Arc-oblique fault systems: their role in the Cenozoic structural evolution and metallogenesis of the Andes of central Chile

Accepted Manuscript Cenozoic structural evolution of the Main Cordillera of Central Chile Jose Piquer, Ron F. Berry, Robert J. Scott, David R. Cooke PII:

S0191-8141(16)30074-8

DOI:

10.1016/j.jsg.2016.05.008

Reference:

SG 3347

To appear in:

Journal of Structural Geology

Received Date: 11 January 2016 Revised Date:

19 May 2016

Accepted Date: 28 May 2016

Please cite this article as: Piquer, J., Berry, R.F., Scott, R.J., Cooke, D.R., Cenozoic structural evolution of the Main Cordillera of Central Chile, Journal of Structural Geology (2016), doi: 10.1016/ j.jsg.2016.05.008. 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 Cenozoic Structural Evolution of the Main Cordillera of Central Chile

1

2

Jose Piquera, b*, Ron F. Berrya, Robert J. Scotta, David R. Cookea

3

a

4

b

5

Eduardo Morales Miranda, Valdivia, Chile

6

*Corresponding author: [email protected], 56 9 4247 5063

7

[email protected]

8

[email protected]

9

[email protected]

RI PT

CODES, University of Tasmania, Private Bag 79, 7001, Hobart, Australia

M AN U

SC

Instituto de Ciencias de la Tierra, Universidad Austral de Chile, Edificio Pugín, Av.

Keywords: Andes; Central Chile; Cenozoic; kinematic and dynamic analysis

11

Abstract

12

The evolution of the Main Cordillera of Central Chile is characterized by the formation

13

and subsequent inversion of an intra-arc volcano-tectonic basin. The world’s largest

14

porphyry Cu-Mo deposits were emplaced during basin inversion. Statistically, the area is

15

dominated by NE- and NW-striking faults, oblique to the N-striking inverted basin-

16

margin faults and to the axis of Cenozoic magmatism. This structural pattern is

17

interpreted to reflect the architecture of the pre-Andean basement. Stratigraphic

18

correlations, syn-extensional deposits and kinematic criteria on fault surfaces show

19

several arc-oblique structures were active as normal faults at different stages of basin

20

evolution. The geometry of syn-tectonic hydrothermal mineral fibers, in turn,

AC C

EP

TE D

10

ACCEPTED MANUSCRIPT demonstrates that most of these structures were reactivated as strike-slip ± reverse

22

faults during the middle Miocene – early Pliocene. Fault reactivation age is constrained

23

by 40Ar/39Ar dating of hydrothermal minerals deposited during fault slip. The abundance

24

and distribution of these minerals indicates fault-controlled hydrothermal fluid flow was

25

widespread during basin inversion. Fault reactivation occurred under a transpressive

26

regime with E- to ENE-directed shortening, and was concentrated around major plutons

27

and hydrothermal centers. At the margins of the former intra-arc basin, deformation

28

was largely accommodated by reverse faulting, whereas in its central part strike-slip

29

faulting was predominant.

30

1. Introduction

31

Segments of the Andean orogenic system have, at specific times, accommodated

32

oblique plate convergence by arc-parallel strike-slip faulting. Examples of this type of

33

faulting in the Chilean Andes can be found in the Atacama fault system (Jurassic-

34

Cretaceous arc of northern Chile; Arabasz, 1971; Scheuber and Andriessen, 1990), the

35

Domeyko or Precordilleran fault system (Eocene-Oligocene arc of northern Chile;

36

Reutter et al., 1991, 1996; Tomlinson et al., 1994) and the Liquiñe-Ofqui fault system

37

(Jurassic-Quaternary arc of southern Chile; Herve, 1976, 1994; Cembrano et al., 1996).

38

These crustal-scale structures have exerted strong controls on magmatism, including the

39

emplacement of porphyry copper deposits and the location of active volcanoes

40

(Maksaev and Zentilli, 1988; Reutter et al., 1991; Herve, 1994; Cembrano et al., 1996;

41

Grocott and Taylor, 2002).

