusite zone.

resulting in the growth of coarse unoriented crystals of biotite, andalusite. staurolite and evidence cordierite, lying in a matrix of muscovite-schists. Microscopic confirms the later of the second with the andalusite age folding regard to zone metamorphism,

In all cases staurolite, andalusite and cordierite contain rows of inclusions which

are not folded. This indicates that first the schistosity must have been produced,

then the crystals were formed, inheriting the undeformed schistosity and finally

the schists were folded in NW-SE direction, producing microfolds in the schist

matrix. In the of andalusite and cordierite folded and many cases crystals were

deformed also. The stout staurolite crystals usually are undeformed.

Upstreams from El Serrat we had ample opportunity to study these rocks.

folded andalusite found and abundant staurolite often with Beautifully was pene- tration twins.

On the the a to collect way back excursion made stop south of El Senat some 23

of tectonic samples the Silurian, which shows the same kind of metamorphism and evolution as the El-Serrat schists. In a crumpled matrix of fine grained carbona-

ceous sericite-schists. andalusite porphyroblasts are at random distributed. The

inherited plane internal schistosity of the andalusite is explained by growth after

the first cleavage folding, and before the microfolding of the schists matrix.

The excursion then drove back to Andorra and from there to Soldeu. One

made examine the Cambro-Ordovician stop was near Encamp to phyllites with

three lineations; the first is the E-W cleavage-bedding intersection, the second

parallel to the crossfolding in El Serrât and the third again with E-W direction.

The last made Canillo where fold in Devonian stop was near a cleavage limestone is exposed. It shows well developed parasitic folds of thin quartzitic layers.

The excursion reached Soldeu where the at darkness, night was spent.

3rd day. Morning: Val d’Incles

From the junction of the Andorra highway and the road in the Incles valley

the excursion climbed the EW of this up slope valley.

The first outcrop we visited, was a strongly folded quartzite, under- and overlain by mica-schists. The quartzite is distinctly linear, the lineations being the fold and the strike in this that is E-W. parallel to axes general region, Very

few indications were seen of the NW-SE crossfolding. Further to the north anda-

lusite-schists are well exposed. In these rocks two different structures can be

The oldest is andalusite-mica-schist. with discerned. one an mica-crystals elongated

in E-W direction and the fold Andalusite and cordierite with parallel to axes.

their longest axis in the direction of the E-W lineation. Staurolite occurs as stout

prisms, often with penetration twins. These schists are affected by the crossfolding in NW-SE direction, consisting of microfolding of the S-plane. A second generation andalusite has grown in these fold axes, resulting in mica-schists in which both

directions are equaly well visible. The intensity of the crossfolding and accom-

panying mctamoi phism is in Incles much less than in El Senat. Another difference

is that the Incles-schists were synkincniatically already andalusite-sehists. in contrast

with the synkinematic phyllites of El Serrât.

Besides the NW—SE crossfolding. another direction, NE—SW. is present

in these micaschist. This direction is well developed in the mica-schists W of

Port de Fontargente, where both directions alternate in different localities.

Rarely the two crossfoldings occur in one rock. They are both characterized by

the same microfolds of the s-plane and oriented andalusites. Together with the lineation original E—W it is a symmetrical set, suggesting that the stress field

still oriented in N— S was direction, during the crossfolding. For some unknown

reason the NW—SE direction predominates, not only in the Incles valley but but of the of the over a large part metamorphic zone Pyrenees. Continuing northward the excursion arrived in the gneisses which underlie the andalusite-schisls. The boundary between both rocktypes is sharp, although

some micaschist-slivers occur in the gneiss close to the contact. The gneisses near the contact are fine grained, but soon become more coarse grained towards

the centre. The gneisses are homogeneous biotite-muscovite augengneisses with

a distinct E—W Iineation and schistosity, both structural elements are parallel

to those of the overlying mica-schists. Signs of crossfolding do not occur in the due the of gneisses, but this is possibly to greater competency the gneiss. The there gneisses are quite homogeneous and are no cTosscutting elements. 24

3rd day, afternoon. Hospitalet-Ax les Thermes-Tarascon

After lunch the excursion drove on to the Port d'Envalira and then to

Hospitalet. Before Hospitalet we passed the Soldeu-Lanoux fault which separ- ates the Cambro-Ordovicien phyllites in the south from the gneisses of the

massif in the north. Near made to examine Hospitalet Hospitalet a stop was

the gneisses of the Hospitalet massif showing here the incipient Stages <>l

granitization. which are absent in the Indes valley but which become more

pronounced in easterly direction. Marens fault The next stop was made near Méretis to examine the zone.

The Mérens faut is a E reversed fault, which can be very long —W-running continued all the from the Pic de Montcalm the Mediterranean. The way to

The northern block is upthrown as most E—W faults do in the Pyrenees.

of this block thickness of hundreds of metres gneisses arc over a several

the sheared with lineations mylonitized; mylonites being to augengneisses steep

in the sense of the main movements. Folds do occur in the mylonites, and

are strictly parallel to the lineations. faull Between Mérens and Port Banyells a second accompanies that of

Mérens. This so-called fault of Pinel inns on a distance of 100—400 in to

the south parallel to the Mérens fault.

The metamorphic.s of the Hospitalet massif are exposed south of the Pinet

and between the faults series which fault, two a sedimentary outcrops, probably the "Canaveilles" scries. The continuation of this the represent zone to west

and that this the of the Hos- east suggests sedimentary zone belongs to cover

pitalet massif, which by the movements along the Mérens fault is thrust over the gneisses of this massif.

The last made the funiculaire of between stop was near le Saquet, Melons and Ax-les-Thermes, where granitized and mobilized augen-gneisses could be

studied. The of the Aston massif in similar augen-gneiss are principle to those of the massif, but have Hospitalet they undergone a longer lasting metamorphism.

This has lead the formation of unoriented rocks the of to granitic at expense

the augen-gneisses. This granitization takes place on a small scale, resulting in

the of small in the well as occurrence irregular granite patches gneiss, as on a in the formation large scale, resulting of mappable granite bodies, as for example Ax-les-Thermes. Tins is near granitization always accompanied by more or less of the of the irregular folding schistosity gneiss and locally of strong mobilization which of disoriented Of explains occurrence gneiss relics in the granite. this could be in of in the process a good example seen one the erratic blocks Ariége river.

After this outcrop the excursion drove to Tarascón, first to Ax through the than from Aston gneisses, Ax to Sinsat through the sedimentary (over of the

Aston massif, and from there to Tarascón through the Mesozoic Tarascón basin.

