AN INTEGRA1&0FIELD. GEOCHEMICAL AND U-Pb GEOCHRONOLOOICAL STUDY OF THE SOUTHWEST HERMITAGE REXURE (NEWFOUNDLAND APPALACHIANS.CANADA) AND TIlE SIERRA DE GUADARRAMA (IBERIAN MASSIF. CENTRALSPAIN): ACOr-rrRIBunONTOTHEUNDERSTANDIN"GOF
THE GEOLOOICAL EVOLtnlON OF CIRCUM-ATlANTIC PERI-GQNDWANA
VOLUME I: Text
By:
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PABLO V ALVFRDE-VAQUERO;Lie.; M.5c.A thesis submitted to[beSchool of GmuaIe Studies in partialfulfl1mcot of[bercquiremcnCifor[bedegree
of Doctor ofPbilosopby
Departmeot of Earth Sciences Memorial University of Newfoundland
September 1997
St.John's Newfoundland
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ABSTRACT:
Anintegrated field and analytical study ofthreeareas in NewfouDdland and Spain was carriedoutto investigate the extent of the linkage between the geologica! evolution of the Peri-Gondwanan margin of thelaperusOcean. n:corded in the southwest Hermitage Aexure of the Newfoundland Appalachians.andtI\atoftheSierra deGuadarramain the Central IberianZoneof the rberian Massif (EuropeanVariscanBelt). This srudy. while resolvingthetimingand character of the respective Appalachian and Variscan overprints.
tUghligbtsthemajor importance of the Early Ordovician (ca.480470Ma) magmatic
TheCioq-Cerf gneiss ispanof the westelllIl10St extent of theLatePm=ambrian basement block of the HermitageAex~.New data from the Cinq-Cerf gneiss demonstmes that this isacomposite unit formed bytUghly strainedmetasedimentaryrocks and675+111-11Magraniticorthogneiss..kxalJyintruded byweakly defomed 584+7/-6Ma HbI-beariDggranodiorite anda transitiona.lfvolcanic an:: tholeiitic 557+141-5 Ma metagabbro. Although variably deformed during the intrusion of thesynhnematic 43L5±1Ma Western Head granite and the subquent,420Ma. greenschist facies overprint.
this set of rocks preserve evidence of pre-5ilurian deformation.This is consistent with a basement-cover relationship betweentheCinq-Cerf-gneissand the nearby low-grade 583- 570 Ma volcanosedimenwy rocks.lbe 675 Ma intrusive event provides a sttoog!.inkwith theAvalonZonefurther demonstratingtllatAvalonian rocks(s.s.)were involved in the Early Paleozoic evolution of the eastern margin of the IapetusOcean.
Further west the gneissic rocks of the Pon-aox-Basques complex. generally adscribed totheGander Zone. separate the Avalonian basement oftheHermitage Aexun: from the
IT
SU~withtheperi-Laurentian margin. Newdata showsthat the oldest set of intrusives.
lIEMargan:eorthogneiss. represent a 20 Ian long. 474-465MamafIC-felsicigneous complex overprinledbySilurian (411-410 Ma) upper amphibolite faciesmetamorphismand deformation.The geochemical signatures of theMargareeorthogneisssuggest thatit:
formedin a b'anSitionai lU'CIbact art:settingatthe time of the major"Late~g-Uanvim back-art: rifting event inthe peri-Gondwananmarginof me Northern Appalachians.
IntheIberian Massif. the orthogneisses of the Siem de Guadarrama form me southern portion ofan enigmatic belt of pte-Variscan augen-gneissesthat extends 600kmalong me northernCentralIberianZone(ClZ).DatingacrosstheBerzosa·Riazashearzone(BRSZ) demonstratesthe presence of 468 Ma granites in the shear zone. 480±2Mavolcanismin the low-medium grade hangingwall and coeval 488-417Magranitic batholithsinthehigh gradefootwall.The 480 volcanism bmckets the Sardic deformation in the CIZ betweenthe Mid-Late Arenig.The BRSZhas anoblique extensional movement coincident withpeak metamorphism (331-321 Ma). which developed duringthe Variscan D2 defonnation(330- 321 Mal. resulting indecom~ionandlate·D2 growht of low PIhighT assemblages (322Ma)inthe infrastJ1JCt\Ue.The shallow intrusion of the posHectonicLaCabrera granite. dated at 292±2 Ma, sealsthe BRSZ andmartsthe end oftheVariscan deformation..Thisnewdala demonstrates. for thefJ.m time. that the Earty-Mid Carboniferous syn-collisionaJ extensionin the CIZ was coeval with extension along the entirehinterlandoftbe Variscan belt.
1beseOrdovician orthogneisses ofthe Siem. de Guadamunaaleinterpretedas reliCts of a soon-lived magmatic arc coeval with the subduction-related break-Up of Avalonia from Gondwana. This new data illusltatesthe striking parallelism between the Early Paleozoic events in the Peri-Gondwanan side ofthe Northern Appalachians and the southern portion oftbeEuropeanVariscan belt.
ill
ACKNOWLEDGMENTS:
Mydeepestgratitude 10thepeopleof Canada who funded thisprojectIhrough!he NSERC operaling gmJl ofDr.Dunning and aMemoriaJUniversity Graduate Scholarship.
Ona more persoaal level. I have 10 praise my lhesis supervisot" Prof. Greg Dunning and myco-supervisors Prof. AphroditeIndarcsandSean CYBrien (Newfoundland Depattmenl of Mines and Energy). for their continuous encouragement and guidance during all s[ages of lhis project.and !heir fanatic obsession with field relationships!! Also. I have tothank Dr.Peler Cawocxl for his guidancein !he early stages of lhis project.
Laboratory training by Prof. Dunning,JimConnelly and. especially. Kathy Manser wascrucial to my mastering oftheU-Pbgeochronological technique. Kathy andRod Chwt:hill also shared the boredom and noise of the crushingroomwithme.Thanks 10 Pal Horan for keeping aneye on the mass-spectrorneter and always being lhcre 10 answer my questions.PamKing. Mike Turbett.l...akma.li Hewa and Maggy Piranhan helped immensc:ly with XRF.ICP·MS analyses andmicroprobeEDS cIelenninations. lloyd and Rick from therock shop always had mythin sections ready ontime.PatBrowne.Geny Ford.Gerry Starkes. Maureen Moore. and Teresalannon helped me withallthe university bureaucraticredtape.
[twas, thanks toCeesvanStaal (GSe. Ottawa),thai. I had the chance of having !he trueCanadian field experiencewith helicopter. tent, black-flies. wet boots and memorable open-water boat rides. He intrOducedme to !he geology ofthe Port-aux-Basques area and was of great assistance and guidance during fieldwork in !he Margaree orthogneiss. Shoufa Lin, Lindsay Hall and Dave Scholfield are thanked for field and general discussions on Port-aux-Basques geology. Discussions on the geology ofthe Cinq-Cerf gneiss and its surroundings with Brian O'Brien (Newfoundland Dept. of Mines and Energy) and Benoit
IV
Dubt(GSQ were of greal assistance.Theboabnanship of Clyde Billard of Grand Bruit was great.ly appreciated while navigatingaround Three Islands and Cinq-Cerf Bay.
CccilioQuesada (SpanishGeologicalSurvey, ITGE). Felix Bellido (ITGE).Enrique Martinez(Univ. Oviedo)andAorentiooDiaz(Univ.de Oviedo) provided a crucial two- weekfield triparound!heOssa-MorenaZone. the SierradeGuadarrama andNWSpain in 1993,during which the Sierra de Guadarramawasselecled asafield area.CecilioQuesada and RobertoRodriguez (ITGE)we~instnnnental in organizing!heclosecollaboration with themapping crew of INYPSA. which partially covered field expenses in Spain. Pedro Pablo Hemm (lNYPSA) and Javier Escuder (Univ. Complutense. Madrid) are thanked for interesting field discussion. free exchange of ideas and general friendship. Antonio Azor (Univ.de Granada) provided a copy of his unpublished "tesina delicenciatura~.Luis Gonz.a.Iez(Univ.de Granada) pbotocopied and sentmea large amount of Spanish bibliography(Iowe you one. Luis!). Also.thanks 10 thepeopleof MontejodeIaSierra whoenrichedmyfieldseasonswiththeiranimatedcharacter (speciallytothe patrons of
"Meson el HayedoWwho provided occasional free-drinks!!) and to my sislerAnafor allowingher car 10 be reroorselesslyabusedduring two full field-seasons
Thanks to Dave Corrigan and John Ketchum who were~assaulted"for geclogical advise and bibliography duringIhcwriting stages of this thesis. Specialthanks to {ngo.
Joy, Sandy. Steve. Arden. Jeroen. Jason, Adam and again 10 Dave for their friendship and companionship. and to my office-mate and fellow "lab rat" Richard Cox for making life easier withhis corrosive sense of humour, friendship and fly-tying tips!!..
Finally I wouldliketo dedicate this work to my family and my girlfriend Pilar, who have endured with metheloog separations, for their love and unconditional support.
v
TABLE OF CONTENTS
VOLUMEI: Text
ABSTRACT .••...•••••••••••.•....•...••...•...••..•••••••••....•. 11
ACKNOWLEDGMENTS 1V
LIST OF TABLES ••••••••....•..••••••••...•..•••.•...••.•.••..•••..•••••• XVI LIST OF MAPS ....•..••••.•••...•.••.•••••••••••••...•..•..•... XVII
LIST OF FIGURES XVIII
LIST OF ABBREVIATIONS XXXI
CHAPTERI
INTRODUcnON TO A STUDY OF THE PRECAMBRIAN AND
PALEOWIC EVOLUTION OF PERI·GONDWANA IN THE
NEWFOUNDLAND APPALACHIANS AND THE IBERIAN MASSIF••••• I
1.1.· PURPOSE AND SCOPE... . 3
1.2.- ANATOMY OF THEORCUM·NORTHAll..ANTICPAlEOZOrC OROOENS.