42

However, major arc-parallel strike-slip fault systems are not developed all along the

43

length of the Andean orogen. One segment where these are absent is the Central

AC C

EP

TE D

M AN U

SC

RI PT

21

ACCEPTED MANUSCRIPT Chilean Andes (Fig. 1); an area of particular economic significance as it contains the

45

world’s largest exploitable concentrations of Cu and Mo in two giant porphyry deposits

46

of late Tertiary age: Rio Blanco-Los Bronces and El Teniente (Sillitoe, 2010). In the

47

absence of obvious arc-parallel fault systems, the structural controls on Tertiary

48

magmatism and hydrothermal fluid flow have remained enigmatic (e.g., Mpodozis and

49

Cornejo, 2012). However, regional-scale geological mapping (Rivera and Cembrano,

50

2000; Piquer, 2015; Piquer et al., 2015) has shown that fault systems oblique to the

51

continental margin and to the magmatic axis played an important role in the tectonic

52

evolution of the Andes of central Chile, and in particular, are relevant for understanding

53

the structural controls on magmatism and hydrothermal activity in this segment.

54

Here we present the first systematic study of fault orientation, kinematics and paleo-

55

stress calculations for the Andes of central Chile. It is based on a structural database of

56

650 fault planes, 391 with kinematic information. Structural data were collected across

57

the entire Main Cordillera of central Chile, east of the city of Santiago, between the

58

Aconcagua River valley in the north, and the Cachapoal River valley in the south (Fig. 1).

59

The study area contains the Rio Blanco-Los Bronces and El Teniente porphyry Cu-Mo

60

deposits (Fig. 1B).

61

2. Regional context: the Andes of central Chile

62

The geological history of central Chile is characterized by eastward migration of the

63

magmatic arc in successive steps from the Jurassic to the Quaternary (Mpodozis and

64

Ramos, 1989). The Coastal Cordillera, a N-trending mountain range parallel to the west

65

coast of South America, marks the position of the Jurassic and Cretaceous magmatic arc,

66

and consists mainly of Mesozoic volcanic, intrusive and sedimentary rocks. These rocks

AC C

EP

TE D

M AN U

SC

RI PT

44

ACCEPTED MANUSCRIPT overlie and intrude Late Palaeozoic to Triassic intrusive and metamorphic rocks,

68

commonly termed the “basement” of the Andes. The Main Cordillera of central Chile is

69

located ca. 100 km further to the east, and can be subdivided into western and eastern

70

sections (Fig. 1). The Western Main Cordillera, which marks the position of the Tertiary

71

magmatic arc and is the focus of this work, is dominated by Tertiary volcanic, intrusive

72

and sedimentary rocks. The Eastern Main Cordillera is dominated by Mesozoic

73

sedimentary units, and is the position of the active Quaternary magmatic arc.

74

The mid-Tertiary magmatic arc of central Chile was characterized by extensional

75

tectonics leading to the formation of the Abanico Basin, an intra-arc volcano-tectonic

76

basin (Charrier et al., 2002). The basin was filled with up to 5 km of volcanic and volcano-

77

sedimentary rocks (Piquer et al., 2015), which have been grouped into the late Eocene-

78

early Miocene Abanico and Coya-Machali formations (Aguirre, 1960; Klohn, 1960). E- or

79

W-dipping, high-angle, arc-parallel fault systems that were active as normal faults during

80

the late Eocene-Oligocene have been interpreted as basin-margin faults at different

81

localities (Charrier et al., 2002; Fock et al., 2005; Farias et al., 2010; Piquer et al., 2010,

82

2015). However, the basin-margin faults appear to be discontinuous – they have not

83

been recognized along the entire area (Fig. 1). The internal structural architecture of the

84

basin around the porphyry Cu-Mo deposits is dominated by steeply-dipping, NE- and

85

NW-striking fault systems, oblique to the basin-margin faults and the magmatic arc

86

(Rivera and Cembrano, 2000; Piquer et al., 2015).

