Submitted: June 18th, 2019 – Accepted: January 17th, 2020 – Published online: February 12th, 2020

To link and cite this article:

doi: 10.5710/AMGH.17.01.2020.3270

1 THE CONTINENTAL CRUST OF NORTHEASTERN PATAGONIA

2

3 CARLOS W. RAPELA(1), ROBERT J. PANKHURST(2)

4

5 (1) Centro de Investigaciones Geológicas (CIG), CONICET, Universidad Nacional de la

6 Plata, Diagonal 113 Nº 275, 1900 La Plata, Argentina. E-mail:

7 [email protected]

8 (2) Visiting Research Associate, British Geological Survey, Keyworth, Nottingham NG12

9 5GG, UK. E-mail: [email protected]

10

11 Total number of pages (text + references): 34, illustrations: 9, Figure captions: 2, tables: 2,

12 supplementary data: 1

13

14 Proposed header: THE CONTINENTAL CRUST OF NORTHEASTERN PATAGONIA

15

16 Corresponding author: Carlos W. Rapela

17

18

19

20

1 21 1- Abstract

22 The basement of northeastern Patagonia is characterized by early Paleozoic igneous and

23 metamorphic rocks that do not crop out in the central, western and Andean sectors of the

24 North Patagonian Massif. A review of U-Pb geochronology, geochemistry, and the Nd, Sr,

25 Hf and O isotope signature of the early Cambrian and Early Ordovician magmatic rocks

26 supports the hypothesis that the continental crust of northeastern Patagonia was essentially

27 continuous with that of the Eastern Sierras Pampeanas in early Cambrian times.

28 Mesoproterozoic lower crust is also inferred for this sector. New zircon Hf and O analyses

29 of early Cambrian (Pampean) granites in the Sierras Pampeanas are indistinguishable from

30 those of Cambrian granite in NE Patagonia, indicating an important crustal component in

31 the source. The detrital zircon age patterns of the inferred basement are also similar in the

32 two regions, strongly suggesting a southern Kalahari provenance. A modified hypothesis to

33 explain the continuity of NE Patagonia with the Pampean belt of the Sierras Pampeanas

34 during early Cambrian times, as well as their SW Gondwana geological affinity, is to

35 consider this entire belt as an outboard sector of the mid-Cambrian rifting observed along

36 the South America–South Africa–Weddell Sea margin. The detached sector would then

37 have become juxtaposed against the Río de la Plata craton across the right-lateral Córdoba

38 fault in late Cambrian times.

39 2- Keywords

40 Northeastern Patagonia, Continental crust, Gondwana, early Paleozoic, U-Pb provenance,

41 Hf-O isotopes

42 3- Resumen

43 LA CORTEZA CONTINENTAL DEL NORESTE DE LA PATAGONIA. El basamento

44 del noreste de la Patagonia es un sector caracterizado por rocas ígneas y metamórficas de

45 edad paleozoica inferior, que no afloran en los sectores central, occidental y andino del

2 46 Macizo Norpatagónico. Una revisión de estudios previos de geocronología U-Pb,

47 geoquímica, e isótopos de Nd, Sr, Hf y O en las rocas magmáticas cámbricas y ordovícicas

48 sostiene la hipótesis de que la corteza continental del noreste de la Patagonia fue continua

49 con la correspondiente a las Sierras Pampeanas Orientales durante el Cámbrico inferior. Se

50 infiere también para este sector, una corteza inferior mesoproterozoica. Nuevos análisis de

51 Hf y O en circón en granitos cámbricos inferiores (pampeanos) de las Sierras Pampeanas

52 son indistinguibles de los granitos de Cámbrico inferior del NE de la Patagonia, e indica un

53 fuerte componente cortical en la fuente de los mismos. El patrón de edades detríticas en el

54 basamento, es también similar en ambas regiones, lo que sugiere una fuerte proveniencia

55 del sur del Kalahari. Otra hipótesis para explicar la continuidad del NE de la Patagonia con

56 el Cinturón Pampeano de las Sierras Pampeanas, así como también su afinidad geológica

57 con el SO de Gondwana, es considerar que el cinturón completo fue un sector externo

58 (outboard) del rifting Cámbrico medio que se observa a lo largo del margen de Sudamérica

59 (Sierra de la Ventana)–Sudáfrica–Mar de Weddell. El sector separado fue luego

60 yuxtapuesto contra el cratón del Río de la Plata por la falla dextral Córdoba, en el

61 Cámbrico superior.

62 4- Palabras clave

63 Noreste de Patagonia, Corteza continental, Gondwana, Paleozoico inferior, Proveniencia

64 U-Pb, Isótopos de Hf y O

65

66

3 1 DESPITE the many geological studies carried out during the last 35 years and the important

2 technological and theoretical advances in almost all geological disciplines during that time,

3 the origin of the continental crust of Patagonia is still being debated. Controversies

4 continue largely because over most of the exposed surface of Patagonia, the early

5 Paleozoic rocks and the allegedly Precambrian lower crust are covered by younger units.

6 The thick cover includes extensive Late Paleozoic–Early Mesozoic plutonic-volcanic

7 complexes, Mesozoic sedimentary basins associated with the opening of the South Atlantic

8 Ocean, and Tertiary plateau basalts.

9 The hypothesis of Patagonia as single exotic continental block that collided with

10 Gondwana during the late Paleozoic (Ramos, 1984) has been challenged and modified.

11 Autochthonous and para-autochthonous models that recognize the assembly of several

12 blocks derived from Gondwana have been proposed (e.g. Pankhurst et al., 2006, 2014;

13 Ramos, 2008; Ramos and Naipauer, 2014; Gregori et al., 2008; Rapalini et al., 2010, 2013;

14 González et al., 2011, 2018; see González et al., 2018, for a more detailed description of

15 the different hypotheses). The aim of the present contribution is to review and provide

16 further evidence for the age, chemical and isotopic composition of the oldest rocks of

17 northeastern Patagonia in order to further constrain any hypothesis regarding their origin.

18 The scattered basement outcrops of northern Patagonia, from Río Colorado in the north

19 to the southern limit of the North Patagonian Massif (NPM) (Fig. 1), reveal differences in

20 the evolution of the upper crust of the eastern and western areas. The northeastern sector,

21 discussed in more detail in this paper (Fig. 2), is dominated by Cambrian low-grade

22 igneous and metamorphic basement and Early Ordovician granites with sparse occurrence

23 of early Cambrian granites. Early Paleozoic magmatism has not been so far found in the

24 central sector of the North Patagonian Massif, which is covered by plutonic-volcanic

25 complexes of a large Permo-Triassic province (Luppo et al., 2018 and references therein)

4 26 and Tertiary plateau basalts (Kay et al., 2007). In the southwestern North Patagonian

27 Massif rather imprecise ages of 420–425 Ma and 360–380 Ma for metamorphic and

28 detrital zircon suggest an unrelated geological history (Pankhurst et al., 2006; Martínez

29 Dopico et al., 2011). Recent studies in the basement of the North Patagonian cordillera

30 show that Devonian magmatism occurred in two contemporaneous belts: one emplaced

31 immediately east of the North Patagonian Massif, the other located west of the Andes in

32 Chile and interpreted as an oceanic island arc represented by pillow lavas, metabasalts,

33 primitive granites and deep-marine fossiliferous slates (Hervé et al., 2016, 2018).

34 The northeastern corner of Patagonia is the only sector where direct comparison of

35 composition and age can be made with the Early Paleozoic crust of the Sierras Pampeanas

36 to the north (Fig. 3), where an extensive dataset of U-Pb ages, geochemistry and Rb, Sr,

37 Nd, Hf and O isotopes is available (Pankhurst et al., 2014; Rapela et al., 2018 and

38 references therein). Here we review the evidence provided by detrital zircon age patterns in

39 the basement rocks of both areas, extended by new data for a metasedimentary enclave in

40 Ordovician granite from the Río Colorado area. Recent studies of Hf and O isotopes in

41 zircons from Early Paleozoic granites in the Sierras Pampeanas and Patagonia are reviewed

42 and equivalent new data for Cambrian granites in the Sierras Pampeanas are reported here

43 for comparison. This combined approach provides solid evidence regarding the

44 composition and age of the northeastern Patagonian crust and new constraints on the

45 provenance of this sector. Alternative para-autochthonous hypotheses that encompass the

46 Eastern Sierras Pampeanas as well are also discussed.

47 GEOLOGICAL BACKGROUND

48 From north to south, the relevant areas of northeastern Patagonia are found around Río

49 Colorado (Sierra de Pichi Mahuida), Valcheta–Aguada Cecilio and Sierra Grande (Fig.

5 50 2.1). The description below is restricted to the igneous-metamorphic basement and the

51 Early Paleozoic granite bodies.

52 Río Colorado area

53 To the south of the modern Andean flat-slab sector at 27–33° S., sparse and scattered

54 outcrops indicate that the Sierras Pampeanas belts extended southwards towards the

55 geographic limit of Patagonia at Río Colorado (Fig. 1) (Chernicoff et al., 1996, 2010,

56 2012). In this latter area, discontinuous and low-relief outcrops located along the river and

57 its tributaries were long ago considered to be a southern extension of the Sierras

58 Pampeanas (Fig. 2.1) (Linares et al., 1980).

59 The first comprehensive description of the lithology and radiometric age of the rocks at

60 Río Colorado was made by Tickyj et al. (1999a, b), who also considered that they were

61 formed during the Famatinian episode of the Sierras Pampeanas. The basement here is a

62 low-grade metasedimentary complex of slates, schists and metasandstones with a WNW

63 foliation considered to have resulted from syn-metamorphic deformation: a second event

64 produced decimetric folding (Tickyj et al., 1999a). The age of metamorphism was poorly

65 defined by rather imprecise K-Ar and Rb-Sr ages between 640 and 340 Ma (Linares et al.,

66 1980).