... 6
12.1.-TheAppalachian -Caledonian belt... . 7
1.22.-TheEuropean Variscanbelt.... . 9
1.3.- CONCEPTIJAL FRAMEWORK FOR PRECAMBRIAN AND PALEOZOIC
NORTH ATI..ANTlC RECONSl'RUcnONS. . . II
1.3.1.·LatePrecambrian and Paleozoic Paleogeographic evolution of the circum-
North Atlantic Gondwanan terranes . 15
VI
CHAPTER
n
THE NEWFOUNDLAND APPALACHIANS .••••••.•••.••.••...••...••••••• 8 2.1.- UTHOTEcrONlCWNES OF TIlE NEWFOUNDLAND APPALAOflANS:
Gf1IlER.AL OVERVIEW.. . 19
2.1.1.- The laurentianlperi·laun:ntianmarginoftheNewfoundland Appalachian'>::
TheHumber zone,theNotre Dame subzone and their equivalents 20
The Humber zone 21
The peri-laurentian Dunnage Zone 22
lbeNorn:;pmncsubzone; . 22
Ib!;pashwoocls !mbzom; . . 24
Ib!;Twjllingate subzone (Unknown afrinity) 25 2.1.2.-Theperi-GondwananmarginoftheNewfoundland Appalachians:the Exploits subzone and the Gander and Avalon zones 25
The peri-Gondwanan Dunnage Zone: The Exploits subzone 26
JbeIndian BaySUblOQ!; 28
The; Gander Zone:.. . 28
Gand<;r l..ale;Subzone 29
MOtlD!Coana!:;kSybzQOC;.... . 30
~I,*,SybzP'K . . . 30
The Avalon Zone:... . 30
2.1.3.-MiddleandI..atePaleozoicevolution oftheNewfoundlandAppalachians.
.... 32 2.2.- GEOlOOICAL ELEMFNTS OF THE SOlITHERN NEWFOUNDlAND
APPALACHIANS: TIlE HERMITAGE FLEXURE 34
TheLaurentianMargin.. . . 34
lbeDaShwoodsSUbzone 34
TheCapeRay[anlt !beWindsorPain!Groupj10dtheBjIljards Brook
lilDnalilm.. . 35
TheGondwanan Margin... . 36
1 $Pon.ayx.8asqu;s complex (ARPA OF STIlpV Cbapler M 36 JbeBay du Nord GroupmUnn'"Zpo; Exploits subz0"S) 36
vn
Jh:; La Poils BISin .. . 37 The:1m; Px;camtman_Early Qulgvicianbag""! block (AREA Of
mJDYChapg:r
un
38Jb;WuJePaMagepm;jM(GandqZqnc;l .. .. 39 The:timnitag;Bayfalll! and ltv;AyalonZone; 39 2.3.- AVALONIAN EVENTS A."IDurnOLOOICAL CORRB..ATIONS IN THE
SOUTHERN NEWfOUNDLAND APPALACHIANS 40
CHAPTERm
THE CINQ.CERF GNEISS (SW Hermitage Fluure)...••..•... 41
3.1.- INTRODUCTION.. . 42
3.2.- LOCATION. LOGISTICS AND OUTCROP 44
3.3.- PREVIOUS WORK._... ...45
3.4.- GEOLOGICAL SETTING... . 46
Evidenceforthe Precambrian ageof theCinq-Cerfgneiss .48
3.5.- PROBLEMS AND OBJECTIVES.. . .49
3.6.- UTHOLOGICAL UNITS. FIELD RELATIONSHIPS AND ABSOLlIffi U-Pb
AGES.. . _ 50
3.6.1.·Thecomposite Cinq-Cerfgneiss:~finition. . 5 I TheSandbankPoint-EastDiverHeadsection .. .._ 52 TheCinq-Cerf Bay and1l1n:eIslands sections.. . 54
U-Pbgeochronology.. . .. _.55
3.6.2.-The584 Ma Sandbank granodiorite. . 56
U-Pbgeochronology... .. 57
3.6.3.-1lle 557 Ma Sandbank Point rnc:tagabbro... ...57
Field relationships ... ... 59
V-Pb geochronology.... ... 60
3.6.4.· The Silurian Western Head granite... . 61
U-Pb geochronology... . ...63
3.6.5.- Lale dykes.. . 64
Felsic granitic dykes. . _.65
Grey-intennediate dykes.... . 65
Green-mafic dykes .. . 65
vm
Amphibole-plagioclaseporpbyriticdykes .. . 66
3.7.- STRUCTURAL EVOLUTION 67
3.7.1.-01deformaliooalevents(~-431Ma) 61
3.7.2.- Silurian 02 deformation 12
D2a. hightemperaturesolidus-subsolidusdefonnation 13
D2b.low-graderetrogradedeformation .. ..14
3.1.3.- Discussion and conclusions... . 75
3.8.- GEOCHFMISffi.Y OF TIlE551MaSANDBANKPOII'ITMETAGABBRO'
METADIORITE... . 18
3.8.1.- Geochemisuy.. . 78
3.8.2.- Discussion: geochemical signatures.leCtonicenvironment and petrogenetic
processes... . . ...79
3.9.- GEOLOGICAL EVOUJI1QN OF THE CINQ-CERF GNEISS AND THE LAlE PRECAMBRIAN BASEMENT OF THE SOUTHWEST HERMITAGE FLEXURE....82
CHAPTER IV
THE MARGAREE ORTHOGNEISS (Port·lux-8ISqU6 complex. SW NewfoundlandAppalachians) ...•...••••••..•••••.•••...•.•..•.•.• 86
4.1.- INTRODUCTION... ... 86
4.2.- LOCATION. ACCESS AND LOGISTICS... . 88
4.3.- THE MARGAREE ORTHOGNEISS: DEFINT1l0N.. . 89
4.4.- PREV10US WORK... . 90
4.5.- GEOLOGICAL SEITING... . 91
4.5.1.-TheCapeRay Igneous Complex andtheWindsor Point Group (l..aurentian
side).. . 92
4.5.2.- The Cape Ray Fault Zone... . 93
4.5.3.-lbe Port-aux·Basques gneiss of Brown (1971). Gondwanan side 93
Th; Ornnd Bay Complex(GBCl .. . 94
ThttPon-Dux.BMan;:;Compl;x(PoBQ .. ...•..94
TheHDrbo"r Ie Cot! Gmll
n
fHlCGl.. .. 95IX
4.6.- MARGAREE ORTHOGNEISS, UfHOLOOICAL UNITS; description. internal
field relationships and age.. . 96
4.6.1.· Hornblende·bearing tooaJitic orthogneiss... . 97 Age (U-Pb); . . ...•... 98
4.6.2.- Granitic gneiss... . 99
Age (U-Pb);.. . 99
4.6.3.· Amphibolite.. . 101
Age{U·Pb);. . 101
4.6.4.- Other lithologies.. . 103
Uhramafic rocks. . . I03
Banded gneiss . 104
~Migmatitic"gneiss.. . 10S
4.7.- THE COUNTRY ROCK PORT-AUX-BASQUES GNEISS AND TIlE LATE lI"ITRUSrvE ROCKS: GENERAL DESCRIPTION, FIE...D RELATIONSHIPS AND
AGE.. .. 106
4.7.1.- Port·aux·Basques gneiss (paragneiss) 106
A~.. . 108
4.7.2.- The Port-aux-Basques granite (PaS granite)... . 108 4.7.3.- Late intrusive rocks; granitic and pegmatitic dykes 110
Late syn·DJ granitic dykes:... . 110
Age (U-Pb).. . 110
Pegrnatites.. . 111
Aplitic andgraniticdykes(post-D3) . 112
PosHectonk mafic dyke... . . 112
4.8.· STRUCTIJRAL EVOLlfIlON OF TIlE MARGAREE ORTHOONEISS AND TIlE
SURROUNDING PORT-AUX-BASQUES GNEiSS.... . 113
4.8.1.-Phasesof defonnation: dertnition and characteristics... . 113
DI-D2deformation.. . 113
03 ductile deformation.. . 11 S
LateDJ·D4 brittle-ductile deformation.. . 116
4.8.2.- Microstructure . 117
472 granitic gneiss.. .. 117
474 gt1lDOdioritic orthogneiss .. (18
Amphloolite.. . I 19
x
Banded gneiss.. . 120
Port-aux-Basques gneiss (paragneiss) 121
D4bci~uetilemicrostructures post-OJ uJtnmylonites 122 4.8.3.- Discussion: Timing and conditions of deformation 123
4.8.4.- Conclusions.. . 123
4.9.·GEOCHEMlSTRY OF THE MARGAREE ORTHOGNEISS 126
4.9.1.- Geochemical signatures .. . 126
Ultramafic rocks... . 126
Ortboamphibolites... . 127
474-472 Ma granodioritic and granitic gneisses 127
4.9.2.- Teclonic signalures:. . 129
Uhramafic rocks. a potential cumulate... . 129
Amphibolites... . . 129
Granodiorilic and granitic gneisses 130
4.9.3.- Discussion: Petrogenetic processes and teclonic signatures 130
4.10.- INTERPRETATION.. . 132
4.10.1.- TheMargareeorthogneiss: its relationships with theEarly Ordovician Peoobscottiane...enlS and theArenig-EarlyUanvirnback-arcextension along the peri-Gondwanan margin of the Newfoundland AppallChians I34
CHAPTER V
THE IBERIAN MASSIF: geological setting and general objectives••••. 137
5.1.- lNTRODUcrION... . 137
5.2.- LffiIOTECfONIC ZONES OF THE IBERIAN MASSIF: general o...erview 138 5.2.1.- The South Portuguese Zone (SP'Z) and lbe Pulo doLoboZone (PlZ}..139 5.2.2.- The Galicia Tras-os-Monles Zone (GTMZ)... .. 140
TheSchistoseDomain.. .. J40
TheDomainof the Complexes.. . . t41
5.2.3.- The Ossa-Morena-Zone (OMZ). . . 144
5.2.4.- The Central Iberian (C1Z), Wesl Asturian-Leonese CWALZ) and Cantabrian
(CZ) zones.. .. .. 147
TheCentrallberianZOne(CIZ) .. .. ...149
Xl
TheWest Asturian-Leonese Zone (WALZ).... . 152
The CantabrianZone(CZ).. . 153
5.3.- TIlE CENTRAL mERlAN ZONE. A CRITICAL AREA OF THE mERIAN
MASSIF: GENERAL OBJECTIVES... . 154
CHAPTER VI
GEOLOGICAL EVOLUTION OF
GUADARRAMA (Central Iberian 6.1.-INTRODUCTION....