87

The basin was partially inverted in the Miocene-early Pliocene (Godoy et al., 1999;

88

Charrier et al., 2002). Some segments of the basin-margin faults were reactivated in

89

reverse mode (Charrier et al., 2002; Fock et al., 2005; Piquer et al., 2010), while other

AC C

EP

TE D

M AN U

SC

RI PT

67

ACCEPTED MANUSCRIPT segments were not reactivated during tectonic inversion with lower-angle, by-pass

91

thrust faults formed instead (e.g. Giambiagi et al., 2014). The first pulses of

92

compressional deformation occurred in the Early Miocene (Charrier et al., 2002;

93

Giambiagi et al., 2003). Lavenu and Cembrano (1999), based on fault-slip data from

94

central and southern Chile, identified two late Cenozoic deformation events. The first

95

was an E-W compressional event of Pliocene age. During the second event, which is of

96

Quaternary age, deformation was partitioned into two distinct domains, with N- to NNE-

97

directed compression in the present-day fore-arc, and transpression in the intra-arc

98

zone with σ1 trending NE. Inversion of the Abanico Basin under a compressive regime

99

was accompanied by a marked decrease in volcanic activity, growth of upper crustal

M AN U

SC

RI PT

90

magma chambers, and during the late Miocene-early Pliocene, the formation of giant

101

porphyry Cu-Mo deposits (Mpodozis and Cornejo, 2012). Miocene volcanic rocks

102

deposited during tectonic inversion are subdivided into the Farellones Formation (Klohn,

103

1960) and the younger Teniente Volcanic Complex (Kay et al., 2005).

104

The last pulses of Tertiary magmatism in the Western Main Cordillera involved porphyry

105

and diatreme emplacement in and around the mineral deposits during the early Pliocene

106

(Maksaev et al., 2004; Deckart et al., 2005). Subsequently, the locus of magmatism

107

migrated further east, to its current position in the Eastern Main Cordillera. The

108

products of Pleistocene–Holocene volcanism cover Mesozoic back-arc basin sedimentary

109

rocks. The latter underwent intense thin-skinned deformation during the Miocene,

110

forming the Aconcagua fold and thrust belt, which is best exposed in the Argentinean

111

flank of the Andes (Ramos, 1996).

AC C

EP

TE D

100

ACCEPTED MANUSCRIPT Volcanoes of the Eastern Main Cordillera of central Chile mark the northern limit of

113

active volcanism in the Southern Volcanic Zone of the Andes. To the north of the study

114

area, the Chilean flat-slab segment underlies the Cordillera, which is reflected both in a

115

widening of the orogenic belt and in the absence of active volcanism (Kay et al., 1999).

116

3. Methodology

117

This study is based on the results of over four months of field work, during which

118

structural and stratigraphic information was collected in the Andes of central Chile.

119

Efforts were made to achieve a broad distribution of structural stations across the study

120

area (Fig. 1), within the limitations imposed by the extreme topography. Transects were

121

completed along major river valleys, and measurements were also collected around

122

mining operations and ski resorts. At each structural station, the strike and dip of all

123

identified fault planes were measured and information about the width of the fault and

124

its damage zone was collected. The pitch of fault plane striations and slickenfibers

125

(where present) were also measured. Where possible, the sense of movement was

126

established using kinematic criteria for brittle faults (e.g., Petit, 1987). The type of

127

kinematic indicator used was always recorded. Stepped slickenfibers were the most

128

common indicator, followed by syn-tectonic minerals precipitated in strain fringes,

129

dilational jogs filled by hydrothermal minerals or intrusive rocks, offset markers and P-

130

only surfaces (Petit, 1987). A total of 651 fault planes were measured, and 391 of them

131

(60%) yielded kinematic information. The complete fault-plane database is provided as

132

supplementary material. Additionally, three samples containing syn-tectonic

133

hydrothermal minerals (Fig. 1) were dated using 40Ar/39Ar geochronology to establish

134

the age of fault activity. 40Ar/39Ar analyses were performed at the Oregon State

AC C

EP

TE D

M AN U

SC

RI PT

112

ACCEPTED MANUSCRIPT University Argon Geochronology Laboratory. Analytical methods are described in

136

Appendix 1, and the results are contained in Appendix 2.

137

Fault plane orientations were studied using the StereonetTM software (Allmendinger et

138

al., 2012). Kinematic and dynamic analyses were completed for 391 fault planes

139

containing kinematic information. The fault-slip data was grouped according to different

140

criteria to determine the spatial and temporal variations in the stress regime. For

141

kinematic analysis, the FaultKinTM software (Marrett and Allmendinger, 1990;

142

Allmendinger et al., 2012) was used to calculate the orientation of the compression and

143

tension axes for each individual fault plane and the average kinematic axes (shortening,

144

stretching and intermediate axes) for different fault populations.