67 This basement is intruded by Early Ordovician peraluminous biotite-muscovite

68 granodiorites and granites that have been dated by conventional U-Pb at 500 ± 27 Ma and

69 431 ± 12 Ma (Tickyj et al., 1999b) and by U-Pb SHRIMP in zircon at 474 ± 6 Ma

70 (granodiorite) and 475 ± 5 Ma (monzogranite) (Pankhurst et al., 2006). At the Salto

71 Andersen dam in Río Colorado, the granodiorite intrudes the Nahuel Niyeu Formation,

72 developing a contact zone with andalusite and cordierite (Tickyj et al., 1999a). The

73 granodiorite has a porphyritic texture with K-feldspar phenocrysts and contains 2–10 cm

6 74 mafic microgranular enclaves and foliated metasedimentary enclaves. A new detrital

75 zircon age pattern for one of these metasedimentary enclaves granite is reported below.

76 Valcheta–Aguada Cecilio area

77 Important aspects of the geology of the Valcheta area have most recently been described

78 by Gozálvez (2009), López de Luchi et al. (2010) and Pankhurst et al. (2014), and in the

79 contiguous Aguada Cecilio area to the southwest by Greco et al. (2015) (Fig. 2.2). The

80 oldest unit here is the early Cambrian Tardugno Granodiorite, originally described by

81 Chernicoff and Caminos (1996) as porphyritic granodiorite, variably foliated. U-Pb

82 SHRIMP zircon ages for this unit of 529 ± 4, 526 ± 3 and 522 ± 4 Ma were reported by

83 Rapalini et al. (2013) and Pankhurst et al. (2014). The country rock of the granodiorite is

84 not exposed, it being in fault contact with the metamorphic Nahuel Niyeu Formation along

85 a steep NE–SW trending mylonitic shear zone. The dominant rock type is porphyritic

86 biotite granodiorite or monzogranite orthogneiss with perthitic K-feldspar megacrysts

87 partially converted to microcline. The dominant fabric is of S–C type, defined by biotite

88 (partly chloritized), chlorite and trails of dynamically recrystallized quartz: kinked and bent

89 muscovite occurs locally.

90 The Nahuel Niyeu Formation in the Valcheta area consists of metasandstone/siltstone,

91 phyllite and metavolcanic clastic rocks. Grading and cross-bedding are preserved in the

92 metasandstones, which are texturally immature, quartz- and microcline-rich, suggesting a

93 proximal granitic source (Rapalini et al., 2013). Metamorphic grade reaches middle/upper

94 greenschist facies in the eastern sector (Martinez Dopico et al., 2011). In the neighbouring

95 Aguada Cecilio sector the formation is mainly composed of alternating metagreywacke

96 and phyllite, minor metasandstone and metaconglomerate, which define relict bedding

97 (Greco et al., 2015). In addition, Greco et al. (2015 and references therein) described

98 ultramafic to felsic meta-igneous sills intercalated in the metasedimentary sequence and

7 99 synsedimentary volcanic activity represented by a 1.5–2 m andesitic lava flow, dated by U-

100 Pb SHRIMP at 513.5 ± 3.3 Ma. This age is consistent with the 515 Ma younger detrital

101 zircons of the Nahuel Niyeu Formation in the Valcheta area (Pankhurst et al., 2006).

102 The Valcheta pluton (Fig. 2.2) is exposed as isolated outcrops, intruded into the Nahuel

103 Niyeu Formation for more than 40 km north and west of the town of Valcheta. The

104 magmatic association comprises muscovite granites with very fine grained granite dykes;

105 the former are grey or pinkish, equigranular and allotriomorphic leucogranites composed

106 of quartz (48%), orthoclase–microcline (30%), weakly zoned oligoclase (15%), muscovite

107 (5%), scarce variably chloritized biotite and zircon, apatite and opaque minerals. Minor

108 amounts of garnet were described by Gozálvez (2009). K–Ar and Ar–Ar cooling ages for

109 the Valcheta granites fall in the interval 470–430 Ma (Lopez de Luchi et al., 2008; Tohver

110 et al., 2008; Gozálvez, 2009; Rapalini et al., 2013).

111 Sierra Grande–Arroyo Salado area

112 The El Jagüelito Formation (Ramos, 1975; Giacosa, 1987) is the metamorphic basement

113 of the Sierra Grande–Arroyo Salado area (Fig. 2.1). Recently González et al. (2018)

114 published a thorough review of the previous literature and provided new geological,

115 structural and geochronological evidence that is briefly summarised here.

116 The lithology is dominated by slate, phyllite, metagreywacke, metasandstone, minor

117 intercalations of metaconglomerate lenses, mafic and felsic subvolcanic and pyroclastic

118 rocks. A low-grade metamorphism affected the unit but primary clastic sedimentary

119 structures and igneous features are well preserved. An archaeocyathid fossil fauna reported

120 from limestone clasts near the town of Sierra Grande is considered to have general

121 affinities with that of the Australia–Antarctica paleobiogeographic province, indicating an

122 early Cambrian age (Atdavian–Botomian: González et al., 2011, 2018). Two dacitic K-

123 ignimbrites dated by U-Pb SHRIMP at 533 ± 7 and 516 ± 2 Ma, and a rhyolitic ignimbrite

8 124 dated by U-Pb ICP-MS at 529 ± 8 Ma were interpreted as representing two stages of

125 synsedimentary volcanism at ca. 530 and ca. 515 Ma, constraining the age of the whole

126 volcano-sedimentary pile of the El Jagüelito Formation to early–middle Cambrian

127 (González et al., 2018).

128 The El Jagüelito Formation was intruded by Early Ordovician granites and is

129 unconformably overlain by Late Ordovician–early Silurian clastic sediments of the Sierra

130 Grande Formation (Fig. 2.1). The Ordovician granites of this area are biotite monzogranite

131 and hornblende-biotite granodiorite, dated by U-Pb SHRIMP in the Sierra Grande area

132 (476 ± 6 Ma), the Arroyo Salado area (475 ± 6 Ma), and at Playas Doradas on the Atlantic

133 coast (476 ± 4 Ma) (Pankhurst et al., 2006 and references therein).

134 In the restricted area of Mina Gonzalito located between the Valcheta–Aguada Cecilio

135 and the Sierra Grande–Arroyo Salado areas (Fig. 2.1) a metamorphic complex considered

136 to be a high-grade equivalent of the El Jagüelito Formation has been described (Giacosa,

137 1994; Pankhurst et al., 2006, Greco et al., 2015 and references therein). A U-Pb detrital

138 zircon age pattern for the paragneiss shows younger inherited peaks at ca. 540 Ma and ca.

139 525 Ma, as well as metamorphic rim overgrowths at 470–472 Ma (Pankhurst et al., 2006;

140 Greco et al., 2014).

141 ANALYTICAL METHODS AND RESULTS

142 We have determined SHRIMP U–Pb ages for detrital zircon from a metasedimentary

143 enclave in peraluminous Ordovician granite from the Río Colorado area (granite sample

144 PIM-113, 474 ± 6 Ma, Rapela et al., 2018). The enclave sample, PIM-111, is a medium-

145 grade foliated gneiss with biotite, quartz, plagioclase and alkali feldspar as the dominant

146 mineral assemblage (Fig. 4).

147 U-Th-Pb analyses of zircon were made using SHRIMP RG at the Research School of

148 Earth Sciences (RSES), The Australian National University, Canberra, Australia, following

9 149 the methods of Williams (1998 and references therein) as in our previous work (e.g.,

150 Rapela et al., 2011). Data were reduced using the SQUID macro of Ludwig (2001) and

151 further processed using ISOPLOT/Ex (Ludwig, 2003) (Tab. 1; Fig. 5).