6.2.~LOCATION. LOGISTICS ..
6.3.- PREVIOUS WORK...
6.4.-GEOLOGICAL SE1TING ...
THE EASTERN SIERRA DE
Zone)••.•••••••••••••.•••..••.•••••••••••I58 ..158
. 160
. 161
..163 6.4.1.- Macrostructure of the Somosierra sector of the Sierra de Guadarrama I66
6.4.2.- Metamorphic zonation . . 168
6.5.-LITHOLOGICAL UNITS OFTHESOMOSIERRA SECTOR OFTHESIERRADE
GUADARRAMA . . 169
6.5.I.·Eastern GuadaJTama Domain . . 169
The AnnoricanQuartzite .. . I70
The ConslaEue Formation and the problem of the Sardic unconformity.. . .170 The"pre-Ordovician~rocksequence (EI Cardoso gneiss).. ... 171 6.5.2.- The Berzosa-Riaza shear zone. upper levels of the Western Guadarrama
Domain ... .. 172
Metasedimentaryrocks.. . . 172
Foliated megacrystic granites (augen-gneisses) 173
Foliated Ieucogranites (S-type granites).. . 174
Pegmatites .. . 175
6.5.3.-TheWestern GuadarramaDomain(Buitrago-Manjir6narea)..•...175 Gamet micaschists with black quartzites (Madarquillos shear zone) 176
Muscovite-sillimanite metapsammites.. . 177
Migmatitic paragneisses... .. 177
Calc-silicates and ampbibolites . . I 7 9
Marbles 180
El Villar biotite-bearing migmatite (non-anatectic migmatite).. . 180 Grnnitic augen gneissesIfoliated megacrystic granites . 181
xn
Gneissic leucogranites.. . .. . I 82 6.5.4.- La Cabrera granite (Lale Variscan pluton) and lale inlrUsions 183
Other late intrusions.... . 184
6.6.-PRE-VARISCAN EVOLlJIlON: U-Pb evidence for a major Early Ordovician felsic
magmaticevent in !he Siermde Guadarrama.. . . 185
6.6.1.- lnlroduction . 185
6.6.2.- V-Pb geochronological results . 186
Cardoso gneiss.. . I 86
Riaza gneiss.... . 187
Buiu-ago gneiss.. . 187
SaroD!!'! BU-I' foHated megagntjc granjte.. . 188
Sample81 1_2'fgljalrd apljtic vein.. . 188
Sample PiB-I' fglja!ed leycogranjte.. . 188
Lozoya gneiss (LO-I): Augen gneissIgranitic onhogneiss .. . 189 6.6.3.- Discussion: Geological significance of the new U-Pb ages... . 190 6.7.-YARISCAN TECTONOTHERMAL EVOLUTION OF THE SOMOSIERRA
SECTOR OF THE SIERRA DE GUADARRAMA: Structural, metamorphic and V-Pb
geochronological conSlraints... . 191
6.7.1.~Inlroduction.. . 191
6.7.2.-SlrUcturai evolution... . 19 I
01deformation... . 192
Eastern GuadaITjlIDa Domajn.. . . 193
Western Gyadarrnrna Porm!in .. . 194
D2deformation.. . 196
ElCardoso antjfgnD andthe02 crenplarjon band . 196
The6erzosa-Rjaz.a shear zon!'! .. . 197
TheManjjrPnamjfoDD Western Gyadarrama [)omajn .. . •...198 TheMadarpllj!!Q<ishear zone Western Guadarrama Domain.. ...•.. 200
Buitrago area WesternDomain.. . 20 I
Latedeformations (03).. . 203
Structural evolution. discussion.. . 204
6.7.3.- Microfabric development and metamorphism.. . 206
Chlorite, biOlite and gamet zones... . 206
Staurolile zone.... . 207
xm
Sillimanite (kyanite) zone 209
Sillimanite+muscovite zone . 210
Sillimanite+ K·feldspar zone 213
6.7.4.- U-Pb geochronologytoconstrain the timingofVariscan metamorphism and
defonnation . . 215
EAS1CRN GUADARRAMA OOMAIN (Cardosoantifonn)
SampleHH'Sl-Gn-<Odl mjcaschisc 2 16
Samp'e Pj.!·SI-Gn micaschjsc 216
Sample CA. I' plagjgd",_rich pan-amphjboljte 2 17 11IE BERZDSA-RlAZA SHEAR WNE Sample 12_9' KY;Wixcmum!jte-gamct-sjlljmanj'e mjcaschjSIS 218 THE WESTERN GUADARRAMA DOMAIN (SW+Ms and SilI+Kfs zones) Sample M26-2 (Sjll±MS zone)' Folded mjgmatixc Manjjmn antifo(DJ 218 Sample BU.2 fSj!!±Kf§ zgne)' 482 Ma apHlic Yejn Blljl@gognejss 219 Sample PiB.1 (Sjll±Kfs zone) 482 Ma foljated leucogranjte Byjtrago
~
..
. 220Sample 10-1 (SjlI±KfS zgnr;)' Cgrdjedte.bearing 477 Ma augen-gneiss
O.ozqvuela glKjjssl... . 220
Braojosdy"fSjII±Kfsz.onc)'ampbjholj'c; 221
THE POST·TECfONIC LA CABRERA GRANITE 222
6.7.5.- Timing and characterofthe VariscanteetOOOlbenna.levents in the Somosierra area of the Sierra de Guadamuna:conclusionsanddiscusstoo ...223 6.8.-PALEOZOIC lCCfONOTIIERMAL EVOU]nON OF THE SOMOSlERRA
SECfOR OF THE S[ERRA DE GUADARRAMA: DlSCUSSION 227
6.8.1.· Arenig felsic magmatisminthe Siena de Guadarrama and thenarun:of the
~Sardic~events in the Central. £herian Zooe: an Arenig continental magmatic arc ... 227 Coeval eventsintheIberianMassifand speculative correlatives along the
Southern Variscides.. . 229
6.8.2.- Timing of Variscan tectonothermal events inthe Sierra de Guadamuna:
tectonic significance for the evolution of the Central Iberian Zone and the Iberian
Massif... . 230
Timingof metamorpbismandplutonism. . 230
Timingof defonnalion: Early-Mid Carboniferous syn-eollisional extensioo.232
XIV
CHAPTER VII
DISCUSSION AND TECTONIC IMPLICATIONS: PRECAMBRIAN AND PALEOZOIC EVOLUTION OF PERI-GONDWANA FROM A COMBINED APPALACHIAN-VARISCAN PERSPECTIVE ...••.••••.•...•.•... 234 7. I.-TECTONOTHERMAL EVENTS IN THE HERMITAGE FLEXURE (SOtITHERN
NEWFOUNDLAND APPALACHlANS):THEEVOLUTION OF WESTERNMOST
PERI-GQNDWANA .... ..235
7.2.- THE EARLY-MID ORDOVICIAN BREAK-UP OF PERl-GONDWANA: IS THERE A CONNEcnON BETWEEN THE SARDIC EVENT IN THE SOtITHERN VARISCIDES AND THE PENOBSCOTIlAN EVENT IN THE NORTHERN
APPALACHIANS?. ..240
7.2.1.-Thesubduction-related Jurassic break-up of Southern Gondwana duringthe opening oftheSouth Atlantic:Ananalog fortheEarlyOrdovician events inthe SouthernVariscidesandNorthern Appalachians... . ....242
7.3.-FINAL REMARKS.. . ..243
7.4.- SUMMARY.. . 244
REFERENCES CITED •••••.•••••...•...••.•••••••..•..•.•.••••250 APPENDIX
ANALYTICAL TECHNIQUES •••.•••...•••..•.•...•••...288
A.l.-U-Pb PROCEDURE . 288
A.I.1.-Sample preparation ... . 288
A.l.2.· Sample cleaning. weighing. spiking. dissolutionandU-Pb separation.289 A.I.3.·U-Pb isotopic analysis and age determination 290
A2.-MAJORANDTRACE ELEMENT ANALYSIS.. . .. 294
A.2.1.-X-ray fluorescence (XRF) analysis... . 295
A.2.2.- Inductively coupled plasma mass spectrometry (ICP-MS) trace element
analysis... . 296
LIST OF TABLES Volume I: Text
APPENDIX
TABLE A.I.-Mineral dissolution procedure .. . 290
TABLE A.2.-Schcmatic U and Pb ion exchange chemical extraction procedure 293 TABLE A.3.- Resuhs ofthe ICP-MS Naz02 sinter duplicate analysis of samples G-MA-B
and G-MA-C (Margaree Complex) ...299
Volume II: Tables, Maps and Figures
TABLE 3.1.- V-Pb DATA CINQ-CERF GNEISS... . 20
TABLE 3.2.- MAJOR AND TRACE ELEMENT ANALYSES OF THE SANDBANK
METAGABBROIDIORITE.. . 39
TABLE 3.3.- Comparative table of post.675 Ma.LatePrecambrian-Early Cambrian V-Ph absolute ages from the Cinq-Ccrf gneiss and the adjacent
Roo
suite and the WhittleHill sandstone.. . .... 43
TABLE 4.1.- V-Ph DATA, MARGAREE ORTHOGNEISS... . .51 TABLE 4.2.- MAJOR AND TRACE ELEMENT ANALYSES, MARGAREE
ORTHOGNEISS.. . ... 65
TABLE 6.1.· V-Ph DATA. PRE-VARISCAN PROTOLITH AGES, SIERRA DE
GUADARRAMA.. . . 94
TABLE 6.2.- V-Pb OATA. VARISCAN AGES, SIERRA DE GUADARRAMA.., .129
XVI
LIST OF MAPS Volume
n:
Table, Maps and FiguresCHAPTER III.- THE CINQ-CERF GNEISS (SW Hermitage Aexure):The make up of a polycicUc Avalonian gneissic complex.
Insened betweenpages·
MAP. 3.1.- Sandbank Point - East Diver Head section 45-46
MAP. 3.2.·Three Islands . .45-46
MAP. 3.3.-Cinq-Cerf Bay ..
xvn
... 45·46
LIST OF FIGURES:
Volume I: Text APPENDIX
Fig.A.I..variatioD of~measurementsof the 206Pb1204Pb and 201Pbl204Pbis<xopic ratios of the NBS 981commonPb slalldard with respect to the reponed ratios (TOOt.