4th day morning: Basal gneisses of the St. Barthélemy massif

From Tarascón we drove to Appy, the starting point of our walk on tin- southern of massif. The first 1500 slope the St Barthélémy outcrop visited at m altitude consists of folded the main gai nct-augengneisses, object of this morning's excursion. The rocks of this outcrop are strongly linear and schistose gneisses,

with s-planes dipping 20 40 X. and lineations in N S direction. The mineraló- gica! composition is quart/, potash feldspar, sodic plagioclase, biotite ami garnet. 25

with They are often banded, dark biotite-rich bands alternating more leuco- and calc-silicate rocks cratic bands. Intercalation with amphibolites are quite visited the folded, the fold-axes frequent. On the locality gneisses are being

parallel to the lineations. Further it became clear that there must have been

eastward of the limbs with the often an movement upper regard to lower,

accompanied by shearplanes or small thrusts. The axial planes of the folds and

to the shearplanes are parallel the general dip of the schistosity in the area,

Microscopic examination reveals that these gneisses show a strong post-crystalline

deformation.

scries of various and The garnet-gneisses are part of a considerable gneisses succession from the lowest the migmatites. The whole exposed part to tion-

metamorphic cover reads as follows:

top ) i • i • • phvlhtes /-, /~v i 1 .' , . metamorphic Cambro-Ordox uien mica-schists \ migmatites (sillimanite-gneiss and quartz-diorite) granitic biotite-muscovite-gneiss

linear garnet augen-gneiss

schistose garnet-gneiss granite and gneissose granite bottom

Our first explanation of the formation of this complicated gneiss succession

was the supposition that the three lower members, clearly belonging together, older eroded and covered the Cambro-Ordovician represent an basement, by which their the sediments, on turn were migmatized during hercynian orogeny

(Zwart, 1954). The main reasons for this supposition were the differences in

— muscovite in the basal in the mineraligocal composition, no series, no garnet

migmatites — the difference in structure, linear augengneisses in the basal

gneisses, schistose gneisses above. Further it seems difficult to explain why the

lineations in the basal gneisses run N—S, in contrast with the general E—W

strike of the Paleozoic, of the Pyrenees. Nevertheless we abandoned this point view consider whole series is conform- of and now it possible that the gneiss a

This is based the fact that the transition able sequence. mainly on garnet augen- is but both gneiss to overlying migmatites not sharp, as formerly stated, gradual

in and micro-structural Moreover similar mineralógica] sense. garnet-gneisses

occur also in the Castillon and Agly massif, and in the latter area in a

different stratigraphie position, immediately below the mica-schists. For a more

detailed description see Zwart, 1959.

On to the examined. the way back Appy an outcrop of schistose gneisses was different of In this of the which shows a style folding. outcrop garnet-gneiss is folded in rather often disharmonious and with schistosity a irregular way, fold-axes not parallel to the N—S lineations. Moreover small granitic patches

are visible in this gneiss, clearly indicating recrystallization after the phase which

made the In all this is similar the mobilized augengneisses. respects folding to

augengneiss of the Ariége valley which were visited the day before.

Immediately above Appy a zone of metamorphosed marbles and calc- silicates is exposed, with minerals as calcic plagioclase, diopside, hypersthene. phlogopite, forsterite. spinel, grossularite, scapolite and large titanite crystals. These marbles which the southern of the run as a discontinuous zone in part

St. Barthélémy massif, are most likely a stratigraphie horizon. 26

4th day afternoon: Talc quarry of Trimouns

At o'clock arrived of one we at Bestiac, where a bus the Talc Company

of Luzenac the An was already waiting, to bring us to quarry. excellent lunch

was offered the after which visit the by Company, a to quarry was made. The strongly tectonized talc, underlying Ordovician dolomite, is worked and

sorted by hand. Several in colour from white to and grades ranging gray green, A few were seen. pegmatite dykes of rounded shape, bordered by a layer of

± cm thickness of clinochlore were one the 10 pure examined. At place in

steatite is which is not sheared. this steatite quarry exposed, so strongly In a due of observed, in typical layering to presence graphite was resembling every

respect a similar stratification in the overlying dolomite. Together with the

frequently observed transitions between dolomite and talc-schist, this leads to the

conclusion that the talc is a metasomatic dolomite. Its formation is contempo-

raneous with the migmatization of the metasediments which lie stratigraphie ¡all) below the talc. The occurrence of pegmatites in the talc with reaction borders

of clinochlore and the absence of pegmatites higher in the series, clearly links the formation of the talc with the migmatization. Except introduction of silica,

aluminium was introduced, resulting in the formation of clinochlore which is

in the talc-schists in smaller It is always present or larger percentages. probable the that dolomite is a metasomatic limestone, the magnesium also originating from the underlying migmatites. The grade of metamorphism of the talc schists

is medium, since biotite-schist occur immediately under and even in the talc schists.

It seems probably that the enormous talc accumulation of Trimouns is in

tectonic. For details Zwart 1954 and de Sitter & Zwart 1959. part more see

5th day: Aston Valley

Tarascón the excursion drove to Cabannes and from there From Les up

the Aston valley to the dam near Riète. The general situation of the Aston

massif was explained. From north to south the following succession occurs in

the Aston valley.

Devonian: limestones and slates

Silurian: black slates

Cambro-Ordovician : phyllites

I andalusite| -mica-schists

granitized augengneisses

granitized flasergneisses migmatites

Mérens fault

This succession also and the represents a stratigraphie sequence migmatites are without doubt the deepest exposed rocks of the Aston massif. Besides a

vertical relation between and the the augen- flasergneiss. augengneisses overlying there in flasergneisses, is a lateral change from flasergneiss to augengneiss an eastward direction with the result that finally the augengneisses overlie im-

mediately the migmatites. Towards the west the flasergneisses become very thick. To the of massif in my opinion augengneisses the Aston are principle comparable to the augengneisses of the Hospitalet massif and are synkinematically meta- morphosed rocks. The transition to flasergneiss is always gradual and takes plait-

the of and of in schistose by disappearance feldspar eyes lineations, resulting a 27

For that the of the gneiss. this reason. I suppose feldspatization flasergneiss occurred somewhat later than in the augengneisses, towards the end of the main of deformation. Both, and flasei have phase augen- gneisses subsequently locally been granitized, which process was accompanied by mobilization and rheomorphism.

