Provenance study of Pliocene–Pleistocene sands based on ancient detrital zircons (Alvalade Basin, SW Iberian Atlantic coast)

    Provenance study of Pliocene-Pleistocene sands based on ancient detrital zircons (Alvalade Basin, SW Iberian Atlantic coast) Lu´ıs Albardeiro, Manuel Francisco Pereira, Cristina Gama, Martim Chichorro, Mandy Hofmann, Ulf Linnemann PII: DOI: Reference:

S0037-0738(14)00083-9 doi: 10.1016/j.sedgeo.2014.04.007 SEDGEO 4743

To appear in:

Sedimentary Geology

Received date: Revised date: Accepted date:

7 January 2014 11 April 2014 28 April 2014

Please cite this article as: Albardeiro, Lu´ıs, Pereira, Manuel Francisco, Gama, Cristina, Chichorro, Martim, Hofmann, Mandy, Linnemann, Ulf, Provenance study of PliocenePleistocene sands based on ancient detrital zircons (Alvalade Basin, SW Iberian Atlantic coast), Sedimentary Geology (2014), doi: 10.1016/j.sedgeo.2014.04.007

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT Provenance study of Pliocene-Pleistocene sands based on ancient detrital zircons (Alvalade Basin, SW Iberian Atlantic coast)

IP

T

Luís Albardeiro a, Manuel Francisco Pereira a, Cristina Gama b, Martim Chichorro c, Mandy Hofmann d, Ulf

a

SC R

Linnemann d

Instituto D. Luiz, Departamento de Geociências ECT, Universidade de Évora

Telephone: +351 266 744 490

Centro de Geofísica de Évora, Departamento de Geociências ECT, Universidade de Évora

D

b

MA

Email: [email protected] (Corresponding author)

NU

Colégio Luís António Verney, Rua Romão Ramalho, 59, 7002-554 Évora, Portugal

c

CE P

Telephone: +351 266 744 490

TE

Colégio Luís António Verney, Rua Romão Ramalho, 59, 7002-554 Évora, Portugal

Centro de Investigação em Ciência e Engenharia Geológica, Universidade Nova de Lisboa

2829-516 Caparica, Portugal

d

AC

Telefone: +351 212 948 300

Senckenberg Naturhistorische Sammlungen Dresden, Museum für Mineralogie und Geologie

Königsbrücker Landstr. 159, D-01109 Dresden, Germany Telephone: phone +49(0)351 795841 4403

Abstract Pliocene-Pleistocene sand of the Alvalade basin was taken from the sea-cliffs of the SW Iberian Atlantic coast for a provenance study using U-Pb dating of detrital zircons. The 492 U-Pb ages obtained revealed a wide interval ranging from Cretaceous to Archean, with predominance of

1

ACCEPTED MANUSCRIPT

2

Paleozoic (31-71%; mainly Carboniferous), Neoproterozoic (19-20%; mainly Crygenian-Ediacaran) and Cretaceous (21-39%; but absent in sand sampled 12 km from Cape Sines) zircon ages. The

T

radiometric results indicate distinct detrital zircon signatures: i) Carboniferous ages younger than ca.

IP

315 Ma are infrequent or absent in sand sampled south of Cape Sines, which are interpreted as

SC R

indicating a provenance associated with the nearby Ossa-Morena and South Portuguese zones and the Alentejo basin; ii) Carboniferous ages younger than ca. 315 Ma (8-9%) in sand sampled north of Cape Sines, suggesting a possible contribution from the Central-Iberian Zone originally; however,

NU

these zircons may be multi-cyclic, having been reworked from Eocene-Miocene siliciclastic deposits

MA

related to transport from central Iberia (Lower Tagus basin drainage evolution); and iii) Cretaceous ages, which are interpreted to indicate a Sines Massif provenance. These three signatures provide

D

important constraints on the location and extent of the Pliocene-Pleistocene topography and drainage

TE

system that were probably controlled by: i) Miocene to Pleistocene landscape rejuvenation driven by Alpine movements along the Torrão-Vidigueira-Mora fault system and Messejana fault; and ii)

CE P

residual reliefs related to regional tectonic structure inherited from the Variscan Orogeny. The U-Pb ages of zircon populations found in the Pliocene-Pleistocene sands also trace the pre-Cenozoic

AC

paleotectonic evolution of SW Iberia recorded in their sources: i) the North Gondwana accretion (Cadomian Orogeny) and breakup that led to the opening of the Rheic Ocean; ii) the Gondwana and Laurussia collision (Variscan Orogeny); and iii) the Pangea breakup and opening of the Atlantic Ocean.

Key-words: U-Pb LA-ICPMS geochronology, source areas, pre-Cenozoic basement, drainage basin evolution, Alpine tectonic activity

1. Introduction

ACCEPTED MANUSCRIPT

3

Exposed rocks are subject to external geodynamic processes that promote erosion, transportation and deposition of detritus into sedimentary basins. The mineralogical composition of detritus that

T

eventually reach the sedimentary basins can vary their proportion depending on the climate which

IP

controls the weathering, sediment transport and the geological setting of their sources (von Eynatten

SC R

and Dunkl, 2012). Commonly, detritic sedimentary rocks contain heavy minerals, such as zircon, which is derived from different source rocks (Davis et al., 2003, Fedo et al, 2003, Kinny and Maas, 2003; Gehrels et al., 2011). Provenance studies using the efficient and reliable technical capability

NU

of Laser Ablation- Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) in regard to detrital

MA

zircon U-Pb age determination are extremely useful in the process of recognizing potential sources and to better understand complex histories of changes in drainage basin evolution during epeirogenic

D

uplift (Galloway et al., 2011).

TE

Such provenance studies based on detrital zircon U-Pb geochronological analysis can lead to the identification of different episodes of detrital sediment deposition and to a better understanding of

CE P

Earth's evolution (Sircombe, 1999; Cawood et al, 2003; Campbell et al., 2005; Morton et al., 2005). In the present study a dataset of detrital zircon U-Pb LA-ICPMS geochronological results is

AC

presented from Pliocene-Pleistocene sands of the Alvalade basin sampled in sea-cliffs in SW Iberian Atlantic coast (Figs. 1, 2). The obtained results are used to statistically compare the detrital zircon age distributions and to trace potential source areas based on existing knowledge of the zirconforming events preserved in the pre-Cenozoic basement of SW Iberia. Despite intense investigation, the origin and transport history of the sediment within the Alvalade basin and the interplay with tectonism remains poorly understood. Field evidence suggests much of the Pliocene-Pleistocene sand in the Alvalade basin was probably derived from nearby Paleozoic and Mesozoic sedimentary and igneous rocks, whereas early paleogeographic reconstructions imply the sand transport was also connected to a large northeast-to-southwest drainage network of the Lower Tagus basin extending

ACCEPTED MANUSCRIPT

4

from central eastern Iberia to the Atlantic coast. Resolving these issues can help improve our

T

understanding of the depositional history during the Pliocene-Pleistocene in SW Iberia.

IP

2. Geological setting

SC R

2.1. The Alvalade basin

In SW Iberia, Cenozoic basins are mainly associated with transport in main rivers whose mouths are located in the Atlantic coast, with the depositional environment influenced by transgressions and

NU

regressions (Lower Tagus, Alvalade, Moura and Algarve basins; Pais et al., 2012) (Fig. 1). The

MA

Alvalade basin (Antunes and Mein, 1989) located south of the Lower Tagus basin, largely corresponds to the present-day Sado hydrographic basin (Pais et al., 2012) and is currently separated

D

from the Moura hydrographic basin by the Messejana fault and reliefs above 200m (Fig. 1). The

TE

Alvalade basin contains a record of Eocene to Pleistocene marine and fluvial sedimentary rocks, with some stratigraphic gaps, which thus differs from the stratigraphy of the Lower Tagus basin (Antunes

CE P

and Pais, 1993) (Fig. 2). After the Miocene (Messinian), these two basins evolved independently, separated by a paleogeographic barrier mainly made of Paleozoic rocks (Senhor das Chagas-

AC

Valverde horst; Antunes and Pais, 1993) bordered by the Torrão fault system (Fig. 2). The stratigraphy of the Alvalade basin includes: i) Eocene to Lower Miocene reddish sandstone, mudstone and conglomerate (Vale do Guizo Formation; Teixeira and Gonçalves, 1980; Antunes, 1983; Oliveira et al., 1984), representing immature alluvial deposition in semi-arid climate (Pimentel, 1997); these deposits have equivalent units in the Lower Tagus basin; ii) Upper Miocene (Messinian) conglomerates, lutite and sandstone containing marine fossils and unconformably overlying alluvial deposits (Esbarrondadoiro Formation; Antunes et al., 1986; Balbino, 1995); with no equivalent units in the Lower Tagus basin; iii) Pliocene-Pleistocene fluvial sequence of sand and mud with occasional levels of gravel coarsening upwards and gradding into orange-colored sand and gravel (Alvalade Formation; Pimentel and Azevedo, 1992; Pimentel, 1997; Cunha et al., 2000, 2009;

ACCEPTED MANUSCRIPT

5

Pais et al., 2012; Marateca Formation; Antunes, 1983; Brito, 2009; Baixo Alentejo Littoral Unit; Oliveira et al., 1992) and the topmost unit is dominated by mud-supported gravel with dark red

IP

T

coarse pebbles (Panóias Formation; Pimentel, 1997).