1993). and calculated values of the Ph isotopic fractionation during mass spectrometry ... 291 Fig.A.2.- Comparative chan of the Y XRF versus ICP·MS analyses 297 Fig.A.3.- Comparative chart of theXRFand ICP·MS Zr andNbanalyses 297
Volume
n:
Tables, Maps and Figures CHAPTER I: INTRODUCTION.Fig.I.I.- (A) Paleogeographic reconsuuction of the Nonh At.lamic atMImagnetic anomaly (131 ~Srivastava andTapscott. 1986) showing the n:lative position of the Appalachian-Caledonian orogen. the Variscan belt and the areas of study. (B) Distribution of the circum-North Atlantic Avalonian·Monian-Cadomian terranes and
relicts of pre-eadomianIAvalonian basement. 1
Fig. 1.2.- Map of the Appalachian-CaJedonian orogen 2
Fig.I.3.- Distribution of the geological elements of the Variscan Belt 3 Fig. 1.4.- Early Paleozoic faunal domainsoftbe European Variscides and location of dated
ophiolitic units... . ....3
Fig.1.5.- Early Cambrian reconstruction of Gondawana showing the relative positions of
Iberia and Avalonia (Courjault-Rade: et aI.• 1992) 4
Fig.1.6.- Paleogeographic reconstructions of Avalonia (A. Cadomianarc).Baltica (B), Gondwana(G)and Laurentia (L)inthe Late Precambrian (Torsvik etal..1996) and the
Ordovician (van der Pluijm etaI., 199:5)... .. 4
CHAPTERU:THE NEWFOUNDLANDAPPALACHIANS.
Fig.2.1.- Subdivisions of the peri-Laun:ntian zones of the NewfoundJand Appalachians
(modified after Williams et aI., 1988) :5
xvm
Fig.2.2.- Subdivisions ofthe peri-Gondwanan lithotectonic zones of the Newfoundland Appalachians (modified after Williams et al., 1988) 6 Fig.2.3.- Geological map of the Hermitage Aexure (showing the field areas). . 7 Fig.2.4.• Generalized geological map of southwestern Newfoundland (showingthe field
areas)... . 8
CHAPTERm.-THE CINQ-CERF GNEISS (SW Hermitage Aexure) Fig.3.!.- Dislribution of Avalonian terranes (patterned)intheNorthern Appalachians
(modified after Barr and While, 1996). showingtheposition oftheCinq-Cerf gneiss and the Late Precambrian basement of the Hennilage Aexure andthe Late Precambrian
inliersin the ExploilS subzone 9
Fig.3.2.- Geological map of the western extent oftheLatePrecambrian basement block of
the Hermitage Flexure.... . 10
Fig.3.3.·Mapof the main geological units in the Sandbank Point -EastDiver Head and
Three Islands sections... .. ... 11
Fig.3.4.- Outcrop plan view of the Cinq-Cerf gneiss. banded gneiss, showing the field relationships betweenthe older granitic orthogneisses (V-Pb sample 94-PV-12) and mafic dykes, the younger mylonitic granite (V-Pb sample 94-PV-ll) and the late mafic dykes. (B) ftOlder" granitic orthogneiss intrusive into metasedimentary banded gneiss overprinted by 01 and cross-cut by "young" mylonitic granite with a D2 mylonitic
fabric.. . 12
Fig.3.5.- Composite Cinq-Cerf gneiss, cross-eutting relationships inthe outcrop of figure 3.4 (V-Ph sampling site). field photographs A,B,C and D. . 13 Fig.3.6.- Sandbank Point· East Diver Head section, amphibolitic banded gneiss (Three
field photographs).. .... 14
Fig.3.7.- Cinq-Cerf gneiss, disharmonic folding of granite injections (Western Head granite) and the country rock paragneiss suggesting viscous non-linear rl1e<llogical behaviour due to {hennal soflening and syn-magmatic deformation 15 Fig.3.8.- Banded quartzo-feldspathic gneiss. dome and basin interference paner (Dl?)
overprinted by F2b folds... . 15
Fig.3.9.- Veined gneiss resembling an anatectic migmatite... ... 16 Fig.3.10.- Field relationships between the tourmaline-bearing veined paragneiss, weakly
defonned Sandbank granodiorite (V-Pb sample 94-PV·6)withmafic enclaves, an intrusive aplitic vein and the syn-veining granite (undated).... ... 16 Fig.3.ll.- Field relationships between the tourmaline-bearing paragneiss, the Sandbank
granodiorite (V-Pb sample 94-PV-6).the aplitic veins and the Western Head granite
XIX
(grnniteJgranodiorilC with mafic cnclaves). location asinFig. 3.10. Field pbOlographs
A.B.Cand D.. . I 7
Fig.3.12.~Amphibole-rich. composite gnciss. Cinq-Cerf gneiss unit at Cinq-Cerf Bay.. 18 Fig.3.13.- Fieldappearanceof U-Pb sample 94-PV-12. granitic orthogneiss part of the
banded gneiss in fig. 3.4 19
Fig.3.14.- U-Pb concordia diagram for the old granitic orthogneiss(V-Phsample 94-PV- 12); Cinq-cerf gneiss. Sandbank Point - East Diver Head section... . ... 19 Fig.3.15.· U-Pb concordia diagram fortheweakly foliated Sandbank granodiorite (U-Ph sample 94-PV-6). intrusive into the tounnaline-bearing paragneiss (Cinq-Cerf gneiss).
... 21 Fig.3.16.- Sandbank Point metagabbro: Mafic metagabbro intruded by felsic
metagabbro/diorite with mafic enclaves showing sharp to diffuse contacts 22 Fig.3.17.- Sandbank Point metagabbro(Three[slands). Left:Latemafic dykes cross-
cutting felsic folded dykes intrusive into mafic metagabbro. Right: Old granitoid !
intennediate dykes intrusive into meragabbro... ..22
Fig.3.18.- U-Ph concordia diagram for the mafic mctagabbro-diorilc at Sandbank. Point
(U-Pb sample 94-PV-4)... . 23
Fig.3.19.- Westem Head granite! granodiorite (undated) with mafic andg~eissicenclaves cross--eut by late mafic dykes (Sandbank Point - East Diver Head secnon) 24 Fig. 3.20.· Mingling of coeval (?) mafic and felsic magmas and high tcmpernture
dcfonnation. Westem Head granite at Sandbank Point. . 24 Fig.3.21.- U-Ph concordia diagrnm for the mylonitic facies of the Westcrn Head granite.
Granitic dyke intrusive into the Cinq-Cerf gneiss. Sandbank Point -EastDiver Head.
... 25 Fig. 3.22.- Microfabric in the 675 Ma onhogneiss (Two microphotographs) 26 Fig.3.23.- ToUt1Ilaline-bearing vcined gneiss. cross country rock tothe 584 Ma
granodiorite (Two microphotographs) 27
Fig. 3.24.- Microtexture orthe 584 Sandbank granodiorite (Two microphotographs) 28 Fig.3.25.- Microtexture of the 557MaSandbank Point metagabbro! diorite (Two
microphotographs) 29
Fig.3.26.- 547Magranitoid dyke. Three Islands. unpublished V·Ph samplc of B.H.
O'Brien and Dunning. Thin section courtesy of B.H. O'Brien (Two
m ic rophoto grap bs). .. . 30
Fig.3.27.- Cinq-Cerf gneiss. paragneiss. Cinq-Cerf Bay section (Two field photographs).
... 31
xx
Fig.3.28.- Field sketches of high temperature D2a deformational features.SandbankPoint.
Western Head granite . 32
Fig.3.29.· Top:H.igbtemperarutesolidus folding (F2a) oflbc Western Head gnutitc at Three Islands.Bottom:D2blowgrade
s.-C
andC(shearbands) suuctuJ'eSinlhc:Western Head granite indicating an apparent dcxual sbearsense.... . ... 32 Fig.3.30.- Equalarealower hcmispbcrc: sterc:ondprojectionsoflhc: S2b mylonitic fabric.
Ulineation. S 1 gneissosity (compositional banding)and lhc: plunge of theF2folds
{bothF2a and F2b)... . 33
Fig.3.31.- Sandbank Point metagabbro: Discrete greenschist faciesrc:trogradc shearzone (10 em thick) with top to the left (i.e. thrusting) shear sense 34 Fig.3.32.-D2rc:trograde grlCenschist facies deformation of the Sandbank Point mafic
metagabbro and felsic mctadiorile around late shear bands andfracturesetsoverprinted
by a later set of joints.... . 34
Fig.3.33.· S2b mylonitic fabricinthe431.5±1Mamylonitic granite dyke, Western Head
granite (Two microphotographs)... . 35
Fig.3.34.- Late mafic prophyritic dyke (post431 Ma) showing grc:enschist facies overprint
of the primary magmatic fabric (Microphotograph) 36
Fig.3.35.-TUlleandfield consuaints on the teetonothcnnal evolution andtimingof
deformation in the Cinq-Cerf gneiss 37
Fig·i~~t~~~~~~~):~~~~~S=na:;o
vs Si02 (Middkmost. 1975):(D)Na20vsSi02 (MiddJernost. 1975):(E) AFMlICrnary
diagram (Miyashiro. 1978)... ... 38
Fig.J.37.-551MaSandbank:metagabbro. Top: chondrite-noonalizcd multielement pattern.
Bottom: MORB (Pearce. 1983) -~mJlticlemenlpaLtcmfOf" the Sandbank Point andThreeIslands samples and modem day basalts (Pearce. 1983) .40 Fig.3.38.- Bivariate series discrimination diagrams: (A) ZrITi vs Nb'Y diagram
(Winchester and Aoyd 1977. modified by Pearce. 1996) ; (B) V vs TIdiagram
(Shervais, 1982).. . .4 1
Fig.3.39.- Ternary tectonicdiscrimination diagrams for lhc: 557 Ma Sandbank mctagabbm'diorillC:(A)LalID-Y/L5-Nb18diagram (Cabanis and Lcc:olle. 1989);(B) Zr/4-2Nb-Ydiagram (Meehesdc, 1986); (C) Zr-TillOQ-Srn diagram (Pearce and Cann.