After this introduction we had the pleasure to hear a very interesting ex- Prof. based his of posure of the views of Raguin, on own mapping experience this region:

levé Mi dans le massif, "Bien que le géologique détaillé, que Raguin poursuit collaboration Mr Destombes, soit certains rsultats en avec ne pas achevé, généraux être Les nombreuses failles subverticales dont il vient d'être ont pu dégagés. question et qui datent, pour la plupart, des dernières phases tectoniques rigides, probablement tertiaires, sont une caractéristique importante de la structure régio-

nale. Les photos aériennes confirment leur importance dans tout le massif de la suivent kilomètres. Contre les couches l' Aston; plupart se sur plusieurs elles, de gneiss sont souvent redressées, et laminées verticalement sur plusieurs dizaines de mètres d'épaisseur. Si l'on fait abstraction de cette tectonique rigide, on con- state le des assises de est faible, inférieur à que pendage gneiss généralement

45° et très souvent subhorizontal (sauf aux bordures nord et sud du massif). Cette Ainsi le massif apparaît dans son ensemble comme un vaste dôme très plat. circonstance rend possible l'établissement d'une stratigraphie dans les formations Certains résultats d'étude, destinés à gneissiques. en cours et une publication

à la Société de prochaine Géologique France, permettront quelques précisions sur de terrains. Il de la "Serie de Canaveilles" l'âge cer est déjà permis penser que des Pyrénées-Orientales (P. Cavet. G. Guitard 1958). attribuée au Cambrien pro- des cristallisé à l'état bable, constitue une partie importante formations qui ont de flasergneiss et de gneiss oeillé." of the The excursion then walked along the track in the western branch Aston valley. Near the dam the augengneisses, locally with granitic patches could be studied. Some folding of the s-planes. representing the incipient mobilization beautiful was seen here. Further mylonites. due to later faulting are excellently

the of in N— S exposed along path. A great number such faults, mainly or

E—W direction occurs in the Aston massif, but the displacement along the faults

is minor. Further the near the small where the track usually up valley pass, goes down, mobilized and granitized flasergneisses are exposed. Here a discussion on

the merits of the explanation as given by Dr Zwart took place.

Mr Guitard defended his opinion, derived from his extensive experience in that the and tin- eastern Pyrenees, augen- flasergneisses represent a particular

stratigraphie horizon (Guitard, 1958). Prof. de Sitter argued that apparenlty the succession of vertical cleavage

and in the sub-horizontal and folded schistosity phyllites on top, overlying

schistosity in the micaschists. which in their turn overlie strongly linear augen-

gneisses. represents also a tectonical succession more or less independent of the

original nature of the rocks.

The excursion then went back to the cars. Here a discussion was carried

on. about the nature of the quartz-pebble gneisses, which according to Raguin.

of the of Marc in the low 1955, are the equivalent quartz-conglomerates grade Cambro-Ordovician. Zwart explained his views, dividing his discussion in two

him these rocks ancient parts, firstly why according to peculiar are no conglo-

merates and secondly how these rocks could be formed in a different way. One of the main objections to Raguin's views refer to his sections, in which in Cambio- ilu Cambro-Ordovician conglomerates near Marc (Allaart, 1954) the 28

connected with the with Ordovician arc Peyregrand gneiss quartz-sillimanite

nodules. In evey section the replacement of the conglomerates by gneiss necessarily

occurs in the air, whereas nowhere this transition can be studied on the ground. The Further- contact between gneisses and micaschists or migmatites is sharp. the of small more conglomerates of Marc are a closely packed aggregate (± 1 cm) whilst the shows distributed nodules, quartz pebbles, gneiss only sparsely quartz

which moreover are distinctly larger than the pebbles of the conglomerates of

Marc. The with mineral quartz-nodules are always intergrown fibrolite, a nol

in the Moreover the nodule rocks show present conglomerates. quartz a granitic texture which is much less oriented than the host rock, the Peyregrand gneiss.

This suggests a relatively late formation contrasted with ancient conglomerates. observed lies On several places we that the quartz pebble gneiss, which usually in direction of off. as layers the Peyregrand gneiss, is in the the strike cut or normal without tectonic involved, replaced by gneiss, any contact being finally vein of off ol an oblique crosscutting quartz-nodule gneiss, branching a Layer

this gneiss, has been found. All these observations arc not in favour of Raguin's

hypothesis.

As far of these nodules is I remark as the origin quartz concerned, can that of the be from the formation of fibro- the origin quartz cannot separated

lite. with which it is without exception intergrown. At many places in the

flasergneiss more or less crosscutting. irregular movement zones occur, which

have of To these be considered a lining quartz-fibrolite. my opinion /ones must

as a sort of stylolite, where part of the material has been dissolved, in this in formation case the alkalis, leaving silica and aluminium behind, resulting the of fibrolite. that quartz and There can be no doubt, these movement /ones are later than the flasergneiss, and consequently the quartz-sillimanite linings also

be later. The these is due must quartz on linings striped, undoubtedly to move- The relation with the nodule rocks is in both ment. quartz that the sann minerals and fibrolite and that More- occur, quartz they usually occur together. that over transitions between both rocks have been found and it is suggested

rccrystallization of the quartz-fibrolite zones brings about the concentration ot

quartz and fibrolite in nodules.

Raguin defended his point <>l view as follows: Les de formenl niveau bien délini. gneiss Peyregrand un stratigraphique au

sommet des gneiss de l'Aston, particulièrement dans la partie occidentale du

massif. Vers leur base on rencontre en général un faciès plus fin et plus leuco-

crate. contenant des lits régulieis à petits ovoïdes de quartz bien distincts de

la mésostase. Ceux-ci la forme de s soit étirés linéation ont pet i t galets, avec une prononcée dans certains bancs, soit systématiquement applatis dans d'autres bancs.

De telles particularités sont usuelles dans les galets de poudingues métamorphisés,

La fidélité de formation Mr stratigraphique cette est pour Raguin un argument

essentiel faveur de Il le dont on en son origine détritique. regrette que temps

ne membres de l'excursion de voir de dispose permette pas aux quelques coupes la base des gneiss de Peyregrand.

De Sitter remarks:

that the nodular with its nodules docs although gneiss relatively very sparse

look to still as to the not very similar a conglomerate bed, Zwarts arguments different of the nodules in the and the aspects quartz gneiss Marc conglomerate Ordovician are not very convincing. These conglomérats vary laterally enormously, from houlderheds. sometimes they range microconglomerates to they are close

and sometimes consist of in sand-shale alter- packed scarce pebbles a stratified 29

from 100 thickness within few nation, they are apt to wedge out a m to zero a

hundred meters.

After lunch the excursion made down the to one stop, halfway valley, examine the granitized augengneisses. Hen- beautiful pegmatites in dykes and

irregular patches are exposed.

Furthermore all transitions between finegrained muscovite granite and coarse both rocks related. pegmatite are exposed, indicating that are closely

6th day, 1st party. Trois Seigneurs massif — St Béat

liait' of the excursion visited Etang d'Artax in the Trois Seigneurs massif. drove Gourbit and from there followed the the lake. By car we to footpath to

Several of with inclusions of outcrops quartzdiorite marbles, calc-silicates, and visited. The is less quartzites amphibolites were quartz-diorite a more or

which formed homogenous sillimanite-cordierite-muscovite-biotite rock, was by

feldspathization of mica-schists. Usually this transformation goes first to a mag-

matitic sillimanite-gneiss which by continuing recrystallization changes into an

unoriented quartz-dioritic rock. Many relics of sillimanite-gneisses were observed This of in the quartzdiorites. process feldspathization was accompanied by strong

rheomorphism. which has lead to complete disorientation of inclusions, which

in this These relics of old are very numerous area. are sedimentary bands, which resisted the of and to process granitization now occur as marbles, quartzites

and calc-silicates. It was observed that the biggest inclusions often have an of the lineations E—W strike, parallel to the general trend Pyrenees, but the

are often very steep, suggesting that rotation has taken place. One of the characteristic features of these quartzdiorites is that although

is deal of the whole has remained in there a great movement, body as a place

and did not rise as a migmatite dome.