152 For further comparison, O and Hf isotope analyses were performed on two typical early

153 Cambrian granites from the Sierra Norte de Córdoba–Ambargasta batholith of the Sierras

154 Pampeanas: the Juan García granodiorite and the Villa Albertina granite (Ianizzotto et al.,

155 2013). Ion-probe pits made during U-Pb dating were removed by light polishing and O

156 isotope compositions were measured in the same positions using SHRIMP II following

157 procedures similar to those described by Ickert et al. (2008). The O isotope ratios and

18 158 calculated δ OVSMOW values were normalized relative to the weighted mean for reference

159 zircon FC1 in the respective analytical session. Hf isotope compositions were then

160 obtained in the same dated spots using a HelEx 193 nm ArF Excimer laser ablation system

161 together with a Neptune multicollector inductively-coupled plasma mass spectrometer

176 177 162 (ICP-MS) (Eggins et al., 2005). The initial Hf/ Hf ratios and ɛHft values were

163 calculated using the U-Pb crystallization age of each grain or area (Tab. 2): complete

164 analytical data are available as Supplementary Online Information.

165 AGE, GEOCHEMISTRY AND ISOTOPIC OVERVIEW OF THE EARLY

166 PALEOZOIC MAGMATISM OF NORTHEASTERN PATAGONIA AND THE

167 SIERRAS PAMPEANAS

168 Early Ordovician (Famatinian) magmatism

169 Early Ordovician granites in Patagonia are exposed in the areas described above. As the

170 U-Pb crystallization age, geochemistry and isotopic signature (whole rock Sr and Nd

171 isotopes and Hf and O isotopes in zircon) of the Famatinian magmatic rocks of the Sierras

172 Pampeanas have been recently thoroughly reviewed, including new data (Rapela et al.,

173 2018), they are a useful basis for comparison with the granites of northeastern Patagonia.

10 174 U-Pb SHRIMP data produced by our research group show that crystallization ages of

175 474–478 Ma for Patagonian granites fall within the 468–478 Ma interval of maximum

176 Famatinian magmatic activity in the Sierras Pampeanas (Fig. 6). Variation of the modified

177 alkali–lime index against SiO2 shows that the Patagonian granites are all calc-alkalic, as

178 are most of the peraluminous granites of the Central Famatinian Domain of the Sierras

87 86 179 Pampeanas (Fig. 7.1). The initial strontium isotope ratios ( Sr/ Sr)i of the hornblende-

180 biotite granodiorites and biotite granites of Sierra Grande are indistinguishable from those

181 of the metaluminous suites of the Central Famatinian Domain (Fig. 7.2). However

87 86 182 ( Sr/ Sr)i ratios of the Río Colorado granites are rather higher and similar to the those of

183 peraluminous granites in the Sierras Pampeanas, falling within the field of

184 Neoproterozoic–Cambrian metasedimentary rocks, which suggests a source with a major

185 crustal component.

186 Oxygen isotope ratios of zircon from Ordovician igneous rocks of the Central

187 Famatinian Domain of the Sierras Pampeanas clearly distinguish the metaluminous suites

188 from the highly peraluminous granites, the latter having high average δ18O‰ of >9‰ (Fig.

189 8.1), indicating crustal reworking of metasedimentary source rocks (Rapela et al., 2018).

190 On the other hand, εHft shows a rather restricted range of negative values, mostly between

191 -2 and -7 for both (Fig. 8.1), with Meso- to Paleoproterozoic depleted mantle model ages

192 of 1.4–1.9 Ga. The granites in the two studied areas of northeastern Patagonia show rather

193 different Hf and O isotope signatures (Fig. 8.2). Zircon from the peraluminous granite from

194 the Río Colorado area (474 ± 6 Ma) has high positive δ18O values of ca. +10‰ and

195 negative ɛHft values (-4 to -6), indistinguishable from those for the peraluminous granites

196 of the Sierras Pampeanas. Granodiorites and granites in the Sierra Grande area (476 ± 4

18 197 Ma, 476 ± 6 Ma) have more variable positive δ O values of +7.5 to + 9.8‰ and εHft

198 values of -4.0 to +1.5, both within the overall ranges of granites from the Central

11 199 Famatinian Domain of the Sierras Pampeanas, although the εHft ratios are slightly less

200 evolved (more positive) than those of most metaluminous rocks in the Sierras Pampeanas.

201 Cambrian magmatism

202 Pankhurst et al. (2014) compared the geochemistry and Sr and Nd isotopes of the

203 Tardugno Granodiorite with the early Cambrian granites of the Sierras Pampeanas, the

204 conclusions of which are here briefly referred. This single calc-alkaline body (68–73%

205 SiO2) cannot be distinguished in terms of major and trace element content from the

87 86 206 Cambrian granites of the Sierras Pampeanas. Initial ( Sr/ Sr)530 ratios for two samples of

207 the Tardugno Granodiorite are distinctly radiogenic (0.7129 and 0.7104) but fall within the

208 wide range shown by the Cambrian granites of the Sierras Pampeanas (0.7060–0.7237).

209 The corresponding εNdt values at 530 Ma are -3.7 to -3.0, while the Sierras Pampeanas

210 plutons generally have εNdt values around -5.5, but range up to -1.8; their crust-derived

211 depleted-mantle model ages range 1400–1700 Ma compared to 1500 Ma for the Tardugno

212 Granodiorite (Pankhurst et al., 2014).

213 New Hf and O isotope analyses of zircons from two early Cambrian granitic bodies of

214 the Sierra Norte de Córdoba–Ambargasta batholith in the Sierras Pampeanas are compared

215 with the Tardugno Granodiorite in Table 2 and Figure 8.3. The latter shows high δ18O

216 (9.3–10.8‰) and variable negative εHft (0 to -12.6), partially overlapping the field of the

217 Cambrian granites of the Sierras Pampeanas and particularly similar to the field of the

218 Famatinian peraluminous granites.

219 DISCUSSION AND INTERPRETATION

220 The metamorphic basement

221 The detrital zircon pattern of the metasedimentary enclave in the Río Colorado area

222 shows two major peaks at ca. 640 Ma and 930–1080 Ma, the latter tailing up to ca. 1200

223 Ma (Fig. 9.1). The original sedimentary protolith cannot be older than the youngest zircon

12 224 age peak at 545 Ma. Minor peaks are observed at 700–820 Ma, 1850–1900 Ma and ca.

225 2600 Ma. Sixteen inherited zircon cores in the early Cambrian Tardugno Granodiorite

226 broadly match these intervals (Fig. 9.1; Tab. 1), suggesting a similar crustal source or

227 strong contamination with similar material. On the other hand, this pattern sharply

228 contrasts with those of the Nahuel Niyeu and El Jagüelito formations, which are dominated

229 by an early Cambrian component at ca. 525–535 Ma, with very subordinate

230 Neoproterozoic and Mesoproterozoic peaks, ca. 1030–1050 Ma being notable (Fig. 9.2, 3).

231 Furthermore, the Nahuel Niyeu Formation contains zircon grains as young as ca. 515 Ma

232 (Pankhurst et al., 2014; González et al., 2018) and therefore cannot be the host rock of the

233 Tardugno Granodiorite.

234 The Nahuel Niyeu Formation is in contact with the Tardugno Granodiorite along a

235 steeply dipping NE-SW trending mylonitic shear zone, in which kinematic indicators

236 demonstrate a top-to-the-SW sense of shear of the hanging wall (von Gosen, 2003). Both

237 the Central and Eastern Famatinian domains show a conspicuous 525 Ma detrital zircon

238 age peak (Fig. 9.4), which has been ascribed to denudation of the Pampean orogen (Rapela

239 et al., 2016 and references therein). As the Nahuel Niyeu and El Jagüelito formations are

240 distinguished by dominant early Cambrian detrital peaks (Fig. 8.2, 3), a nearby source is

241 inferred to include a major early Cambrian component. Apart from the Tardugno

242 Granodiorite itself, the basement granitoids beneath the Magallanes basin of southernmost

243 Patagonia are early Cambrian (529 ± 8, 521 ± 4, 538 ± 6, 523 ±7, 522 ± 4, 521 ± 6 Ma;

244 Söllner et al., 2000; Pankhurst et al., 2003; Hervé et al., 2010) and are the source of the

245 Permian magmatism in Tierra del Fuego (Castillo et al., 2017). This evidence in both

246 northeastern and southern Patagonia implies that a poorly exposed basement of early

247 Cambrian age is in fact an important component of the middle continental crust beneath the

13 248 whole of Patagonia. Such rocks are also most probably present in the offshore continental

249 platform of Patagonia.

