Detrital Zircon Provenance of Triassic Sandstone of the Algarve Basin (SW

Geological Magazine Detrital zircon provenance of Triassic sandstone

www.cambridge.org/geo of the Algarve Basin (SW Iberia): evidence of Gondwanan- and Laurussian-type sources of sediment Original Article 1 1 2 3 Cite this article: Gama C, Pereira MF, Cristina Gama , M Francisco Pereira , Quentin G Crowley , Ícaro Dias da Silva Crowley QG, Dias da Silva Í, and Silva JB (2021) and J Brandão Silva4 Detrital zircon provenance of Triassic sandstone of the Algarve Basin (SW Iberia): 1 evidence of Gondwanan- and Laurussian-type Instituto de Ciências da Terra, Departamento de Geociências, Escola de Ciências e Tecnologia, Universidade de 2 sources of sediment. Geological Magazine 158: Évora, Portugal; Department of Geology, School of Natural Sciences, Trinity College, Dublin 2, Ireland; 311–329. https://doi.org/10.1017/ 3Instituto D. Luiz, Departamento de Geologia, Faculdade de Ciências da Universidade de Lisboa, Portugal and S0016756820000370 4Instituto D. Luiz, Departamento de Geologia, Faculdade de Ciências da Universidade de Lisboa, Portugal

Received: 2 October 2019 Revised: 6 February 2020 Abstract Accepted: 8 April 2020 Detrital zircon populations from six samples of upper Triassic sandstone (Algarve Basin) were First published online: 19 May 2020 analysed, yielding mostly Precambrian ages. zircon age populations of the Triassic sandstone Keywords: sampled from the western and central sectors of the basin are distinct, suggesting local recycling U–Pb geochronology; detrital zircon; Triassic and/or lateral changes in their sources. Our findings and the available detrital zircon ages from sandstone; Algarve Basin; Palaeozoic terrane; the Palaeozoic terranes of SW Iberia, Nova Scotia and NW Morocco were jointly examined sediment source; Pangaea palaeogeographic using the Kolmogorov–Smirnov test and multidimensional scaling diagrams. The obtained reconstruction results enable direct discrimination of competing Laurussian-type and Gondwanan-type Author for correspondence: sediment sources, involving recycling and mixing relationships. The detrital zircon populations M Francisco Pereira, of the Algarve Triassic sandstone are very different from those of the lower–upper Email: [email protected] Carboniferous Mértola and Mira formations (South Portuguese Zone), upper Devonian – lower Carboniferous Horta da Torre, Represa and Santa Iria formations (Pulo do Lobo Zone), and the late Carboniferous Santa Susana and early Permian Viar basins, which are ruled out as potential sources. The detrital zircon populations of Triassic sandstone from the central sector and those from the Ossa–Morena Zone Ediacaran–Cambrian siliciclastic rocks, upper Devonian – Carboniferous Ronquillo, Tercenas, Phyllite-Quartzite and Brejeira formations (South Portuguese Zone), and Frasnian siliciclastic rocks of the Pulo do Lobo Zone are not statistically distinguishable. Thus, sedimentation in the central sector was influenced by Gondwanan- and Laurussian-type putative sources exposed in SW Iberia, in contrast to the western sector, where Meguma Terrane and Sehoul Block Cambrian siliciclastic rocks allegedly constituted the main (Laurussian-type) sources. These findings provide insights into the denudation of distinctive source terranes distributed along the late Palaeozoic suture zone that juxtaposed the Laurussian and Gondwanan margins.

1. Introduction The petrography and geochemistry of siliciclastic rocks has widely been used to identify different sources, providing reliable information about provenance. In regions where information on the source of sediments and the occurrence of sediment recycling is difficult to evaluate using petrography and geochemistry, detrital zircon U–Pb geochronology may provide a useful means for testing potential sources (Andersen, 2005; Gehrels et al. 2011). Zircon grains found in siliciclastic rocks may derive directly from primary sources and/or represent recycled material from intermediate sediment repositories (Pereira et al. 2016a,b) associated with multiple sedimentary cycles (Morton et al. 2008; Thomas, 2011). Detrital zircon U–Pb ages are hence critically important to the process of creating a geological historical profile of sedimentary basins and their surrounding (local) and remote (external) source regions (Fedo et al. 2003). Often such a relationship is not readily recognizable because sources may have been displaced or separated, with a distance of hundreds of kilometres between them, as a result of the movement of the lithospheric plates. Following the complex process of the formation of Pangaea as a result of the collision © The Author(s), 2020. Published by Cambridge between Laurussia and Gondwana that led to the juxtaposition of distinct Palaeozoic terranes, University Press. both basements experienced uplift and erosion. As debris derives from different sources it is very likely that contrasting zircon age populations are recognizable in the Triassic basins formed during the first stages of the fragmentation of this supercontinent, where they were deposited. Mixed provenance may also be a significant phenomenon depending on the complexity of the dispersal paths connecting sources to the basins. According to palaeogeographic maps showing

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the plate configuration, palaeoenvironment and lithofacies during and presents distinct features in terms of sedimentation and mag- late Triassic time, Iberia is located at the core of Pangaea and is matism (Fig. 2). A singular aspect of this area of the Variscan belt is bounded in the east by the Neotethys Ocean (Golonka, 2007). the absence of Silurian and Devonian plutonic rocks, whereas In the fragmentation stages of Pangaea, the separation of North Carboniferous plutons are found on both sides of the Rheic suture: America and Gondwana (Europe and NW Africa), initiated in the Sierra Norte batholith (c. 359–335 Ma; de la Rosa et al. 2002; early Triassic time, continued during late Triassic time with the Gladney et al. 2014), the Beja igneous complex (c. 353–350 Ma; Pin development of terrestrial clastic depositional systems in the region et al. 2008), the Valencia del Ventoso plutonic complex (c. 337–330 where the Central Atlantic spreading axis (Golonka & Ford, 2000) Ma; Cambeses et al. 2015) and the great variety of plutons from the later emerged during late Sinemurian time (c. 195 Ma; Sahabi et al. Évora massif (c. 341–324 Ma; Lima et al. 2012; Moita et al. 2015; 2004). In order to identify the potential sources of the late Triassic Pereira et al. 2015a; Dias da Silva et al. 2018). basins from the Central Atlantic Ocean realm, the configuration of The OMZ metasedimentary sequence extends from the the late Palaeozoic orogen, showing the probable spatial distribu- Ediacaran (Serie Negra Group) to the lower Devonian (Terena tion of the distinct provenances of the Palaeozoic terranes, before Formation), presenting large volumes of magmatic rocks ranging Pangaea fragmentation, must be reconstructed. Terrestrial from Ediacaran to early Ordovician in age (Sánchez-García et al. deposition was diachronous in Iberia (López-Gómez et al. 2003; Robardet & Gutiérrez Marco, 2004; Chichorro et al. 2008; 2019), presenting Late Permian – Middle Triassic ages in eastern Pereira et al. 2011, 2012b; Cambeses et al. 2017) (Fig. 3). and southeastern basins (Pyrenees, Iberian Ranges and Betics; Cambrian to lower Devonian metasedimentary sequences (Ossa, López-Gómez et al. 2005; Sánchez Martínez et al. 2012) and Fatuquedo, Barrancos, Colorada, ‘Xistos com Nódulos’, ‘Xistos Late–Middle Triassic ages in western and southwestern ones Raiados’, Russianas and Terena formations; Oliveira et al. 1991) (Lusitanian, Alentejo and Algarve basins: Palain, 1976; Azerêdo and Cambrian (Early-Rift and Main-Rift volcanism; Sánchez- et al. 2003; Alves et al. 2006; Soares et al. 2012; Pereira et al. García et al. 2010, 2013) to Ordovician (Sánchez-García et al. 2016b, 2017c; Dinis et al. 2018). 2003; Díez Fernández et al. 2015) magmatism are related to the The aim of this paper is to present findings for detrital zircon geodynamic evolution of the outermost Gondwanan passive mar- ages obtained from six samples of Triassic siliciclastic rocks of the gin of the Rheic Ocean (Sánchez-García et al. 2003; Linnemann Algarve Basin that complement information already published et al. 2008; Pereira et al. 2012b; Díez Fernández et al. 2016) (Fig. 3). (Pereira et al. 2017c; Dinis et al. 2018) and test for the existence Overlying sequences are represented by lower Carboniferous syn- of more than one potential source or mixed provenance. The orogenic marine sedimentary and volcanic rocks (Cabrela U–Pb data for the Algarve Triassic sandstone obtained in the Formation and Toca da Moura volcanic–sedimentary complex; present study are compared with a compilation of detrital zircon Pereira et al. 2012a and references therein), early to late ages from siliciclastic rocks of SW Iberia (upper Neoproterozoic Carboniferous Baleizão porphyries and upper Carboniferous ter- to Permian; Pereira et al. 2008, 2012a,b, 2017b; Linnemann restrial siliciclastic rocks of the Santa Susana Basin (Oliveira et al. et al. 2008; Braid et al. 2011; Rodrigues et al. 2015; Pérez- 1991; Machado et al. 2012) (Fig. 3). In SW Iberia, the Rheic suture Cáceres et al. 2017; Dinis et al. 2018), Nova Scotia (lower has been interpreted as being marked by a narrow band of Neoproterozoic to Devonian; Waldron et al. 2009, 2011; amphibolite, with c. 340 Ma protolith ages (Azor et al. 2008) from Henderson et al. 2016; White et al. 2018) and NW Morocco the Beja-Acebuches Ophiolitic Complex (Quesada et al. 1994), (Cambrian; Pérez-Cáceres et al. 2017) using the Kolmogorov– separating the OMZ, to the north, from the PLZ and the SPZ, Smirnov (K–S) statistical test (DeGraaff-Surpless et al. 2003; to the south. Middle–upper Devonian strata are almost absent Barbeau et al. 2009; Vermeesch, 2013) and multidimensional scal- in the OMZ (Robardet & Gutiérrez Marco, 2004). ing (MDS; Vermeesch, 2013, 2018; Spencer & Kirkland, 2015). The PLZ stratigraphy includes upper Devonian (and possibly These statistical tools provide useful means for verifying whether older) to lower Carboniferous metasedimentary formations. The the zircon age populations found in the Ediacaran to Permian oldest strata of the Pulo do Lobo, Gafo, Atalaia and Ribeira de siliciclastic rocks of SW Iberia were reproduced faithfully in the Limas formations are unconformably overlain by the siliciclastic Algarve Triassic sandstone as a result of sediment recycling, or rocks of the Horta da Torre, Santa Iria and Represa formations whether there was input from other sources, such as Nova (Pereira et al. 2007) (Fig. 3). In this zone, two stratigraphic units Scotia (Maritime Canada) and NW Morocco (NW Africa). are described as block-in-matrix mélanges: (i) the Alájar Mélange, which resulted from the deformation of quartzitic beds of the Horta da Torre Formation, and (ii) the Péramora Mélange, which 2. Geological setting consists of blocks of mafic rocks in a schistose mafic matrix. Both SW Iberia, Nova Scotia and NW Morocco are separated segments these mélanges have been assigned to the lower Carboniferous of the late Palaeozoic Appalachian–Variscan orogenic belt (Matte, (Dahn et al. 2014; Pérez-Cáceres et al. 2015) (Fig. 3). The PLZ 2001; Nance et al. 2010; Murphy & Nance, 2013) (Fig. 1) showing a was recently interpreted as being a Devonian back-arc basin pre-Mesozoic stratigraphy that demonstrates common periods of located on the Laurussian active margin associated with Rheic evolution but also points to periods during which they evolved Ocean subduction (Rubio Pascual et al. 2013; Pereira et al. independently, and are thus marked by notable stratigraphic 2017b), a tectonic framework also being proposed for equivalent differences. units in the Rheno-Hercynian Zone in Central Europe (Eckelmann et al. 2014; von Raumer et al. 2017). In the SPZ, the oldest strata known consist of siliciclastic (São 2.a. SW Iberia Luis Formation; Oliveira, 1984) and volcanic rocks, dated at c. 374 In SW Iberia, the Variscan belt includes the Ossa–Morena Zone Ma (Cercal volcanic rocks; Rosa et al. 2009), of the Pyrite Belt (OMZ, Gondwanan side) that is separated from the Pulo do (Oliveira et al. 2013 and references therein) (Fig. 3). The Pyrite Lobo and South Portuguese zones (PLZ and SPZ, Laurussian side) Belt stratigraphy also includes upper Devonian – lower by the Beja-Acebuches Ophiolitic Complex (Variscan suture zone) Carboniferous siliciclastic rocks (Phyllite-Quartzite Formation;