SC R

2.2. The basement of the Alvalade basin

The Alvalade basin unconformably overlies Paleozoic sedimentary, metamorphic and igneous rocks of the Ossa-Morena and South-Portuguese zones (Fig. 2). The Lower Paleozoic sedimentary rocks of

NU

the Ossa-Morena Zone derived from erosion of the Cadomian basement made of back-arc basin

MA

sedimentary and magmatic arc rocks of Neoproterozoic age (Eguiluz et al., 2000; Pereira et al., 2011, 2012c). The Upper Devonian of the South Portuguese Zone is represented by the Phyllite-Quartzite

D

Formation (Oliveira, 1990) which is overlain by a volcanic-sedimentary Complex of Devonian-

TE

Carboniferous age (Frasnian to Tournaisian; Rosa et al., 2008; Oliveira et al., 2013). Above these follow Visean to Moscovian turbidite deposits of the Baixo Alentejo Flysch Group (Oliveira, 1990).

CE P

The Early Carboniferous is represented in the Ossa-Morena and South Portuguese zones by marine deposits, whereas the Upper Carboniferous sequence is continental (Quesada et al., 1990). SW Iberia

AC

exhibit exposures of Carboniferous and Permian plutonic rocks (Jesus et al., 2007; Rosa et al., 2008; Pin et al., 2008; Solá et al., 2009; Pereira et al., 2009; Lima et al., 2012). The basement of Alvalade basin also includes Mesozoic rocks (Fig. 2). The Late Triassic deposition is characterized by a thick sequence of continental sediments (Palain, 1976). During the Early Jurassic time the rift changed into marine basin (Manuppella, 1988). Volcanic tuffs, pyroclastic rocks and basaltic lavas are interlayered with the early Jurassic marine sedimentary rocks (Martins et al., 2008). The Cretaceous sedimentary record is dominated by clastic rocks deposited in fluvial and deltaic coastal marine environments, but also includes shallow marine carbonate platforms (Dinis et al., 2008). Cretaceous magmatism took place in a post-rift environment during initiation of Alpine tectonic activity (Miranda et al., 2009 and references therein; Merle et al., 2009; Grange et al., 2010).

ACCEPTED MANUSCRIPT

6

3. Methods

T

Six samples of Pliocene-Pleistocene clastic sedimentary rocks of the Alvalade basin were collected

IP

for U-Pb geochronology on detrital zircon, in the sea-cliffs of the SW Portuguese coast near to Cape

SC R

Sines (Figs. 2, 3). The selected sites correspond to a sandy sequence that is included in the lowermost part of the Baixo Alentejo Littoral Unit (Oliveira et al., 1992). Four samples were taken at locations north of Cape Sines (Fig. 3): medium to fine grained orange colored sands from the Areias Brancas

NU

beach sea-cliff (samples AB-3 and AB-4); and fine grained whitish-yellowish sands (sample PN-1)

MA

and a whitish level of gravels with pebbles of quartz supported by medium to fine grained sands (sample PN-2) from the Norte beach sea-cliff ca. 12 km south. The remaining two samples comes

D

from São Torpes beach sea-cliff south of Cape Sines. Here, a reddish-brown level of gravel with

TE

pebbles of volcanic and plutonic rocks, quartz, slates, quartzite and greywacke are supported by

(sample ST-6).

CE P

medium to fine grained sands (sample ST-5) and medium to fine grained iron-like colored sands

AC

3.1. Sample preparation, data acquisition and treatment Sands were submitted to standard procedures for heavy minerals gravity and magnetic separation (Mange and Maurer, 1992). Zircons (63-250 µm) were mounted in epoxy-type resin and coated with a golden cap after polishing. Mounts were subjected to cathodoluminescence (CL) imaging technique to study zircon internal morphology and select the targets for isotopic analysis avoiding fractures and inclusions (Boggs and Krinsley, 2006; Mange and Wright, 2007). Isotopic analyses of were performed at the Mineralogy and Geology Museum of the Senckenberg Naturhistorische Sammlungen Dresden, using a Thermo-Scientific Element 2 XR sector field ICP-MS coupled to a New Wave UP-193 Excimer Laser System (e.g., Košler and Sylvester, 2003; Guillong, 2004; Kosler, 2007). To enable sequential sampling of heterogeneous grains (e.g., growth zones) during time

ACCEPTED MANUSCRIPT

7

resolved data acquisition a teardrop-shaped, low volume laser cell was used. Each analysis (laser spot-sizes of 15–35 μm) consisted of 15 s background acquisition followed by 35 s data acquisition.

T

A common-Pb correction based on the interference and background corrected 204Pb signal and a

IP

model Pb composition (Stacey and Kramers, 1975) was applied when necessary. The necessity of the

SC R

correction is judged on whether the corrected 207Pb/206Pb lies outside of the internal errors of the measured ratios. An Excel® spreadsheet program developed by Axel Gerdes (Institute of Geosciences, Johann Wolfgang Goethe-University Frankfurt) was used for raw data correction for

NU

background signal, common Pb, laser induced elemental fractionation, instrumental mass

MA

discrimination, and time-dependent elemental fractionation of Pb/Th and Pb/U. Reported uncertainties were propagated by quadratic addition of the external reproducibility obtained from: (i)

D

the standard zircon GJ-1 (~0.6% and 0.5–1% for the 207Pb/206Pb and 206Pb/238U, respectively) during

TE

individual analytical sessions, and (ii) the within-run precision of each analysis. Data interpretation in the form of concordia diagrams were accomplished at 2 sigma error ellipses

CE P

and concordia ages with 95% confidence interval, using Isoplot 4 (Ludwig, 2009). Probability density plots (PDP) were graphed with the AgeDisplay (Sircombe, 2004) software application.

AC

Kernel density estimator (KDE), were graphed using DensityPlotter (Vermeesch, 2012). PDP and KDE curves are based on U-Pb data within the interval of 90-110% of concordance. The 207Pb/206Pb age was taken for data presentation and interpretation for all zircons >1.0 Ga, and 206Pb/238U ages for younger grains. For further details on analytical protocol and data processing, see Frei and Gerdes (2009). In the attribution of radiometric ages to chronostratigraphic subdivisions/units we followed the International Chronostratigraphic Chart v2013/01 (www.stratigraphy.org).

3.2. Kolmogorov–Smirnov test To statistically test hypotheses of correlation between the populations of zircon ages of the PliocenePleistocene sands sampled at the same beach, the Kolmogorov–Smirnov test was used (Fig. 4). The

ACCEPTED MANUSCRIPT

8

Kolmogorov-Smirnov non-parametric test has been successfully used in zircon geochronological studies (Berry et al., 2001; DeGraaff-Surpless et al., 2003; Guynn and Gehrels, 2010). This test

T

calculates the maximum probability distance between two cumulative distribution functions (CDF)

IP

of two age distributions (Barbeau et al., 2009), or in other words, the test produces a probability p of

SC R

two samples be derived from the same population (Berry et al., 2001). The null hypothesis states that the two distributions are the same (Guynn and Gehrels, 2010). Barbeau et al. (2009) suggest a p value of 0.05 for provenance studies with a 95% confidence interval. Values which fall in the range

NU

0.001

MA

(Fernández-Suárez et al., 2013). Considering this, it can be established that if p>0.05 it is unlikely that the samples belong to different populations, or, it is likely that the two age distributions are

D

derived from the same population; in the other hand, if p<0.05 it is probable that the two samples

TE

were from different populations (Guynn and Gehrels, 2010). This non-parametric test can be used to test the quality of the fit between populations with any data distribution, with the advantages of not

CE P

having to group the data into arbitrary categories and not being constrained to the size of the samples allowing the use of either big (n>40) or small samples. The samples to be compared may be

AC

presented together in cumulative curves from 0.0 to 1.0 (Fig. 4). The Kolmogorov–Smirnov test was applied in this study to test the similarity between the different samples of Pliocene-Pleistocene sand, comparing them in batches of two. The distance between the cumulative curves is proportional to the degree of similarity between them: the closer together they are the greater the similarity.

4. Results

4.1. CL imaging Igneous zircons without an inherited core are dominant in sample AB-3/AB-4 and PN-1/PN-2 while most of the grains of sample ST-5/ST-6 are detrital. CL imaging shows that igneous zircons (Fig. 5)

ACCEPTED MANUSCRIPT

9

have concentric oscillatory zoning (Sample AB-4, analysis C19; Sample PN-1, analysis A30; Sample ST-5, analysis B13), are banded (Sample AB-4, analysis B4; Sample PN-1, analysis B32; Sample

T

ST-5, analysis B40), have irregular zoning (Sample AB-4, analyses A45 and B49) or are unzoned

IP

(Sample AB-4, analyses C3 and A22) (Fig. 5). Other grains are characterized by cores with

SC R

concentric zoning or by an irregular to unzoned core surrounded by rims with concentric oscillatory zoning or irregular zoning (Sample AB-4, analyses B47; Sample PN-1, analyses A52 and A20; Sample ST5, analysis B16; Sample ST6, analysis A22; Fig. 5). Most zircons probably derived from

NU

magmatic rocks without inherited grains. But there is also a population of zircons with a more

MA

complex history that were involved in several sedimentary cycles showing inherited cores that have resisted to high temperature conditions and were surrounded by new magmatic zircon growths.