145

For dynamic analysis, the Multiple Inverse Method (Yamaji, 2000) was used to calculate

146

the orientation of paleo-stress tensors from the inversion of fault-slip data. This method

147

allows the identification of separate stress states from heterogeneous data sets. A stress

148

state is defined by four parameters: the orientation of the three principal stresses and

149

the stress ratio Φ = (σ2–σ3)/(σ1–σ3). The stress ratio varies from 0 to 1, and describes the

150

shape of the stress ellipsoid. In a strike-slip stress regime, a stress ratio close to 1 means

151

that the magnitude of σ2 is similar to the magnitude of σ1, a situation associated with

152

faults active under a transtensional regime transitional to normal faulting. Similarly, a

153

stress ratio close to 0 means the magnitudes of σ2 and σ3 are similar, which relates with

154

groups of faults active under a transpressional regime transitional to thrust faulting. To

155

obtain the stress states, the program evaluates all the possible groups of k faults from

156

the fault-slip database. The number of faults (k), which defines the size of the groups to

157

be evaluated, is termed the “fault combination number”, and is entered by the user; the

AC C

EP

TE D

M AN U

SC

RI PT

135

ACCEPTED MANUSCRIPT software developers recommend k = 5 for most datasets, or k = 4 if the dataset is

159

particularly large (more than 122 fault planes). A larger k value does not significantly

160

change the results, while for k < 4 the inversion solution is under-determined. To

161

calculate the optimal stress tensor for each of the groups of k fault planes, the software

162

uses classical stress inversion methods based on the Wallace-Bott hypothesis (Wallace,

163

1951; Bott, 1959). It attempts to minimize the misfit angle, defined as the angle

164

between the observed and theoretical slip direction on a fault plane (with the latter

165

obtained from an assumed stress state). If the software cannot find an optimal stress

166

state for one of the groups of k faults, that group is said to be incompatible and

167

discarded. An optimal stress state is defined as one with a misfit angle of less than 20°

168

for each of the k fault planes contained in the group.

169

The program produces paired stereoplots showing σ1 and σ3 orientations corresponding

170

to the calculated optimal stress tensors for each group of k faults. If all of the calculated

171

stress orientations for each of the groups of k faults plot in a single cluster, it means that

172

the fault-slip data are homogeneous and can be explained by a unique stress state. If the

173

data are heterogeneous, then they will form different clusters, each representing a

174

different stress state.

175

4. Structural evolution of the Main Cordillera of central Chile

176

Two discontinuous, arc-parallel, N-striking high-angle reverse fault systems bound the

177

Tertiary belt of central Chile (Fig. 2). They juxtapose Tertiary rocks in the hanging wall

178

with Mesozoic rocks in the footwall and consequently are interpreted as inverted basin-

179

margin normal faults (Charrier et al., 2002; Piquer et al., 2015).

AC C

EP

TE D

M AN U

SC

RI PT

158

ACCEPTED MANUSCRIPT Between the inverted basin-bounding faults, the Main Cordillera is dominated by

181

steeply-dipping NW- and NE-striking faults (Fig. 2). Some of these arc-oblique faults

182

preserve evidence of early normal displacement, with syn-extensional deposition of

183

volcanic rocks in their hanging walls. One such example is illustrated in Figure 3, which

184

shows a sequence of Oligocene pyroclastic rocks of the Abanico Formation that are

185

restricted to the hanging wall of a NW-dipping, high-angle fault. The thickness of this

186

sequence increases away from the fault to more than 800 meters in the hinge of a low

187

amplitude hanging wall syncline (Fig. 3). Kinematic indicators on the fault planes,

188

however, reflect strike-slip ± reverse displacement (Fig. 4), suggesting that these

189

structures, as for the basin-margin faults, were reactivated during basin inversion.