250 The metasedimentary basement of the Eastern Sierras Pampeanas and NW Argentina

251 deposited before or during the late Ediacaran–early Cambrian Pampean orogeny is largely

252 dominated by the "Puncoviscanan Series" (Rapela et al., 2016). The zircon age pattern of

253 these rocks is strongly bimodal, with peaks at ca. 600 and ca. 1000 Ma and minor peaks at

254 1840–1930 Ma and 2600 Ma (Fig. 9.5). It should be emphasized here that in the type

255 sector of the Famatinian orogen of the Sierras Pampeanas, this series is restricted to the

256 Foreland Domain, where it was the main country rock of the early Cambrian magmatism

257 (Fig. 3). As the zircon pattern of the analysed metasedimentary enclave closely resembles

258 that of the Puncoviscanan Series (Cf Figs. 9.1 and 9.5), it seems that the basement of this

259 domain extends southwards at least as far as the Río Colorado area. As noted above, this

260 region has been considered an extension of the Eastern Sierras Pampeanas by several

261 authors (e.g., Tickjy et al., 1999a; Pankhurst et al., 2014 and references therein).

262 Identification of the source rocks that produced the characteristic bi-modal pattern of

263 the "Puncoviscanan Series" is critical to resolving the origin of the northeastern Patagonian

264 crust. Neither the adjacent ca. 2200 Ma Paleoproterozoic (Rhyacian) Río de la Plata craton

265 to the east, nor the adjacent Western Sierras Pampeanas, from which the ca. 600 Ma

266 component is absent, can provide the provenance indicated by this pattern (Rapela et al.,

267 2016). The absence of Rhyacian detrital zircon from the now large dataset obtained for the

268 "Puncoviscanan Series" is remarkable (Fig. 9.5) and the most likely interpretation is that

269 these rocks were deposited prior to juxtaposition with the craton (Verdecchia et al., 2011).

270 In contrast, to the southeast of the Sierras Pampeanas, the early Paleozoic sedimentary

271 formations of the Sierra de la Ventana System, also adjacent to the Río de la Plata craton

272 (Fig. 1), shows completely different zircon patterns, dominated by 2000–2200 Ma peaks

14 273 that have been ascribed to direct provenance from the craton (Ramos et al., 2014a). Thus,

274 even if the craton had been available as a source, it did not supply sediments to the

275 "Puncoviscanan Series".

276 Likely potential sources for the extensive bi-modal ca. 600 Ma and ca. 1000 Ma zircons

277 may be found in other cratons, blocks and belts of SW Gondwana: (i) the Mesoproterozoic

278 rocks of the Natal–Namaqua belt, southern Kalahari craton, (ii) the Brasiliano–Panafrican

279 granites of southern Africa, SE Brazil and Uruguay, and (iii) the huge East African–

280 Antarctic Orogen (Jacobs and Thomas, 2004). Clastic rocks with the same typical bi-modal

281 pattern have been ascribed to derivation from one of more of these potential sources, such

282 as along the East Antarctic margin (e.g., Goodge et al., 2004), eastern Uruguay (Basei et

283 al., 2005), and the Ellsworth–Whitmore Mountains (Flowerdew et al., 2007). Southern

284 Africa and the Kalahari craton seem to be situated at the core of these sources and

285 therefore have been inferred as an important source of the Puncoviscana Formation

286 (Schwartz and Gromet, 2004; Rapela et al., 2007, 2016 and references therein). Recently,

287 Casquet et al. (2018) proposed that the Puncoviscana Formation and the sedimentary rocks

288 of the Malmesbury terrane of western South Africa (Frimmel et al., 2013) were deposited

289 in a continental marginal basin to the south of the Kalahari craton at 570–537 Ma.

290 Subsequent oblique subduction started ca. 552 Ma with intrusion of Cape Granite Suite and

291 I-type granites between 537 and 528 Ma, coeval with Puncoviscana sedimentation,

292 culminating in continental collision with the MARA continental block during the early

293 Cambrian Pampean orogeny (Casquet et al., 2018).

294 Another possible explanation for a 570–670 Ma component was proposed by Escayola

295 et al. (2007) and Ramos et al. (2014b), and involves the collision of a juvenile

296 Neoproterozoic island arc against the Río de la Plata craton. However, there is no current

297 geological evidence for relics of such a juvenile terrane in the Sierras Pampeanas and no

15 298 deformation of the basement has been identified that could be associated with such a

299 collision. More simply, the evidence described above suggests that the southeastern

300 Kalahari Mesoproterozoic basement, the Panafrican–Brasiliano granites and the East

301 African Antarctic Orogen are all suitable and available sources for the “Puncoviscanan

302 Series” of the Sierras Pampeanas and northeastern Patagonia. Mixing of sediments from

303 these sources is even possible (Rapela et al., 2007, 2016).

304 The El Jagüelito and the Nahuel Niyeu formations show consistent detrital zircon age

305 patterns, but the minor Neoproterozoic peaks of Nahuel Niyeu are not apparent in El

306 Jagüelito (Fig. 9.3). As in the Cambrian sedimentary and metasedimentary units formed

307 after the early Cambrian Pampean deformation in NW Argentina (e.g., the Mesón Group,

308 Fig. 9.6) and the type sector of the Sierras Pampeanas (Central and Eastern Famatinian

309 domains, Fig. 3.1, Fig. 9.4), the Patagonian metasedimentary formations share a dominant

310 525–535 Ma peak. Denudation of the early Pampean orogen is the most obvious source for

311 this component. Compared with the bi-modal “Puncoviscanan” pattern (Fig. 9.5), the

312 Mesoproterozoic group (970–1080 Ma) decreases markedly to less than 20% while the ca.

313 630 Ma component is still conspicuous in NW Argentina and the Sierras Pampeanas, but is

314 only a minor peak in northeastern Patagonia.

315 Limestone clasts in meta-conglomerate belonging to the El Jagüelito Formation in the

316 Sierra Grande area contain a fairly diverse but poorly preserved archaeocyathid sponge

317 fauna, but recrystallization and deformation prevents identification at genus or species

318 level (González et al., 2011). According to these authors, the specimens show general

319 affinities with archaeocyathid assemblages in the Australia–Antarctica

320 palaeobiogeographic province, indicating an early Cambrian (Atdabanian–Botomian)

321 maximum age for deposition. Although the largest diversifications of these fossils occurred

322 during the early Cambrian in carbonate sequences in the Transantarctic Mountains, they

16 323 were also reported species firmly dated by trilobitesin the mid Cambrian of the in the

324 Pensacola Mountains (Wood et at., 1992) and a late Cambrian carbonate sequence of the

325 Ellsworth Mountains (Debrenne et al., 1984).

326 We conclude that the metamorphic basement that comprises the middle and upper crust

327 of northeastern Patagonia shows similar zircon detrital age patterns to those of the roughly

328 coeval metasedimentary formations of NW Argentina and the Eastern Sierras Pampeanas.

329 The dominant early Cambrian detrital peak is ascribed to erosion of the voluminous I- and

330 mainly S-type magmatic rocks associated with the Late Neoproterozoic-early Cambrian

331 Pampean orogeny (Rapela et al., 1998, 2016). In turn these patterns are typical of southern

332 Gondwana sources (Kristoffersen et al., 2016), and particularly the Brasiliano–Panafrican

333 orogeny and the Neoproterozoic East African–Antarctic orogen (Rapela et al., 2007;

334 Frimmel et al., 2013; Casquet et al., 2018 and references therein). However, it should be

335 pointed out that evidence described here for the basement of northeastern Patagonia does

336 not apply farther west at the same latitude. Detrital zircon age patterns of metasedimentary

337 units along the western edge of the North Patagonian Massif (Cushamen Formation, Mamil

338 Choique Formation, Colohuincul Formation) reveal a different geological history as well

339 different sources (e.g., Hervé et al., 2005, 2016, 2018; Pankhurst et al., 2006; Ramos et al.,

340 2010; Serra Varela et al., 2019). This is consistent with Sm-Nd systematics on

341 metamorphic rocks that indicate 440–360 Ma Silurian and Devonian metamorphic events

342 related to collisional episodes (Martínez Dopico et al., 2011; Hervé et al., 2016).