D

4.2. U-Pb ages

TE

The results obtained with the Kolmogorov–Smirnov test (Fig. 4) indicate that U–Pb age distributions in Pliocene-Pleistocene sand from the same sea-cliff are not significantly different at the 5 %

CE P

confidence level and can therefore be joined in pairs (Figs. 5, 6): AB-3+AB-4 (Areias Brancas beach; from a total of 307 analyses, 214 206Pb/238U isotopic ages U-Pb ages fall in the interval of 90-

AC

110% concordance), PN-1+PN-2 (Norte beach; from a total of 195 analyses, 171 206Pb/238U isotopic ages U-Pb ages fall in the interval of 90-110%) and ST-5+ST-6 (São Torpes beach; from a total of 146 analyses, 107 206Pb/238U isotopic ages U-Pb ages fall within the interval 90-110% concordance). Comparison of 3 pairs of samples of Pliocene-Pleistocene sands (AB-3/AB-4, PN-1/PN-2 and ST5/ST-6) reveals that there are remarkable similarities as regards their population of pre-Devonian ages as well as differences with regard to their younger ages (Fig. 5, 6). The Precambrian detrital zircons of the Pliocene-Pleistocene sands have a very characteristic age population (1.0 Ga-541 Ma; 2.2-1.7 Ga; Fig. 5, 6). In the population of Neoproterozoic detrital zircons, Cryogenian-Ediacaran ages are dominant (17-19%; ca. 846-541 Ma) and Tonian ages less common (1-2 %; ca. 1.0 Ga to 854 Ma). Mesoproterozoic grains are scarce and best represented in

ACCEPTED MANUSCRIPT

10

AB-3/AB-4 sands (4 %; ca. 1.0 Ga) as compared with PN-1/PN-2 sands (1%; ca. 1.0 Ga) and ST5/ST-6, in which grains of this age are absent. Zircons with Paleoproterozoic and Archean ages (ca.

T

2.2-1.7 Ga and ca. 2.7-2.5 Ga) are scarce and scattered. The PN-1/PN-2 pair shows the highest

IP

percentage of Paleoproterozoic ages (8%; ca. 2.2 Ga-1.8 Ga) as compared with the other two pairs

SC R

(4-5%; ca. 2.1-1.7 Ga). A few detrital zircons with Archean ages are a feature in all pairs (1-2%; ca. 2.9-2.5 Ga). In AB-3/AB-4 and PN-1/PN-2 sands, Cryogenian ages are dominant over Ediacaran ages while in ST-5/ST-6 sands the reverse occurs (Fig. 6).

NU

Paleozoic detrital zircons constitute the largest population sampled in the Pliocene-Pleistocene ST-

MA

5/ST-6 and AB3/AB4 sands (53-71%; Fig. 6). Middle Ordovician to Silurian zircon ages are scarce but not completely absent. Only few detrital zircons with Silurian ages (ca. 442 Ma and 422 Ma) are

D

present in the AB-3 sands. All samples of Pliocene-Pleistocene sands from the Alvalade basin have

TE

very similar populations of Cambrian-Ordovician detrital zircons (Fig. 6). For Paleozoic ages younger than the Silurian, the differences are marked between the all sample groups: 10 to 38%,

CE P

whereas for older ages the similarities are greater than the differences, which account for no more than 5% (Figs. 8, 9). Devonian-Carboniferous ages are more common in samples AB-3/AB-4 (65%)

AC

than in ST 5/ST-6 (44%) and PN-1/PN-2 (25%; Fig. 6). Early Devonian ages are less commonly represented than late Devonian or Carboniferous ones and show a principal age peak at ca. 412 Ma. For all samples, Carboniferous grains are dominant, followed by late Devonian ages (Fig. 6). Late Devonian and Carboniferous detrital zircons have ages ranging ca. 388-300 Ma with greater representation of ages older than ca. 315 Ma and PDP curves showing different main age peaks (Fig. 6). AB-3/AB-4 sands have 19 grains with ages in the range ca. 315-300 Ma, PN-1/PN-2 includes 14 grains dated at ca. 315-277 Ma and in ST-5/ST-6 sands were found 8 grains in the range ca. 314-305 Ma. A secondary age cluster around 376 Ma is found in AB-3/AB-4 sands that are the only sample that includes detrital zircons with Silurian crystallization ages. In ST-5/ST-6 sands, Cambrian-

ACCEPTED MANUSCRIPT

11

Ordovician ages are most common (8%) as compared with the other two pairs (4-5%). PN-2 is the only sample containing zircons of Permian age (five zircons, 3%; ca. 298-277 Ma).

T

For all samples it was noticed an absence of detrital zircons from the Triassic and Jurassic. The

IP

presence of late Cretaceous detrital zircons in PN-1/PN-2 and ST-5/ST-6 sands (21-38%), both

SC R

sampled in the vicinity of the Sines Massif, contrasts with their absence in the AB-3/AB-4 sands, sampled 12 km further North (Fig. 6). Cretaceous zircons occur in the interval ca. 95-72 Ma and their PDP curves show main age peaks at ca. 82 Ma and 80 Ma (Samples PN-1 and ST-5/ST-6) and

MA

NU

younger peaks at ca. 72 and 76 Ma (Sample PN-2; Fig. 6).

5. Discussion

D

5.1. The origin and transport history of sediment within the Alvalade basin

TE

Paleogeographic maps for Miocene-Pliocene time display directions of sediment transport from source areas to sediment repositories in SW Iberia (Cunha et al., 2009; Pais et al., 2012; Fig. 7 A-C).

CE P

These representations do not focus on the interplay of drainage basin evolution and tectonism that has caused a protracted and general uplift of Iberia since the Paleogene (Vegas et al., 1990; De

AC

Bruijne and Andriessen, 2000; Cloetingh et al., 2002; Brum da Silveira et al., 2009). In the Miocene, NW–SE Betic compression caused landscape rejuvenation with the reactivation of pre-existing structures and formation of elevated areas in Iberia (Ribeiro et al., 1990; Vegas et al., 1990;De Bruijne and Andriessen, 2000, 2002; Cloetingh et al., 2002; De Vicente et al., 2011). In this tectonic context, denudation rates were high in the mountainous regions, like the Central System (Spanish and Portuguese), and drainage systems (Tagus river) were very effective at erosion and transportation of sediment. During the Miocene (Fig. 7A-B) alluvial fan deposits of the distal sector of the Lower Tagus basin (Vale de Guizo Formation in Lisboa-Setúbal Peninsula) were fed from uplifted areas of central Iberia (Pais et al., 2012) while in the Alvalade basin may have been a contribution from source areas of southwestern Iberia (Azevedo and Pimentel, 1995; Pimentel,

ACCEPTED MANUSCRIPT

12

1997). After the Miocene (Fig. 7C), the two depressions were separated by a high topographic relief bordered by the Torrão fault, and therefore evolved independently having a distinct history of filling

T

(Antunes and Mein, 1989; Antunes and Pais, 1993). The Alpine tectonic activity in creating this

IP

elevated relief probably exposed to erosion sedimentary rocks of the distal sector of the Lower Tagus

SC R

basin (Vale do Guizo Formation) that contributed in part to the Pliocene-Pleistocene filling of the Alvalade basin with detritus from original source areas located in the Central Iberia Zone (Fig. 8). Paleocurrents in the Pliocene-Pleistocene fluvial sandy-conglomeratic deposits of the Alvalade

NU

Formation indicate sediment transport from east to northwest (Pimentel, 1997). This transport

MA

direction is also known in the Moura basin (Pais et al., 2012) whose drainage evolution was controlled by the Vidigueira-Moura fault (Brum da Silveira et al., 2009). The Vidigueira-Moura fault

D

may represent the eastern extension of the Torrão fault and thus be a clue to admit that the Alvalade

TE

and Moura basins evolved together during the Pliocene-Pleistocene. Thus, the origin of the Pliocene-Pleistocene sediment might be related to a complex drainage system

CE P

developed in different source areas surrounding the Alvalade basin and controlled by active W-E and NE-SW-trending faults (Fig. 7D): i) one elevated area with Eocene-Miocene sedimentary rocks