190

4.1 Syn-tectonic hydrothermal and magmatic activity

191

Throughout the study area, fault surfaces are coated by a wide range of hydrothermal

192

minerals precipitated during fault slip, which form stepped slickenfibers (Fig. 4) or, less

193

commonly, non-fibrous infillings in strain fringes. Some of the observed syn-tectonic

194

hydrothermal activity forms part of the distal halo of hydrothermal alteration

195

surrounding the porphyry Cu-Mo deposits of the area (Rio Blanco-Los Bronces and El

196

Teniente; Fig. 1B). Syn-tectonic hydrothermal mineral fibers or infillings were found in

197

different generations of veins, ranging from high-temperature biotite and actinolite

198

veins associated with early stages of hydrothermal activity to lower temperature, later-

199

stage veins composed of minerals such as tourmaline or muscovite, and more distal

200

epidote, chlorite, calcite and/or barite veins (Fig. 4).

201

Arc-oblique fault systems appear to have exerted a strong control on the location and

202

geometry of Miocene-early Pliocene plutons (Fig. 2). Intrusions are either strongly

AC C

EP

TE D

M AN U

SC

RI PT

180

ACCEPTED MANUSCRIPT elongated parallel to the faults, or they have rhombic shapes bound by NE- and NW-

204

striking faults. Previous studies have reported evidence for syn-tectonic magmatism

205

(Godoy, 1998; Piquer et al., 2015), with magmas emplaced in dilational jogs along arc-

206

oblique strike-slip faults and in sets of sub-horizontal, en-echelon dilational lenses.

207

4.2 Chronological constraints on fault activity

208

The measured fault planes cut Late Jurassic to early Pliocene rocks. As mentioned

209

previously, the most common kinematic indicators are stepped slickenfibers, and in

210

general, evidence for syn-tectonic deposition of hydrothermal minerals is ubiquitous

211

(Fig. 4). Hydrothermal activity within the Andean segment considered in this study is

212

constrained to the middle Miocene-early Pliocene (~14–4 Ma; Maksaev et al., 2004;

213

Toro et al., 2012; Deckart et al., 2013), giving a first order approximation for the age of

214

fault reactivation.

215

Syn-tectonic biotite has previously been dated (40Ar/39Ar) in the Los Bronces sector of

216

the Rio Blanco-Los Bronces cluster (Silva and Toro, 2009). Biotite crystals with textural

217

evidence for syn-tectonic crystallization were collected from a NNW-striking shear zone

218

of unknown sense of movement. All the calculated ages are between 7 and 6 Ma (Silva

219

and Toro, 2009).

220

To further constrain the age of fault movement in the study area, three samples (Fig. 1)

221

were collected from fault planes containing syn-tectonic hydrothermal minerals. These

222

minerals were then dated using the 40Ar/39Ar step-heating method (Table 1, Fig. 5,

223

Appendices 1 and 2).

AC C

EP

TE D

M AN U

SC

RI PT

203

ACCEPTED MANUSCRIPT Sample AN12JP008 was collected on a fault plane striking N75°E and dipping 80°N,

225

which contains syn-tectonic actinolite fibres. These slickenfibers define a slip vector

226

pitching 10°W, with a dextral sense of shear. 40Ar/39Ar analysis of the actinolite yielded a

227

plateau age of 10.32 ± 0.09 Ma (late Miocene) from five consecutive heating steps

228

(corresponding to 43.84% of the 39Ar released). The fault cuts a granodiorite pluton with

229

a U-Pb zircon age of 11.68 ± 0.26 Ma (Piquer et al., 2015), about 1.3 million years older

230

than the fault movement.

231

Sample AN13JP012 was also collected from a fault plane with actinolite slickenfibers.

232

The fault strikes N65°W and dips 65°S. The slip vector pitches 18°E, and steps in the

233

slickenfibres indicate sinistral displacement. Twelve steps, corresponding to 71.58% of

234

the 39Ar released, define a plateau age of 9.68 ± 0.24 Ma (late Miocene). The faulted

235

rock is a monzonite with a K-Ar age for magmatic biotite of 14.2 ± 0.5 Ma (Rivera and

236

Navarro, unpublished report for CODELCO-Chile, 1996).