1973):(0)Zr-TilI0D-3Y diagram (pearce and Cann, 1973); (E)lOMnQ-Ti02-l0P205 diagram (Mullen, 1983);(F)Th-ZrIl17-NblI6 diagram (modified from Wood. 1980).
...42 Fig.3.40.- Model of the Late-Pl'ecambrian·Early Cambrian bascment-cover rc:lationship between the Cinq·Cerf gneiss and the Whittle Hill sandstone .43
XXI
Fig.3.41.-LatePm=ambrian10l....ate Paleozoicgec>logica1evolution of the AvaJorual1 basement of theLaPoile Bay - Coaleau Bay area of the Hermitage Aexure (Central
mobile bell. SW Newfoundland AppaJachians) 44
CHAPTER IV: THE MARGAREE ORTIIOONElSS (Port-aw:-Basques gneissk complex. SW Newfoundland Appalachians).
Fig.4.1.- GeologicalmapoflheIleabetween Port-aux-Basques and Garia Bay .45 FigA.2.- Map ofmagneticanomaliesfor the Port-aux-Basquesarea(Kilfoil. 1993),
including tbe lrace or the Margaree orthognelS.$ 46
FigA3.- Geological map of the MargarcelJsle-aux-Mortsportion nf the Marg:aree
orthogneiss. . . 47
FigA.4.- Lithological map or the Fox Roost section of theMargareeorthogneiss including
U-Pb sampling locations... . 48
FigA.5.-Macro-and mesoscopic relationships between the amphibotite-rich~tonalitic"
orthogneiss and the granitic gneiss of the Margaree orthogneiss. Fox Roost section (A,
B. Cand0,field photographs)... . 49
Fig.4.6.- Margaree orthogneiss. homblende-bearing granodioritic gneiss (U-Pb sample 93-
PY-3)... .. 50
Fig.4.7.- U-Pb concordia diagram for the granodioritic gneiss (U-Pb sample 93-PV-3).
... 50 FigA.8.- Granitic gllCiss (Fox Roost. U-Pb sample 9J..PV-5) and folded amphibolite
enclave.. . . 52
Fig.4.9.- Partially mingled amph.ibotite dyke intrusive into granitic gneiss(Fox:ROOSt)..S2 Fig.4.10.- U-Pb concordia diagram for sample 93-PY-S, granitic gneiss (Fox ROOSt)...S2 Fig.4.11.- Geological map of the lower part of the Grandys Brook section showing the
location of the U-Pb sample 94-PY-2 (granitic gneiss) and the intrusive contact between the Margaree orthogneiss (M.D.) and the counuy rockPaBgneiss S3 Fig.4.12.- U-Pb concordia diagram for the granitic gneiss al Grandys Brook. (U-Pb sample
94-PY-2} S3
Fig.4.13.- Amphibotite dykes intrusive into 465 Ma granitic gneiss 53 FigA.14.- Fox Roost -Margaree. amphibolite (U-Pb sample 93-PY-6) intrusive inco
hornblende-bearing felsic granoclioritic orthogneiss S4 Fig.4.1S.- U-Pb concordia diagram for titanite from sample 93-PY-6 S4 FigA.16.- Titanite (410MaU·Pb coolingIrecrystalliz.ation age) aligned with green
hornblende and biotite deflning the fabric inU~Pbsample 93-PY-6 54
xxn
Fig.4.L7.- Port-aux.-Basques gneiss - Margaree orthogneiss contact, quarry east of lsle-
aux-Morts.... . 55
Fig.4.18.- Grandys Brook. intrusive contact between Port-aux-Basques gneiss and granitic
Margaree orthogneiss (undated) 55
Fig.4.19.- Late syn-D3 granitic dyke intrusive into"migmatitic~gneiss (Fox Roost. V-Pb
sample 92-GO-ll ) 56
Fig.4.20.- Detail of the intrusive contact and the syn-magmatic fabric in the granitic dyke.
.. ... 56 Fig.4.21.- V-Pb concordia diagram forthelate-syn 03 granitic dyke (V-Pb sample 92-
GO-II).. . 56
Fig.4.22.- Cross view.Margareeorthogneiss. Fox Roost:F2-F3interference folding
pattern cross-cut by late pegmatites... . .51
Fig.4.23.- Plan view.F3overprint ofa D2boudinin thePort-aux-Basques paragneiss.
contael betweenthe Port-aux-Basques gneiss andtheMargaree orthogneiss at
Margaree... . ... 57
Fig.4.24.- Plan view. closure of an F2 fold overprinted by F3 folding in migmatitic Port-
aux-Basques gneiss.... . 51
Fig.4.25.- Plan view. amphibolite in F3 ductile shear zone (Margarce orthogneiss.
Margaree - Fox Roost).. . .. 57
Fig.4.26.- Equal area stereonets for the gneissosity. mineral lineation (90% amphibole) and plunge ofF3 folds in the Margaree orthogneiss andthesurrounding Pon-aux-Basques
gneiss.... . 58
Fig.4.21.- 03 ductile shear zone in the Port-aux-Basques gneiss 59 Fig.4.2&.- 03 deformation.detail of backrotatedsegments of a competent quartzo-
feldspathic layer in the Pon-aux-basques gneiss .59 Fig.4.29.- Margaree orthogneiss. microtexture of the 412 Magranitic gneiss.. . 60 Fig.4.30.- Margaree orthogneiss. granoblastic texture in amphibolite 60 Fig.4.31.- Margarce orthogneiss. D3 microstructural features in weakly recrystallized
banded gneiss 61
Fig.4.32.- Margaree orthogneiss. microtexture of late-I post-D3 mylonites 62 Fig.4.33.- Absolutetimeconstraints for deformation oftheMargarce orthogneiss andthe
associated Port-aux-Basques gneiss 63
Fig.4.34.- P-T-t-d path fortheMargaree orthogneiss and stable mineral assemblages....63
xxm
Fig.4.35.- Margaree orthogneiss: mafic and ultramafic rocks: (A) Alkalic Index ys. A120:3 classification (Middlernost., 1975); (B)K20 vs. Si02 classification (Middlemost.,
1975); (C)Na20 vs. Si02 (Middlemost. 1975)... . 64
Fig.4.36.* Margaree orthogneiss: mafic and ultramaficrocks.(A)REEmultielement patterns.(B)MORB (pearce, 1983) nonnalizcd multielement patterns.... . 64 Fig.4.37.* Margaree orrthogneiss. tooalitic and granitic onhogneiss. (A)REEelement
multielement patterns.(B)Primitivemantle(Sun, 1980)nonnalizedmultielement
pattern.... . 66
FigA.38.- MORB (Pearce, (983) * nonnaIized multielemcnr patterns frommodemtectonic environments (after Pearce, 1983) superposed to the amphibolites fromtheMargaree
orthogneiss.. . .. 66
FigA.39.- Tectonic discrimination diagrams for the amphibolites of the Margaree onhogneiss: (A) Ti-Zr-Sr diagram (Pearce and Cann, 1973);(B)Tivs.Zrdiagram (Pearce and Cann, 1973);(0Ti-Zr-Y diagram (Pearce and Cann. (973); (0) Zr-Th-Nb diagram(Wood. 1980 with modifications in Jenner, 19(6); (E) Ti02·MnQ.P205 diagram (Mullen. 1983); (F) Nb-Zr-Y diagram (Mecbesde. 1986) 67 FigAAO.* Tectonic discrimination diagrams for granitic rocks, Margaree tonalitic and
granitic onhogneisses. (Pearce etaI.,1984; Maniar and Piccoli. 1989) 68 FigAAI.- ORG (Ocean Ridge granite; Pearce, 1984) - normalized multielement diagram.
. 68
Fig.4,42.- Margaree onhogneiss, amphibolites: (A,B.C andD)log-log highly compatible (Ni. Cr) vs. incompatible(La.Zr, Yb. Nb) diagrams. (E) MgO vs. Si02 diagram..69
FigA,43.· Crystal fractionation REE modelling.... . 69
Fig.4.44.- MORB (Pearce, 1983) - normalized multielement diagram for the Margaree
onhogneiss (ultramaficrocksexcluded).. . 70
Fig.4.45.- Interpretative model for the generation of the mafic-felsic Margaree igneous complex. Coeval magmatism along the peri-Gondwanan margin of the Newfoundland Appalachians (Exploits subzone and Gander Zone)... . 7I Fig.4A6.• Hypothetical tectonic sening for the Margaree igneous complex 7I CHAPTERV: THE mERIANMASSIF: GEOLOGICAL SElTINGAND GENERAL
OBJECfIVES.
Fig.5.1.* Location of the IberianMassif in the European Variscides and lithotectonic zones
of the Iberian Massif... .. 72
Fig.5.2.- Geological constraints on the timing of the Variscan orogenyinthe Iberian
Massif... .. ... 73
XXIV
Fig.5.3.- Lilhotectooicunitsof theIberian Massifwith the location of thegeoiogjca.l
elements described in sections 5.2.1.10 5.2.3... . 74
Fig.5.4.- Compiled pre-Variscan stratigrapbicsequencesof theCIZ.WALZand
cz. ...
75 Fig.5.5.-Domainsof theCentralIberianZone(CIZ)andlocationof themaiDoutcropsofpre-Variscanorthogneisscs. including tbc available pre-Variscan absoluteages(Ma) in theCIZand theCZand the off-shore granulitic basement 76 Fig.5.6.- Distributionof sillimanite-bearing mewnorpbic complexes (yeUow) and
Barrovianmetamorpttic sequences(~)intheClZ.WAI.Z. andC2(blue)after Martinez(199Oa,b)andMartinezCatalanet:aI.(1990).location of tbc Archean basement granulites off-shore theCantabrianSea(Guerrol etaI.,1989) and relative relationships between deformation.metamorphismand plutonism in theCIZ(1ulivert
and Martinez, 1987)... . 77
CHAPTER VI: NEWINSIGHTSINTO TIlEPALEOZOIC EVOltrrION OFTIrE EASTERNSlERRA DE GUADARRAMA (Central Iberian Zone).
Fig.6.1.- Map of the lithoteclonic zones of the Iberian Massif showing the distribution of theOUo deSapopre-Variscan orthognei.sses andthelocation ofthearea of study .... 78 Fig.6.2.- Geologicalmapof the Spanish Central System, including main macrosuuctures
of the Siena de Guadarrama. also shown in cross-section (ModifiedafterMacaya et aI., 1991)and the location of the previouspre-Variscanabsolute age detenninations.