AC

(sandstone and conglomerate) overlying Paleozoic basement rocks of the South-Portuguese Zone, located north of the Sines massif and bordered by the W-E- trending Torrão-Vidigueira-Moura fault system. This source area could explain the the supply of detrital zircons with Paleozoic ages younger than ca. 315 Ma that are not usual in the Ossa-Morena and South-Portuguese basement rocks (Figs. 8, 9); ii) another elevated area located further east controlled by NW-SE-trending residual reliefs with outcropping resistant rocks of the Ossa-Morena and South-Portuguese zones (gabbro, diorite, quartzite, greywacke and rhyolite) defining the inherited Variscan structure. This network was possibly connected with the Moura basin which has similar basement geology. This connection was likely lost by reactivation of the Messejana fault system, and iii) a western area closer to the Atlantic Ocean that exposed South Portuguese Zone sedimentary rocks, Triassic sedimentary rocks of the

ACCEPTED MANUSCRIPT

13

Alentejo basin with detrital zircon populations derived from the Ossa-Morena and South-Portuguese zones and Cretaceous gabbro and syenite from the Sines massif.The gravel was transported from

T

source areas of Paleozoic basement of the Phyllite-Quartzite Formation, the Baixo Alentejo Flysch

IP

Group and the Carboniferous plutonic rocks. Red sandstone pebbles were derived from the Triassic

SC R

(Alentejo basin); and gabbro and syenite pebbles from the Sines massif. The Sines massif is interpreted here as the source of Cretaceous zircons found in the PN-1/PN-2 and ST-5/ST-6 sands (Figs. 8, 9), since other sources are located outside the limits of the Alvalade hydrographic basin, and

NU

the external morphology of these younger grains indicate a short transport distance. The absence of

MA

detrital zircons with Cretaceous ages in AB-3/AB-4 sands either implies source area changes or episodes of deposition without provenance from the Sines massif, indicating that the influence of this

TE

D

source is limited to the north.

interpretation

CE P

5.2. Detrital zircon populations in the Alvalade basin: sediment sources and paleotectonic

The Precambrian detrital zircons of the Pliocene-Pleistocene sand exhibit the characteristic age

AC

populations (ca. 1.0 Ga-541 Ma and ca. 2.2-1.7 Ga) found in the oldest sedimentary rocks (Ediacaran) outcropping in the Ossa-Morena Zone and southern domains of the Central-Iberian Zone (Linnemann et al., 2008; Pereira et al., 2008, 2012a, 2012c; Figs. 8, 9). The absence of Mesoproterozoic ages is a characteristic of the Ossa-Morena Zone (Pereira et al., 2008 and references therein). Other potential sources for Precambrian detrital zircons are (Figs. 8, 9): i) the Cambrian and Ordovician sedimentary and igneous rocks of the Ossa-Morena Zone and CentralIberian Zone, that contain inherited zircons with 206Pb/238U ages of ca. 660-520 Ma, 2.1-1.6 Ga and 3.3-3.2 Ga (Linnemann et al., 2008; Pereira et al., 2008, 2011, 2012b, 2012c; Solá et al., 2008; ii) the Carboniferous sedimentary rocks of the Flysch Group of Baixo Alentejo, with 206Pb/238U ages of detrital zircons of ca. 548-844 Ma, 992-891 Ma, 1.4-1.0 Ga, 1.9-1.7 Ga, 2.4-1.8 Ga, 2.9-2.8 Ga

ACCEPTED MANUSCRIPT

14

(Pereira et al., 2013a); iii) the Carboniferous granitoids of the Ossa-Morena Zone, with inherited zircons in the interval ca. 698-577 Ma, 2.6-1.8 Ga, 3.3-3.2 Ga (Pereira et al., 2009; Solá et al., 2008,

T

2009; Lima et al., 2012); and iv) the Late Triassic sandstones of the Alentejo basin, with detrital

IP

zircon 206Pb/238U ages of ca. 821-555 Ma, ca. 1.2-1.0 Ga and ca. 2.1-1.6 Ga and of the Algarve

SC R

Basin, with ages of ca. 851-558 Ma, ca. 1.5-1.0 Ga and ca. 2.82-1.62 Ga (Vilallonga, 2013, Pereira et al., 2013b). From a paleotectonic perspective, the Paleoproterozoic and Neoarchean detrital zircon grains of the Pliocene-Pleistocene sand (ca. 2.2-1.7 Ga and ca. 2.7-2.5 Ga) are typical of the West-

NU

African Craton, located in inland North Gondwana (Kouamelan et al., 1997; Dirks et al., 2003; Drost

MA

et al., 2011 and references therein). Cryogenian-Ediacaran ages (ca. 846-541 Ma; this study) are possibly related to arc-magmatism preserved in the Cadomian belt (ca. 700-545 Ma; Linnemann et

D

al., 2004, 2008; Pereira et al., 2008, 2012a; Drost et al., 2011, and references therein).

TE

Probable sources of the Cambrian-Ordovician grains found in the Pliocene-Pleistocene sand (with crystallization ages of ca. 541-457 Ma; Figs. 8, 9) are: i) Ordovician and Cambrian igneous and

CE P

sedimentary rocks of the Ossa-Morena Zone and Central-Iberian Zone (ca. 540-488 Ma; Linnemann et al., 2008; Solá et al., 2008; Sánchez-Garcia et al., 2010; Pereira et al., 2011, 2012b, 2012c); ii)

AC

Carboniferous sedimentary rocks of the Flysch Group of the Baixo Alentejo with detrital zircons bearing 206Pb/238U crystallization ages of ca. 517-503 Ma (Pereira et al., 2013a); and iii) Late Triassic sandstones of the Alentejo basin with detrital zircon bearing 206Pb/238U crystallization ages of ca. 539-522 Ma (Vilallonga, 2013; Pereira et al., 2013b). The Cambrian and Ordovician detrital zircons are probably associated with post-Cadomian rifting in North Gondwana prior to opening of the Rheic Ocean (dated at ca. 530-470 Ma; Chichorro et al., 2008; Sanchez-Garcia et al., 2008, 2010, Pereira et al., 2013a). Middle Ordovician to Silurian zircon grains are rare in the Pliocene-Pleistocene sand. The origin of the Silurian grains (ca. 442-422 Ma) can be traced to recycled detrital grains contained in the Late Carboniferous flysch deposits (ca. 447-416 Ma; Pereira et al., 2013a) and in the Devonian Phyllite-

ACCEPTED MANUSCRIPT

15

Quartzite Formation (ca. 430-420 Ma; Pereira et al., 2012a) that in both cases have been associated with possible sources in Peri-Laurentian terranes (bearing similar detrital zircon radiometric

T

fingerprints; Van Staal et al., 2009).

IP

Middle to Early Devonian detrital grains were probably sourced from (Figs. 8, 9): i) volcanic rocks

SC R

of the Pyrite Belt (South Portuguese Zone) dated at ca. 384 Ma (Oliveira et al., 2013); ii) Carboniferous sedimentary rocks of the Flysch Group of the Baixo Alentejo with detrital zircons bearing 206Pb/238U ages of ca. 402-385 Ma (Pereira et al., 2013a); and iii) Lower Carboniferous

NU

sedimentary rocks of the Ossa-Morena Zone carrying detrital zircons with ca. 387-359 Ma 206Pb/238U

MA

ages (Pereira et al., 2012a).

The Late Devonian-Carboniferous zircon crystallization ages discovered in Pliocene-Pleistocene

D

sands (ca. 388-300 Ma) coincide with the ages obtained for the Late Paleozoic rocks that crop out in

TE

SW Iberia (Figs. 8, 9): i) Late Devonian-Early Carboniferous volcanic rocks of the volcanicsedimentary complex (Pyrite Belt in the South Portuguese Zone) with 206Pb/238U ages from ca. 374 to

CE P

ca. 346 Ma (Rosa et al., 2009; Oliveira et al., 2013); ii) sedimentary rocks of the Carboniferous Flysch Group of the Baixo Alentejo with 206Pb/238U ages of ca. 385-312 Ma (Pereira et al., 2013a);

AC

iii) Carboniferous igneous rocks of the Ossa-Morena Zone with zircon crystallization ages in the interval ca. 320-355 Ma (Pin et al., 2008; Pereira et al., 2009; Lima et al., 2012); iv) Early Carboniferous clastic and volcanoclastics rocks of the Ossa-Morena Zone with detrital igneous zircons with 206Pb/238U ages of ca. 353-319 Ma (Pereira et al., 2012a); and v) Late Triassic sandstones of the Alentejo basin with detrital igneous zircons with 206Pb/238U ages of ca. 358-327 Ma (Vilallonga, 2013). Remote source areas of inland Iberia such as the Carboniferous granitoids (Fig. 8) rendered 206Pb/238U crystallization ages of: i) ca. 313-319 Ma, ca. 306-311 Ma and ca. 300 Ma in the Central-Iberian Zone (Dias et al., 1998; Valle Aguado et al., 2005; Neiva et al., 2009), and ii) ca. 318 to 305 Ma on the Ossa-Morena Zone-Central-Iberian Zone boundary (Solá et al., 2009; Pereira et al., 2010). As regards the Carboniferous detrital zircon populations, they can be related to the

ACCEPTED MANUSCRIPT

16

synorogenic magmatism preserved in SW Iberia (Pereira et al., 2009, 2012d; Gutierrez-Alonso et al., 2011, and references therein).