237

Sample AN13JP007 was collected in the southeastern corner of the study area (Fig. 1). It

238

contains syn-tectonic muscovite in strain fringes, developed on a fault plane striking

239

N65°E and dipping 85°N. Striations pitch 18°E, and indicate dextral displacement. Step-

240

heating yielded a plateau age of 13.04 ± 0.07 (upper late Miocene; Fig. 6.5), calculated

241

from 38 steps during which 94.11% of the 39Ar was released. The host volcanic rocks

242

belong to the Oligocene – early Miocene Coya-Machali Formation.

243

5. Analysis of fault plane data: results

244

The strike of the 651 fault planes in our database are illustrated by the half-circle rose

245

diagram in Figure 6A. Consistent with the regional-scale fault architecture illustrated in

AC C

EP

TE D

M AN U

SC

RI PT

224

ACCEPTED MANUSCRIPT Figure 2, strong arc-oblique strikes predominate. N-striking, arc-parallel faults are

247

subordinate and spatially restricted to the margins of the inverted basin. The dominant

248

ENE- and WNW-striking faults evident in the rose diagram are slightly oblique to the NE

249

and NW strikes of most of the regional-scale faults (Fig. 2). Slip on the ENE-striking fault

250

planes most commonly involves a dextral component, whilst slip on the WNW-striking

251

faults is predominantly sinistral (Fig. 6B, C). Collectively, these kinematic and geometric

252

relations suggest that many of the measured fault planes are R-type Riedel faults,

253

developed in the damage zones of larger NE- and NW-striking faults.

254

5.1 Structural blocks

255

To further elaborate on the kinematic and dynamic analysis, the study area was

256

subdivided into a series of discrete structural blocks, defined here as geographically

257

restricted areas with a homogeneous deformation style and well-defined lithotype and

258

age range. The 31 structural blocks thus defined (Fig. 7, Table 2) contain from 1 to 21

259

structural stations.

260

Figure 8 shows the result of the kinematic and dynamic analysis for each of the

261

structural blocks. Principal axes were determined using the FaultKin software (Marrett

262

and Allmendinger, 1990; Allmendinger et al., 2012) in the case of the kinematic analysis,

263

while the Multiple Inverse Method (Yamaji, 2000) was used for the dynamic analysis.

264

Four of the domains (2, 4, 15 and 29) contain less than four measured fault planes, and

265

consequently were not used for the dynamic analysis. Structural blocks 19 and 28

266

contain four and five measured fault planes respectively, but all the possible subgroups

267

of more than three faults were found to be incompatible with any common stress

AC C

EP

TE D

M AN U

SC

RI PT

246

ACCEPTED MANUSCRIPT tensor. As a result of this, it was only possible to carry out dynamic analyses on 25 of the

269

31 structural blocks shown on Figure 7.

270

Strong spatial patterns emerge from the analysis of structural blocks. In structural blocks

271

located close to the Rio Blanco-Los Bronces porphyry Cu-Mo cluster (structural blocks 7,

272

9, 10 and 11; Figs. 7, 8), fault-slip data are consistent with a strike-slip regime and an E-

273

W direction of maximum compression (E-W trending, sub-horizontal shortening axis and

274

σ1; N-S trending extension axis and σ3; and sub-vertical intermediate kinematic axis and

275

σ2). No secondary clusters were recognized by the Multiple Inverse Method. Further

276

east, structural block 6 shows a similar pattern of E-W shortening and N-S extension, but

277

a sub-vertical secondary σ3 cluster is evident using the Multiple Inverse Method. To the

278

east of block 6, block 5 is composed of strongly deformed rocks of Abanico Formation,

279

close to the eastern inverted basin-margin faults and the contact with the Mesozoic

280

units (Fig. 7). Faulting at block 5 is also consistent with an E-trending σ1, but the

281

stereographic projection for σ3 shows two steeply plunging clusters, while the average

282

stretching kinematic axis is sub-vertical (Fig. 8). This indicates that in this area E-W

283

shortening was mostly accommodated by reverse faulting. The rocks affected by faulting

284

at blocks 5 and 6 belong to the same stratigraphic unit (Table 2), and the same syn-

285

tectonic hydrothermal minerals are found on fault planes in both areas. This suggests

286

that different stress regimes operated at the same time in different parts of the Abanico

287

Basin during tectonic inversion. Similar deformation partitioning occurred in the vicinity

288

of the El Teniente porphyry Cu-Mo deposit, at the transition between structural blocks

289

30 and 31 (Figs. 7, 8) which are both composed of late Tertiary volcanic rocks. In block

290

30, located in the central part of the inverted Abanico Basin, faulting is consistent with a

AC C

EP

TE D

M AN U

SC

RI PT

268

ACCEPTED MANUSCRIPT strike-slip deformational regime, while at block 31, located immediately to the east and

292

closer to the basin margin, a dominant sub-vertical cluster for σ3 indicates shortening

293

was accommodated by reverse faulting.