Near d'Artax These rocks the étang chlorite-albite rocks were seen. are

result of sodium introduction under strong epizonal circumstances, producing

rocks consisting almost entirely of chlorite and albite. The megascopic appear-

of the with and is ance rocks, quartz-diorites pegmatites inclusions, preserved

during this process, but the microscopic structures have changed completely. Girons In the afternoon we drove over Massât; St. to Portet, where a is made collect ophite body of cretaceous age exposed. A stop was to some The last of the made lherzolite of samples. stop day was at the Moncaup.

2nd party. Estours and Salat valley - St. Béat

The road from Tarascón to Massât takes us to the Col de Port up passing through Mesozoic rocks of the Tarascón basin, and beyond Saurat into the

rocks the Arize From the Col de Port has metamorphic of massif. one a niagni-

ficienl view the blocks of Mesozoic limestones of the Tarascón basin on great and its continuation in the North-Pyrenean faultzone between the Barthélémy- demonstrated massif and the axial zone. It is in this basin that Casteras (1933) the unconformity between »the Genomanian and the Lower-Cretaceous. Towards

is the the west tlie silhouet ol the Monvalier conspicuous on skyline. Descending

the road the branch of the north- the valley tow aids Massât stays roughly on Pyrenean fault between the Arize and Trois Seigneurs massifs. Beyond Massât

the road enters into the intrusive granite of Lacourt belonging to the Arize massif.

Arriving in the Salat valley we turn upstream to the south, cross first the Ous1 basin and then the Lower Cretaceous band lying between the Trois Seigneurs 30

massif and the axial zone. The Urgonian limestone and the Albian schists both have acquired a metamorphic habit during the Cretaceous. pre-Cenomanian This is characterized folding. metamorphic phase by scapolitization and mar-

morization of the limestones and is accompanied by intrusions of basic rocks

varying from gabbro to peridotite composition (Zwart 1954, Ravier 1959). which

are restricted to the north-Pyrenean faultzone. The basic intrusives have all the characteristics of initial an magmatic phase of géosynclinal facies, but as their

to intrusion is distinctly posterior the Lower Cretaceous it can not be related to the basin forming of this external zone, but certainly is related to the faulting; it is of fundamental faultzone typical a (de Sitter, 1956).

Turning to the right at the village of Couflens de Betmajou we ascend

the of Estours where road show valley (Wissink, 1956). outcrops us again the Devonian/Carboniferous boundary with abundant cherts with occasional

nodules followed shales of the Carboniferous. In the phosphate by one outcrop show latter a remarkable wavy surface, which suggests large ripple marks, but is most probably of tectonic origin because its shape is exactly repeated in successive layers.

The visit the to large white-green patched griotte quarry of Estours is very interesting. The original layering of the rock is preserved by the alternation of

green, greenish and white bands. The cleavage is admirably expressed by the orientation of the broken fragments of the white pure-limestone layers. The stretching of the rock is demonstrated by the roughly ESE long rods of these limestone white fragments, and the folding can be inferred from the bedding, which shows flat but many gentle folds in a NE direction in the quarry turns the The and of this steep at entrance. cleavage rodding is independent folding, because the rodding-lineation and the cleavage planes are not parallel to the

fold and themselves unfolded. here in the axes are Apparently we are presence of a Similar features been encountered else- pre-cleavage folding stage. have

where also, for instance in the southernmost griotte outcrop of the Ribagorzana

river, and in the Carboniferous south of Col de Mente.

Returning to Couflens de Betmajou, and then driving upstream along the Salat river first Carboniferous then the one passes through a synrline, through Upper Devonian and Lower Devonian, finally entering the Silurian of the

Couflens anticline. This anticline is also fault/one characterized a by large

ophite bodies further east. These ophite intrusions are here as well as elsewhere of Cretaceous here surrounded Paleozoic rocks. age, although completely by This is small block of limestone in the fault- proven by a Urgonian preserved

zone a little east and some 500 m above the Salat river valley. The faultzone

branches off the main North-Pyrenean branch near the village of Aulus. and then the road of The party returned and drove to St. Girons along the Garonne The road often branches the river Bouigane to valley. runs along

of the North-Pyrenean fault and gives the opportunity to see some of the diorite-

of the intrusive in the Garonne peridptite sequence accompanying rocks. Arriving the drove St. Béat for the This lies in valley party to night. village a narrow

limestone, brecciated and gorge, cutting through Urgonian marmorized, belonging

to the North-Pyrenean faultzone.

7th day. Col de Mente and along the Garonne river to Viella

small road leads from St. Beat to the Col de Mente. The first A up the this shows the brecciated character of the outcrop along road near village 31

marmorized Urgonian limestone, the second, a little further one, an ophite in- trusion character. of very basic The Col de Menté itself is heavily wooded and shows only numerous ophite blocks.

southwards in the woods with occasional Going up one stays blocks of red Triassic rocks. On of the Tue the red rocks top d'ltang one sees overlying the Carboniferous slates. From the of this mountain has unconformably top one beautiful view a westwards on the North-Pyrenean faultzone and northwestwards on the section of Pic du Gars with Mesozoic overlying Devonian-Silurian-meta- morphic rocks of the Barousse satellite massif.

the towards the the Carboniferous Walking along ridge west we enter shales,

which contain here few remarkable sandstone These latter a very layers. partly of consist a typical arkose with white feldspar crystals in a finer matrix and

with scarce well rounded In other the rock shows pebbles. outcrops strong synsedimentary disturbances with light coloured arkose and pebble units in black

shale, typical gliding structures. One could call the rock a slide-conglomerate

or slide-arkose.

Another pecularity of these arkose beds is that the strike is almost N—S and therefore demonstrate also a pre-main folding fold structure.

Our walk takes us, further down, several times across the Carboniferous-

Devonian boundary with Devonian griottes, green Upper-Devonian slates and black Carboniferous slates and cherts. Near Argut we enter into the black

Sil iiiian slates.

the In afternoon we drove the Garonne river upstreams. passings the frontier

.11 the Puente del Rey, where the valley narrows.

A few kilometers Lez beside the road of beyond a very good outcrop just

alternating sandstone and slate bands in the Cambro-Ordovician, show an interest-

ing type of folding. The principal small folds appear to belong to the first

E—W Parallel their axial vein which shows its folding. to plane runs a quartz

own peculiar folding, oblique to the first folds. In some of the slates a faint

trace of fracture cleavage is visible, running roughly parallel to the axial plane

of the folds of the quartz vein. the of and have look the We pass village Bosost, a at pegmatite exposure kilometer of this the one upstreams village opposite hydroelectric plant.