T

Finally, the Late Cretaceous ages obtained for the detrital zircon grains of the Pliocene-Pleistocene

IP

sand studied (ca. 95-72 Ma) coincide with (Fig. 8): 1) the Sintra Massif that contains igneous zircons

SC R

with 206Pb/238U crystallization ages of ca. 85-75 Ma, whereas the Sines Massif contains igneous zircons with 206Pb/238U ages of ca. 78-72 Ma (Miranda et al., 2009; Grange et al., 2010); and 2) the Monchique Massif bearing igneous zircons with 206Pb/238U ages of ca. 73-67 Ma (Grange et al.,

NU

2010). This late Cretaceous zircon forming event is associated with within-plate magmatism and is

D

Merle et al., 2009; Grange et al., 2010).

MA

coeval with the opening of the North Atlantic Ocean (Miranda et al., 2009, and references therein;

TE

5. Conclusions

The improved resolution of sediment provenance from detrital zircon analysis of Pliocene-

CE P

Pleistocene sands from the Alvalade basin enables recognition of previously poorly documented origin and transport history of the sediment and the evolution of the regional drainage system related

AC

to Alpine tectonic activity. The detrital zircon age data obtained confirm previous studies that indicate the locus of the sediment source in the Paleozoic basement of SW Iberia (Ossa-Morena and South Portuguese zones) but also suggest a more complex history of drainage than previously documented involving other sources located to the north. Pliocene-Pleistocene sands were transported by a drainage system controlled by Alpine faults and from three areas. i) An elevated source area located at north of the Sines massif, bordered by the WE-trending Torrão-Vidigueira-Moura fault system and containing Miocene sedimentary rocks with inherited Central-Iberian Zone detrital zircon signature that probably supplied 8-9% of Carboniferous ages younger than ca. 315 Ma. ii) An eastern source area controlled by the NE-SWtrending Messejana fault, mainly associated with denudation of parallel elongate landforms

ACCEPTED MANUSCRIPT

17

representing inherited Variscan NW-SE-trending structures in the Paleozoic rocks of the OssaMorena and South-Portuguese zones and, iii) a source area close to the Atlantic Ocean with residual

T

of Mesozoic sedimentary (Alentejo basin) and igneous rocks (Sines massif). The radiometric age

IP

populations of detrital zircons ages also enables recognition of previously undocumented sources of

SC R

Pliocene-Pleistocene sands and decipher their paleotectonic meaning: i) Neoproterozoic to Lower Paleozoic meta-sedimentary and meta-igneous rocks of the Ossa-Morena and Central-Iberian zones, that formed in North Gondwana during the Cadomian Orogeny and opening of the Rheic Ocean; ii)

NU

Devonian to Carboniferous sedimentary and igneous rocks of the Ossa-Morena, Central-Iberian, and

MA

South-Portuguese zones formed when Gondwana and Laurussia collided (Variscan Orogeny); and iii) Late Triassic sedimentary rocks of the Alentejo (and Algarve) basin and Late Cretaceous igneous

TE

D

rocks of the Sines massif related to Pangea breakup and the opening of the Atlantic Ocean.

Acknowledgements

CE P

This paper is a contribution to research projects: GONDWANA-PTDC/CTE-GIX/110426/2009, GOLD- PTDC/GEO-GEO/2446/2012; COMPETE: FCOMP-01-0124-FEDER-029192 and

AC

ECOTRIS- EXPL/GEO-GEO/1253/2013; COMPETE: FCOMP-01-0124-FEDER-041504 (Portugal). L. Albardeiro acknowledges a FCT PhD grant SFRH/BD/72581/2010. C. Gama acknowledges a U.S. Department of State- Fulbright grant (Exchange visitor program: G-1-00005). We thank the careful review of the Editor and two reviewers who contributed decisively to improve the content of this paper.

References Antunes, M.T., 1983. Carta Geológica de Portugal na escala 1:50.000, Folha 39-C (Alcácer do Sal) e Notícia Explicativa. Serviços Geológicos de Portugal, Lisboa.

ACCEPTED MANUSCRIPT

18

Antunes, M.T., Mein, P., Pais, J., 1986. Depósitos messinianos do sul de Portugal, mamíferos (incluindo rodentia e lagomorpha) e idades K-Ar. Ciências da Terra (UNL) 8, 55-64.

T

Antunes, M.T., Mein, P., 1989. Petit mammifères du miocène terminal du Bassin de Alvalade

IP

(Portugal): comparaisons avec des faunes de l’Espagne et du Maghreb. Bolletino della

SC R

Societa Paleontologica Italiana 28, 161-170.

Antunes, M.T., Pais, J., 1993. The Neogene of Portugal. Ciências da Terra 12, 7-22. Azevedo, M.T., Pimentel, N.L., 1995. Dados para a discussão da génese da Bacia do Tejo-Sado no

NU

Paleogénico. Atas do IV Congresso Nacional de Geologia, Museu Laboratório Mineralogia E

MA

Geologia., Porto, Portugal. Memória 4, pp. 897-902.

Azevedo, M.R., Valle Aguado, B., 2006. Origem e Instalação de Granitóides Variscos na Zona

D

Centro-Ibérica. In: Dias, R. Araújo, A., Terrinha, P., Kullberg, J.C., (Coord.), Geologia de

TE

Portugal no Contexto da Ibéria, pp. 107-122. Balbino, A.C., 1995. Seláceos (Pisces) do Miocénico terminal da Bacia de Alvalade (Portugal).

CE P

Sistemática, ecologia, paleoambientes, comparação com faunas actuais. Ph.D Thesis, University of Évora.

AC

Barbeau, D.L., Davis, J.T., Murray, K.E., Valencia, V., Gehrels, G.E., Zahid, K.M., Gombosi, D. J., 2009. Detrital-zircon geochronology of the metasedimentary rocks of north-western Graham Land. Antarctic Science 22, 65-78. Berry, R.F., Jenner, G.A., Meffre, S., Tubrett, M.N., 2001. A North American provenance for Neoproterozoic to Cambrian sandstones in Tasmania. Earth and Planetary Science Letters 192, 207-222. Boggs, S., Krinsley, D., 2006. Application of Cathodoluminescence Imaging to the Study of Sedimentary Rocks. Cambridge University Press, Cambridge. Braid, J., Murphy, B., Quesada, C., Bickerton, L., Mortensen, J., 2012. Probing the composition of unexposed basement, South Portuguese Zone, southern Iberia: implications for the

ACCEPTED MANUSCRIPT

19

connections between the Appalachian and Variscan orogens. Canadian Journal of Earth Sciences 49, 591-613.

T

Brito, S., 2009. História da Terra durante os últimos 65 Ma: exemplos portugueses com interesse

IP

para o ensino. MsC thesis, University of Lisbon.

SC R

Brum da Silveira, A., Cabral, J., Perea, H., Ribeiro, A., 2009. Evidence for coupled reverse and normal active faulting in W Iberia The Vidigueira–Moura and Alqueva faults (SE Portugal). Tectonophysics 474, 184–199.

NU

Campbell, I.H., Reiners, P.W., Allen, C.M., Nicolescu, S., Upadhyay, R., 2005. He-Pb double dating

MA

of detrital zircons from the Ganges and Indus Rivers: Implication for quantifying sediment recycling and provenance studies. Earth and Planetary Science Letters 237, 402-432.

D

Canilho, M., 1989. Elementos de geoquímica das rochas do maciço ígneo de Sines. Ciências da Terra

TE

(UNL) 10, 65-80.

Cawood, P.A., Nemchin, A.A., Freeman, M., Sircombe, K., 2003. Linking source and sedimentary

CE P

basin: detrital zircon record of sediment flux along a modern river system and implications for provenance studies. Earth and Planetary Science Letters 210, 259-268.

AC

Chichorro, M., Pereira, M.F., Díaz-Azpiroz, M., Williams, I.S., Fernández, C., Pin, C., Silva, J.B., 2008. Cambrian ensialic rift-related magmatism in the Ossa-Morena Zone (Évora–Aracena metamorphic belt, SW Iberian Massif): Sm–Nd isotopes and SHRIMP zircon U–Th–Pb geochronology. Tectonophysics 461, 91-113. Cloetingh, S., Burov, E., Beekman, F., Andeweg, B., Andriessen, P., Garcia-Castellanos, D., De Vicente, G., Vegas, R. 2002. Lithospheric folding in Iberia. Tectonics 21, 1041–1067. Cunha, P.P., Pimentel, N., Pereira, D.I., 2000. Assinatura tectono-sedimentar do auge da compressão bética em Portugal: a descontinuidade sedimentar Valesiano terminal-Turoliano. Ciências da Terra (UNL) 14, 61-72.

ACCEPTED MANUSCRIPT

20

Cunha, P., Pais, J., Legoinha, P., 2009. Evolução geológica de Portugal continental durante o Cenozóico-sedimentação aluvial e marinha numa margem continental passiva (Ibéria

T

ocidental). Nuevas contribuciones al margen Ibérico Atlântico, 6º Simposio sobre el Margen

IP

Ibérico Atlántico MIA09, Oviedo, Spain, pp. 11–20.