294

Fault-slip data of most structural blocks is consistent with faulting under E- to ENE-

295

directed σ1. However there are several exceptions, notably in the Maipo area. Some

296

structural blocks in this area (e.g., blocks 17, 18, 23 and 24) clearly show a cluster of sub-

297

vertical σ1 and compression axes, indicating that faulting occurred in response to

298

extensional deformation. Also, a unique characteristic of structural block 17 is the

299

presence of a major cluster of almost N-S trending σ1.

300

5.2 Regional-scale analysis

301

Structural patterns and variations at a larger scale were studied by grouping the

302

structural blocks into three large-scale regions: the Rio Blanco-Los Bronces and the El

303

Teniente regions, around the porphyry Cu-Mo deposits of the same name, separated by

304

the Maipo region in the central part of the study area, which lacks any known major

305

mineral deposit (Fig. 9). There are 13 structural blocks located in the Rio Blanco-Los

306

Bronces region (structural blocks 1 to 13), 9 in the Maipo region (14 to 22) and 9 in the El

307

Teniente region (23 to 31).

308

Fault plane kinematics in the Rio Blanco-Los Bronces and El Teniente regions are

309

consistent with a sub-horizontal, E- to ENE-trending direction of maximum compression

310

(Fig. 9). Inversion of fault plane data using the Multiple Inverse Method does not reveal

311

any secondary clusters for σ1 (Fig. 9). Both the stretching kinematic axes (FaultKin

312

software) and the main cluster of σ3 (Multiple Inverse Method) are sub-horizontal and

AC C

EP

TE D

M AN U

SC

RI PT

291

ACCEPTED MANUSCRIPT N-trending, indicating a predominantly strike-slip faulting regime. However, in both

314

regions there is also a secondary cluster of sub-vertical σ3, consistent with the analysis of

315

structural blocks, which showed that in the areas adjacent to the inverted basin margins

316

compression was accommodated by reverse faulting. Several groups of faults have

317

stress ratios close to 0 (violet and blue colors in Figure 9), consistent with a stress state

318

transitional between strike-slip and reverse faulting, a situation which prevents the

319

software from distinguishing between σ2 and σ3. All of the above suggest fault activity in

320

these two regions occurred under a transpressive regime, with sub-horizontal, E- to ENE-

321

trending σ1 and local fluctuations in stress magnitude leading to reversals between

322

strike-slip and reverse faulting regimes. The homogeneity of the calculated stress

323

tensors for these two regions is remarkable, considering that they include numerous

324

structural stations from a large area with important altitudinal variability (~500 to 4,000

325

m.a.s.l.) and rock ages ranging from late Eocene to early Pliocene. The main difference

326

between the calculated paleo-stress tensors and kinematic axes for the two regions is a

327

~10° change in the direction of maximum compression: in the Rio Blanco-Los Bronces

328

region the shortening axis and the average σ1 have azimuths of 91° and 90° respectively,

329

whereas in the El Teniente region the azimuths are 77° and 83°.

330

The Maipo region shows a completely different pattern of deformation (Fig. 9), in rocks

331

of the same age range as those in the adjacent El Teniente and Rio Blanco-Los Bronces

332

regions. The orientations of kinematic axes and stress tensors are both highly variable,

333

with an overall large population of steeply plunging compression axes and σ1. In the plot

334

for σ1 in particular, it is possible to identify two main clusters: one is sub-vertical and the

335

other shows E-directed maximum compression. The main σ3 cluster plunges gently to

AC C

EP

TE D

M AN U

SC

RI PT

313

ACCEPTED MANUSCRIPT the NNE. This indicates that fault activity in this region occurred in response to two

337

contrasting stress regimes: one is extensional (vertical σ1 and NNE-trending σ3) and the

338

other is characterized by strike-slip faulting in response to E-W shortening.