(a) Caledonian belt

A BALTICA LAURENTI Appalachian-Variscan belt

Paleotethys Ocean GONDWANA BA

CAL (b)

BA- Baltica CAL- Caledonides RH- Rheno-Hercynian Zone ST- Saxo-Thuringian Zone MGC- Mid-Ferman Crystalline High ST NP- Northern Phyllite Zone RH GD- Ganderia ´ EA- East Avalonia LR- Laurentia MGC CZ- Cantabrian Zone GD WALZ- West Asturio-Leonese Zone NP GTMZ- Galicia-Trás-os-Montes Zone CIZ- Central-Iberian Zone EA CB- Coastal Block CM- Central Meseta riscan Front Va GD

Front

WALZ LR ppalachian A ariscan suture zone CZ V

LR GD GTMZ Porto-Tomar CIZ fault zone GD Fig. 1. (Colour online) (a) Inset with location of SW Ossa-Morena Zone Iberia, Nova Scotia and NW Morocco in the West Avaloni a Appalachian–Variscan belt (modified from Matte, Minas fault zone 2001; Murphy & Keppie, 2005). (b) Tectonic map with PulodoLobo Zone SW IBERIA regional distribution of the main Palaeozoic terranes Meguma Terrane South Portuguese Zone of the Appalachian–Variscan belt showing location of NOVA SCOTIA the South Portuguese, Pulo do Lobo and Ossa– SehoulBlock Morena zones (SW Iberia), Sehoul Block (NW Morocco) and West Avalonia and Meguma Terrane (Nova NW MOROCCO Scotia). CIZ – Central Iberian Zone; CZ – Cantabrian – – – CB Zone; WALZ West Asturian Leonese Zone; GTMZ CM Galicia-Trás-os-Montes Zone; STZ – Saxo-Thuringian Zone; GD – Ganderia; LR – Laurentia (modified from van Staal & Barr, 2012; von Raumer et al. 2017; Pereira et al. 2017b).

Oliveira, 1990) conformably overlain by an upper Devonian – Oliveira, 1990) overlie the Mira and Quebradas formations lower Carboniferous Volcanic–Sedimentary Complex (Oliveira, (Fig. 3). The Permian terrestrial siliciclastic and volcanic rocks 1990) (Fig. 3). The Phyllite-Quartzite Formation unconformably of the Viar Basin present an unconformable sedimentary contact overlies the Ronquillo Formation, presenting siliciclastic rocks with the Devono-Carboniferous rocks of the SPZ to the south that have yielded a maximum depositional age of c. 400 Ma (Sierra et al. 2009). The basement of the SPZ is not exposed but (Pérez-Cáceres et al. 2017) (Fig. 3). Upper Devonian – lower its identity has been inferred geochemically to be that of Carboniferous siliciclastic rocks also occur in the Aljezur and Meguma/Avalonian type (de la Rosa et al. 2002; Braid et al. Bordeira antiforms of SW Portugal (Tercenas Formation; Oliveira, 2011, 2012; Murphy et al. 2015; Pereira et al. 2017b). 1990), and are overlain by lower to upper Carboniferous turbiditic rocks of the Carrapateira Group (Bordeira, Murração and 2.b. Nova Scotia Quebradas formations; Oliveira, 1990) (Fig. 3). The Volcanic– Sedimentary Complex of the Pyrite Belt is overlain by lower to In Nova Scotia, the northern Appalachian belt includes the upper Carboniferous siliciclastic rocks of the base of the Baixo Meguma Terrane to the south, separated by the Minas fault zone Alentejo Flysch Group (Mértola and Mira formations; Oliveira, extending from West Avalonia to the north (Murphy et al. 2011) 1990) (Fig. 3). The youngest upper Carboniferous siliciclastic (Fig. 1). Some authors consider that Meguma and West Avalonia strata of the Baixo Alentejo Flysch Group (Brejeira Formation; shifted together as part of the same terrane after drifting away from

N PTFZ Cabrela 40 km 1

9º00’W Evora Santa 2 Susana

ALENTEJO St4Sc4 BASIN St4St3 Monesterio Beja Ts3St4 Sines

3 Viar Pulo do Lobo 4 Cercal

37º30’N Mértola Alznalcollar

Meso-Cenozoic sedimentary rocks

MESOZOIC

Amado beach Cretaceous granitic rocks and gabbros samples for U-Pb geochronology: Silves Cm2 AMA-1, AMA-3, Am1 Cretaceous-Jurassic AMA-4 & AMA-5 sedimentary and volcanic rocks Tl1 Triassic sedimentary rocks ALGARVE BASIN Th4 PRE-MESOZOIC (western sector) Faro Sagres S.Bartolomeu de Messines Granitic rocks & gabbro-diorites N=42 0 Permian samples for U-Pb geochronology: (Tournaisian-Bashkirian)) sedimentary and volcanic rocks (3- VIAR basin) SBM-6 & SBM-7 OSSA-MORENA ZONE SOUTH PORTUGUESE ZONE ALGARVE BASIN Bordeira and Aljeur antiforms Ediacaran-Carboniferous; (Southwest Portugal): 270 90 (central sector) 0 (1- Tournaisian-Visean CABRELA Fm.; N=54 2- Kasimovian-Gzhelian SANTA SUSANA Fm.) BREJEIRA Fm. (Bashkirian-Moscovian) BEJA-ACEBUCHES BORDALETE-MURRAÇÃO- OPHIOLITIC COMPLEX QUEBRADAS Fm. 180 270 90 (Early Carboniferous) (Tournaisian-Bashkirian) Sites with paleocurrent measurements (N) TERCENAS Fm. PULO DO LOBO ZONE Measurements N>4 (Famennian-Tournaisian) Mensurements N<4 HORTA DA TORRE Fm. SOUTH PORTUGUESE ZONE Standard deviation 180 (Tournaisian-Visean) Pyrite Belt: Average direction SANTA IRIA & REPRESA Fm. MIRA Fm. (Famennian-Tournaisian) (Serpukhovian-Bashkirian) Late Triassic samples GAFO Fm. MÉRTOLA Fm. (previous studies of U-Pb geochronology): (Frasnian) (Visean-Serpukhovian) Dinis et al. 2018 RIBEIRA DE LIMAS Fm. VOLCANIC-SEDIMENTARY COMPLEX (Frasnian) (Famennian-Visean; Pereira et al. 2017a 4- Famennian CERCAL felsic volcanic rocks) ATALAIA Fm. (Frasnian) PHYLLITE-QUARTZITE Fm. (Upper Famennian-Tournaisian) PULO DO LOBO Fm. (Frasnian-Givetian?) RONQUILLO Fm. (Frasnian-Givetian?)

Fig. 2. (Colour online) Simplified geological map of SW Iberia showing the late Triassic Algarve and Alentejo basins and the pre-Mesozoic basement comprising the South Portuguese, Pulo do Lobo and Ossa–Morena zones (modified from Oliveira, 1990; Pereira et al. 2017b; Pérez-Cáceres et al. 2017) with sample locations used for U–Pb geochronology. Rose diagrams shows palaeocurrent directions measured in the Algarve Triassic sandstone of the central and western sectors (modified from Palain, 1979). PTFZ – Porto- Tomar fault zone.