SC R

Davis, D. W., Williams, I. S., Krogh, T. E., 2003. Historical development of zircon geochronology. In: Hanchar M., Hoskin, P.W.O. (eds), Zircon. Reviews in Mineralogy and Geochemistry 53, Mineral Society of America, Washington, D.C., pp. 145-181.

NU

De Bruijne, C.H., Andriessen, P.A.M., 2000. Interplay of intraplate tectonics and surface processes

MA

in the Sierra de Guadarrama (central Spain), assessed by Apatite Fission Track analysis. Physics and Chemistry of The Earth, Part A. Solid Earth and Geodesy 25, 555-563.

D

De Bruijne, C.H., Andriessen, P.A.M., 2002. Far field effects of Alpine plate tectonism in the Iberian

TE

microplate recorded by fault-related denudation in the Spanish Central System. Tectonophysics 349, 161-184.

CE P

De Vicente, G., Cloetingh, S., Van Wees, J.D., Cunha, P.P., 2011. Tectonic classification of Cenozoic Iberian foreland basins. Tectonophysics 502, 38–61.

AC

DeGraaff-Surpless, K., Mahoney, J.B., Wooden, J.L., McWilliams, M.O., 2003. Lithofacies control in detrital zircon provenance studies: Insights from the Cretaceous Methow basin, southern Canadian Cordillera. Geological Society of America Bulletin 115, 899-915. Dias, G., Leterrier, J., Mendes, A., Simões, P.P., Bertrand, J.M., 1998. U-Pb zircon and monazite geochronology of post-collisional Hercynian granitoids from the Central Iberian Zone (Northern Portugal). Lithos 45, 340-369. Dinis, J., Rey, J., Cunha, P.P., Callapez, P., Reis, R.P., 2008. Stratigraphy and allogenic controls of the western Portugal Cretaceous: an updated synthesis. Cretaceous Research 29, 772–780. Dirks, P., Jelsma, H., Blenkinsop, T., 2003. The Geology of Africa. In: Stuwe, K., Grasemann de Vivo (Eds.), EOLSS UNESCO Publishing, Oxford, UK, http://www.eolss.net.

ACCEPTED MANUSCRIPT

21

Drost, K., Gerdes, A., Jeffries, T., Linnemann, U., Storey, C., 2011. Provenance of Neoproterozoic and early Paleozoic siliciclastic rocks of the Teplá-Barrandian unit (Bohemian Massif):

T

evidence from U–Pb detrital zircon ages. Gondwana Research 19, 213–231.

IP

Eguiluz, L., Ibarguchi, J., Ábalos, B., Apraiz, A., 2000. Superposed Hercynian and Cadomian

Society of America Bulletin 112, 1398-1413.

SC R

orogenic cycles in the Ossa-Morena zone and related areas of the Iberian Massif. Geological

Fedo, C.M., Sircombe, K.N., Rainbird, R.H., 2003. Detrital zircon analysis of the sedimentary

NU

record. In: Hanchar M., Hoskin, P.W.O. (eds), Zircon. Reviews in Mineralogy and

MA

Geochemistry 53, Mineral Society of America, Washington, D.C., pp. 277-303. Fernández-Suárez, J., Gutiérrez-Alonso, G., Pastor-Galán, D., Hofmann, M., Murphy, J., Linnemann,

D

U., 2013. The Ediacaran–Early Cambrian detrital zircon record of NW Iberia: possible

TE

sources and paleogeographic constraints. International Journal of Earth Sciences (Geol Rundsch). DOI 10.1007/s00531-013-0923-3.

CE P

Frei, D., Gerdes, A., 2009. Precise and accurate in situ U-Pb dating of zircon with high sample throughput by automated LA-SF-ICP-MS. Chemical Geology 261, 261-270.

AC

Galloway, W.E., Whiteaker, T.L., Ganey-Curry, P.E., 2011. History of Cenozoic North American drainage basin evolution, sediment yield, and accumulation in the Gulf of Mexico basin. Geosphere 7, 938–973. Gehrels, G.E., Blakey, R., Karlstrom, K.E., Timmons, J.M., Dickinson, B., Pecha, M., 2011. Detrital zircon U-Pb geochronology of Paleozoic strata in the Grand Canyon, Arizona. Lithosphere 3, 183–200. Grange, M., Scharer, U., Merle, R., Girardeau, J., Cornen, G., 2010. Plume-Lithosphere Interaction during Migration of Cretaceous Alkaline Magmatism in SW Portugal: Evidence from U-Pb Ages and Pb-Sr-Hf Isotopes. Journal of Petrology 51, 1143-1170.

ACCEPTED MANUSCRIPT

22

Guillong, M., 2004. Laser Ablation Inductively Coupled Plasma Mass Spectrometry: Laser ablation system developments and investigations on elemental fractionation. Phd Thesis, Eidgen

T

Äossischen Technischen Hochschule Züurich.

IP

Gutiérrez-Alonso, G., Fernández-Suárez, J., Jeffries, T.E., Johnston, S.T., Pastor-Galán, D., Murphy,

SC R

J.B., Franco, M.P., Gonzalo, J.C., 2011. Diachronous post-orogenic magmatism within a developing orocline in Iberia, European Variscides. Tectonics 30, doi:10.1029/2010 TC002845.

NU

Guynn, J., Gehrels, G., 2010. Comparison of detrital zircon age distributions using the K-S Test.

MA

Arizona LaserChron Center. https://laserchron.org/.

Inverno, C.M.C., Manuppella, G., Zbyszewski, G., Pais, J., Ribeiro, M.L., 1993. Notícia explicativa

D

da Folha 42-C (1/50 000) – Santiago do Cacém. Serviços Geológicos de Portugal, Lisboa.

TE

Jesus, A., Munhá, J., Tassinari, C., Nutpan, A., 2007. The Beja layered gabbroic sequence (OssaMorena Zone, Southern Portugal): geochronology and geodynamic implications.

CE P

Geodinamica Acta 20, 139-157.

Kinny, P.D., Maas, R., 2003. Lu-Hf and Sm-Nd isotope systems in zircon. In: Hanchar M., Hoskin,

AC

P.W.O. (eds), Zircon. Reviews in Mineralogy and Geochemistry 53, Mineral Society of America, Washington, D.C., pp. 327-341. Košler, J., 2007. Laser ablation ICP-MS – a new dating tool in Earth Sciences. Proceedings of the Geologists’ Association 118, 19-24. Košler, J., Sylvester, P.J., 2003. Present Trends and the Future of Zircon in Geochronology: Laser Ablasion ICPMS. In: Hanchar M., Hoskin, P.W.O. (eds), Zircon. Reviews in Mineralogy and Geochemistry 53, Mineral Society of America, Washington, D.C., pp. 243-275. Koulamelan, A.N., Delor, C., Peucat, J.J., 1997. Geochronological evidence for reworking of Archean terrains during the Early Proterozoic (2.1 Ga) in the western Côte d’Ivoire (Man Rise, West African craton). Precambrian Research 86, 177–199.

ACCEPTED MANUSCRIPT

23

Lima, S.M., Corfu, F., Neiva, A.M.R., Ramos, M.F., 2012. Dissecting complex magmatic processes: an in-depth U-Pb Study of the Pavia Pluton, Ossa-Morena Zone, Portugal. Journal Petrology

T

53, 1887–1911.

IP

Linnemann, U., McNaughton, N.J., Romer, R.L., Gehmlich, M., Drost, K., Tonk, C., 2004. West

SC R

African provenance for Saxo-Thuringia (Bohemian Massif): did Armorica ever leave prePangean Gondwana? U/Pb–SHRIMP zircon evidence and the Nd-isotopic record. International Journal of Earth Sciences 93, 683–705.

NU

Linnemann, U., Pereira, M., Jeffries, T., Drost, K., Gerdes, A., 2008. Cadomian Orogeny and the

MA

opening of the Rheic Ocean: new insights in the diachrony of geotectonic processes constrained by LA-ICP-MS U-Pb zircon dating (Ossa-Morena and Saxo-Thuringian Zones,

D

Iberian and Bohemian Massifs). Tectonophysics, 461, 21–43.

TE

Ludwig, K.R., 2009. Isoplot v.4 for Excel 2007. Berkeley Geochronological Centre, Berkeley, California.

CE P

Mange, M.A, Maurer, H.F.W., 1992. Heavy Minerals in Color. London, Chapman and Hall. Mange, M.A., Wright D.T., 2007. High-resolution heavy mineral analysis (HRMA): a brief

AC

summary. In: Mange, M.A., Wright, D.T. (eds) Developments in Sedimentology 58, Elsevier, Amsterdam, pp. 433-436. Manuppella, G., 1988. Litostratigrafia e tectónica da Bacia Algarvia. Geonovas 10, 67-71. Martins, L.T., Madeira, J., Youbi, N., Munhá, J., Mata, J., Kerrich, R., 2008. Rift-related magmatism of the Central Atlantic magmatic province in Algarve, Southern Portugal. Lithos 101, 102– 124. Merle, R., Jourdan, F., Marzoli, A., Renne, P.R., Grange, M., Girardeau, J., 2009. Evidence of multiphase Cretaceous to Quaternary alkaline magmatism on Tore Madeira Rise and neighboring seamounts from 40Ar/39Ar ages. Journal of the Geological Society of London 166, 879-894.