... 79 Fig.6.3.-Main suuctuta.Ielements and distribution of the metamorphicisograd.sof the
Somosierra area of the Siemt de Guadarrama... . ...80 Fig.6A.- Lilbologicalmapof the Somosierra area of tbc Siemt deGuadarrama. ..••....8 I Fig.6.5.- Paleozoic stratigraphicsequenceof the Easlem Guadarrama Domain 82 Fig.6.6.- Lilbologica.l map of the Mootejo-Berzosa-Buitrago-Lozoya area 83 Fig.6.7.- Lithological changes along the Berzosa-Riaza shear zone: A) chlorilOid micaschist at the lOp of the: shear zone; B) St-Gn micaschisl.basalpartof the Eastern Domain; C) Ky-Grt metapsammite at the base oftIEsbeac zone; D) Migmatiticgneissallhe footWall
oflhe shear zone 84
Fig.6.8.- Metasedimentary rocks in lhe Manjiron antifonn. Sill+Ms zone 85 Fig.6.9.- Quartzo.feldspathic paragoeisses oftheWestern Guadarrama Domain. Buitrago
area (Sill+Kfs zone. western side oftbe Puentes Viejas dam) 86 Fig.6.JO.- Anatectic melts in the Buitrago area. Sill+Kfs zone... ... 87 Fig.6.11.· Analectic migmatiles of the Weslern Guadarrama Domain... . 88
Fig.6.12.- Calc-silicate lithologies... . 89
xxv
Fig.6.13.• El Villar biotite-bearingmigmatites., solidus migmatitC$., WcsternGuadarrama
Domain... . .. 90
Fig.6.14.- Augen gneisses and foliatedmcgacrysticgranitcs ofthe Wcstern Guadarrama
Domain 91
Fig.6.15.- Gneissic Ieucogranites ofthe Western GuadarnmaDomain.Manjiron antiform
(Ms+Sill zone) ... 92
Ftg.6.16.- U-Ph concordia diagram for the Cantoso gneiss and a weakly deformed hand sample showing the volcaniclastic character of thisnx:k..•.•...•...93 Fig.6.17.-U·Pbcoocordiadiagramforthe Riaza gneiss and fieldappearanceof the
strongly mylonitized facies.. . 95
Fig.6.18.· Builrngo gneiss. outcrop relationships attbe U·Pb sampling site for samples BU-I (foliated megacrystic granite) and BU-2 (foliated aplitic vein) 96 Fig.6.l9.· U·Pb concordia diagram forthe foliated megacrystic granite facies of the
Buitrago gneiss, sample BU-l.... ..97
Fig.6.20.- U-Pb concordia diagram for sample BU-2. foliated aplitic vein intrusive info
BU-I. Buitrago gneiss... . .. 97
Fig.6.21.- U-Pb conconiia diagram for sample pm·l, gamet·bearing foliated.leucogranire in lhe Buitrago gneiss, and field characrer of the dated sample 98 Ftg.6.22.- U-Pb coococdiadiagramforthe Lozoya gneiss. sample LO-I, and fieldaspect
oftbeda.ledsarnple.. . 99
Fig.6.23.- Location of the new protolith U-Pbagesfor lhepre-Variscanorthogneisses of
the Sierra de Guadarrama... . 100
Fig.6.24.- Schematic geologicalmapandinterprewive cross-section ofthe Berzosa-Riaza shear zone, the CaIdoso antifonn,the Majalrayo syncline andthewestern flank of lhe Galbe theSortIeantiform (After Hemaiz Huertaela1.. 1996) 101 Fig.6.25.- Geological map of the Buitrago-Montejo-Berzosa~.. ..102 Fig.6.26.-MiCfOleXtweSalongthemelamOrphic zoncs ofthe lower levels of the Eastern Guadarrama domain and the upper levels of the Western domain(BRSZ):A) S2 crenulation of S I in a chloritoid black sla1e of the Btzone;B)Partial 02 transposition ofSlandlare-D2 growth of staurolite. St zone;C)Relict inter 01-02 winged kyanite porphyroblast showing 02growthof fibroliteandbiotireinthepressureshadows.
... 103 Fig.6.27.- Equal area lower hemisphere stereooet projections ofthe main foliationf
gneissosity, mineral and stretching lineation (L min) and F2 fold axis north of the area
shownin detail in fig.6.2S... . . 104
XXV!
Fig.6.28.- Equal area lower hemisphere stereonet projections of the main foliations(Sp) and gneissosity (Gn), mineral lineation (Lmin).F2 fold axis,Cplanes (extensional shear bands) and best fit plane and theoretical fold axis for the Berzosa-Riaza shear zone(BRS~Sill(Ky) zone) and the Manjir6n antiform.... . 105 Fig.6.29.- Defonnation in the southern part of the Manjiron antiform 106 Fig.6.30.- Microtextures along the metamorphic zones of the Western Guadarrama Domain in theareaof study:A) D2microfolding in a sillimanite+muscovite micaschist; B) S-C microstructure with stable biotite+sillimanite+muscovite; C) stable SiII+Kfs rnicrofabric with elongated and flattened garnet porphyroblasts.. . 107 Fig.6.31.-F2folds and 01-02 relationships in the Madarquillos shear zone 108 Fig.6.32.- 02 microstructures in Sill+Ms rnicaschists 109 Fig.6.33.- Relationships betweenD2 boudinaged and F2 folding of a competent layer
during top down to the SE shearing... . 110
Fig.6.34.- Stereonet projections of the structur'al data from the Madarquillos shear zone and
the Buitrago area... . 111
Fig.6.3S.- Shear bands(Cplanes) in the MadarquiUos shear zone indicating a shear sense
of top down to the SE... . 112
Fig.6.36.· L-fabric band: L-fabric and associated quartz-rods... . .... 112 Fig.6.37.- Kinematic indicators with opposite top to theNW02 shear senseinthewestern
marginof the Madarquillos shear zone.. . I L3
Fig.6.38.-02high temperarure deformation band in the Buitrago area, Puenles Viejas dam
(Sil1+Kfs zone)... . 114
Fig.6.39.- Relationship betweenF2fold axis and mineral (stretching) lineation inside the lenses of quartzo-fe1dspathic gneiss of thehightemperature defonnation band ... 115 Fig.6AO.- Top to the SE sbear bandsinthequamo-feldspathic gneisses of the Western
Guadarramadomain .. .•...Il6
Fig.6.41.- Late 02 pegmatitic patches in the Buitrago area. Sill+Kfs zone . 117 Fig.6.42.- 03 structural features, Berzosa-Riaza shear zone... . 1l8 Fig.6.43.-Proposedalternativestructuralcross-section from Berzosa to the Rio Sequillo
dam oftheBRSZ andtheWestern GuadamunaDomain(traceof the cross-section in Fig.6.25) and previously interpretation of AzoretaI(1991a).. . ... 119 Fig.6.44.- Distnbution ofmineralisogradsand mineral assemblages in metapcl.itesinthe
areaofsrudy 120
Fig.6.4S.- Mineralgrowth Ideformation relationshipsinthe arc3- of study.... ... 121
xxvn
Fig.6.46.- Staurolile growing al the expense of chloritoid while biotire apparentlyremains
stable., staurolite-chloritoid tl3Dsitioo.. . 122
Fig.6.47.- SimplifiedKFMASH petrogenetic grid (after Spear. 1993) for the metapclites of
the Berzosa-Riaza shearzooe.. . 123
Fig.6.48.- Kyanite and staurolite relicts in the SiJI+Ky micaschists of the BRSZ. ... 124 Fig.6.49.- Staurolite inclusionsinagarnet porphyroblastrimmedbyfibrotiticsillimanite
... 125 Fig.6.50.. GraniticIeucosomesin the SiJI+Mswoe (Manjir6n antiform) showing
interstitial quartz in contactwith subhedra.lplagioclase (AnIG-15) laths and K-feldspar ... 126 Fig.6.5!.- Biotite micafish with monazite inclusions (pleocroic l\aloes)ina Cld·St
micaschist. . . I27
Fig.6.52.- Sample distribution and Variscan U-Pb prololithandmetamorphic ages (Ma)for the Somosieml area oftheSierra de Guadarrama.. . 128 Fig.653.- U-Ph concordia diagram for IT'IOnll2ite from sample Hi-t, St+Grt+(Cld)
micaschisl. Lower staurolite zone (Eastern Guadarrama domain) 130 Fig.6.54.- U-Pb concordia diagram for monazite from sample Pi-I. St+Grt+Bt micaschist.
Upper staurolitezone (EasternGuadarrama domain) 130 Fig.655.- Sample Pi-I, St-Grt micaschist:A)Microc.exnn. biotite defming the S2 fabric:
B) Monazite inclusions in52biotite: C) Platy, subhedral monaziteparallelograms.
fraction MI.. . 131
Fig.6.56.· U-Ph coocorWadiagramfor titanitefrom. sample CA-l, para-amphibolite from thecoreof the Cardoso antiform. and microtexture showing titanite associatedwith randomiy oriented amphibole porpbyroblaslS (static post-{CCtonic porphyroblastesis).
... 132 Fig.6.S7.. U-Pb concon:liadiagramfor monazite fromsample12-6. Ky+St+Gn+Sill micaschistfromthe Sill (Ky)zoneanddetailof a IIlOr18%ite inclusioninaD2 biotite
... . 133
Fig.6.58.· U-Pb coocordia diagram forsampleM26-2, leucosomefroma folded (F2)
:~~:in~~f:re~~°f::ef~::f:~~.~~ .. ~ .. ~.~.~ .. ~~e
Fig.6.59.- U-Pb concordiadiagramof monazite fractions from sample BU-2 (482Ma foliated aplitic vein, Buitrago gneiss). Sm+Kfs zone l3S Fig.6.60.· U-Ph concordia diagram of monazite and xenotime fractions from sample PiB-1 (482 Ma foliated leucogranite, Buitrago gneiss). SilI+Kfs zone 136
xxvm
Fig.6.61.- U-Pb concordia diagram of IDOI1aZite and xeootime fractions from[he477Ma Lozoyagneiss(augen gneiss). Sill+Kfs zone. sillimanite+cordierite-bearing sample...