Gondwana in early Ordovician time, and resided on the same mar- (Fig. 3). The oldest strata belong to the Gamble Brook Formation gin of the Rheic Ocean from early Silurian to early Devonian times siliciclastic rocks, presenting a c. 975 Ma maximum depositional (Keppie & Krogh, 2000; Murphy et al. 2004b). Others infer a two- age (Henderson et al. 2016), while the youngest siliciclastic rocks stage accretion of the West Avalonia and Meguma terranes along interbedded with c. 628–618 Ma volcanic rocks are included in the the Laurentian margin from late Silurian to late Devonian times Georgeville and Jeffers groups, which are intruded by c. 607–604 (van Staal et al. 2009). The question remains unresolved as to Ma granitic rocks (Murphy et al. 1997) (Fig. 3). The Palaeozoic rec- whether West Avalonia and the Meguma Terrane were definitely ord begins with Cambrian to lower Ordovician siliciclastic rocks, a separated by oceanic lithosphere rather than thinned continental few carbonate rocks and bimodal volcanic rocks from the Iron and/or transitional crust (van Staal & Barr, 2012). Late Brook and McDonalds Brook groups (Keppie et al. 1997 and refer- Devonian – early Carboniferous subduction of the Rheic oceanic ences therein), unconformably overlain by siliciclastic rocks of the lithosphere is suggested as a cause of widespread arc magmatism Dunn Point and McGillivray Brook formations associated with in the Meguma Terrane (Moran et al. 2007), which preceded the c. 460–455 Ma volcanic rocks (Hamilton & Murphy, 2004; Laurussia–Gondwana collision. Murphy et al. 2012). These Ordovician rocks are overlain by The stratigraphy of West Avalonia includes Neoproterozoic to Silurian to lower Devonian siliciclastic rocks and minor ash beds middle Devonian rocks (Nance et al. 2002 and references therein) of the Arisaig Group (Murphy et al. 2004a,b, 2008) (Fig. 3). The

SW IBERIA NOVA SCOTIA NW MOROCCO

SOUTH PORTUGUESE ZONE PULO DO LOBO ZONE OSSA-MORENA ZONE MEGUMA TERRANE WEST AVALONIA SEHOUL BLOCK

Age (Ma) Bordeira and Aljezur antiforms Permian 299 (Southwest Portugal) VRB 8 PC Upper Carboniferous Pyrite belt SS CBL 323 BJ GW LR 7 QB GW MR LR LR MB Lower LR LR BAOC MU MT HT AJ CB WD Carboniferous GW 11 BD VSC 5 SI PR 5 4 TM 4, 6 13 HR 359 LR TC LR PQ REP FLK 14 Upper Devonian LR CVR SL 12 383 GF RL MAB Mid Devonian RO LR LR AT PL LR 393 TR Lower Devonian GW 419 RS 10 RN XR AR Silurian XN WR 444 CL Laurussian (Avalonia and/or Meguma terrane) basement? GW BR DP, MGV Ordovician 3 HF 485 GW OS,FT AM, KN MRV GD Cambrian GW ERV 2 IB, MB 541 9 GW SNG 1 GV, JF Neoproterozoic Gondwanan-type source CZO GW Carbonate rocks Maﬁc volcanic rocks GB

Siliciclastic marine rocks Gondwanan basement? LR Laurussian-type source Maﬁc-Ultramaﬁc rocks (West Avalonia and/or Meguma) Siliciclastic terrestrial rocks Plutonic rocks LR Laurussian-type source (Laurentia and/or Baltica) Felsic volcanic rocks

Abbreviations: South Portuguese Zone- TC, Tercenas Fm;BD , Bordalete Formation;MU , Murração Fm;QB , Quebradas Fm;BJ , Brejeira Fm;RO , Ronquillo Fm;PQ , Phyllite-Quartzite Fm;SL , São Luis Fm;CVR , Cercal porphyries; VSC, Pyrite belt Volcanic-Sedimentary Complex;VRB , Viar basin;MT , Mértola Fm;MR , Mira Fm; Pulo do Lobo Zone- PL, Pulo do Lobo Fm;AT , Middle- Atalaia Fm;GF , Gafo Fm;REP , Represa Fm;RL , Ribeira de Limas Fm;SI , Santa Iria Fm;HT , Horta da Torre Fm;PR , Péramora Mélange;AJ , Alájar Mélange; BAOC, Beja-Acebuches Ophiolitic Complex; Ossa-Morena Zone- CZO, Calzadilla Ophiolite;SNG , Serie Negra Gp;ERV , Early Rift Volcanism;MRV , Main Rift Volcanism;OS , Ossa Fm;FT , Fatuquedo Fm;BR , Barrancos Fm;CL , Colorada Fm;XN , “Xistos com Nódulos” Fm; XR, “Xistos Raiados” Fm;RS , Russianas Fm;TR , Terena Fm;CB , Cabrela Fm;SS , Santa Susana Fm;TM , Toca da Moura Volcanic-Sedimentary Complex; Meguma Terrane- GD, Goldenville Gp; HF , Halifax Gp; RN , Rockville Notch Gp; WR , White Rock Fm; West Avalonia- GB, Gamble Brook Fm;GV , Georgeville Gp;JF , Jeffers Gp;IB , Iron Brook Gp;MB , McDonalds Brook Gp;DP , Dunn Point Fm;MGV , McGillivray Fm;AR , Arisaig Group; Meguma Terrane/West Avalonia- MAB, McArras Brook Fm; FLK , Fountain Lake Gp; HR , Horton Gp; WD , Windsor Gp; MB , Mabou Gp; CBL , Cumberland Gp., PC , Pictou Gp. Sehoul Block- KN, Kern Nesrani Fm., AM , Allal ben Mehdi Fm.;

Fig. 3. (Colour online) Time–space distribution of potential sources for Algarve Triassic sandstone. Summary of the stratigraphy of the South Portuguese, Pulo do Lobo and Ossa–Morena zones (modified from Oliveira, 1990; Robardet & Gutiérrez-Marco, 2004; Pereira et al. 2017b and references therein; Pereira & Gama, 2017; Arenas et al. 2018), Meguma Terrane and West Avalonia (modified from Waldron et al. 2013; Murphy et al. 2018; White et al. 2018) and Sehoul Block (modified from El Hassani, 1994a; Michard et al. 2010). Plutonic rocks: 1 – Sardoal orthogneiss and Mouriscas amphibolite (Henriques et al. 2015); 2 – Barreiros granitic rocks (Sánchez-Garcia et al. 2013); 3 – Arronches and Cevadais orthogneiss and Elvas syenite (Díez Fernández et al. 2015); 4 – Beja gabbro and diorite (Pin et al. 2008); 5 – Sierra North batholith granitic rocks (Gladney et al. 2014); 6 – Évora Massif granitic rocks and gabbro-diorite (Pereira et al. 2015a; Moita et al. 2015); 7 – Pavia Massif granitic rocks (Lima et al. 2012; Dias da Silva et al. 2018); 8 – Santa Eulália–Monforte Massif granitic rocks and gabbro-diorite (Pereira et al. 2017a); 9 – Debert River granodiorite and Greendale Complex appinite (Doig et al. 1991; Murphy et al. 1997); 10 – Mavillette gabbro (Warsame et al. 2017); 11 – Hart Lake–Byers Lake granite (Pe-Piper & Piper, 2002 and references therein); 12 – South Mountain Batholith leucogranite and Birchtown diorite (Tate & Clarke, 1995 and references therein; Clarke et al. 1997); 13 – Seal Island Pluton and Wedgeport Pluton monzogranites (MacLean et al. 2003; Moran et al. 2007); 14 – Rabat granitic rocks (Tahiri et al. 2010).

contact between the Arisaig Group and the youngest Devonian transition is marked by terrestrial siliciclastic sequences of the volcanic and siliciclastic rocks of the McAras Brook Formation Mabou and Cumberland groups, with upper Carboniferous – is marked by an angular unconformity (Braid & Murphy, 2006). lower Permian terrestrial red beds of the Pictou Group towards The McAras Brook Formation, predominately composed of inter- the top (Fig. 3). In Nova Scotia, the Permian terrestrial siliciclastic bedded siliciclastic rocks and basalts, is coeval with the Fountain rocks of the Honeycomb Point Formation are included in the Lake Group, which includes felsic volcanic rocks associated with Fundy Group, which is essentially composed of middle–upper plutons dated at c. 363–350 Ma (Doig et al. 1996; Pe-Piper & Triassic terrestrial siliciclastic sequences (Sues & Olsen, 2015 Piper, 2002; Murphy et al. 2018 and references therein) (Fig. 3). and references therein). The Meguma Terrane stratigraphy is composed of Cambrian to lower Ordovician siliciclastic rocks (Goldenville and Halifax 2.c. NW Morocco groups) unconformably overlain by Silurian to lower Devonian siliciclastic and volcanic rocks (Rockville Notch Group) (White & In NW Africa, the Moroccan Meseta is the southernmost extension Barr, 2010 and references therein) (Fig. 3). At the base of the of the Variscan belt. It includes the Sehoul Block, which is sepa- Rockville Notch Group there is the White Rock Formation rated from the northern tip of the Western Meseta by the Rabat (White & Barr, 2017), including volcanic rocks dated at Tiflet fault zone/Sehoul thrust (Simancas et al. 2009; Tahiri c. 446–434 Ma (Keppie & Krogh, 2000;Whiteet al. 2018)(Fig.3). et al. 2010). The Sehoul Block stratigraphy includes lower–middle These lower Palaeozoic units are intruded by c. 382–357 Ma plutons Cambrian phyllites and metasandstones (Allal ben Mehdi and (including the South Mountain Batholith; Moran et al. 2007 Kern Nesrani formations; El Hassani et al. 1994a) unconformably and references therein). In Nova Scotia, upper Devonian – lower overlain by lower Carboniferous terrestrial conglomerates Carboniferous siliciclastic rocks unconformably overlie both (Michard et al. 2010 and references therein; Pérez-Cáceres et al. West Avalonia and the Meguma Terrane (Murphy et al. 2008; 2017) (Fig. 3). Cambrian siliciclastic rocks experienced late Waldron et al. 2013 and references therein). Upper Devonian – Ordovician deformation and metamorphism (El Hassani et al. lower Carboniferous fluvial and lacustrine siliciclastic rocks of the 1994b; Michard et al. 2010) and are intruded by the late Horton and Fountain Lake groups are overlain by lower Devonian Rabat Massif granitic rocks (c. 367 Ma; Tahiri et al. Carboniferous marine siliciclastic, carbonate and evaporitic rocks 2010). The Sehoul Block has been interpreted as a fragment of the Windsor Group (Fig. 3). The early–late Carboniferous of Avalonia (Hoepffner et al. 2005; Simancas et al. 2005;

(schematic section of Telheiro-Amado beach) (schematic section of São Bartolomeu de Messines)

Palain, 1975, Manuppella, 1988; Manuppella, 1988; Palain, 1976 1976 Rocha, 1976 Rocha, 1976

Volcanic-sedimentary C I complex

S Volcanic-sedimentary

S complex Hettangian-Sinemurian A

R Hettangian-Sinemurian

C Limestone overlying basalt

I U

S (ca.199-198 Ma; Verati et al., 2007) J

S and maﬁc pyroclastic layers with R

Pelite-Carbonate- A E

AB 3 Evaporitic Complex R interbedded pelitic dolostone (20-70m) U

W Non-exposed J

O Hettangian L Pelitic dolostone and R Pelite-Carbonate- dolostone (5-15m) E AB 3 Evaporitic Complex ? W 100m