ACCEPTED MANUSCRIPT

24

Miranda, R., 2010. Petrogenesis and geochronology of the late Cretaceous alkaline magmatism in the west Iberian margin. PhD Thesis, Universidade de Lisboa.

T

Miranda, R., Valadares, V., Terrinha, P., Mata, J., Azevedo, M., Gaspar, M., Kulberg, J, Ribeiro, C.,

IP

2009. Age constrains on the Late Cretaceous alkaline magmatism on the West Iberian

SC R

Margin. Cretaceous Research 30, 575-586.

Morton, A.C., Whitham, A.G., Fanning, C.M., 2005. Provenance of Late Cretaceous to Paleocene submarine fan sandstones in the Norwegian Sea: Integration of heavy mineral, mineral

NU

chemical and zircon age data. Sedimentary Geology 182, 3-28.

MA

Neiva, A.M.R., Williams, I.S., Ramos, J.M.F., Gomes, M.E.P., Silva, M.M.V.G., Antunes, I.M.H.R., 2009. Geochemical and isotopic constraints on the petrogenesis of Early Ordovician

D

granodiorite and Variscan two-mica granites from the Gouveia area, central Portugal. Lithos

TE

111, 186-202.

Oliveira, J.T. (Coord.) and further authors, 1984. Carta Geológica de Portugal, escala 1/200000,

CE P

Notícia Explicativa da Folha 7. Serviços Geológicos de Portugal, Lisboa. Oliveira, J.T., 1990. Stratigraphy and synsedimentary tectonism. In: Dallmeyer, R.D., Martinez-

AC

Garcia, E. (Eds), Pre-Mesozoic Geology of Iberia. Springer Verlag. Berlin, Heidelberg, pp. 334 – 347.

Oliveira, J.T., Pereira, E., Ramalho, M., Antunes, M.T., Monteiro, J.H., 1992. Carta Geológica da Região de Portugal, escala 1/500 000. Serviços Geológicos de Portugal, Lisboa. Oliveira, J.T, Rosa, C.J.P., Pereira, Z., Rosa, D.R.N., Matos, J.X., Inverno, C.M.C., Andersen, T., 2013. Geology of the Rosário-Neves Corvo antiform, Iberian Pyrite Belt, Portugal: new insights from physical volcanology, palynostratigraphy and isotope geochronology studies. Mineralium Deposita 48, 749-766. Pais, J., Cunha, P., Pereira, D., Legoinha, P., Dias, R., Moura, D., Brum da Silveira, A., Kullberg, J., González-Delgado, J., 2012. The Paleogene and Neogene of Western Iberia (Portugal) – A

ACCEPTED MANUSCRIPT

25

Cenozoic Record in the European Atlantic Domain. Springer Briefs in Earth Sciences, Springer, Berlin.

IP

Portugal. Memórias Serviços Geológicos Portugal 25, Lisboa.

T

Palain, C., 1976. Une série détritique terrigène. Les «Grès de Silves»: Trias et Lias inférireur du

SC R

Pereira, M.F., Chichorro, M., Williams, I.S., Silva, J.B., 2008. Zircon U–Pb geochronology of paragneisses and biotite granites from the SW Iberian Massif (Portugal): evidence for a paleogeographic link between the Ossa-Morena Ediacaran basins and the West African

NU

craton. In: Liégeois, J. P., Nasser E. (eds), The Boundaries of the West African Craton.

MA

Geological Society of London Special Publication 297, pp. 385–408. Pereira, M.F., Chichorro, M., Williams, I.S., Silva, J.B., Fernandez, C., Diaz-Azpiroz, M., Apraiz,

D

A., Castro, A., 2009. Variscan intra-orogenic extensional tectonics in the Ossa-Morena Zone

TE

(Évora-Aracena-Lora del Río metamorphic belt, SW Iberian Massif): SHRIMP zircon U-ThPb geochronology. In: Murphy B. (ed), Ancient and modern analogues. Geological Society

CE P

London Special Publication 327, pp. 215-237. Pereira, M.F., Silva, J.B., Drost, K., Chichorro, M., Apraiz, A., 2010. Relative timing of transcurrent

AC

displacements in northern Gondwana: new U–Pb laser ablation MS–ICP–MS zircon and monazite geochronology of gneisses and sheared granites from the Western Iberian Massif (Portugal). Gondwana Research 17, 461-481. Pereira, M.F., Chichorro, M., Solá, A.R., Silva, J.B., Sánchez-García, T., Bellido, F., 2011. Tracing the Cadomian magmatism with detrital/inherited zircon ages by in situ U-Pb SHRIMP geochronology (Ossa-Morena Zone, SW Iberian Massif). Lithos 123, 204-217. Pereira, M., Chichorro, M., Johnston, S., Gutiérrez-Alonso, G., Silva, J., Linnemann, U., Hofmann, M., Drost, K., 2012a. The missing Rheic ocean magmatic arcs: Provenance analysis of Late Paleozoic sedimentary clastic rocks of SW Iberia. Gondwana Research 22, 882-891.

ACCEPTED MANUSCRIPT

26

Pereira, M.F., Linnemann, U., Hofmann, M., Chichorro, M., Solá, A.R., Medina, J., Silva, J.B., 2012b. The provenance of Late Ediacaran and Early Ordovician siliciclastic rocks in the

T

Southwest Central Iberian Zone: Constraints from detrital zircon data on northern Gondwana

IP

margin evolution during the late Neoproterozoic. Precambrian Research 192, 166-189.

SC R

Pereira, M.F., Solá, A.R., Chichorro, M., Lopes, L., Gerdes, A, Silva, J.B., 2012c. North-Gondwana assembly, break-up and paleogeography: U-Pb isotope evidence from detrital and igneous zircons of Ediacaran and Cambrian rocks of SW Iberia. Gondwana Research 22, 866–881.

NU

Pereira, M., Chichorro, M., Silva, J., Ordóñez-Casado, B., Lee, J., Williams, I., 2012d. Early

MA

Carboniferous wrenching, exhumation of high-grade metamorphic rocks and basin instability in SW Iberia; Constrains derived from structural geology and U-Pb and 40Ar-39Ar

D

geochronology. Tectonophysics 558-559, 28-44.

TE

Pereira, M.F., Ribeiro, C., Vilallonga, F., Chichorro, M., Drost, K., Silva, J.B., Albardeiro, L., Hofmann, M., Linnemann, U., 2013a. Variability over time in the sources of South

CE P

Portuguese Zone turbidites: evidence of denudation of different crustal blocks during the assembly of Pangea, International Journal Earth Sciences (Geol Rundsch), DOI

AC

10.1007/s00531-013-0902-8 Pereira, M., Chichorro, M., Gutierrez-Alonso, G., Vilallonga, F., Drost, K., Ribeiro, C., Silva, J., Albardeiro, L., Hofmann, M., Linnemann, U., 2013b. The significanse of changes in the source areas during the Carboniferous turbiditic deposition (SW Iberia). STRATI2013 Proceedings, 1st International congress on Stratigraphy. Lisbon. Ciências da Terra vol. esp. VII, 118. Pimentel, N., 1997. O Terciário da Bacia do Sado. Sedimentologia e análise tectono-sedimentar. PhD Thesis, Universidade de Lisboa. Pimentel, N.L., Azevedo, T.M., 1992. Os depósitos de Raña no sudoeste ibérico (Baixo Alentejo ocidental, Portugal). Monografias C. C. Medioambiente 2, 59-69.

ACCEPTED MANUSCRIPT

27

Pin, C., Fonseca, P., Paquette, J-L., Castro, P., Matte, F., 2008. The ca. 350 Ma Beja Igneous Complex: A record of transcurrent slab break-off in the Southern Iberia Variscan Belt?

T

Tectonophysics 461, 356-377.

IP

Quesada, C., Robardet, M., Gabaldón, V., 1990. Ossa-Morena zonestratigraphy: synorogenic phase

SC R

(upper devonian-carboniferous-lower permian). In: Dallmeyer, R.D., Martínez García, E. (eds), Pre-mesozoic geology of Iberia. Springer, Berlin, pp. 273-279. Ribeiro, A., Quesada, C., Dallmeyer, R., 1990. Geodynamic Evolution of the Iberian Massif. In:

NU

Dallmeyer, R.D., Martinez Garcia, E. (Eds.), Pre -Mesozoic Geology of Iberia, Springer-

MA

Verlag, pp. 398-409.