Here as in all other regional metamorphic areas of the Pyrenees the zonal

sequence of the metamorphism is: chlorite zone, biotite zone, andalusite zone.

Somewhere in the andalusite zone starts a pegmatite and granite bearing zone

and no pegmatite ever comes higher in the succession, neither here, nor in the

Aston dome or in any of the other metamorphic areas. The outcrop in question with of consists of fine-grained muscovite-granite irregular patches coarse grained pegmatite, consisting of big (10—20 cm) microcline crystals, often graphically

with surrounded rim of biotite intergrown quartz, by a radially intergrown coarse

and plagioclase crystals. In the microcline occurs plumose mica, an intergrowth

of and which the microcline. Besides these quartz muscovite, replaced minerals,

garnet, tourmaline and beryl are present.

Further the road the river and road after this on, crosses a outcrop just

bridge shows horizontal schistosity in micaschists. The micaschists are distinctly- micas. folded linear due to the occurrence of elongated The s-planes are along mineral lineation. This is later than axes which make an angle with the folding which and lineations the first phase during the schistosity were produced. Somewhat further limestone on. highly metamorphir Upper-Ordovician crops

out along the road. 32

reach the Bordas Before we bridge leading to Las liiere is an outcrop <>l - folds in somewhat marrnorized Devonian limestone with an E W trend.

The drove Viella for dinner and the party on to nighl

8th day. Morning. Jueu valley.

The river from Las Bordas above the Jueu upstreams to a little large

of the Guëlls de = of first the source Jueu ( eye Jupiter) cuts through com- isoclinal folds of the plicated Devonian, then it crosses the central antic line which

mns from the Lys-Caillouas region in the west to the Marimafia dome and

beyond that to the Aston dome in the East, and finally arrives in the Carbonifer-

ous of the core of the Jueu syncline.

from Viclla and Driving up passing the village of Las Bordas die first shows the sandstone the good outcrop us graded of Las Bordas sandstone group. The Devonian of the Valle de Aran consists from bottom top to of:

I 'iclla slates and arkostic slates, green green sandstone

Las Bordas sandstone, graded and increasing in thickness and slate content

from west to east

Escaleta slates and limestone

Basal limestone

Silurian blacks slates.

As none of these fossils know relative groups yielded any we only their position in the Devonian (Fig. 6).

Some of these sandstones of Las Bordas well quartizitic are very graded and a careful survey of the ridge above the road outcrops revealed six well

exposed hinges, partly synclines, partly anticlines. The total thickness can there- be fore not measured but is not thought to be here much more than 50 m. Some of the sandstones have developed beautiful mullions parallel to the fold axis, plunging eastwards.

the Ermita de de Lin, the central Driving up we cross, beyond l'Aitiga anticline with Cambro-Ordovician slates in the core and Silurian black slates

starts in both flanks. Where the road its hairpins, we find the first outcrops of the Devonian basal limestone of the south flank of the Jueu syncline and the the of the Guëlls de and tin- descending path leading to big source Jueu

construction works of its between these capturing water, we cross a faultzone

limestones and the black Carboniferous slates and sandstones. As the Carbonifer-

ous of the Plan d'Etang, containing plant remains ( Lepidodendron. Sigillaria),

lies the basal limestone of the Devonian that the always directly on we suppose levels of before higher the Devonian have been eroded its deposition, but ever)

time do find between the formations it has he a we a contact two proven to We in- fault contact. hope that the Upper Esera will give us more definite formation.

The Guëlls originate in a morainie cover on the slope consisting exclusively Carboniferous rocks Devonian of Mocks of apparently overlying an outcrop of

limestone. The sink holes which collect the water are situated in the same

Devonian limestone cropping oui ahum the border of the Maladeta massif in

Esera and has to beneath much formed the Upper region pass a higher ridge by Carboniferous rocks belonging to the syncline in order to reach the source area (Fig. 7). the Driving up the road beyond the Guëlls to the glacial basin of Upper 33

Fig. 6. Devonian of Valle de Arán. After Kleinsmiede, 1960. 34

sources.

and

holes

sink

with 1960. river

Jueu

the Kleinsmiede,

of basin After Hydrogeological

7.

Fig. 35

river Jueu one can admire the concentric folds of Carboniferous syncline, the

steep southern flank of the secondary Devonian anticline of the Artiga basin and study the Carboniferous rocks in the blocks that lie around here. Manx of those consist of the which is of quartzite conglomerate typical the lower part of the Carboniferous and similar to that which on the first very we saw day

on the southern border in the Nogueras zone.

8th day, afternoon: Barrados valley pegmatito

Las Bordas the excursion From drove up the Barrados valley, first passing

the folded Devonian and a thick Silurian section, and then the Bosost fault.

North of this fault the metamorphic Cambro-Ordovician is exposed, consisting of andalusite-mica-schists with small pegmatites and granite bodies. The main

of this afternoon's excursion conformable folded object was a pegmatite, together with the enclosing mica-schists (fig. 8) (Zwart, 1958). The pegmatite consists

Fig. 8. Folded pegmatite in micaschists, Barrados valley. After Zwart, 1960.

of than several parallel veins and sills, ranging in thickness between more one

metre to less than one cm. The thickness of the individual pegmatites remains

the The mica-schists between the also constant throughout outcrop. pegmatites in thickness and in thin of less than vary one pegmatite occurs a screen l/i cm

thickness. The is and contains further sodic pegmatite cordierite hearing, quart/,

plagioclase, muscovite and tourmaline. The mica-schist consists of quartz, sodic

plagioclase, muscovite, biotite. cordierite and andalusite. Near the contact with the pegmatite there is an enrichment of tourmaline in the schists. In the schist of the fold same occurs a strongly boudinaged calc-silicate rock, apparently horizon. representing a sedimentary

folds of the of of schists The pegmatite are clearly concentric type: part the show the of but in the the same type folds, strongly bent hinges schists are and show axial fracture there crumpled an plane cleavage, moreover is a flattening

of the schists in the flanks and a thickening in the hinges.

The pegmatites have an unoriented texture, although muscovite crystals

perpendicular to the walls are quite common. In the hinges the minerals like

plagioclase and muscovite are often folded or broken, indicating postcrystalline 36

deformation. Very typical are, however, the fan-shaped muscovite crystals, sug-

that and formation of the muscovite were gesting folding contemporaneous. The described features the can be explained with following development:

1 ) shear folding, formation of mica-schist with plane, undeformed schistosity,

boudinage of the calc-silicate rock, no pegmatite

2) beginning of the formation of the pegmatite, either by intrusion or by

replacement 3) folding of the schistosity, accompanied by furthei crystallization of the pegmatite.

The Barrados pegmatite is one of the clearest examples of contemporaneity of a second folding phase (folding of a pre-existing schistosity) and emplacement of granites and pegmatites, which belong to the regional metamorphism.