343 Finally, indirect evidence suggests a mafic lower crust of Mesoproterozoic age for

344 northeastern Patagonia. The extensive Early Jurassic volcanic rocks of the Marifil complex

345 (175–190 Ma) that overlie the Nahuel Niyeu and El Jagüelito formations comprise the

346 northern and initial magmatism of the Chon Aike province, one the largest silicic provinces

347 known. The mostly rhyolitic and dacitic volcanic rocks are isotopically uniform, with

17 87 86 348 initial Sr/ Sr = 0.7067 ± 0.0003 and ɛNdt= -4 ± 2 corresponding to depleted mantle

349 model ages (TDM) of 1150–1600 Ma (Pankhurst and Rapela, 1995). Lower crustal

350 pyroxene granulite xenoliths considered to be the residual source of the Jurassic magmas,

351 yield Nd TDM ages in the range 1190–1540 Ma, which is considered the age of lower crust

352 of this area (Pankhurst and Rapela, 1995). A U-Pb age of 176 ± 5 Ma obtained on such a

353 xenolith confirms their relationship to the same Jurassic volcanism (Castro et al., 2011). As

354 the detrital zircon age peaks of the Cambrian metasediments also show Mesoproterozoic

355 peaks (Fig. 9.1–3) it is concluded that the lower crust probably includes an important

356 Mesoproterozoic component.

357 Early Paleozoic magmatism and paleogeographic reconstructions

358 As shown above, in terms of age, geochemistry and isotopic signature (whole-rock Sr-

359 Nd; zircon Hf-O) the Early Paleozoic magmatic rocks of northeastern Patagonia are very

360 similar to those in the typical, modern flat-slab sector of the Sierras Pampeanas. At the

361 same time, similarity in the geology of the respective basements suggests crustal continuity

362 between the Eastern Sierras Pampeanas and the northeastern sector of North Patagonia

363 (Rapalini et al., 2013; Pankhurst et al., 2014 and references therein). The location of the

364 Tardugno Granodiorite to the west of the Famatinian granites is similar to that observed in

365 the FFD (Fig. 3), where calc-alkalic and TTG early Ordovician plutons are emplaced in

366 the same place or to the west of the bulk of Early Cambrian peraluminous granites in the

367 Sierra de Córdoba (Rapela et al., 2018).

368 Reported U-Pb zircon ages from pyroclastic and volcanogenic sedimentary rocks of the

369 El Jagüelito Formation (González et al., 2018) suggest two stages of synsedimentary

370 volcanism at 516 ± 2 Ma and 533 ± 7 Ma, and a possible third stage at 510 Ma.

371 Geochemical and geological features of these rocks led to the interpretation they might

372 have been erupted in an extensional back-arc setting linked to subduction. It was proposed

18 373 that the whole North Patagonian Massif was originally outboard of the Pensacola–Queen

374 Maud–Ellsworth Mountain blocks of Antarctica and that the Tardugno magmatic episode

375 represents subduction beneath that margin, with the Nahuel Niyeu and El Jagüelito

376 formations representing fore-arc and back-arc deposits, respectively. Becoming detached

377 after the mid-Cambrian and following a short drifting interval, the North Patagonian

378 Massif block was thought to have collided with South America in Furongian/Tremadocian

379 times. It was further inferred that the early Ordovician granites of Sierra Grande were

380 produced by ‘flipped’ subduction of a Southern Patagonia block beneath the North

381 Patagonian Massif as the previously passive conjugate margin became active (González et

382 al., 2018, their figure 21). One problem with this model is that the Tardugno Granodiorite

383 is too old to explain the mid Cambrian back-arc and fore-arc environments suggested for

384 the El Jagüelito and Nahuel Niyeu formations, respectively, necessarily requiring a 510–

385 500 Ma active continental magmatic arc across the full width of northern Patagonia for

386 which there is no evidence. As mentioned above, the western sector of the North

387 Patagonian Massif is instead characterized by 440–360 Ma Silurian and Devonian

388 magmatic and metamorphic episodes. Furthermore, in our view, it is difficult to envisage

389 an independent Early Ordovician subduction system generating granites in the Sierra

390 Grande area of exactly the same age as the Famatinian magmatism of the Sierras

391 Pampeanas (Fig. 6) with similar geochemistry and isotopic signatures (Figs. 7, 8) and,

392 moreover, located on the extended axis of the Famatinian belt that is found along the entire

393 Pacific margin of South America (Rapela et al., 2018).

394 A modified hypothesis of the original "allochthonous Patagonia” model of (Ramos,

395 1984, 2008) that takes into account the idea that the archaeocyathids in the El Jagüelito

396 Formation resemble taxa in the Transantarctic Mountains (González et al., 2011) has been

397 proposed by Ramos and Naipauer (2014 and references therein). This model involves the

19 398 whole of Patagonia as part of a conjugate margin of the Transantarctic Mountains from

399 Southern Victoria Land to the Pensacola Mountains in East Antarctica, that was finally

400 amalgamated with Western Gondwana in late Paleozoic times (Ramos, 2008; Ramos and

401 Naipauer, 2014 and references therein). The opposing arguments of Pankhurst et al. (2014)

402 have been further discussed in this paper with new evidence and indicate that the

403 northeastern North Patagonian Massif at least is a crustal sector genetically related to the

404 Pampean and Famatinian events belts of the Sierras Pampeanas. A similar conclusion was

405 reached by comparing the O and Hf isotope compositions of zircon in the widespread

406 Permian magmatism on both sides of the proposed suture (Castillo et al., 2017).

407 We consider that the available evidence may reconcile, at least in part, some of the

408 controversies over the origin of the continental crust of northeastern Patagonia. The

409 evolution of the Precambrian igneous-metamorphic basement of Sierra de la Ventana (Fig.

410 1) culminated with intrusion of early Cambrian A- and I-type granites and eruption of mid-

411 Cambrian high-Zr peralkaline rhyolites derived from an undepleted lithospheric mantle

412 (509 ± 5 Ma, ɛNd509 +0.5 to +1.0, TDM 1181–1214 Ma: Rapela et al., 2003). The latter rift-

413 related volcanic rocks were covered by shelf sediments along a once continuous passive

414 margin, encompassing the Sierra de la Ventana fold belt, the Cape Fold Belt, the

415 Falkland/Malvinas microplate and the Ellsworth Mountains block in Antarctica (Curtis,

416 2001; Rapela et al., 2003 and references therein). This very large mid to late Cambrian

417 rifted sector of West Gondwana was unaffected by the end-Cambrian orogenic event of

418 Antarctica (Ross orogeny), but was strongly affected by the Permo-Triassic Gondwanan

419 orogeny (Curtis, 2001; Rapela et al., 2003). The rifting could have been intracontinental

420 (Pankhurst et al., 2014), perhaps culminating in the opening of an ocean, as suggested by

421 overlying marine passive margin sediments. A schematic paleogeographic reconstruction

20 422 of the southern margin of Gondwana during the mid-Cambrian continental rift was shown

423 in figure 10 of Rapela et al. (2003).

424 If conjugate continental fragments were detached from West Gondwana during the mid

425 to late Cambrian rifting following the Pampean orogeny, the basement of the detached

426 microcontinent(s) is likely to have included juvenile ca. 1000 Ma complexes, as in the

427 Natal–Namaqualand basement of Southern Africa, as well as the ca. 600 Ma Panafrican–

428 Brasiliano granites.

429 The volcanic and sedimentary facies of the Nahuel Niyeu and El Jagüelito formations

430 show many similarities with correlative units in the Ellsworth Mountains (González et al.,

431 2018). The zircon age distribution of the late Cambrian Frasier Ridge Formation exhibits a

432 typical Gondwana signature in which the two largest age clusters occur at ca. 1070 Ma and

433 ca. 610 Ma, while zircons older than 1120 Ma (early Mesoproterozoic, Paleoproterozic,

434 and Archean) make up only a minor part of the detrital population (Flowerdew et al.,

435 2007). This is very similar to the patterns in northeastern Patagonia and the

436 "Puncoviscanan Series" (Fig. 9.1, 5). We consider that northeastern Patagonia might have

437 been a conjugate margin of the Ellsworth Mountains block or equivalent sectors as

438 proposed by González et al. (2018), but that the inboard area was restricted to the South

439 American sectors of SW Gondwana affected by the mid-Cambrian rifting (i.e., Sierra de la

440 Ventana and sectors of the off-shore platform of southern Africa and the Ellsworth

441 Mountains). In this case the outboard detached sector could have included not only

442 northeastern Patagonia but also the Pampean belt of the Sierras Pampeanas. A first-order,

443 late-stage, extension event affected the Pampean orogen of the Sierras Pampeanas

444 (Foreland Famatinian Domain), as inferred from widespread ca. 515 Ma rhyolitic and 519–

445 515 mafic OIB volcanism related to uplifting and slab break-off in this orogen (Ramos et

446 al., 2015). The mid-Cambrian continental rifting of SW Gondwana provides a suitable

21 447 tectonic alternative to explain the detachment of the Pampean orogen from the Saldanian

448 belt, and subsequent juxtaposition with the Río de la Plata craton across the right-lateral

449 Cordoba fault (Fig. 2.1) (Rapela et al., 2007; Casquet et al., 2018). A 20 km wide

450 magnetotelluric discontinuity in a W-E profile at 29º 30´ S across this boundary, is

451 considered to represent a major tectonic boundary that was associated with the NE-SW

452 dextral transpressive system, evidenced in mylonitic belts in the eastern edge of the early

453 Cambrian metasedimentary basement of the Foreland Famatinian Domain (Fig. 3) (Peri et

454 al., 2015).