O Hettangian L Pelite with interbedded Pelitic dolostone and

AB 2 sandstone and dolostone, ? dolostone (5-15m) C I inclunding evaporite S (2-100m) S Pelite with interbedded

A AB 2

I sandstone and dolostone,

C R

Silves Sandstone I inclunding evaporite T AB 1 S (2-100m)

Carnian S

R Sample AMA-5

A E

Sandstone with I Sample SBM-7

P Sample AMA-4

interbedded conglomerate R Silves Sandstone P Sample AMA-3 T Carnian U and pelite (25-70m) Sample SBM-6 Sample AMA-1 R AB 1 Angular E Sandstone with interbedded

P conglomerateand mudstone P S unconformity

U (25-70m)

R South Portuguese Zone

E São Bartolomeu

F Brejeira Formation I de Messines Mudstone N Previously deformed AA

O R Bashkirian-Moscovian Mudstone with interbedded

R P turbidites silstone a dolostone (1-90m)

P A

U C Angular

S unconformity

R South Portuguese Zone

F Mira Formation

- N Previously deformed

R O Serpukhovian-Bashkirian

E Dolostone and limestone B

R W turbidites

C Yellowish-gray pelitic dolostone

Maﬁc volcanic rocks

Greenish gray mudstone and siltstone Reddish sandstone Greywacke, siltstone and mudstones Phytosaur fossils rocks Evaporitic rocks Yellowish-pink sandstone Conglomerate Greywacke, siltstone and mudstones

Reddish-brown mudstone and siltstone

Fig. 4. (Colour online) Schematic stratigraphy of the late Triassic Algarve Basin western and central sectors. Modified from Palain (1976), Pereira et al. (2017c)andPereira&Gama(2017).

Pérez-Cáceres et al. 2017) or the Meguma Terrane (Schenk, 1997; deformed lower to upper Carboniferous Baixo Alentejo Flysch Michard et al. 2010). The Sehoul Block is separated from the Group (Oliveira, 1990). Thus, stratigraphic contact is made with Gondwanan margin by the Sehoul thrust (Tahiri et al. 2010), being the Brejeira Formation (Bashkirian–Moscovian) in the western the Palaeozoic suture most probably located offshore Morocco sector, the Mira Formation (Sepukhovian–Bashkirian) in the cen- (Michard et al. 2010). The Laurussia–Gondwana boundary in tral sector and the Mértola Formation (Visean–Serpukhovian) in Africa could correspond to the Rheic Ocean suture described the eastern sector (Fig. 4). The sedimentary record of the Triassic southwards in the Mauritanides (Gärtner et al. 2013 and references (Silves Group) starts, in the central sector, with a discontinuous therein), but this topic is still under debate. unit of brown-reddish mudstone with interbedded siltstone, which is up to 100 m thick (the São Bartolomeu de Messines Mudstone, 2.d. Algarve basin Manuppella, 1988; AA unit, Palain, 1976) (Fig. 4). This member is The upper Triassic sedimentary rocks of the Algarve Basin (Silves overlain by a 10 to 150 m thick unit mainly composed of reddish to Group) rest with an angular unconformity on the previously yellowish, fine- to coarse-grained sandstone and minor siltstone

and mudstone with parallel and oblique bedding, including palaeo- 20 measurements, regardless of whether they are of different sizes) channels filled with conglomerate (Silves Sandstone, Manuppella, showing that the two populations do not derive from the same 1988; AB1 unit, Palain, 1976) (Fig. 4). These terrestrial deposits are source (Barbeau et al. 2009). The probability of the observed typical of sedimentary environments with alluvial fans separated D-value being unrelated to age differences between the two pop- by rivers and alluvial plains with temporary meander-form rivers ulations is given by a P-value corresponding to a confidence inter- under semi-arid climatic conditions, in which evaporites formed val of 95 % (Barbeau et al. 2009). High D-values and low P-values (Choffat, 1887; Palain, 1976, 1979; Azerêdo et al. 2003). indicate that the observed difference between the two populations Samples Sbm-6 and Sbm-7 and samples Ama-1, Ama-3, Ama-4 may be explained by the existence of distinct origins (Pereira et al. and Ama-5 were collected from the Silves Sandstone beds of the 2016a and references therein). Two detrital zircon age populations central and western sectors of the Algarve Basin, respectively are linked to the same source if P-values are higher than 0.05 (Figs 2, 4). The overlying Silves Sandstone, a 50 to 180 m thick (Guynn & Gehrels, 2010). P-values falling within the range sequence composed of reddish and greenish mudstone, siltstone 0.001 < P-value < 0.05 suggest a degree of proximity between and yellowish dolostone, is interlayered with discontinuous beds the two populations. If P-values are lower than 0.001, the two pop- of fine-grained sandstone and evaporitic rocks (AB2 unit, ulations are probably significantly different, indicating distinct Palain, 1976; Pelite–Carbonate–Evaporite complex, Manuppella, sources (Fernández-Suárez et al. 2014). 1988) (Fig. 4), suggesting a shallow-marine and/or coastal lagoon In the present study, a detailed analysis was conducted by com- environment (Azerêdo et al. 2003). The palaeontological remains paring the different detrital zircon age populations of the Triassic of a terrestrial and semi-aquatic vertebrate (bones and teeth of a sandstone of the Algarve Basin with potential sources from SW phytosaur specimen) were found in the AB2 unit indicating a late Iberia and Nova Scotia using the K–S test complemented by Triassic (Carnian–Norian) biostratigraphic age (Steyer et al. 2011; MDS diagrams. The MDS technique provides a means to compare Mateus et al. 2014). Lower Jurassic grey-yellowish dolostone beds samples based on quantified pairwise comparisons of their detrital interlayered with basalt, mafic breccia and tuff (AB3 unit, Palain, zircon ages, and is extremely useful for visualizing the level of sim- 1976; volcanic–sedimentary complex, Manuppella, 1988; Martins ilarity of samples in a two-dimensional space (Vermeesch, 2013; et al. 2008) overlie the Triassic strata of the Algarve Basin. Spencer & Kirkland, 2015). MDS was used to transform a matrix of pairwise similarities among detrital zircon age populations into Cartesian coordinates in a two-dimensional space, where greater 3. Methods distances between samples represent a greater degree of dissimilar- Zircon grains for U–Pb geochronology were selected using traditional ity between points on the MDS diagrams (Wissink et al. 2018). K–S techniques: density separation using a Wilfley table (Universidad analyses were carried out using an Excel spreadsheet published on Complutense de Madrid); granulometric separation using sieves with the University of Arizona Geochronological Center website at: mesh size less than 500 microns; and mineral identification using a https://sites.google.com/a/laserchron.org/laserchron/. MDS dia- binocularlensandpreparationofepoxyresinmountswithzircon grams were produced using IsoplotR (Vermeesch, 2018). grains (University of Évora). Cathodoluminescence imaging used to select targets and U–Pb measurements were performed at Trinity College Dublin using laser ablation inductively coupled 4. Results plasma mass spectrometry (LA-ICP-MS), following the previously described procedure by Crowley & Strachan (2015). Probability den- Samples Ama-1, Ama-3, Ama-4 and Ama-5 are fine to medium sity plots and histograms were done using Isoplot 4 (Ludwig, 2003), grained and poorly to well sorted, with sub-angular to rounded using 90–110 % concordant 206Pb–238U ages for grains younger than grains. Quartz grains are dominant while white mica, K-feldspar 1.0 Ga, and 207Pb–206Pb ages for the older grains (for details see Frei & and plagioclase are poorly represented. Some centimetre-thick Gerdes, 2009). U–Th–Pb results are listed in online Supplementary layers of sandstone are only constituted by opaque minerals. Material Tables S1–S6. Rock fragments are mostly made of pelite and have an elongated The K–S test was used to compare the distinct populations of shape, and there is also some limestone, chert and quartzite. The detrital zircon U–Pb ages obtained. This is a non-parametric stat- composition of the cement is characterized as being carbonate and istical tool that has been used successfully for sedimentary prov- ferruginous. enance studies due to the fact that it enables the comparison of Of a total of 120 spots measured in sample Ama-1, 117 yielded two populations of detrital zircon U–Pb ages by evaluating whether 90–110 % concordant ages (Fig. 5a). Only 5 % of ages are they are significantly different, i.e. indicating whether zircon age Palaeozoic, 93 % are Proterozoic and 2 % are Archaean (c. 3.3, populations correlate with a similar source or not (DeGraaff- 2.9 and 2.6 Ga). Palaeozoic ages range from c. 531 Ma to c. 408 Surpless et al. 2003; Barbeau et al. 2009). The test procedure Ma, including 3 % Silurian grains (c. 444, 424 and 420 Ma). involves a ‘null hypothesis’, which assumes that if the two popula- Neoproterozoic grains (74 %) are widespread at c. 633–547 Ma tions are similar they probably share a common source, and an (49 % Ediacaran), c. 698–636 Ma (18 % Cryogenian) and ‘alternative hypothesis’, which assumes that the two populations c. 997–722 Ma (7 % Tonian). Palaeoproterozoic zircon grains are distinct and do not come from the same source (Guynn & (11 %) are distributed over the age interval of c. 2.4–1.7 Ga, and Gehrels, 2010). The K–S test is carried out by ordering the zircon Mesoproterozoic ages (8 %) are 1.5–1 Ga. ages of two different populations separately and then plotting Of a total of 121 spots measured in sample Ama-3, 118 yielded cumulative curves of the frequency of zircon ages. The maximum 90–110 % concordant ages (Fig. 5b). The majority of zircon grains vertical difference between the cumulative curves is compared present Precambrian ages (97 %), and only 3 % Palaeozoic ages using D-values (Guynn & Gehrels, 2010). The K–S test fails if (Cambrian, c. 519 Ma; Devonian, c. 416 and 414 Ma). The the D-value is greater than a critical distance (set by choosing a Proterozoic population is dominated by Neoproterozoic grains confidence interval that contributes to the cumulative function (74 %: 51 % Ediacaran, c. 634–549 Ma; 19 % Cryogenian, if the values obtained are shown to be significant after more than c. 717–636 Ma; and 4 % Tonian, c. 866–736 Ma), followed by