9th day. Moncasau-Aguamoix

the Arties The car took us from Viella to Arties and then upstreams valley

to Moncasau, the last stretch with the funicular. The horizontal path along the alt. section of the of the Maladeta slope at 1965 m gives us a good granite its thermal aureole. There is and the hornfelses of one particular interesting

of of colour the chloritization of its outcrop mylonitised granite a greenish by mica and This crossed inside the mountain felspar. narrow zone was by one of the watertunnels bringing the water of the Colomés basin to the hydro- This electric plant of Arties and caused grave difficulties in the construction. E- -W faultzone has been found also at the opposite side of the valley and

east. at of movement is further There is a good evidence that least some its whole axial besides Tertiary because the only outcrop of Triassic in the zone this fault. is that on its border zones, is situated quite near Its preservation the fault be older. The certainly due to this young movement, but original may

path, we follow, brings us to the Pruedo platform belonging to the 2000 m

covered with thick morainic and aplanation surface, a blanket, turning east we

find this Triassic outcropping over a small distance. It consists of the usual reddish micaceous shale and sandstone.

best The platform itself is part of the 2000 m aplanation surfait', the pre-

served surface of the Pyrenees, the same level as the Aston platform we saw fourth massif southwards. on the day looking from the St. Barthélémy towards the few north oi Descending Aguamoix valley a hundreds meurs

the Triassic the 40—50 thick morainic the outcrop we find below m blanket, of remarkable section of Miocene top sediments a an Upper deposit preserved in a filled E—W between the and Arties up running canyon Aguamoix valleys. hori- The top sediments consist of hard clays and thin lignites, perfectly zontal. The lignites contain pollen which allowed to fix their age as probable Upper Miocene. (Jelgersma, 1957). Downwards the section becomes sandier and of stratified with coarser and the bottom half consists mostly a conglomerate from the but otherwise from all kinds rounded pebbles, many derived Triassic, of the Paleozoic rocks. The bottom of the lies at ± 1800 surrounding canyon alt. 200 above the floor of the river on granite some m valley Aguamoix (fig. 9).

this Miocene has been because the Apparently deposit preserved present N — S valley left it intact. Apparently this E—W valley lias hem eroded jus1 after the morphogenetic uplift of the 2000 m surface and ilius dales this move- 37

Fig. 9. Upper Miocene deposit of Aguamoix. After de Sitter. 38

ment as Upper-Miocene. There is one higher and older surface between 2400-

2600 m alt., much less well preserved. In the afternoon the excursion visited the valley of Gessa and studied there the beautiful exposed isoclinal folds of the Devonian limestones and slates imbricated accompanied by small thrusts giving the whole structure an nature

(fig. 10). The black slates below the deepest exposed limestone failed again to

Fig. 10. Narrow fold in Devonian of the Gessa valley, Valle de Arán

After de Sitter.

fossils. look almost like Silurian slates hut have never give us any They given

any fossil evidence, and might well be Devonian.

10th day. Morning: Marimaña granodiorite (by Prof. Brindley)

We drove car to the Pia de Béret which forms the watershed of by up of here one the branches of the Garona river and the l'allaresa. From a general 39

view of the granodiorite body, located at the north-western termination of the

main Lower Palaeozoic massif of the Pyrenean axial zone, is obtained. Along its the steep northern contact upright, tightly packed, isoclines in Ordovician

ümestones can be pointed out. In the region between the Rio Malo and Rio

Ruda these incline gently off the plunge of the Lower Palaeozoic massif, and

further to the south-west from the south-western flank interfering structures steep of the latter feature are developed.

A traverse on foot across the Ordovician contact rocks showed spotted slates, andalusite hornfelses, and metamorphic limestones of the aureole. From the high the of the Rio Malo view of spur overlooking gorge a striking the gently in-

clined, discordant, western termination of the granodiorite was obtained. Here

the lower members of the ordovician succession - - and psammitic-pelitic groups

the "Sandwich" limestone — truncated the which are by plutonic boundary, at the site visited lies against the main Ordovician limestone. They persist, however, in of a zone rafts, virtually undisturbed, within the normal granite. Granitic

dykes extend into the country rocks at the main contact, and were observed at

one point to end abruptly against the massive limestone after traversing the

bedded hornfelses - a of the behaviour consequence, apparently, more plastic of the limestone in contrast to the rocks beneath. It seems as if the plutonic

body arose, at this point, essentially by dilation and disarticulation of its sur- rounding. descent from the During the by car Pia de Béret we had a good view of

the Salardu — small stock a granodiorite body, bluntly lenticular in outline, which, vertical walls without indication of the displays presence of a roof. It

shows clear evidence of a displacement, laterally, of the isoclinally folded Devonian

rocks examined on the previous day at Gessa. The eastern portion of this body

is concealed surface of the Iñola but the elaborate by deposits valley, on west an

fingering contact shows local development of a hornblende-bearing facies against

limestone groups in the surroundings.

Near the Bonaigua Pass the Tredos granite was viewed from the opposite-

side of the Rudi It is truncated the 2000 Valley. a steep-walled body, by in

aplanation surface and is a more or less circular in plan, smoothly enveloped by

the Ordovician and Devonian limestones.

10th day. Afternoon, drive from Salardu to Sort

the Puerto de the road in the Driving up to Bonaigua stays mostly Upper Ordovician marbles. the blocks of the Ordovician Just beyond pass large Upper lie around. The consist of conglomerate pebbles exclusively quartzite or quartz and the matrix has often a finely stratified sandy constitution, and has been folded. strongly Some of the flatter pebbles are conform to these folds, but most of them show little A bit further down road shows flattening. a good outcrop

the quartzite grits of the Upper Ordovician. The road follows the the south Bonaigua stream, to we sec the Maladeta

massif and the north the Marimaña is hidden from granite to granite our view In Cambro-Ordovician rocks. The road reaches the Pallaresa valley in the

village of Esterri de Aneu and follows this river downstreams. We make one other of Ordovician slates in stop to study a secondary knicking an outcrop

on the east side <>l the valley near the village of Bogari. The knicking planes

dipping southwards are very numerous and only a few centimeters apart. A

few of a of knickzones be observed. very conjugate set can 40

downstream the north of the Driving one enters Hank Llavorsi syncline where the Espot river joins the Pallaresa. The black Silurian slates contain

graptolites here. They are followed by Devonian limestone, strongly cleaved and

further down by Carboniferous slates. On the opposite side of the valley, the

eastern slope, some recumbent folds can be detected in the Devonian when the

is which it light favourable, was not when the excursion passed. These folds

emphasize again the fact that everywhere in the Central Pyrenees the structure

is much than time more complicated a simple mapping can reveal, every an exceptional is available features show good outcrop new secondary up.

The southern flank of the Llavorsi syncline is not so well exposed and the

road downstream soon enters the Cambro-Ordovician of the southern anticline.

11th day. Morning from Sort to Lladore

the Tabescan in the Driving up valley we started the north and studied the road from outcrops along north to south, each of them showing a particular of tectonization. type cross cutting

visited concerned with rock The first Cambro-Ordovician outcrop we was a of alternation of shale and of millimeter centimeter type a quick sandlayers or

thickness, a "schist rubané". which allows a close analysis of the tectonization.