455 CONCLUSIONS

456 Evidence obtained from the comparison of detrital zircon age patterns in the basement,

457 direct geochronology, geochemistry, and the Nd, Sr, Hf and O isotope signature of the

458 early Cambrian and Early Ordovician magmatic rocks, supports the hypothesis that the

459 continental crust of northeastern Patagonia was continuous with that of the Pampean

460 orogen of the Eastern Sierras Pampeanas, as concluded by Rapalini et al. (2013) and

461 Pankhurst et al. (2014). New Hf and O analyses of early Cambrian granites in the Sierra

462 Norte de Córdoba are indistinguishable from those of Cambrian granite in NE Patagonia.

463 This is consistent with the new detrital zircon age pattern of a metamorphic enclave in

464 Ordovician granite from the Río Colorado area, suggesting that the otherwise unexposed

465 metamorphic country rocks of the early Cambrian granite of the Valcheta area are similar

466 to those of early Cambrian granites of the Pampean orogen. These metasedimentary rocks

467 have a very consistent ca. 600 and ca. 1000 Ma bi-modal detrital pattern not usually found

468 in either the proto-Pacific margin (Arequipa–Antofalla block) or rocks associated with the

469 proto-Atlantic Adamastor ocean, but typical of SW Gondwana. As in the Sierras

470 Pampeanas, this basement is inferred to be older than the Cambrian Nahuel Niyeu and El

471 Jagüelito formations of northeastern Patagonia. These metasedimentary rocks, in fault

22 472 contact with the Cambrian granite, show a conspicuous 525–535 Ma detrital zircon age

473 peak, similar to that characteristic of the sedimentary successions formed after the

474 Pampean deformation in the Sierras Pampeanas. Both are inferred to have resulted from

475 rapid denudation of the Pampean orogen. As Cambrian granites are reported from

476 basement of the Magallanes basin in Tierra del Fuego (Fig. 1, see references above), it is

477 inferred that early Cambrian igneous and metamorphic rocks are an important component

478 of the middle crust throughout several sectors of Patagonia, including the offshore

479 continental platform. This does not, however, appear to continue westwards in northern

480 Patagonia, where Silurian and Devonian episodes are evident.

481 The SW Gondwana affinities of the early Paleozoic magmatism of northeastern

482 Patagonia do not fit well with derivation of this sector as a conjugate margin of the

483 Transantarctic Mountains in East Antarctica (González et al., 2011, 2018; Ramos and

484 Naipauer, 2014). As pointed out by Pankhurst et al., 2018), neither the Cambrian nor the

485 Ordovician granites of northeastern Patagonia seem to be synchronous with any stage of

486 Ross orogen magmatism in the central Transantarctic Mountains.

487 Another hypothesis to explain the continuity of northeastern Patagonia with the Eastern

488 Sierras Pampeanas, as well as their SW Gondwana geological affinity, is to consider this

489 entire belt as an outboard sector of the mid-Cambrian rifting observed along the South

490 America–South Africa–Weddell Sea sector (Curtis et al., 2001; Rapela et al, 2003). The

491 conjugate inboard sector during rifting would have been the Saldania basin, the

492 Falkland/Malvinas microplate and the Ellsworth Mountains block, which are considered to

493 have been originally located together in the Natal embayment off southern Africa

494 (Flowerdew et al., 2007). This provides a suitable opening to explain the detachment of the

495 Pampean belt from the Saldanian belt prior to juxtaposition against the Río de la Plata

496 craton across the right-lateral Cordoba fault (Fig. 2.1).

23 497 ACKNOWLEDGEMENTS

498 Financial support for this paper was provided by Argentine public grants CONICET

499 PIP0229, PUE 2290160100083 and FONCYT PICT 2013-0472. C. Mark Fanning greatly

500 helped with SHRIMP and ICP-MS-LA isotopic analyses at the Australian National

501 University. E. Bjerg and V. Ramos provided constructive reviews.

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716 basin, Sierras de Córdoba, Argentina. Precambrian Research 129:1–21.

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718 pre-Andean basement of Tierra del Fuego (Chile): The missing link between South

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721 Pichi Mahuida Group, crystalline basement of south-eastern La Pampa province,

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723 139–144.

724 Tickyj, H., Llambías, E.J. and Sato, A.M., 1999b. El basamento cristalino de la región sur-

725 oriental de la provincial de La Pampa: Extensión austral del Orógeno Famatiniano de

726 Sierras Pampeanas. 14 Congreso Geológico Argentino (Salta), Actas 1: 160–163.

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731 Abstract T23C-2052.

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737 southwestern Gondwana: age constraints from U-Pb SHRIMP detrital zircon ages from

738 Sierra de Ambato and Velasco (Sierras Pampeanas, Argentina). Journal of the

739 Geological Society, London 168: 1061–1071.

33 740 Vervoort, J.D. and Blichert-Toft, J. 1999. Evolution of the depleted mantle: Hf isotope

741 evidence from juvenile rocks through time. Geochimica et Cosmochimica Acta 63: 533–

742 556.

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744 implications for a Patagonian plate. Tectonics 22 (1) 1005.

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747 Understanding Mineralizing Processes. Reviews of Economic Geology 7: 1–35.

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749 archaeocyath from Antarctica. Geological Magazine 129: 491–495.

750 FIGURE CAPTIONS

751 Figure 1. Location of main geological units in south-central Argentina (adapted and

752 modified from Pankhurst et al., 2014). The southern extension of the Precordillera terrane

753 and the Sierras Pampeanas south of 33°S are tentatively shown in light grey and pink,

754 respectively, due to the paucity of outcrops outside the modern Andean flat-slab sector.

755 The red dashed line shows the proposed Patagonian suture (Ramos, 2008 and references

756 therein).

757 Figure 2.1. Sketch map of northeastern Patagonia showing the Early Paleozoic units in the

758 Río Colorado and Sierra Grande areas discussed in the text (modified from Rapela et al.,

759 2018); 2, Early Paleozoic units of the Valcheta area (simplified from Pankhurst et al.,

760 2014). U-Pb zircon SHRIMP ages of the Tardugno Granodiorite are from Rapalini et al.

761 (2013) and Pankhurst et al. (2014).

762 Figure 3. Geology of the Sierras Pampeanas in the type sector of the Famatinian orogen

763 (simplified from Rapela et al., 2018).

34 764 Figure 4.1–2. Thin section photomicrographs of the metasedimentary enclave PIM-111; 1,

765 under parallel nicols; 2, crossed nicols.

766 Figure 5. Tera-Wasserburg plot for detrital zircon U–Pb SHRIMP data of

767 metasedimentary enclave PIM-111 from the Pichi Mahuida granodiorite (474 ± 6 Ma,

768 sample PIM-113, Rapela et al., 2016).

769 Figure 6. Distribution of U–Pb zircon ages of Ordovician igneous rocks in northeastern

770 Patagonia and in the type section of the Famatinian orogen in the Sierras Pampeanas

771 (simplified from Rapela et al., 2018). The range of high-precision TIMS U-Pb zircon ages

772 of Ducea et al. (2017) for Sierra de Valle Fértil is also shown.

773 Figure 7. Variation of the modified alkali-lime diagram (Frost et al., 2001) and initial

87 86 774 Sr/ Sr vs. SiO2 in the Central Famatinian Domain of the Sierras Pampeanas and

775 northeastern Patagonia (modified after Rapela et al., 2018).

776 Figure 8.1–3. Plots showing εHft vs. δ18O‰ values in zircon; 1, from the Central Domain

777 of the Famatinian orogen; 2, from Ordovician granites of northeastern Patagonia; 3, from

778 the early Cambrian Tardugno Granodiorite in northeastern Patagonia and early Cambrian

779 granites of the Pampean orogen in the Sierras Pampeanas. The δ18O limits for mantle-

780 derived zircon are from Valley et al. (2005) while ɛHft for depleted mantle at 475 Ma is

781 calculated using the parameters of Vervoort and Blichert-Toft (1999). Sample data from

782 Ordovician granites are from Rapela et al. (2018) while those of the Cambrian granites are

783 from Pankhurst et al. (2014) and this paper.