Rosa, D., Finch, A., Andersen T., Inverno, C., 2008. U-Pb geochronology of felsic volcanic rocks

D

hosted in the Gafo Formation, South Portuguese Zone: relationship with Iberian Pyrite Belt

TE

magmatism. Mineralogical Magazine 72, 1103-1118. Rosa, D., Finch, A., Andersen, T., Inverno, C., 2009. U-Pb geochronology and Hf isotope ratios of

CE P

magmatic zircons from the Iberian Pyrite Belt. Mineralogy Petrology 95, 47-69. Sánchez-García, T., Bellido, F., Pereira, M.F., López-Guijarro, R., Quesada, C., Chichorro, M.,

AC

Silva, J.B., Pin, Ch., 2008. Expresión magmática temprana de un rift intracontinental en el margen de Gondwana durante el Cámbrico Inferior: Zona de Ossa-Morena (SW Macizo Ibérico, Portugal, España). Geo-Temas 10, 1567–1572. Sánchez-García, T., Bellido, F., Pereira, M.F., Chichorro, M., Quesada, C., Pin, C., Silva, J.B., 2010. Rift related volcanism predating the birth of the Rheic Ocean (Ossa-Morena Zone, SW Iberia). Gondwana Research 17, 392-407. Sircombe, K., 1999. Tracing provenance through the isotope ages of littoral and sedimentary detrital zircon, eastern Australia. Sedimentary Geology 124, 46-67.

ACCEPTED MANUSCRIPT

28

Sircombe, K.N., 2004. AGEDISPLAY: an EXCEL workbook to evaluate and display univariate geochronological data using binned frequency histograms and probability density

T

distributions. Computer & Geosciences 30, 21-31.

IP

Solá, A.R., Pereira, M.F., Williams, I.S., Ribeiro, M.L., Neiva, A.M.R., Montero, P., Bea, F., Zinger,

SC R

T., 2008. New insights from U–Pb zircon dating of early Ordovician magmatism on the northern Gondwana margin: The Urra Frormation (SW Iberian Massif, Portugal). Tectonophysics 461, 114–129.

NU

Solá, A.R., Williams, I.S., Neiva, A.M., Ribeiro, M.L., 2009. U–Th–Pb SHRIMP ages and oxygen

MA

isotope composition of zircon from two contrasting late Variscan granitoids, Nisa– Albuquerque batholith, SW Iberian Massif: petrologic and regional implications. Lithos 111,

D

156–167.

TE

Stacey, J.C., Kramers, J.D., 1975. Approximation of terrestrial lead isotope evolution by a two-stage model. Earth and Planetary Science Letters 26, 207–221.

CE P

Teixeira, C., Gonçalves, F., 1980. Introdução à Geologia de Portugal. Instituto Nacional de Investigação Científica, Lisboa.

AC

Valle Aguado, B., Azevedo, M.R., Schltegger, U., Martínez Catalán, J.R., Nolan, J., 2005. U-Pb zircon and monazite geochronology of Variscan magmatism related to syn-convergence extension in Central Northern Portugal. Lithos 82, 169-184. van Staal, C.R., Whalen, J.B., Valverde-Vaquero, P., Zagorevski, A., Rogers, N., 2009. PreCarboniferous, episodic accretion-related, orogenesis along the Laurentian margin of the northern Appalachians. In Murphy, J.B., Keppie, J.D., Hynes, A.J. (eds), Ancient Orogens and Modern Analogues. Geological Society of London, Special Publication 327, pp. 271-316. Vegas, R., Váizquez, J. T., Surifiach, E., Marcos, A., 1990. Model of distributed deformation, block rotations and crustal thickening for the formation of the Spanish Central System. Tectonophysics 184, 367-378.

ACCEPTED MANUSCRIPT

29

Vermeesch, P., 2012. On the visualization of detrital age distributions. Chemical Geology 312-313, 190-194.

T

Vilallonga, F., 2013. Análise de Proveniência Sedimentar das Bacias do Carbónico e do Triásico do

IP

SW de Portugal (Alentejo e Algarve) - Contributo para o conhecimento dos Processos de

SC R

Formação e Fragmentação do Supercontinente Pangeia. PhD Thesis, University of Évora. von Eynatten, H., Dunkl, I., 2012. Assessing the sediment factory: The role of single grain analysis.

NU

Earth Science Reviews 115, 97-120.

MA

FIGURE CAPTIONS

Figure 1. (A-) Location map of the Cenozoic basins of Iberia (Adapted from Pais et al., 2012); (B-)

D

Schematic geological map of SW Iberia showing the Pre-Cenozoic basement main units, topography

TE

and hydrographic basins; (C-) Schematic geological map of SW Iberia showing the Cenozoic basins (Lower Tagus, Alvalade and Moura (Adapted from Oliveira et al., 1992).

CE P

Figure 2. Schematic geological map of the SW Portuguese coast near to Cape Sines based on 1/200 000 map (after Oliveira et al., 1984 and Oliveira et al., 1992). Locations of Pliocene-Pleistocene

AC

sands taken from the sea-cliffs of the Areias Brancas, Norte and S. Torpes beaches are indicated. Figure 3. Schematic stratigraphy of the Alvalade basin in the Areias Brancas, Norte and S. Torpes beaches sea-cliffs; photographs of the sampling sites of Pliocene-Pleistocene sands. Figure 4. Results of the Kolmogorov-Smirnov test showing the U-Pb age cumulative frequency plots applied to the U-Pb ages of detrital zircons from the Pliocene-Pleistocene sands sampled in the Areias Brancas, Norte and São Torpes beaches sea-cliffs. Figure 5. Cathodoluminescence images of representative zircons (circle represents the ablation diameter spot size of 25 µm) and U-Pb Concordia plots (all data) of: (A-) Areias Brancas beach (samples AB-3/AB-4), (B-) Norte beach (samples PN-1/PN-2) and (C-) S. Torpes beach (samples ST-5/ST-6) Pliocene-Pleistocene sands.

ACCEPTED MANUSCRIPT

30

Figure 6. Age histogram, Probability Distribution Plot and Kernel Density Estimation with U-Pb detrital zircon ages of the Pliocene-Pleistocene sand from the Alvalade basin.

T

Figure 7. Correlations between Miocene-Pliocene facies and paleogeographic reconstructions of the

IP

Lower Tejo, Alvalade and Moura basins for the: (A-) Tortonian; (B-) Messinian and (C-) Pliocene

SC R

(after Azevedo and Pimentel, 1995; Cunha et al. 2009; Pais et al., 2012). (D-) Paleogeographic context of the Pliocene-Pleistocene alluvial fans and stream deposition within the Alvalade basin, characterized by the presence of marginal reliefs probably generated by Paleozoic Variscan

NU

structuration, Miocene landscape rejuvenation during the Betic compression and by Pliocene-

MA

Pleistocene block movements along the Torrão and Messejana faults (Adapted from De Vicente et al., 2011).

D

Figure 8. Schematic geological map of SW Iberia with the location of potential sources of Pliocene-

TE

Pleistocene sands (Alvalade basin). CIZ- Central-Iberian Zone; OMZ- Ossa-Morena Zone; SPZSouth Portuguese Zone (Adapted from Pais et al., 2012 and Oliveira et al., 1992). Data sources: (1)

CE P

Villalonga, 2013; (2) Miranda, 2010; (3) Grange et al,, 2010; (4) Canilho. 1989; Invernp et al., 1993; Miranda et al., 2009; (5) Pereira et et al., 2012a; (6) Pereira et al., 2013a; (7) Rosa et al., 2009; (8)

AC

Oliveira et al., 2013; (9) Azevedo and Aguado, 2006; (10) Chichorro et al., 2008; (11) Pereira et al., 2011; (12) Pereira et al., 2012b; (13) Lima et al., 2012; (14) Miranda et al., 2009; (15) Solá et al., 2009; (16) Pereira et al., 2009; (17) Braid et al., 2012; (18) Linnemann et al., 2008; (19) SanchezGarcía et al., 2010; (20) Solá et al., 2008; (21) Gutierrez-Alonso et al., 2011; (22) Neiva et al., 2009; (23) Dias et al., 1998; (24) Pereira et al., 2008; (25) Pereira et al., 2012c; (26) Pin et al., 2008. Figure 9. Histogram, Probability Distribution Plot and Kernel Density Estimation U-Pb detrital zircon ages plots of all data of Pliocene-Pleistocene sand (Alvalade basin). Comparison of detrital zircon age distribution plots of Pliocene-Pleistocene sand (black bars- bottom) with age spectra of potential sources areas located in SW Iberia (black bars- top).

AC

CE P

TE

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

Figure 1

31

AC

CE P

TE

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

Figure 2

32

AC

Figure 3

CE P

TE

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

33

AC

CE P

TE

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

Figure 4

34

AC

CE P

TE

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

Figure 5

35

AC

CE P

TE

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

Figure 6

36

TE

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

Figure 7

37

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

CE P

TE

Figure 8

38

AC

Figure 9

CE P

TE

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

39

ACCEPTED MANUSCRIPT

Highlights Ages of ancient detrital zircons from Pliocene-Pleistocene sands of SW Iberian coast



Source areas of Pliocene-Pleistocene sands associated to different drainage systems



Record of the evolutionary stages of the Gondwana and Pangea supercontinent cycles

AC

CE P

TE

D

MA

NU

SC R

IP

T



40