(a) (d) 60 Sample Ama-1 1%Devonian 80 Sample Ama-5 Amado beach Amado beach 2%Archean 3%Silurian sandstone (n=117) 70 sandstone (n=121) 2%Devonian 50 1%Cambrian 11%Paleoproterozoic 17%Paleoproterozoic

R R 60

a 40 a

i i 11%Mesoproterozoic

v v 50

r 8%Mesoproterozoic r

e e

r r

m m

o 30 o 40

b 7%Tonian b

a a

b b 4%Tonian

t 30 t 20 y y 18%Cryogenian 20 14%Cryogenian 52%Ediacaran 10 49%Ediacaran 10

0 0 0 500 1000 1500 2000 2500 3000 3500 4000 0 500 1000 1500 2000 2500 3000 3500 4000 Age (Ma) Age (Ma) (b) (e) Sample Ama-3 Sample Sbm-6 2%Ordovician 70 35 Amado beach 2%Devonian S. Bartolomeu Messines 1%Silurian sandstone (n=118) sandstone (n=109) 2%Archean 1%Cambrian 1%Permian 7%Cambrian 60 30 13%Archean

R 12%Paleoproterozoic R

a 50 25 a

i 9%Mesoproterozoic i

v v

r r 17%Paleoproterozoic

e e

p p

b b 40 20

o o

b 4%Tonian b

i 30 15 i

l 7%Mesoproterozoic l

i i

y y 8%Tonian 20 19%Cryogenian 10 14%Cryogenian 10 51%Ediacaran 5 30%Ediacaran

0 0 0 500 1000 1500 2000 2500 3000 3500 4000 0 500 1000 1500 2000 2500 3000 3500 4000 Age (Ma) Age (Ma) (c) (f) 40 90 Sample Sbm-7 1%Carboniferous Sample Ama-4 1%Carboniferous 1%Devonian Amado beach 1%Devonian 35 S. Bartolomeu Messines 1%Permian 80 sandstone (n=132) 3%Archean 1%Ordovician sandstone (n=105) 1%Triassic 1%Ordovician 1%Cambrian 9%Archean 4%Cambrian 70 30

R 11%Paleoproterozoic R

e e

l l 16%Paleoproterozoic

a 60 a 25

t 7%Mesoproterozoic t

e e

b b 50

r r 20

b b 9%Mesoproterozoic

a a

N N 40 11%Tonian

b b

l l 15

y 30 9%Tonian 10%Cryogenian 10 20 32%Ediacaran 56%Ediacaran 17%Cryogenian 5 10

0 0 0 500 1000 1500 2000 2500 3000 3500 4000 0 500 1000 1500 2000 2500 3000 3500 4000 Age (Ma) Age (Ma)

Fig. 5. (Colour online) Zircon age spectra and pie charts showing the age distribution of detrital zircons from the Triassic sandstone sampled in the western (a–d) and central (e, f) sectors of the Algarve Basin.

Palaeoproterozoic (12 %, c. 2.5–1.8 Ga) and Mesoproterozoic c. 484 Ma and Cambrian, c. 501 Ma) and Archaean (3 %, c. 2.5, (9 %, c. 1.5–1 Ga) grains. Archaean grains are rare (2 %, 2.6 and 2.8 Ga). The Precambrian population is dominated by c. 3.3–2.6 Ga). Neoproterozoic grains (77 %: 56 % Ediacaran, c. 635–551 Ma; Of a total of 135 spots measured in sample Ama-4, 132 yielded 10 % Cryogenian, c. 716–636 Ma; and 11 % Tonian, c. 991–983 90–110 % concordant ages (Fig. 5c). Proterozoic zircon ages are Ma), followed by Palaeoproterozoic (11 %, c. 2.1–1.6 Ga) and dominant (94 %) and the remaining grains are Palaeozoic (3%: Mesoproterozoic (7 %, c. 1.4–1 Ga) grains, and rare grains with Carboniferous, c. 348 Ma; Devonian, c. 413 Ma; Ordovician, Archaean ages (c. 2.8–2.5 Ga).

Of a total of 123 spots measured in sample Ama-5, 121 yielded (ii) OMZ Ediacaran–Cambrian siliciclastic rocks as a potential 90–110 % concordant ages (Fig. 5d). A total of 101 yielded Gondwanan-type source. In addition, a comparison was made Precambrian ages (98 %), and only two grains presented between the detrital zircon ages of the Algarve Triassic sandstone Palaeozoic ages (2 %: Devonian, c. 413 Ma and c. 383 Ma). The and those of Cambrian siliciclastic rocks from the Sehoul Block, Proterozoic population is dominated by Neoproterozoic grains which has been identified as part of the Laurussian margin (70 %: 52 % Ediacaran, c. 633–547 Ma; 14 % Cryogenian, (Schenk, 1997; Hoepffner et al. 2005; Simancas et al. 2005; c. 719–635 Ma; and 4 % Tonian, c. 929–721 Ma), followed by Michard et al. 2010). The most significant differences between Palaeoproterozoic (17 %, c. 2.4–1.7 Ga) and Mesoproterozoic the detrital zircon populations of the Algarve Triassic sandstone (11 %, c. 1.6–1 Ga) grains. There are no Archaean ages. are the higher percentages of Neoproterozoic ages (70–77 %), in Samples Sbm-6 and Sbm-7 are fine to medium grained, poorly particular Ediacaran (49–56 %), in the western sector, contrasting to well sorted, with sub-angular to rounded grains and carbonate with the higher percentages of Archaean (9–13 %) and Palaeozoic and ferruginous cement. Quartz grains are dominant, opaque min- (9–11 %) zircon grains found in the central sector (Fig. 5). This erals are present in thin-layers, while K-feldspar and white mica are lateral change in sources may be caused by sediment transport rare. Rock fragments include pelite, chert and quartzite. derived from independent drainage systems, which is most likely, Of a total of 117 spots measured in sample Sbm-6, 109 yielded where the catchment zones of palaeo-rivers were located in distinct 90–110 % concordant ages (Fig. 5e). The population of detrital zir- terrane sources (Gondwanan- and Laurussian-type) (Fig. 8). con is dominated by Proterozoic (76 %), Archaean (13 %) and The fact that Palaeozoic detrital zircon grains occur in the Palaeozoic (11 %) ages. Proterozoic grains are dominated by Algarve Triassic sandstone without a great representation of late Neoproterozoic ages (52 %: 30 % Ediacaran, c. 621–548 Ma; Palaeozoic ages made the K–S test very sensitive in terms of achiev- 14 % Cryogenian, c. 719–638 Ma; and 8 % Tonian, c. 988–736 ing a comparison with Devonian, Carboniferous and Permian sil- Ma), and also contain Palaeoproterozoic (17 %, c. 2.2–1.8 Ga) iciclastic rocks from SW Iberia, indicating that some of these do and Mesoproterozoic (7 %, c. 1.6–1 Ga) ages. The Palaeozoic pop- not provide potential sources. The K–S test results show that the ulation includes Cambrian (7 %, c. 541–502 Ma), Ordovician (2 %, U–Pb age distributions of detrital zircons from the Triassic sam- c. 471 and 454 Ma) and rare Silurian (1 %, c. 424 Ma) and Permian ples are ‘significantly different’ at the 5 % confidence level (P-value (1%, c. 256 Ma) grains. < 0.001) from those of the lower–upper Carboniferous siliciclastic Of a total of 110 spots measured in sample Sbm-7, 105 yielded rocks of the Mértola and Mira formations (Pereira et al. 2012a, 90–110 % concordant ages (Fig. 5f). The majority of detrital 2014; Rodrigues et al. 2015), and the upper Devonian zircon grains are Proterozoic (83%)followedbyArchaean(9%, (Famennian) – lower Carboniferous siliciclastic rocks from the c. 3.1–2.6 Ga), Palaeozoic (8%: 4% Cambrian, c. 541–489 Ma; 1 % Horta da Torre, Represa and Santa Iria formations are ‘significantly Ordovician, c. 477 Ma; 1 % Devonian, c. 413 Ma; 1 % different’ at the 5 % confidence level (P-values < 0.001) (Pereira et al. Carboniferous, c. 357 Ma; and 1 % Permian, c. 289 Ma), while one 2017b; Pérez-Cáceres et al. 2017), as are the upper Carboniferous grain is Triassic (c. 240 Ma). Neoproterozoic grains (58 %) are wide- Santa Susana and lower Permian Viar siliciclastic rocks (Dinis spread in the age interval c. 992–543 Ma (32 % Ediacaran, c. 633–543 et al. 2018)(Fig.6). All of these samples contain a significant number Ma; 17 % Cryogenian, c. 695–637 Ma; and 9 % Tonian, c. 992–750 of detrital zircon grains with Carboniferous and Devonian ages. Ma). Palaeoproterozoic zircon (16 %) is c. 2.4–1.7 Ga, and This difference is confirmed by the MDS diagrams, on which the Mesoproterozoic ages (9 %) are 1.6–1Ga. detrital zircon populations of the above-mentioned SW Iberian A comparison of samples of the Algarve Triassic sandstone from upper Devonian to lower Permian siliciclastic sequences are located each sector using the K–S test shows that P-values are very close to 1 at some distance from those of the Algarve Triassic sand- (western sector: 0.852 ≤ P-value ≤ 1; central sector: P-value = 0.962) stone (Fig. 7a). (Fig. 6), indicating a common source for the two sectors. D-values are smaller between the cumulative curves of the samples from each sec- 5.a. Gondwanan-type source of detrital zircon tor (western sector: 0.04 ≤ D-value ≤ 0.079; central sector: D-value = 0.069) but greater between the sectors (0.136 ≤ D-value ≤ 0.195) The K–S test results show that the detrital zircon populations of the (Fig. 6), suggesting some differences in terms of source between Algarve Triassic sandstone of the western sector are ‘not suffi- the two sectors. The U–Pb age distributions of samples Ama-1, ciently significantly different’ at the 5 % confidence level (P-values Ama-3, Ama-4 and Ama-5 compared with sample Sbm-7, and those < 0.001) from the Ediacaran–Cambrian siliciclastic rocks of the of sample Sbm-6 compared with Ama-5, are ‘not significantly differ- OMZ (Fig. 6), indicating that they could provide a source for them. ent’ at the 5 % confidence level (P-values ranging from 0.059 to 0.25 However, if we consider that in the Ama-1, Ama-3 and Ama-4 and P-value = 0.103, respectively) (Fig. 6), indicating the same samples there are Mesoproterozoic, Silurian and late Ordovician provenance. But, the U–Pb age distribution of sample Sbm-6 is detrital zircon grains, we have to consider the contribution from ‘not sufficiently significantly different’ from samples Ama-1, another source, which may be the Meguma Terrane (see Ama-3 and Ama-4 (P-values ranging from 0.027 to 0.043). The rel- Section 5.b.). evant MDS diagram demonstrates a lack of similarity with the U–Pb In contrast, the detrital zircon populations of the Triassic sand- detrital geochronology dataset of the Triassic sandstone sampled in stone of the central sector (Sbm-6 and Sbm-7) and sample Ama-5 the western and central sectors of the Algarve Basin (Fig. 7b). from the western sector are ‘not significantly different’ from those of the OMZ (Fig. 6), suggesting derivation from a Gondwanan- type source. This is supported by the fact that the cumulative curve 5. Discussion for the OMZ siliciclastic rocks is somewhat closer to that of the In the present study, Algarve Triassic sandstone detrital zircon central sector Triassic sandstone (D-values of 0.102 and 0.105) populations were compared with those of (i) Ediacaran to lower when compared to the western sector as regards the distance Devonian siliciclastic rocks from the Meguma Terrane and between the curves (0.238 ≤ D-value ≤ 0.254) (Fig. 6). This differ- West Avalonia as potential Laurussian-type sources, and ence is also evident on the MDS diagrams (Fig. 7b), where the