Fig. 11. Knicking in Ordovician slates near Llavorsi. After Zandvliet, 1960.

The outcrops show roughly vertical, steep, but not iosclinal folds of 10—20 cm width accompanied either by close cleavage in the slates or by a coarse fracture cleavage, both strictly parallel to the fold axial plane. A closer scrutiny reveals, thai however, a much more intense isoclinal folding existed before, because we thai centimeter wide folds with can sei the sandlayers show minor pronounced 41

thickening in the hinges and flattening in the flanks. It is quite clear th.it the

vertical folds have folded with its minor Layer a pre-existing schistosity plane own isoclinal folding.

The second in the of the Cambro-Ordovician showed outcrop, upper part

very good exposed knicking planes. The schistosity plane dips northwards, the knicking zones southwards. The knicking, always between a pair of planes en-

Alter Fig. 12. Kn icking in Ordovician slates near Llavorsi. Zandvliet, 1960.

knick 1—20 wide shows subsidence of the southern closing a zone cm invariably a block and dilatation in the horizontal 11 & The represents a sense (figs. 12). knickzones the mountain flank. go straight up

Walking down along the river one passes through the Upper Ordovician

with i\vo conglomerate zones with a limestone in between and a few coarse gritt)

sandstone beds. We are here in the north flank of the Llavorsi syncline and

further south the Silurian slate belt which is not going we soon pass through in because .1 the valley its outcrop is occupied by a lauge landslide con-

sisting almost exclusively of debris of the black Silurian slates. The top of the consists of limestone its first beautiful Devonian and exposure shows a boudinaged

massive limestone bed between a slate-limestone alternation, which curves round

the boudins in curious also of second- a way (fig. 13) most probably witnessing a ary folding phase.

core the The Carboniferous slates of the of syncline do not show here any disturbance of particular their regular cleavage, but higher up towards the village of Tirvia knicking has folded both the Devonian and the Carboniferous.

Driving down from Llavorsi to Son through the Cambro-Ordovician of the southern anticline notice the the which one can gradual flattening of cleavage, 60' north but their southern have 20 first dips some near boundary only a 10 northern dip. Just before the southern boundary of the Cambro-Ordovician the 42

road crosses the Pallaresa river from its eastern to its western bank and the

south of the shows a Iso- outcrop just bridge very complicated folding picture. horizontal clinal folds of sandbanks of 20 cm thickness have a axial fold plane isolated sandstone but perpendicular fold axes. Occasionally one sees elliptical

bodies in the shale or recumbent folds of sandstone with variable fold axes.

folded Prof. Gill, This outcrop might represent a slumpbed as was suggested by

and not a refolded schistosity.

Fig. 13. Boudinaged Devonian limestone of Llavorsi syncline north flank. After de Sitter.

Between Rialp and Sort the excursion took the road branching off to Olp.

In this village is exposed one of the best examples of the recumbent folds in

the Silurian of the south flank of the southern anticline. The rock consists of black slate in thin layers between 10 cm thick bands of orthoceras limestones

14 & These recumbent folds in this southern (figs. 15). occur everywhere steep

flank until on the top of the anticline in the Monseny region. Originally it was

thought that they represent cascade folds gliding down from the top of the fact anticline, but the that they occur also on the top of the anticline and that the the Cambro-Ordovician cleavage planes in core are roughly parallel with the axial planes of these folds, makes this conclusion doubtful.

The flat axial planes and cleavage is not a result of later Alpine defor-

mation because one can limit the action of this later deformation to a narrow

zone varying from 100 m to one or two km breadth along the Permo-Triassic of border the axial zone. In this zone the recumbent folds or the flat cleavage bent down are again to a drooping sometimes vertical position.

Afternoon. Drive from Sort to Pobla de Segur and Pont de Suert

situated in belt of The village of Sort itself is a narrow Keuper gypsiferous

on rocks with ophiolite bodies trending N—S along the river valley flanked

Cambro-Ordovician and the bank Devonian the east bank by on west by recum- bank the bent folds. Descending the valley one can see that on the eastern unconformable Pernio-Triassic lies Cambro-Ordovician post orogenic cover ou the

the Boca di whereas the it lies the Devonian folds. in Cantó, on right bank on

Evidently there was a N—S late Hercynian fault or fault-trough running rough!) sediments. in the present river valley, which has been filled up with Keuper 43

Recumbent folds Silurian-base Fig. 14 & 15. in top Devonian near Olp (Rialp) Pallaresa valley. After de Sitter. 44

Further downstream the road cuts through the red beds of the Permo-Triassic

which is folded here together with its Devonian basement in a large anticlinal

fold with south axial a dipping plane.

the of Arcalis at km 101 there of black Opposite village occurs an outcrop

Carboniferous shales with abundant plant remains belonging to another anticlinal beneath Permo-Triassic core its cover. The flora of this outcrop with Walchia

dates the rock as Permian according to Dalloni, 1930. The unconformity of the

Permo-Triassic is well and the of the conglomerate very exposed discolouring black slates the and reddish colours witnesses of the at top to green weathering before the conglomerate deposition.

The Alpine refolding of the Devonian is well exposed where the Pallaresa

river cuts through the Devonian griotte of the Coma di To, where one can see

a large fold with an almost vertically plunging axis exposed on the eastern bank. Looking back to the north from the village of Gerri del Sal situated in

a Keuper zone south of the Coma di Tó zone, one ran see the vertically standing

red beds of the Permo Triassic against complicated folds of the Devonian. The Gerri gypsum layers of contain occasional salts beds which give rise to the which in the riverbed for salt very salty springs are exploited drying pans along

production. One sees on both sides of the river chaotic structures of muschel-

kalk folds and bodies in the ophiolite Keuper gypsum.

After passing through another zone of red beds and Devonian griotte one

the in the limestone. The between this enters canyon cut out Urgonian zone

Urgonian limestone and the first Permo-TriasMi rover of axial zone in the north

has been called the Nogueras zone and represents the strongly folded, both by and Alpine Hercynian orogenesis, southern border zone, which the excursion also

visited on its first day.

In the one can the almost isoclinal folds in the canyon sec strong Urgonian

partly covered by travertine and a bit further on, the first remnants of the dis- cordant cover of Oligocène conglomerates. These post-tectonic conglomerates

have been deposited on a strongly dissected landscape of Cretaceous limestone,

and are found now as pockets at wildly different altitude levels. Somewhat further down the river the basis of the conglomerates is below the valley floor

and both sides of the river formed walls. are by steep conglomerate Approaching Pobla de Segur the basis of the conglomerates rises again above

the valley floor level and when the road has passed through this village and

turned to the west in the direction of Font de Suert one has a wonderful view

of the flat lying Oligocène conglomerates on the steeply folded Upper Creta- These old with ceous. conglomerates sometimes are deposited directly on screes

the rocks and consist the onl\ angular components of Cretaceous near contact of Cretaceous boulders and pebbles. In the valley of the Flamisell where this follow! conglomerate immediately on the Permo-Triassic. it consists only of Pcrmo- Triassic Further from association boulders and rocks. away the basis the of the

pebbles becomes more diversified.