784 Figure 9.1–6. Detrital zircon U-Pb age patterns; 1, for the metamorphic enclave PIM-111

785 included in Ordovician granite from the Río Colorado area (with inherited zircon core ages

786 from the Cambrian Tardugno Granodiorite (Pankhurst et al., 2014) indicated at the top of

787 the plot. This pattern is compared with diagrams constructed from previously published

788 analyses from NE Patagonia: 2, Nahuel Niyeu Formation (Pankhurst et al., 2006; Rapalini

35 789 et al., 2013); 3, El Jagüelito Formation (Pankhurst et al., 2006; González et al., 2018); 4–6,

790 Neoproterozoic–Early Paleozoic metasedimentary rocks from the Sierras Pampeanas and

791 NW Argentina (from Rapela et al., 2016 and references therein); see text for explanation.

36

TABLE 1. Summary of U-Th-Pb results for enclave sample PIM-111 zircons Total (Measured) Ratios Radiogenic Ratios Ages (Ma) U Pb 238 U/ 207 Pb/ 206 Pb/ 207 Pb/ 206 Pb/ 207 Pb/ Disc. 206 206 238 206 238 206 Grain ppm Th/U ppm f206 % Pb ± Pb ± U ± Pb ± U ± Pb ± % 1.1 34 0.24 4.9 1.13 6.031 0.118 0.0741 0.0017 0.1653 0.0032 0.0714 0.0018 986 19 969 51 -2 2.1 185 0.47 27.3 <0.01 5.811 0.074 0.0735 0.0008 0.1721 0.0022 0.0735 0.0008 1024 12 1028 22 0 3.1 6 0.01 0.5 8.09 10.206 0.460 0.0657 0.0055 0.0901 0.0051 556 30 4.1 271 0.30 23.5 0.02 9.898 0.128 0.0613 0.0009 0.1010 0.0013 0.0611 0.0010 620 8 644 36 4 5.1 530 0.02 47.5 0.10 9.569 0.111 0.0612 0.0006 0.1044 0.0012 0.0607 0.0007 640 7 628 23 -2 6.1 385 0.04 54.4 0.03 6.088 0.083 0.0734 0.0019 0.1642 0.0022 0.0731 0.0019 980 12 1016 54 4 6.2 226 0.22 36.4 0.17 5.343 0.076 0.0686 0.0059 0.1873 0.0027 0.0693 0.0059 1107 15 909 175 -22 7.1 111 0.44 17.5 0.21 5.456 0.085 0.0725 0.0012 0.1832 0.0029 0.0720 0.0012 1084 17 987 34 -10 8.1 109 0.44 14.8 <0.01 6.327 0.101 0.0714 0.0013 0.1581 0.0025 0.0714 0.0013 946 14 969 38 2 9.1 366 0.66 61.6 0.03 5.106 0.062 0.0760 0.0007 0.1958 0.0024 0.0757 0.0007 1153 13 1088 18 -6 10.1 396 0.52 30.6 2.49 11.116 0.130 0.0812 0.0011 0.0877 0.0011 542 6 11.1 389 0.22 52.4 <0.01 6.370 0.080 0.0705 0.0006 0.1571 0.0020 0.0709 0.0006 941 11 955 18 1 12.1 94 0.45 13.6 0.44 5.923 0.097 0.0760 0.0013 0.1681 0.0028 0.0723 0.0018 1002 15 995 50 -1 13.1 182 0.25 27.4 0.11 5.711 0.077 0.0728 0.0009 0.1752 0.0024 0.0732 0.0009 1041 14 1020 26 -2 14.1 493 0.42 75.7 <0.01 5.604 0.064 0.0738 0.0005 0.1785 0.0020 0.0738 0.0005 1059 11 1036 15 -2 15.1 292 0.55 28.0 <0.01 8.981 0.114 0.0627 0.0009 0.1113 0.0014 0.0627 0.0009 681 8 699 30 3 16.1 265 0.26 35.4 0.08 6.442 0.081 0.0698 0.0008 0.1551 0.0020 0.0691 0.0008 929 11 903 24 -3 17.1 356 0.14 41.0 0.05 7.462 0.090 0.0659 0.0011 0.1341 0.0016 0.0662 0.0011 811 9 814 34 0 18.1 255 0.31 41.8 0.07 5.239 0.066 0.0750 0.0008 0.1909 0.0024 0.0752 0.0008 1126 14 1075 20 -5 19.1 52 0.43 8.6 0.55 5.159 0.101 0.0783 0.0017 0.1934 0.0038 0.0765 0.0017 1140 22 1107 45 -3 20.1 397 0.31 35.2 0.04 9.669 0.116 0.0599 0.0007 0.1035 0.0012 0.0607 0.0007 635 8 628 26 -1 21.1 270 0.19 42.4 0.03 5.470 0.068 0.0757 0.0008 0.1828 0.0023 0.0754 0.0008 1082 12 1080 20 0 22.1 238 0.20 21.4 0.12 9.561 0.126 0.0624 0.0009 0.1045 0.0014 0.0615 0.0012 641 8 655 41 2 23.1 520 0.28 77.7 <0.01 5.745 0.066 0.0719 0.0005 0.1741 0.0020 0.0719 0.0005 1034 11 983 15 -5 24.1 235 0.21 32.0 0.13 6.306 0.082 0.0709 0.0009 0.1584 0.0021 0.0698 0.0011 948 11 923 32 -3 25.1 14 6.33 6.1 0.54 1.951 0.062 0.1755 0.0033 0.5138 0.0163 0.1773 0.0033 2673 278 2627 31 -2 25.2 262 0.61 113.0 0.02 1.995 0.024 0.1764 0.0009 0.5012 0.0061 0.1762 0.0009 2619 26 2617 8 0 26.1 355 0.38 56.8 <0.01 5.373 0.064 0.0750 0.0006 0.1861 0.0022 0.0750 0.0006 1100 12 1070 17 -3 27.1 313 0.64 49.1 <0.01 5.481 0.068 0.0728 0.0007 0.1825 0.0023 0.0731 0.0007 1081 12 1015 20 -6 28.1 438 0.06 58.3 0.05 6.452 0.075 0.0711 0.0006 0.1549 0.0018 0.0707 0.0006 928 10 949 18 2 29.1 124 0.54 19.5 <0.01 5.433 0.082 0.0742 0.0011 0.1841 0.0028 0.0742 0.0011 1089 15 1047 30 -4 30.1 234 0.71 36.8 <0.01 5.459 0.071 0.0757 0.0008 0.1832 0.0024 0.0757 0.0008 1084 13 1088 22 0 31.1 470 0.06 72.2 0.03 5.596 0.064 0.0736 0.0007 0.1787 0.0021 0.0734 0.0007 1060 11 1025 19 -3 32.1 713 0.01 62.6 <0.01 9.776 0.110 0.0613 0.0006 0.1023 0.0012 0.0613 0.0006 628 7 648 20 3 33.1 481 0.21 43.6 0.01 9.460 0.112 0.0601 0.0007 0.1057 0.0012 0.0600 0.0008 648 7 604 28 -7 34.1 128 0.66 37.2 <0.01 2.960 0.043 0.1136 0.0011 0.3380 0.0049 0.1141 0.0011 1877 24 1866 17 -1 35.1 822 0.34 120.6 0.06 5.857 0.064 0.0736 0.0005 0.1706 0.0019 0.0731 0.0005 1016 10 1017 14 0 (TABLE 1 cont.) 36.1 531 0.39 55.5 0.41 8.221 0.094 0.0699 0.0007 0.1211 0.0014 0.0664 0.0017 737 8 820 55 10 37.1 1303 0.06 110.9 0.03 10.096 0.108 0.0603 0.0004 0.0990 0.0011 0.0600 0.0004 609 6 605 15 -1 Second Session 38.1 457 0.89 141.7 0.02 2.772 0.030 0.1219 0.0004 0.3607 0.0039 0.1217 0.0004 1985 19 1982 6 0 39.1 989 0.15 89.6 0.09 9.478 0.100 0.0611 0.0004 0.1055 0.0011 0.0609 0.0004 646 7 637 13 -2 40.1 98 0.49 13.7 0.14 6.156 0.098 0.0714 0.0015 0.1624 0.0026 0.0709 0.0015 970 16 954 43 -2 2.2 318 1.03 48.2 <0.01 5.673 0.066 0.0738 0.0006 0.1763 0.0021 0.0738 0.0006 1047 11 1036 16 -1 41.1 125 0.24 16.7 0.20 6.465 0.097 0.0748 0.0012 0.1544 0.0023 0.0732 0.0015 925 13 1019 41 9 42.1 57 0.47 7.6 1.31 6.428 0.112 0.0810 0.0015 0.1535 0.0028 0.0701 0.0044 921 15 930 129 1 43.1 679 0.15 95.9 0.01 6.088 0.067 0.0755 0.0019 0.1643 0.0018 0.0754 0.0019 980 10 1079 50 9 44.1 202 0.34 31.9 0.17 5.451 0.067 0.0759 0.0007 0.1835 0.0023 0.0759 0.0007 1086 13 1092 18 1 45.1 149 0.48 43.1 <0.01 2.980 0.037 0.1207 0.0011 0.3356 0.0042 0.1207 0.0011 1865 20 1967 17 5 46.1 201 0.20 17.6 0.19 9.832 0.124 0.0613 0.0008 0.1017 0.0013 0.0608 0.0008 624 8 632 28 1 47.1 653 0.03 53.9 0.05 10.415 0.114 0.0599 0.0005 0.0960 0.0010 0.0599 0.0005 591 6 599 16 1 48.1 111 0.74 15.7 <0.01 6.092 0.081 0.0763 0.0009 0.1642 0.0022 0.0765 0.0009 980 12 1108 23 12 49.1 159 0.22 15.3 0.05 8.960 0.116 0.0606 0.0008 0.1116 0.0014 0.0606 0.0008 682 9 627 30 -9 50.1 298 1.15 70.2 0.08 3.653 0.043 0.1139 0.0007 0.2735 0.0032 0.1132 0.0007 1559 16 1852 11 16 51.1 206 1.22 60.1 0.05 2.949 0.036 0.1138 0.0009 0.3389 0.0041 0.1133 0.0010 1882 20 1854 15 -1 52.1 437 0.68 75.7 <0.01 4.963 0.055 0.0762 0.0004 0.2024 0.0022 0.0801 0.0006 1188 13 1200 16 1 1. Uncertainties given at the one
level. 2. Error in FC1 Reference zircon calibration was 0.31% & 0.80% for the two analytical sessions. (not included in above errors but required when comparing 206 Pb/ 238 U data from different mounts). 206 3. f 206 % denotes the percentage of Pb that is common Pb. 4. For areas older than ~800 Ma correction for common Pb made using the measured 204 Pb/ 206 Pb ratio. 5. For areas younger than ~800 Ma correction for common Pb made using the measured 238 U/ 206 Pb and 207 Pb/ 206 Pb ratios following Tera and Wasserburg (1972) as outlined in Williams (1998). 6. For % Disc, 0% denotes a concordant analysis. Preferred age and uncertainty (1
) indicated in bold type Sample locality: 38° 48´ 23.2´´S; 64° 59´47.2´´W