Cumulative Curves

1,2 Samples AMA-1, AMA-3, AMA-4 & AMA-5 Algarve Basin West Avalonia (Nova Scotia) (western sector) Neoproterozoic-E.Devonian 1 L.Triassic

MegumaTerrane Cambrian 0,8

Samples SBM-6 & SBM-7 0,6 MegumaTerrane Algarve Basin Cambrian-E.Devonian (central sector) L.Triassic

0,4 Ossa-Morena Zone Neoproterozoic-E.Devonian

0,2

0 600 1000 1400 1800 2200 2600 3000 3400 Age (Ma)

Kolmogorov-Smirnov Test

SW Iberia Nova Scotia L.Devonian-E.Carboniferous Neoproterozoic- Cambrian- L.Triassic L.Carboniferous E.Devonian E.Devonian E.- L.Carboniferous Ossa- Morena West Meguma Western sector Central sector South Portuguese Zone Avalonia Zone Ama-1 Ama-3 Ama-4 Ama-5 Sbm-6 Sbm-7 MT-CB MR BJ PQ-TC 0,242 0,180 0,114 Ama-1 0,982 1,000 0,852 0,027 0,059 0,000 0,000 0,011 0,012 0,243 0,171 0,117 Ama-3 0,061 0,999 0,942 0,027 0,074 0,000 0,000 0,003 0,004 0,254 0,214 0,130 Ama-4 0,040 0,047 0,872 0,043 0,134 0,000 0,000 0,003 0,004 0,238 0,171 0,109 Ama-5 0,079 0,069 0,075 0,103 0,250 0,000 0,000 0,001 0,001 0,102 0,191 0,110 Sbm-6 0,195 0,195 0,179 0,161 0,962 0,000 0,000 0,164 0,051 0,105 0,137 0,088 Sbm-7 0,178 0,172 0,152 0,136 0,069 0,000 0,001 0,211 0,107 F F

L.Devonian L.Devonian- L.Carboniferous Neoprot. Neoprot. Cambrian- E.Carboniferous Permian E.Cambrian E.Devonian E.Devonian Cambrian Pulo do Lobo Z./ Pulo do Lobo Santa Viar Ossa- West Sehoul S Portuguese Z. Zone Susana Meguma Meguma Basin Morena Avalonia Block PL,GF,RL,A,RO SI-REP HT Basin Zone 0,078 0,000 0,000 0,000 0,000 0,045 0,003 0,148 0,691 0,049 Ama-1 0,059 0,000 0,000 0,000 0,000 0,041 0,005 0,126 0,372 0,010 Ama-3 0,018 0,000 0,000 0,000 0,000 0,027 0,000 0,047 0,422 0,021 Ama-4 0,232 0,000 0,000 0,000 0,000 0,076 0,005 0,173 0,239 0,006 Ama-5 0,139 0,000 0,000 0,000 0,000 0,088 0,002 0,204 0,002 0,001 Sbm-6 0,255 0,000 0,000 0,000 0,000 0,185 0,066 0,485 0,011 0,003 Sbm-7 F

P-value>0.05: 0.05>P-value>0.001: P-value<0.001: "not significantly different" "not enough significantly different" “significantly different"

Fig. 6. (Colour online) Results of the K–S (Kolmogorov–Smirnov) test showing: the U–Pb age cumulative frequency plots applied to the U–Pb ages (90–110 % concordance) of detrital zircon grains from the Algarve Triassic sandstone (Ama-1, Ama-3, Ama-4, Ama-5 – western sector; Sbm-6, Sbm-7 – central sector), South Portuguese Zone (MT-CB – Mértola and Cabrela formations; MR – Mira Formation; BJ – Brejeira Formation; PQ-TRC – Phyllite-Quartzite and Tercenas formations; RO – Ronquillo Formation), Pulo do Lobo Zone (PL; PL-GF-RL-A – Pulo do Lobo, Gafo, Ribeira de Limas and Atalaia formations; HT – Horta da Torre Formation; SI-REP – Santa Iria and Represa formations) and Ossa–Morena Zone, Meguma Terrane and West Avalonia siliciclastic rocks. Table showing the comparison of detrital zircon populations of the Algarve Triassic sandstone, South Portuguese, Pulo do Lobo and Ossa–Morena zones, Santa Susana and Viar basins, Sehoul Block, Meguma Terrane and West Avalonia siliciclastic rocks. Data sources are mentioned in the text.

(a) MDS diagram (Nance et al. 2008; Pereira et al. 2008; Linnemann et al. 2008) and older West African craton sources (Eburnian–Birimian (Schofield et al. 2006; Youbi et al. 2012; Pereira et al. 2015b), HT (L.Devonian-E.Carboniferous) Liberian (Potrel et al. 1996; Key et al. 2008) and Leonian 0.4 (Thieblemont et al. 2004 and references therein) magmatic events). Cambrian–early Ordovician grains (5–9 %) may have been recycled from magmatic rocks that are abundant in the OMZ

0.2 and have been assigned to a major rifting event on the continental margin of Gondwana (Sánchez-García et al. 2003; Murphy et al. 2006; Linnemann et al. 2008; Pereira et al. 2012b; Díez VR SS (E.Permian) (L.Carboniferous) Fernández et al. 2015). 0 III I MT-CB Cm2 MR (E.Carboniferous) 5.b. Laurussian-type sources of detrital zircon II (L.Triassic) (E.-L.Carboniferous) In palaeogeographic reconstructions for the Palaeozoic period, the -0.2 SI-REP (L.Devonian-E.Carboniferous) palaeolocation of the Meguma Terrane and West Avalonia in relation to the continental margin of Gondwana has changed over time 0 0.2 0.4 0.6 from the Cambrian to Devonian (Keppie et al. 1997; Cocks & (b) MDS diagram Torsvik, 2002, 2006; Waldron et al. 2009). In Neoproterozoic– Cambrian times, both terranes were part of the northern West Avalonia Ama-5 Am1, Th4 (Ediacaran-E.Devonian) Gondwanan margin, but they later drifted away and were sub- (L.Triassic) (L.Triassic) sequently accreted to the continental margin of Laurussia in Ama-3 III (L.Triassic) Silurian time, remaining part of it until Carboniferous time 0.05 (Murphy et al. 2006; Nance et al. 2010). This explains why the PL-GF-RL-A-RO Ossa-Morena Zone Ama-4 (L.Devonian) Palaeoproterozoic and Neoproterozoic detrital zircon age distribu- (L.Triassic) (Ediacaran-Cambrian) Meguma tion of these two Laurussian-type sources is consistent with deri- Meguma Ama-1 (Cambrian-E.Devonian) (Cambrian) (L.Triassic) vation from the northern Gondwanan continental margin during a 0 certain period of their stratigraphic record, and therefore, these Sbm-7 sources show some similarities with the detrital zircon population (L.Triassic) of the OMZ Ediacaran–Cambrian siliciclastic rocks. However, Sbm-6 contrary to the OMZ (which is defined in the present paper as a -0.05 Tl1 (L.Triassic) II (L.Triassic) ‘Gondwanan-type source’ because it never drifted away from the northern continental margin of Gondwana), the Meguma Sehoul Block BJ Terrane and West Avalonia are distinguishable by the fact that they (Cambrian) -0.1 (L.Carboniferous) PQ-TRC present a significant population of Mesoproterozoic, late (L.Devonian- Ordovician, Silurian and early Devonian zircon grains. The E.Carboniferous) Mesoproterozoic detrital zircon grains found in West Avalonian Ediacaran and Cambrian sedimentary rocks are compatible with -0.1 -0.05 0 0.05 0.1 an Amazonian provenance (Barr et al. 2012). The presence of a – Fig. 7. (Colour online) MDS diagrams showing: (a) the comparison of detrital zircon detrital zircon population dated at c. 1.6 1 Ga in Silurian and populations of the Algarve Triassic sandstone, South Portuguese, Pulo do Lobo and Devonian siliciclastic rocks of the Meguma Terrane has been inter- Ossa–Morena zones (the acronyms are the same as in Fig. 6), Santa Susana (SS) and preted as having been derived from a source composed of Viar (VR) basins, Sehoul Block, Meguma Terrane and West Avalonia siliciclastic rocks; Mesoproterozoic crust (White et al. 2018), or recycling from (b) a detail of (a) comparing the samples with greater affinity. Data sources are mentioned in the text. West Avalonian sources from Silurian times (Murphy et al. 2004b). In addition, Mesoproterozoic zircon grains are found in the oldest Neoproterozoic siliciclastic rocks of West Avalonia detrital zircon population of the OMZ rocks is located some (Gamble Brook Formation; Henderson et al. 2016), which could distance from that of the western sector Triassic sandstone (with have been later recycled into younger formations during the exception of sample Ama-5, which is at the same distance from Ediacaran to Devonian times. However, this hypothesis lacks the OMZ as samples Sbm-6 and Sbm-7). This difference may be validity as the Gamble Brook Formation includes, along with owing to the almost complete absence of Archaean (3 %) detrital the Mesoproterozoic grains, a significant population of early zircon grains and the presence of Mesoproterozoic (7–11 %) detri- Palaeoproterozoic ages, typical of Baltica sources (Sveconorwegian: tal zircon grains in the western sector Triassic sandstone, which Andersen et al. 2002), which have not been fully recognized in the contrasts with the detrital zircon register for the OMZ rocks. At Neoproterozoic–lower Devonian siliciclastic rocks of West Avalonia the same time, the detrital zircon population of the central sector (Henderson et al. 2016) and the Meguma Terrane (Murphy et al. Triassic sandstone (samples Sbm-6 and Sbm-7), which is also 2004b;Waldronet al. 2009;Whiteet al. 2018). dominated by Cryogenian–Ediacaran (44–49 %) grains, also con- The lack of late Ordovician, Silurian and early Devonian tains Palaeoproterozoic (16–17 % Rhyacian to Statherian) and magmatism is another feature of the OMZ, which may provide a Archaean (9–13 %) grains (Fig. 5). These Precambrian detrital zir- criterion for distinguishing between Gondwanan- and Laurussian- con grains were most probably recycled from both the Avalonian– type sources (West Avalonia and Meguma terranes). In West Cadomian magmatic arc system, which developed on the Avalonia, the bimodal volcanism of the Dunn Point and continental margin of Gondwana in Neoproterozoic times McGillivray Brook formations yielded c. 460–454 Ma ages