... 136
Fig.6.62.- U-Pb coocordia diagram for titanite separatesfromthe Braojos dyke and rrncrocextureof the U-Pb sample.. . 137 Fig.6.63.- U-Pb concordia diagnun for the post-tectonic LaCabrera granite and microtexture of the V-Pb sample. HeterogranuJar undeformed Bt-granite/granodiorite..
... 138 Fig.6.64.- Time constraints on the Variscan !eCtonothermal evolution of the Somosierra
sector of the Sierra de Guadarrama 139
Fig.6.65.- Tectonotbennal evolution of the Somosierra sector of the Siem de Guadarrama.
OUodeSapo domain. CentralIberianZone. Iberian Massif(Central Spain) 140 Fig.6.66.-Comparativetable of Ordovician U-Pb and Rb-Sr absolute agesfrom the
CentralIberianZone andV-Phagesfrom.otherparts of theIberianMassif and the location oflheseareas within theEuropeanVariscides... . 141 Fig.6.67.-Mapof the Iberian Massif showing theDeW timecOllSO'"aints onthe
teetonothetmal events from the Somosierra sector of the Sierra de Guadatrama. other timeconstraints on the timing of Variscan deformation and the distribution of the Carboniferous Variscan metamorph.ism and p1utonism 142 Fig.6.68.- Timing and distribution of the Early -Mid Carboniferous syncoUisional extension and metamorphism along the Variscan belL [43 CHAPTER VII: DISCUSSION AND TEcrONIC IMPLICATIONS: PRECAMBRIAN AND PALEOZOIC EVOLUTION OF PERI-GONDWANA FROM A COMBlN'ED
APPALACHIAN- VARlSCANPERSPEcrIVE..
Fig.7.J.-Teaonotbermal evolutioo of the GondwananmarginoftheNewfoundland
AppaJachians. HermitageFlexure... . 144
Fig.7.2.-Geologic.almap of the Hermitage Rexure showing thelocationof the new V-Pb
data... . 145
Fig.7.3.- Comparativetableof eventsinthe Lare Precambrian. pe:ri-Goodwanan.
CadomianIAvalonian belt and the Hermitage Aex~of the Newfoundland
Appalachians... . . 146
Fig.7.4.- Distribution of theI....att:Ittcambrian CadomianIAvalonian terranes on pre-drift
reconstruction of the circum-North Atlantic 147
Fig.7.5.- Comparison of the Early Ordovician eventsinthe peri-Gondwanan margin of the
Nonhem Appalachians and theSouthernVariscides 148
Fig.7.6.-Locationof the interpreted relictArenigfelsic magmaricarcof the CIZinthe
Southern Variscides 149
XXIX
Fig.7.7.-Interpreted Paleozoic evolution of North Atlantic peri-GoDdwana 150 Fig.7.8.-Paleozoic reconstruetions of Avalonia.Baltica.Gondwanaand Laurentiain the:
Late Pm::ambrianandtheOrdovician(afterTonvik d aI.• 1996; vande!"Plu.ijm d al..
1995)... . 151
xxx
LIST OF ABBREVIATIONS:
Symbols for rock-fonning minendsCafter Bucher and Frey. 19(4)
Am amphibole Cn! cordierite Qlz qwutz
An anorthite Ep epidote Sill sillimanite
A"d andaJusite Gn gamel 51 staurolite
"'
biotite K" K.feldspar T," titaniteCam clinoamphibole Ky kyanite TO' tourmaline
ChI chlorite Mnz ~le Zm r i _
ad chloritoid Op, ortbopyro~ene
Cp, dinopyro~ene PI plagioclase
Other abbreviations (The rest of abbreviations are specified in thete~t):
centimetre Ut stretching lineation
e
degrees Celsi us""""
0 episode millimeter
of dcformatiOll N "orth
""
P pressurefold. episode ppm partsper million
of folding 5 south
HP highpressure T temperature
HT high temperature W
Kb kilobar 0 di",""""
Ian kilometer approJoimately
!min rninemliDeatiOll
...
weightJmodalLP low pressure p=cn<ag<
XXXI
CHAYI'ER I
INTRODUCTION TO A STUDY OF THE PRECAMBRIAN AND PALEOZOIC GEOLOGICAL EVOLUTION OF
PERIGONDWANA IN THE NEWFOUNDLAND APPALACHIANS AND THE mERIAN MASSIF.
This thesis was originally conceived10assess the extent of the similarities between the Precambrian and Paleozoic geological evolution of the peri-Gondwanan elements of the Newfoundland Appalachians (e.g. O'Brien etaI., 1996) and the Iberian Massif (Fig.I.IA) and, in doing so. to attempt to frnd the prc-CadomianiAvalonian basementin bothareas.
ReportedLatePrecambrian events from the Iberian Massif andtheAvalon Zone of the Newfoundland Appalachians suggested a similarLatePrecambrian geological evolution (Fig.UB; lberian Massif: Quesada. 199Oa; Quesada. 199Ob; AvalonZone:O'BrienetaJ ..
1983; O'Brienet aI., 1990: O'BrienetaI.• 1996). This Precambrian evolution was connectedwiththedevelopment ofthePan-African orogens aroundthemarginsof Gondwana (Strachan and Taylor. 1990; Rogers, 1996). Twomainareas.both with reported vestiges of CadomianiAvalonian events, were selected for this study (Fig.l.t).
Theone in the Newfoundland Appalachians isinthewestern Hermitage flexure (Williams et al., 1970; Brown, 1975; Dunning and O'Brien. 1989; O'Brien et aI., 1991; O'Brien et aI., 1993), which conrains some of the most outboard relicts of Avalonian rocks of the Appalachian-Calc:donian orogen (Fig.I.l).IntheIbc:rian Massif.the: medium· andhigh·
graderocksof the eastern SierradeGuadarrama (Fig. 1.1 ; Fern<1ndez Casals, 1979; Macaya etal.,I99I;Viale:ttec:tal., 1986;Vialeuec:tal., 1987; Wildbergc:tal., 1989; Amrc:tal.,
1992), in the Central Iberian Zone (l.otzc. 1945; Julivert etaI.•1972;Quesada.1991) wen:
selected for study. AdditionaLly,thestudy involved the unraveling oftheintensityand the charncter of the AppaJachian and Variscan ovcrprinlSinthesedifferenl areas and offen:d an opportunity to further uOOcl'5laod Ibcse PaIcozoic events. responsible for the rearnalgamation of the Late Precambrian pcri-Gondwanan relicts of the North Atlantic.
This study also provides a series of differenl strategies10constrain absolute timing of deformationinmedium· and high-grade terranes.lbcsc srnuegics arebasedon the combinationof detailed classic fICld and pcuographic work with high-precision U-Pb geoc:!uooology. whicb allows tbeinlCgralion of precise U-Pb proIolith and mewnorphic ages wilh clear fieldandpetrographic:relationships. MetamOrphic conditions wereassessed using stableminc.ral assemblages. It should be noted that the emphasiswasplacedmore00 assessing lhe conditions during deformation rather than having a precise estimation of the PTconditions. Additionally, wholerock. major-and t:raee-elemcnt geocbemistry ofa selectednumber of sampleswasdelennincdto rtllUimizetheinformation obtained fromthe protolilh ages fromthe fieldareasin!heNewfoundland Appalachians.
This thesis has threemainpartS.TheflIStpartdealswith tbe areasin!hesouthwCS!
Newfoundland Appalachians (Chapters
m
andM,and includes a general introduction10!hegeology of the Newfoundland Appalachians (01apler
m.
Thesecondpartcovers the Sierra de Guadarramain!heCentralIberianZooc(Chapter YO; an inuoduc:tion to the geology oftI:JCIberian Massifisalso provided (Cbapter V). The third andflJla1partfocuses on !he significance ofthecontributions of the data from southwest Newfoundland and Central Spain to the understanding of the evolution of the Paleozoic circum-North Atlantic orogens (ChapterVll).The following introductory sectionsprovidejustiftcation for the field aru selection. as well as ageneral.geologic overview of the Paleozoic circum-NorthA1la.ntic orogens. Also.
toclarifyfurtherdiscussions. a series of paleogeographic concepts are defined. followed by a synopsis of the evolution of the peri-Gondwanan circum-North Atlantic Icmme5. and an assessment of the possible connections between the Newfoundland Appalachians and thc Iberian Massif.
1.1.- PURPOSE AND SCOPE.-
Therationalebehind seJocting gneissic complexes for this study is !hat these are in IIlOSI cases blocks of lower or middle crust wilh acomplexandin places prolonged teetonolhennal evolution. constiwting poIeIltiai~lictsof pre-orogenic crystalline basement in any orogenic belt. By unraveling the timing and characlcr of the different defonnational, metamorphic andintrusive events. it could be possiblenOI only 10 assess the contemporaneity of the teclonic processes that operated at different crustal levels within the same segment of the orogen or along differenl parts of the orogen bot to l'eCOD$UUCtpanof its p!e-omgcnic evolution. II isthispre-orogenicevolution wtlich formsthe basis of this compar.Uive swdy of the exlent of the peri-Goodwanan linkage between gneissic complexc:sin!be hinlerland of !he Newfoundland AppaIachians and Iberian Massif.
Basementinthe peri-Gondwanan margin of the Newfoundland Appalachians and most of the Iberian Massif is formed byLate~rian rocks deformed during the AvalonianlCadomian orogeny and variably reworked during !he subsequent Paleozoic orogenies (Fig.I.I). Archean-Proterozoic granulites oUlcrop offshore the Iberian Massif in theCantabrian sea (nonbwesl Spain; GuerrotetaI.,1989) and 2.1 Ga gncisses are known from the Cadomian block in the Armorican Massif (Clavaand Vidal, 1918). Such pre-
Cadomian/AvaJonian aystalline basement. aJthough suspected. bas yet to be identified in boththeperi-Gondawanan margin ortheNewfoundland Appalachiansand!he lberian Massif. The gneissic complexes selc:cted ror this study offem:1 the highest chance of finding such relicts. so a greatdeal ofeffort was put into sean:hing ror the oldest members or these complexes.
IntheNewroundland Appalachians. there is no evidence or gneissic basement to Ulte Precambrian volcanosedimentary sequences or the peri-Gondwanan Avalon Zone nor gneissic country rock. to itsLatefucambrian plutons, except ror a small area or low PI nigh T metasedimentary rocks in the island or Miquelon (France) (Dunning et aI., 1995).