TABLE 2. Comparison of Pampean O- and Hf-isotope composition of zircon in granites from NE Patagonia and Sierras Pampeanas Sample No. εHf(t) TDM (Ga) δO‰ Range Range Mean Juan García granite NF-IS-23 -6.3 to -3.8 1.7 - 1.8 +7.5 to +9.6 (+11.6) +8.8

Villa Albertina granite NF-IS-20 (-11.7) -7.7 to -1.1 1.5 - 1.9 (2.1) +7.2 to +10.2 +9.2 NF-IS-62 -4.6 to -1.8 1.5 - 1.7 +7.7 to +9.5 +8.4

Tardugno granite * VAL-010 (-12.6, -8.5) -3.8 to +0.2 1.4 to 1.6 (1.9, 2.2) +9.3 to +10.8 +10.1 VAL-011 -4.9 to -0.3 (+1.5) 1.3 - 1.7 +8.4 to +11.6 +9.9 Apparent outliers in parentheses TDM is two-stage model age based on Bulk Earth 176 Lu/ 177 Hf (Goodge & Vervoort, 2006) * Data for VAL-010 from Pankhurst et al., 2014 (Cambrian zircons only), otherwise this work (see TABLE 1)

Supplementary Table: Previously unpublished O-Hf Isotope Data

U-Pb Age 18 176 177 176 177 Analysed spot d O‰ 2s * Hf/ Hf 2se Lu/ Hf 2se Ma ± eHft 2se TDM (Ma)

NF-IS-23 Juan García granite (30°39.10'S, 64°14.19'W) # NF023-1.1 8.5 0.4 0.282283 0.000071 0.00101 0.00009 544.7 5.7 -5.97 2.51 1802 NF023-4.1 8.7 0.4 0.282280 0.000105 0.00117 0.00011 539.7 5.6 -6.24 3.71 1815 NF023-5.1 9.0 0.4 0.282314 0.000050 0.00176 0.00017 540.0 5.5 -5.24 1.79 1752 NF023-7.1 9.6 0.4 0.282311 0.000069 0.00194 0.00005 543.1 5.7 -5.34 2.45 1761 NF023-9.1 11.6 0.4 0.282326 0.000070 0.00161 0.00008 539.3 5.7 -4.77 2.48 1722 NF023-11.1 9.5 0.4 0.282353 0.000108 0.00129 0.00010 528.4 5.7 -3.94 3.84 1661 NF023-12.1 8.2 0.3 0.282285 0.000071 0.00128 0.00006 535.4 6.1 -6.19 2.51 1808 NF023-13.1 8.4 0.4 0.282303 0.000065 0.00168 0.00020 544.1 5.5 -5.51 2.28 1773 NF023-14.2 8.1 0.4 0.282288 0.000057 0.00153 0.00009 540.3 5.6 -6.07 2.01 1805 NF023-15.1 8.4 0.4 0.282290 0.000055 0.00094 0.00007 535.7 5.7 -5.89 1.94 1790 NF023-16.1 8.3 0.4 0.282353 0.000067 0.00133 0.00016 535.4 5.5 -3.80 2.37 1658 NF023-17.1 7.5 0.4 0.282286 0.000061 0.00153 0.00002 535.4 5.6 -6.25 2.15 1812 NF023-19.1 8.4 0.4 0.282314 0.000099 0.00181 0.00034 529.5 6.7 -5.48 3.52 1759

NF-IS-20 Villa Albertina granite (30°41.40'S, 64°18.81'W) # NF020-3.1 7.2 0.4 0.282296 0.000078 0.00216 0.00003 540.1 5.4 -6.02 2.77 1801 NF020-6.2 9.5 0.4 0.282377 0.000086 0.00114 0.00018 531.0 5.5 -2.98 3.04 1603 NF020-8.1 9.3 0.4 0.282430 0.000087 0.00126 0.00006 535.1 5.7 -1.06 3.07 1485 NF020-9.1 10.1 0.4 0.282295 0.000080 0.00169 0.00012 532.5 6.0 -6.05 2.83 1797 NF020-12.1 7.6 0.4 0.282303 0.000118 0.00341 0.00019 525.8 5.4 -6.51 4.17 1821 NF020-13.1 9.8 0.4 0.282249 0.000079 0.00143 0.00013 536.4 5.9 -7.50 2.80 1891 NF020-14.1 10.2 0.4 0.282240 0.000071 0.00139 0.00005 543.8 5.9 -7.65 2.51 1906 NF020-15.1 8.8 0.4 0.282353 0.000118 0.00276 0.00025 527.4 5.5 -4.48 4.17 1694 NF020-18.1 9.9 0.4 0.282143 0.000118 0.00205 0.00069 526.3 5.4 -11.68 4.17 2145 NF020-20.1 10.2 0.4 0.282354 0.000059 0.00138 0.00027 528.5 5.7 -3.93 2.08 1661

NF-IS-62 Villa Albertina granite (30°41.61'S, 64°18.67'W) # NF062-1.2 7.7 0.4 0.282331 0.000053 0.00078 0.00004 526.7 5.8 -4.58 1.87 1700 NF062-2.1 7.9 0.4 0.282406 0.000063 0.00073 0.00003 529.5 5.9 -1.84 2.23 1530 NF062-6.1 9.5 0.4 0.282333 0.000073 0.00130 0.00004 529.3 5.5 -4.63 2.59 1706

VAL-011 Tardugno granite (40°36.67'S, 66°40.35'W) ## VAL011-2.1 10.1 0.5 0.282513 0.000118 0.00134 0.00012 519.4 5.7 1.51 4.17 1309 VAL011-4.1 0.282430 0.000053 0.00120 0.00004 512.5 5.3 -1.52 1.89 1496 VAL011-5.1 8.4 0.5 0.282430 0.000055 0.00175 0.00007 517.2 5.3 -1.61 1.96 1505 VAL011-6.1 9.4 0.5 0.282428 0.000057 0.00097 0.00004 517.9 5.9 -1.40 2.03 1493 VAL011-7.1 9.4 0.5 0.282373 0.000057 0.00127 0.00003 517.9 5.4 -3.45 2.03 1622 VAL011-11.1 8.7 0.5 0.282452 0.000069 0.00145 0.00010 537.3 5.5 -0.30 2.45 1439 VAL011-12.1 10.5 0.5 0.282437 0.000074 0.00208 0.00020 522.2 5.3 -1.37 2.62 1494 VAL011-15.1 11.6 0.5 0.282395 0.000078 0.00031 0.00003 499.4 5.6 -2.75 2.77 1563 VAL011-16.1 11.6 0.5 0.282329 0.000052 0.00021 0.00002 505.2 5.8 -4.93 1.85 1705 VAL011-20.1 9.3 0.5 0.282454 0.000053 0.00095 0.00007 495.2 5.2 -0.97 1.89 1447

TDM is two-stage model age based on Bulk Earth 176Lu/177Hf from Goodge and Vervoort, EPSL 243, 711-731 (2006) # Spot numbers from Iannizzotto et al. (2013) ## Spot numbers from Pankhurst et al. (2014) * Includes uncertainty in Standard calibration Oxygen isotope ratios normalised relative to FC1 = 5.61 ‰ or AS3 = 5.61‰ 176Lu decay constant from Soderlund et al. EPSL 219, 311-324 (2004). Chondritic values from Bouvier et al EPSL 273, 48-57, (2008) Present day Depleted Mantle values from Vervoort & Blichert-Toft, GCA 63, 533-557 (1999)