(Hamilton & Murphy, 2004; Murphy et al. 2012). Late Ordovician – Phyllite-Quartzite Formation. In the western sector, with the early Silurian magmatic events are found in the Meguma Terrane. exception of sample Ama-5, which is ‘significantly different’ The White Rock Formation of the Rockville Notch Group is com- (P-value < 0.001), samples are ‘not sufficiently significantly differ- posed of felsic volcanic rocks dated at c. 446–434Ma(Whiteet al. ent’ at the 5 % confidence level from either the Brejeira Formation 2018), and in addition, the Mavillete gabbro intrusive in the White turbidites (P-values ranging from 0.003 to 0.011) or both the Rock Formation was dated at c. 426 Ma (Warsame et al. 2017). The Phyllite-Quartzite and Tercenas formations (P-values of 0.004 to occurrence of c. 440 Ma detrital zircon grains in the upper Silurian 0.012), suggesting a lesser degree of affinity, which is also evident siliciclastic rocks of the Arisaig Group could derive from erosion of a from the distance between them on the relevant MDS diagram Silurian volcanic belt and/or they may have originally been trans- (Fig. 7b). A similar analysis conducted with the detrital zircon pop- ported as airborne ash and subsequently reworked from coeval vol- ulations of the Algarve Triassic sandstone and the Frasnian silici- canic beds (Murphy et al. 2004a). Another group of detrital zircon clastic rocks of the PLZ and the SPZ (Pereira et al. 2017b; grains that is characteristic of Laurussian-type sources present early Pérez-Cáceres et al. 2017) showed that they are ‘not significantly Devonian ages (c. 419–393 Ma). Detrital zircon grains included in different’ at the 5 % confidence level (P-values ranging from this age interval were found in the Lochkovian siliciclastic rocks 0.059 to 0.255). The same result is evident from the relevant of the Arisaig Group (c. 418–397 Ma, Knoydart Formation; MDS diagram (Fig. 7b), showing a proximity between sample B. Henderson, unpub. Ph.D. thesis, Univ. Adelaide, 2016). These Am1 (Pereira et al. 2017c; Fig. 2) and the Frasnian siliciclastic early Devonian zircon grains may have derived from a few inter- rocks. Sample Ama-4 provides the exception to this, with a P-value bedded volcanic beds (Murphy et al. 2008), and/or the Acadian = 0.018 (‘not sufficiently significantly different’). The affinity magmatic rocks of the nearby Newfoundland segment of the between the detrital zircon populations of the Frasnian siliciclastic Appalachian belt (Gander Zone of the Ganderia Terrane; van rocks and of the Meguma Terrane Ediacaran to lower Devonian Staal et al. 2009; van Staal & Barr, 2012). siliciclastic rocks (Krogh & Keppie, 1990; Murphy et al. 2004a; K–S test results indicate that the U–Pb age distributions of all Waldron et al. 2011) is also evident from the relevant MDS dia- samples of the Triassic sandstone are ‘not significantly different’ at gram (Fig. 7b), suggesting that the more recent rocks resulted from the 5 % confidence level (P-values ranging from 0.047 to 0.485) the recycling of older ones that contained abundant Cryogenian– from the Ediacaran–lower Devonian siliciclastic rocks of the Ediacaran detrital zircon grains, and Palaeoproterozoic, Meguma Terrane, strongly suggesting they are possible sources. Mesoproterozoic, late Ordovician, Silurian and early Devonian At the same time, sample Sbm-7 is the only Triassic sandstone with ages. Upper Devonian – lower Carboniferous formations of the aU–Pb age distribution that is ‘not significantly different’ at the SPZ and the PLZ may have acted as intermediate sediment reposi- 5 % confidence level (P-value = 0.066) from the Cambrian–lower tories composed of detritus recycled from older sedimentary/ Devonian siliciclastic rocks of West Avalonia. The remaining sam- igneous sources from West Avalonia and the Meguma Terrane. ples are ‘not sufficiently significantly different’ with P-values rang- As for the Algarve Triassic sandstone of the central sector, it is ing from 0.002 to 0.005, in contrast to sample Ama-4, which is evident from the K–S test result and MDS diagrams (Figs 6, 7) that ‘significantly different’ (P-value < 0.001). When performing the its detrital zircon populations have a greater degree of affinity with K–S test for the comparison of the Algarve Triassic sandstone those of the West Avalonian Ediacaran to lower Devonian silici- and Meguma Terrane Cambrian siliciclastic rocks, there is a clastic rocks (Pollock et al. 2015; Henderson et al. 2016) and the greater degree of similarity with the samples of the western sector OMZ Ediacaran–Cambrian siliciclastic rocks (Linnemann et al. (P-values = 0.239–0.691) (Fig. 6), which is also evident from the 2008; Pereira et al. 2008, 2012b), which may indicate these two MDS diagram (Fig. 7). as sources. The degree of similarity between the detrital zircon pop- Although the zircon age spectra in the Algarve Triassic sand- ulations of the West Avalonian Ediacaran to lower Devonian stone may indicate ultimate derivation from the Meguma siliciclastic rocks and sample Th4 (Pereira et al. 2017c; Fig. 2)is Terrane with a contribution from West Avalonia, the upper evident on the MDS diagram (Fig. 7b). Devonian–Carboniferous formations of the SPZ and the PLZ cannot be ruled out as additional potential sources since zircon age 5.c. Palaeogeographic context of the late Triassic deposition signatures are closely comparable (Braid et al. 2011; Pereira in SW Iberia et al. 2014, 2017b; Pérez-Cáceres et al. 2017), as evident from the relevant MDS diagram (Fig. 7b). As regards the detrital zircon Our new detrital zircon U–Pb geochronology findings demon- age populations of the Algarve Triassic sandstone as compared strate that the Triassic sandstone is recycled, and the range of its with those of the SPZ siliciclastic rocks, upper Devonian – lower ages indicates a number of terrane sources forming the exposed Carboniferous Phyllite-Quartzite and Tercenas formations basement during the deposition of the Algarve Basin in late (Braid et al. 2011; Pereira et al. 2012a; Pérez-Cáceres et al. Triassic time. Traditionally, prior to geochronological studies, an 2017), and lower to upper Carboniferous Mértola, Mira and OMZ provenance has been attributed to the Algarve Triassic sand- Brejeira formations (Pereira et al. 2012a, 2014; Rodrigues et al. stone. However, the recycling of the detrital zircon population of 2015), there are significant differences. The K–S test results show the OMZ Ediacaran–Cambrian siliciclastic rocks cannot account that U–Pb age distributions of the Triassic sandstone from the cen- for the presence of late Ordovician, Silurian, Devonian and tral sector are ‘not significantly different’ at the 5 % confidence level Mesoproterozoic zircons in the Algarve Triassic siliciclastic rocks. from the Brejeira Formation (P-values of 0.164 and 0.211) and The most likely sources of the Triassic sandstone are the Palaeozoic both the Phyllite-Quartzite and Tercenas formations (P-values terranes of Nova Scotia and SW Iberia itself, supporting previous of 0.051 and 0.107), which may be regarded as probable sources interpretations of provenance data (Pereira et al. 2017c). In the (Fig. 6). The same result is evident from the relevant MDS diagram Algarve Basin, palaeocurrent indicators exist with local-scale direc- (Fig. 7b), which also indicates similarities between the detrital zir- tions of transport of detritus moving from the northeast (current con populations of sample Tl1 (Dinis et al. 2018; Fig. 2) and the geographic coordinates; Palain, 1976) from the pre-Mesozoic