However, funher west, gneissic roeles are described as the oldest members or aI...ate Precambrian Avalonian basement (Dunning and O'Brien, 1989) within the Hermitage Flexure (Fig. I. I). orthesegneissic rocles. the best candidate to host pre.Avalonian rocks was the Cinq-Cerf gneiss (ChapterIII).This gneissic complex is in contad with a low·
gradel...atePrecambrian volcanosedimentary sequence and its contact reportedly stitched by 570 Magranite (Dunning and O'Brien. 1989; D.H. O'Brien etaI••1991: B.H. O'Brien et aI..1993). Separating the Cinq-Cerf gneiss from the SUlUJ'e with the Laurentian margin.
then:is a 100 KIn wide belt or amphibolite to upper amphibolite racies rocks.
met.amorpbosed during the Silurian Salinic orogeny (Dunning et al.. 1990), withpre- Silurian intrusive rocles and local evidence ror pre-4TI Mateetonicimbrication (fucker et aI.1994). To investigate the evolution or this western extent or the peri-Gondwanan marginor the southwestern Newroundland Appalachians a gneissic paclcage with lithological resemblance to the Cinq-eerf gneiss, the Margaree orthogneiss (ChapterTV) was selected for study.lbecombined new data rrom these two field areas is expected to rurther the understanding orthetectonothermal record or themarginaledge or l...a1c:
Precambrian northwest Gondwana (Fig.l.lA) and its Paleozoic evolution.
In the Iberian Massif.Lare Pm=ambrianrocksand evidence forLatePrecambrian events is widespread (Quesada. 1991). Cadomian gneissic rocks~known 10 oulCTOp as fauJt bounded blocks within a large megashear zoneinlhe Ossa-Morena Zone (Fig. I. I : Badajoz-Cordoba shear zone: Schafer. 1990), where Cadomian Iedonothenna.l events are weU documented (e.g. Quesada. 1991; Ochsner. t993). and in the metamorphic complexes of the Central IberianZone(Lancelot el aL 1985; Wildberg etaI.•1989). Stratigraphic and faunal evidence (chapterV)indicales lhallhe Central Iberian (C1Z). West Aswrian·I...eooese (WAlZ) and the Cantabrian Zones {CZ; Fig.I.I} formed a single Paleozoic Iberian terrane against which other elementsliketheOssa-Morena (OMZ). the South Ponuguese (SPZ) and Galicia-Tras-os-Montes (GTMZ)zoneswereaccretedduringthe Late Paleozoic.
Variscandefonnation was traDsferred fromtheCIZ towards the more external WALZ and CZ. WorkintheCIZhad aIWOfold objective, 10 resolve the timing of !he pre-Variscan events while scarching for relicts of a pre-Cadomian basement and 10 unravel lhe timing and characlCr of the Variscan overprinl.
The Siena de Guadamunainthe CIZ was selected for lhissrudy(Fig. I. I ) becauseitis the largesl single massif ofpn:·variscan ortbogneisses in the lberian Massifandit is pan of an enigmatic 600Kmlong bell of onhogneisses which eXlendsfromthe Sierrade Guadarramaincentral Spain 10 tbe NW coast of Spain (e.g.•A:lDretaI.•1992).These orthogneisses are below an Ordovician unconformity (Sardic unconformity;DiezBaIdaC:I ai., 1990).ThisOrdovicianuncoofonnitiyis characlCristic of tbeelZ.In!he CIZ. there is also local evidence for aweU~fUlCdLate~ambrianCadomian unconfonnity. which is also common 10 the W AlZ andthe
cz.
The age oftheseormogneissesintheSienade Guadarrama bas remained controversial due to alimited and unreliable age data SCi (Early Ordovician. Rb-Sr. VialeneetaI., 1986, 1987; vs. PTecambrian-Cambrian. U-Pb:WiJdberget al., 1989). Zircon analyseswithlarge degreesof Proterozoic-Archean
inheritance indicatethepresence of 2.0 Gacrustalsources(Wikfbergel al.• 1989)and the poIentialforIhepresence of a pre-<:adomian basement(Quesada.19(2). Additionally!he SiemdeGuadarramaconlainsa poorlydaled (Wildberg etaI.•1989) rcl.icr: Barrovian melamOrphic sequeoce.partiallyoverprintedbya VariscanlowPIhighTmetamorphic event. andla1eVariscanpost<ollisiooalplulOl\S(Bellido etaI.•1981). Therefore.ir:
providesIheidealareafOf a delailed combined investigation ofdiepre-Variscanand Variscan evolution ofIheClZ.
Lale Cretaceous paleogeographic reconslruCtion oftheNorth Atlantic showsthat the Avalon Zone oflhc: NewfoundJand Appalachianswas facingthelberian Massif prior to!he opening oftheNonh Atlanticocean(Fig.I. I ). indicating that lberia collided againsl Avalonia during the Variscan orogeny. It is possible thai exotic Appalachian elements were amalgamated totheIberian Massif as a result of!heVariscan collision. This thesis.
however.attempts[0 exploreif!herewas a common Precambrian-Early Paleozoic connection priorto theseparation of Avalonia from Gondwana (see section13).
1.2.-ANATOMY OF THE CIRCUM-NORTH ATLANTIC PALEOZOIC
OROGENS.-
ThePaleozoic geology ofthecil'tWll-Atlanticrealmischaracterized bythepresence of fWO Paleozoic orogenic belts,the:Caledonian-Appalachian bell andtheVariscan belt.These beltsare separate and well defrned[0!henorth. but merge 10wardsthesouth. as a result of theflnal amalgamation of Pangea (Fig.I.1 and1.2).The following is a brief description of themost fundamenlalfea~ofthesebelts.to famil.iari1.etheAppalachianreaderwiththe Variscan and Iberian geology and vice versa.
1.2.1.- Tbe: Appala(:blan·Cale:donianbelt.-
The Appalacbian-CaJedooian bdt (Fig.I.2) is alinearorogenic system Iha! extends from southernAlabama(USA) through the easternseaboardoftheUSA and Atlantic Canada co Newfoundland. mland.theU.K.•Norway and eascern Greenland. This belt records the amalgamation of difreR:nl elements co Laurentia (i.e.NorthAmerican craton) as a result of Paleozoic development and closure of a protO-Atlantic ocean (Wilson.1966).the Iapetusocean(Harland and Gayer. 1972). Initiation of the Iapetus ocean is marked byL..ate PrecambrianriftingintheLaurentianmargin(e.g.• Williams.. 1979) and in the opposing marginin the ScandinavianCaIedonidcs(e.g.. Andriasson. 1994). The situation is however more complica1ed in the British Caledonides and the Northern Appalachians since the presently opposing margin. Avalon Zone (e.g.• Williams. 1979: Nance and Thompson.
1996)wasUndergoihgart:magmatismanddeformationalthat time(Avalonian-Cadomian events: e.g., O'Brien et aI.• 1996; O'Lemos et aI.(eds.), 1990; Strachan and Taylor (eds.), 1990).Duringmost of the Cambriantherewas apauseintectonic activity onallsides of the IapetusOceanand major paleontological diff'eR:OCCS were established betweenall margins ofmeIapetus (Cocks and Foncy.1982;Faney and Cocks.1986:Cocksand Fortey. 1990; Neuman and Harper. 1992; Williams S.H. ecaI .•1995; Landing, 1996).In theOrdovician tectonic activity was renewed. The Northern and Southern Appalachians record Ordovician~of volcanic an: elements to theLaurentianmargin. known as the Taconic orogeny (Williams. 1979; Williams and Hatcher, 1983); the Grampian orogeny is the equivalent eventinthe BritishCaledonides(Rast andCrimes. 1969: RastetaI., 1988). Early-Mid Ordovician compressional events also took. placeintheopposing side, theFinnmarkian orogenyinthe Scandinavian Caledonides (Stun, 1978; Oallmeyer. 1988:
Andreasson. 1994) and the Penobscottian orogenyintheNorthern Appalachians (Neuman, 1967; Neumann and Max. 1989: Coiman·Sadd etaI.•1992a; Van Staal and de Roo. 1995;
Van Staal et aI.. 19900). DuringtheLareOniovician...silurian the final closure of the Iapetus involved a continent-continent collision which is~ponsiblefor the Salinic -1are Caledonian - Scandian orogenies (Dunning et aI., 1990; Barnes d aJ.. 1989;Gee.1915:
Robinson dat.1988). The colfuioointheNorwegianCaJledonideswas between Baltica and Laun:ntia whereas in the British Caledonides and the Northern Appalachiansitwas between Laurentia and Avalonia (a peri-Gondwanan terrane; Fig.I.I). This collision is apparently slightly diachronousinthe New England Appalach.ians (USA) (Devonian Acadian orogeny. Dewey. 1969; Robinson d aI.• 1988; Eusdcn and Lyons, 1993) . However new precise geochronology from Maine (Stewart et aI., 1995;Osberget aI., 1995) and Massachusetts (Hepburn etal.,1995) points to a Silurianpeakof orogeny in parts of New England. The Southern Appalachians also record a Taconic event wh.ich is foUowed by a continent-continent collision between Laurentia and Gondwana (i.e. African craton) during the Carboniferous-Early Permian (Alkghenian orogeny; Bailey. 1935:
Williams and Halcher, 1983).
All the geological elements ofthe Northern AppaJachians are best exposedintheisland of Newfoundland (Canada). ThisisJandiskatedin the center of the orogenicbel[ and offers the mosl complete: cross·section oftheorogen. excepc. forthe Meguma Zone (Fig.I.2).Thezooes and subzooes of the Newfoundland Appalachians can betracedalong the Northern Appalachians and the BritishCaledonides(Dewey. 1969: Williams, 1978 a.b;
Colman-8add etaI.•1mb; Winchester and van Staal,1995:van Staal etaI.•1996a). For thisreason tectonic models for both the Nonhern Appalachians and the British Caledonides have relied nOt only on the local geology but also on the constraints provided by the rocks exposedintheNewfoundland Appalachians (Wilson, 1966: Williams, [978b: Williams and Hatcher. 1983: Colman·Sadd et aI., 1992b: Williams. S.H. et aI., 1995).