12th day. Morning visit to Stephanian and Triassic of Malpas

the A short drive brought us from Pont de Suert to the confluence oi

Barranco de Viu and the Barranco de Peranera river. The first outcrops along the followed a thick limest Peranera river shows the Keuper gypsum by ■ member of tht- Triassic commonly (ailed Muschelkalk. Upstreams of these the and road and river cut through the red shale and sandstone of the Triassic then into the Devonian, which is soon replaced again by Stephanian tuis on 45

hank the river. We drive further and the the left of upstreams see beyond of road which bifurcation the to Malpas village again muschelkalk outcrops are again replaced by red Triassic rocks before arriving at loading station of the

Malpas coalmine. This repetition of the sequence of Triassic-Stephanian-upper Paleozoic, often in upside down position is typical of the complicated tectonics of the Further narrow Nogueras zone. upstreams we enter again in the Stephanian. The of the road the colliery exploits a coal scam Stephanian age. As stops at coalmine foot the which the excursion proceeded on following stream, a course caused considerable discomfort due to the unusual high water level of the stream.

particularly in the narrow gorge cut through andesitic lava. Beyond that the canyon widens somewhat and narrows again entering the Devonian belonging

m the border of the axial zone. The horizontal structure of the Devonian can

be seen a tew hundred meters beyond the unconformable contact with the

vertical and it looks if in this the Devonian has Stephanian. as intervening /one been considerably crushed. Going back to the Stephanian and crossing the stream

fool find the that leads the on a very rickety bridge we path upwards to village of Erill-Castell. Along this path the volcanic rocks of the Stephanian are well exposed, tuffs, mostly unstratified often containing well preserved bombs and numerous lapilli sometimes stratified witness of the volcanic character of this formation and of the close even by position of a volcanic centre. About half unconformable the Devonian way up the hill, the contact with

is well exposed. The basal layer consists of reel shale with numerous fragments of Devonian shale limestone weathered or badly rounded pebbles deposited on crevassed Devonian limestone and filling the crevasses. Elsewhere the base has

to be been observed strongly conglomeratic and further east near the village of Aguiró a coal scam between two conglomerate Livers has delivered an I'pper Westphalian flora.

On the other side of the steep valley we are climbing up, the extremely sedimentation, evidence of in this volcanic is irregular showing gliding core,

well The of Erill-Castell is the hard rock of exposed. village perched on an andesite lavastream which we passed already in the riverbed. Going south we in (he of the The rocks become pass upwards stratigraphie sequence Stephanian. less shales, fresh sandstones exclusively volcanic, containing some water cherts, and the coal seam mentioned before, in a regularly bedded series. On the flank of the opposing hill the slight unconformity of the Triassic on the Stephanian is clearly visible.

unconformities: In the last two days we saw thus three important Stephanian

on Devonian, Trias on Stephanian and Oligocène on Upper Cretaceous. The towards the Triassic alter- footpath Malpas leads us through red rocks,

shales hedded sandstones with of nating and cross occasional development cleavage

in the shales or rather unstratiiiecl mudstone. The southern dip increases south-

ward almost until arrive much to vertical, we suddenly on a Hatter slope where

the red Trias is also flat lying, but overturned as can be ascertained by the

Beneath these red heel first the Muschelkalk and below that the ci'osi bedding.

is in An drillhole for coal, ol gypsum outcropping a steep valley. exploratory

;> on the which gypsum core was found the drill site, did not take into account reversed position of the Triassic and instead of finding the supposed Stephanian coal below Trias the which the it entered into gypsum of the Kcuper. anyhow

is location at the bottom the outcropping very near this <>f steep valley. The Muschelkalk dolomite, accompanied by a cavernous originally an anhydrite-dolomite rock, typical for this facies of this formation. 46

Afternoon. Rio de Tor section

the north from Pont de the Rio By driving upstream to Suert, following first the with Muschelkalk slabs and Tor, we pass through Keuper mingled

ophite bodies in a chaotic mixture and then through the steeply south dipping

red Trias. Beyond the Trias we enter into the Lower Carboniferous slates which

have not fossil evidence for its contain yet yielded us dating, although they folded the Her- some corals. These Carboniferous rocks certainly have been by with the Visean cynian folding and we call them Lower Carboniferous in analogy of the North and in order them from the Pyrenean zone to distinguish post-

Hercynian Upper carboniferous Stephanian. Near the village of Llesp we enter

into the Upper Devonian griotte limestone, which is folded in a most complicated

east —west strike. fold with two fold axes, one almost vertical, the other with an

An outcrop in the Rio Ribagorzana in the same horizon, and better exposed,

shows that a N— S striking fold is older than the E—W striking cleavage. and that Further on, the road crosses a thick griotte limestone section, beyond view thick reddish coloured limestone bed from the we get a on a rising up river valley along its eastern slope with a dip to the north. In this band, and also in similar band the a on western slope one can distinguish many secondary flat recumbent folds. They belong to a unit of Devonian limestone alternating

with occasional below the This rock also in quartzites griotte. crops out a good

Fig. 16. Recumbent and pinced folds of basal Devonian and Silurian

sheared off from the Ordovician Montañeta, Rio de Tor.

After de Sitter.

anticline with flat north axial road exposure forming an asymmetric a dipping doubt here plane. There can be little that many fold repetitions occur probabh similar the described further in the flank of the very to ones on. exposed

Montañeta (fig. 16), but perhaps on a larger scale. Beyond the village of SET OF N-S CROSS SECTIONS

CENTRAL PYRENEES 47

the Barrilera) road (Kisses the intrusive hornblende bearing granite of Barruerp which the is accompanied by a swarm of north dipping dykes parallel to cleavage of the isoclinal folds. show well the of the river They up very on western slope coloured bands. The the Barrilero as light eastern slope, opposite granite, con- sists of Gambro-Ordovician.

the of Erillavall road another excellent Beyond village a exposure gives demonstration of the cross folding phenomena, with fold axes almost perpendicular to one another. When the road has crossed to the eastern side of the river we

of the Montaiieta in get a good view of the steep eastern slope mountain, which three isoclinal synclines of the basal Devonian limestones are visible

(fig. 16) flanked on both sides by narrow bands of Silurian which form iso- clinal anticlinal cores. Although the structural details of this section have not

been the warrant that the structure yet worked out, reported complications is very complicated with certainly two and probably three folding phases. One the has been phase is anterior to the cleavage folding and as cleavage plane folded also, there must be, locally at least, also a third post cleavage folding. The then returned Pont de had its final dinner there and party to Suert, for its home in different directions. split up next day journey REFERENCES

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