basement of SW Iberia (SPZ, PLZ and OMZ) and from the south- conjugate margin connections are illustrated: Newfoundland– east (Fig. 2), suggesting source areas located outside SW Iberia, Iberia (Skogseid, 2010) and Nova Scotia–Morocco (Labais et al. probably in NW Morocco (perhaps the Sehoul Block). However, 2010), which are separated by the Newfoundland–Azores– in the western sector of the Algarve Basin, palaeocurrents also indi- Gibraltar fault zone. In such plate reconstruction models, the lack cate transport from the southwest (current geographic coordinates; of representation of the spatial distribution of the Palaeozoic ter- Palain, 1976), which may indicate other sources located outside ranes associated with the Appalachian–Variscan belt that under- Iberia. In accordance with late Triassic palaeogeographic recon- went denudation in late Triassic time is common. The Meguma structions, SW Iberia was probably located close to Nova Scotia Terrane, exposed only in southern mainland Nova Scotia, under- before the opening of the Central Atlantic Ocean, supporting lies much of the continental shelf of New England and Maritime the suggestion of a likely West Avalonian and Meguma Terrane Canada (Nance et al. 2010). Accordingly, the Meguma Terrane derivation for the Triassic sandstone. could be regionally extensive to the North Atlantic African and Therefore, we suggest that the detrital zircon grains of the European margin, with correlatives in SW Iberia and NW Algarve Triassic sandstone mostly derived directly from Nova Morocco. However, the connection of the Nova Scotia Scotia Neoproterozoic to lower Devonian siliciclastic sequences Palaeozoic terranes with SW Iberia has been overlooked. This of the Meguma and West Avalonia terranes, the Sehoul Block has occurred because the spatial distribution of the Palaeozoic ter- and the SW Iberian Meguma and West Avalonia terrane deriva- ranes just before the beginning of the fragmentation of Pangaea has tives, i.e. the Frasnian siliciclastic rocks of the PLZ and the SPZ, not yet been completely defined in Iberia. One obstacle to defining and the upper Devonian – lower Carboniferous (Phyllite- late Palaeozoic crustal architecture is the lack of pre-upper Quartzite and Tercenas formations) and upper Carboniferous Devonian stratigraphy in the SPZ and PLZ. Another difficulty (Brejeira Formation) siliciclastic rocks of the SPZ. Nevertheless, in this regard has to do with Carboniferous deformation and meta- possible concurrent derivation from the Ediacaran to Cambrian morphism occurring within major shear zones located along the siliciclastic rocks of the OMZ and the Sehoul Block cannot be ruled boundary that separates the SPZ and PLZ (Laurussian side) from out, since they show a similarity with the detrital zircon signature the OMZ (Gondwanan side), which obliterates the original strati- of the Meguma Terrane and West Avalonian siliciclastic sequen- graphic relationships. If the effect of post-Triassic tectonic move- ces. Another important finding is the almost complete absence of ment along the Newfoundland–Azores–Gibraltar fault is late Devonian–Carboniferous zircon grains in the Triassic sand- discounted, a spatial connection between the Minas (Nova stone of the Algarve Basin. This probably indicates that the catch- Scotia; Murphy et al. 2011) and Porto-Tomar (Iberia; Pereira ments of palaeo-rivers include, or are closely adjacent to, regions of et al. 2010 and references therein) dextral fault zones can be the Variscan–Appalachian belt with no large-scale occurrences of recreated (Fig. 8). Such reconstruction of late Palaeozoic crustal the exposure of late Devonian–Carboniferous magmatic rocks architecture is extremely useful for providing an understanding because they were never emplaced there or they all were uplifted of the spatial distribution of Palaeozoic terranes before the opening and eroded before late Triassic time. However, it is important to of the Central Atlantic Ocean illustrating the extension of the underline that detrital zircon grains with Carboniferous and Meguma Terrane through NW Morocco and SW Iberia, which Devonian ages are recognized in the upper Triassic siliciclastic is crucial for demonstrating the existence of Gondwanan- and rocks from the easternmost sector of the Algarve Basin (sample Laurussian-type sources of sediment in the late Triassic Cm2; Dinis et al. 2018), having a great degree of similarity with Algarve Basin. the zircon age populations of the equivalent unit from the In Iberia, the Triassic terrestrial sedimentation related to ero- Alentejo Basin (samples St3 and Sc4; Pereira et al. 2017c). sion of the Appalachian–Variscan orogenic belt was formed Our new detrital zircon U–Pb geochronology data support the through local or widespread drainage systems (Arche & L´opez- interpretation that the Devonian–Carboniferous siliciclastic rocks G´omez, 2005; Soares et al. 2012; Sánchez Martínez et al. 2012; of the SPZ and the PLZ are most probably the recycled product of Pereira & Gama, 2017). Sánchez Martínez et al.(2012), based pre-upper Devonian sequences from the Meguma and West on the U–Pb dating of detrital zircon, argued that the provenance Avalonia terranes. This is essential for advancing the hypothesis of the Triassic sediments of the Iberian Ranges changes over time. that the provenance of the Triassic sandstone from the Algarve This change was probably owing to variations in the activity of flu- Basin is intrinsically linked to the crustal architecture of the vial systems and tectonic causes during the development of a rift Appalachian–Variscan belt immediately prior to the fragmenta- system. For these authors, sediments were transported in early tion of Pangaea. According to palaeogeographic reconstruction Triassic time from long distances when the rift propagated to maps describing the continent configuration, palaeoenvironment the northwest into North America (i.e. Avalonia and Laurentia), and lithofacies during late Triassic time, Nova Scotia, NW while during middle Triassic time, sediments mainly derived Morocco and Iberia are located at the core of Pangaea (Stampfli from local source areas (i.e. the axial zone of the Iberian & Kozur, 2006; Golonka, 2007; Leleu et al. 2016), where the Variscan belt). Recent studies have suggested that the diverse Appalachian–Variscan belt extends (Fig. 8). The separation of detrital zircon age populations of the upper Triassic strata from North America (Nova Scotia) and Gondwana (SW Iberia and the Lusitanian, Alentejo and Algarve basins are most probably NW Morocco) began with the Permian–Triassic transition, with related to the local erosion and recycling of the Iberian Variscan the development of continental interior clastic depositional sys- belt (Pereira et al. 2016a,b; Pereira & Gama, 2017). Sediments tems, and continued during Jurassic time for shallow-marine probably derived directly from primary crystalline sources and basins with associated volcanism, in the area of the future from recycling of intermediate sediment repositories. The Central Atlantic Ocean (Golonka & Ford, 2000). In palaeogeo- Alentejo Basin may have shared sources with the Lusitanian and graphic reconstruction models of late Triassic to early Algarve basins, while the Algarve Basin upper Triassic sediments Cretaceous rifting in the Central Atlantic region, two main mostly derived from zircon-bearing rocks currently located

Late Triassic

CZ NORTH WALZ AMERICA GTMZ NEOTETHYS CIZ AVL GONDWANAN SOURCES

SW IBERIA OMZOMZ PLZ LAURUSSIANSOURCES SPZ AVL MGU SB NOVA NW MOROCCO SCOTIA 100km

NORTH AFRICA

Spreading direction Land surface (potential source areas) Transport of sediment Fluvial systems Late Triassic deposition Deep water (SW Iberia) Coastal environments Late Carboniferous Minas (Nova Scotia)- Porto-Tomar (Iberia) dextral fault zones

West Avalonia Pulo do Lobo Zone ALGARVE BASIN

NOVA SCOTIA SW IBERIA

Fig. 8. (Colour online) Palaeogeographic Ossa-Morena context of: (a) late Triassic continental rifting Meguma Zone at the core of Pangaea (adapted from Terrane Golonka, 2007; Pereira & Gama, 2017); (b) late Triassic alluvial fan and river Sehoul deposition within the Algarve Basin, showing Block the underlying Appalachian–Variscan belt NW MOROCCO architecture with distinct Palaeozoic source terranes. South Portuguese Zone

in SW Iberia (i.e. the SPZ and the PLZ), Nova Scotia (i.e. West Represa and Santa Iria formations (PLZ), and the late Avalonia and Meguma terranes) and NW Africa (i.e. Sehoul Carboniferous Santa Susana and early Permian Viar terres- Block) that would have represented juxtaposed local source trial basins, which excludes them as potential sources for areas before the opening of the Atlantic Ocean (Pereira & SW Iberia. Gama, 2017). (3) Statistically indistinguishable detrital zircon populations from the central sector Algarve Triassic sandstone, OMZ Ediacaran–Cambrian siliciclastic rocks, SPZ upper 6. Conclusions Devonian–Carboniferous Ronquillo, Tercenas, Phyllite- (1) The U–Pb geochronology of detrital zircon grains of Triassic Quartzite and Brejeira formations, and PLZ upper Devonian sandstone from the western (70–77 % Neoproterozoic, 11–17 % Pulo do Lobo, Gafo, Atalaia and Ribeira de Limas formations Palaeoproterozoic, 7–11 % Mesoproterozoic, 2–5 % Palaeozoic suggest that detritus was reworked into the Algarve Basin and 0–3 % Archaean) and central (52–58 % Neoproterozoic, from Gondwanan- and Laurussian-type sources exposed in 16–17 % Palaeoproterozoic, 9–13 % Archaean, 8–11 % SW Iberia. Palaeozoic and 7–9 % Mesoproterozoic) sectors of the Algarve (4) The detrital zircon U–Pb ages presented in this study support Basin are significantly different, indicating lateral changes in the hypothesis that the Meguma Terrane and Sehoul Block sources. Cambrian siliciclastic rocks are the main (Laurussian-type) (2) K–S test results and MDS diagrams enable the conclusion to sources of the western sector Algarve Triassic sandstone, be drawn that the detrital zircon populations of the Algarve while SW Iberian locations such as the SPZ, the PLZ and Triassic sandstone are quite different from those of the lower the OMZ located to the north (current geographic coordi- to upper Carboniferous siliciclastic rocks of the Mértola and nates) may be ruled out as being unique sources. Mira formations (SPZ), the upper Devonian – lower (5) Statistical analysis enables the advancement of the suggestion Carboniferous siliciclastic rocks from the Horta da Torre, that the zircon age populations of West Avalonia and

Meguma Terrane sources were reproduced faithfully in inter- Braid JA and Murphy JB (2006) Acadian deformation in the Shallow Crust: an mediate repositories as the result of sediment recycling in late example from the Siluro-Devonian Arisaig Group, Antigonish Highlands, Devonian–Carboniferous times (SPZ and PLZ), and later Nova Scotia. Canadian Journal of Earth Sciences 43,71–81. reworked into the late Triassic Algarve Basin. Braid JA, Murphy JB, Quesada C, Bickerton L and Mortensen JK (2012) (6) Deposition in the late Triassic Algarve Basin involved the Probing the composition of unexposed basement, South Portuguese Zone, denudation of the pre-Mesozoic basement of SW Iberia Southern Iberia: implications for the connections between the Appalachian and Variscan orogens. Canadian Journal of Earth Sciences 49, 591–613. (OMZ, PLZ and SPZ) with additional material deriving from Braid JA, Murphy JB, Quesada C and Mortensen M (2011) Tectonic escape outside present-day Iberia (Nova Scotia: West Avalonia, of a crustal fragment during the closure of the Rheic Ocean: U–Pb detrital Meguma Terrane; and NW Morocco: Sehoul Block). The late zircon data from the Late Palaeozoic Pulo do Lobo and South Portuguese Triassic Algarve Basin presents different (Gondwanan- and zones, southern Iberia. Journal of the Geological Society, London 168, Laurussian-type) sources as sediment transport was probably 383–92 determined by a drainage system in which the catchments of Cambeses A, Scarrow JH, Montero P, Lázaro C and Bea F (2017) palaeo-rivers were located in distinct Palaeozoic terrane Palaeogeography and crustal evolution of the Ossa-Morena Zone, sources. 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