339

6. Discussion

340

The results of dynamic and kinematic analysis of fault plane data reveal marked spatial

341

and temporal variations in stress state during inversion of the Abanico Basin. Most of

342

the fault-slip data used in the analysis are consistent with E- to ENE-directed shortening,

343

sub-parallel to the direction of convergence between the Nazca and South American

344

plates since the late Oligocene (Somoza and Ghidella, 2005). Radiometric ages for both

345

the affected rocks and syn-tectonic hydrothermal minerals constrain transpressive fault

346

activity to the middle Miocene – early Pliocene. Field observations demonstrate that

347

middle Miocene-early Pliocene hydrothermal activity in central Chile, including that in

348

the Rio Blanco-Los Bronces and El Teniente porphyry Cu-Mo districts, was largely

349

synchronous with fault movement (i.e. syn-kinematic, Fig. 4). This period of syn-tectonic

350

hydrothermal activity coincides with the previously postulated age of tectonic inversion

351

of the Abanico Basin (e.g., Godoy et al., 1999; Charrier et al., 2002). However, our

352

analysis demonstrates different segments of the basin accommodated E-W shortening in

353

different ways; with strike-slip faulting (vertical σ2) in some areas, and reverse faulting

354

(vertical σ3) in others. In a few areas (e.g., structural blocks 17 or 23), there is no

355

evidence for fault activity under E-directed maximum compression. The thickness of the

356

Tertiary volcanic deposits, the proportion of volcano-sedimentary intercalations, and

357

fluctuations in fluid pressure related to magma and hydrothermal fluid flow are all

358

potential factors that influenced deformation style during tectonic inversion. Their

AC C

EP

TE D

M AN U

SC

RI PT

336

ACCEPTED MANUSCRIPT effects on different segments of the Abanico Basin are discussed in the following

360

section.

361

6.1 Segmentation of the Abanico Basin

362

The spatial pattern defined by the analysis of individual structural blocks (Figs. 7, 8)

363

indicates reverse faulting was dominant at the margins of the inverted Abanico Basin

364

(e.g., structural blocks 5, 26 and 31), whereas strike-slip faulting dominates in the central

365

part of the former basin (e.g., structural blocks 7, 9, 10, 11, 25 or 30). These contrasting

366

deformation styles may have been coeval, or they might represent discrete deformation

367

pulses affecting the area during the Miocene – early Pliocene. However, even if the two

368

stress states were not entirely coeval, they show near complete spatial segregation, with

369

no evidence for superposition of contrasting stress states (e.g. Multiple Inverse Method)

370

in structural blocks located at the central part of the former basin or at the inverted

371

basin margins. The relative increase in vertical stress from the margins to the center of

372

the inverted basin could be explained by changes in the Tertiary topography,

373

stratigraphic thickness and volcanic facies. The axis of the Tertiary magmatic arc was

374

located in the central part of the basin, and the stratovolcanoes associated with it were

375

the most prominent topographic feature of the Central Chilean Cordillera. They were the

376

main source of sediments for the Argentinean foreland basins until uplift of Mesozoic

377

units in the Eastern Main Cordillera in the middle Miocene and of basement blocks at

378

the Frontal Cordillera in the late Miocene (Giambiagi et al., 2003). The maximum

379

thickness of the Cenozoic stratigraphic succession increases from less than 2 km close to

380

the basin margins to 7 km in the central part of the basin (Piquer et al., 2015). In the

381

center of the inverted basin, with a high volcanic topography and a thick sequence of

AC C

EP

TE D

M AN U

SC

RI PT

359

ACCEPTED MANUSCRIPT relatively dense volcanic rocks (proximal lava flows and pyroclastic deposits), the easiest

383

escape direction is N-S and shortening was accommodated mostly by strike-slip faulting.

384

Closer to the former basin margins, in contrast, pre-existing N-S faults, lower topography

385

(at least until the middle Miocene), and the reduced thickness and density (higher

386

proportion of volcano-sedimentary intercalations) of Cenozoic strata allowed reverse

387

faulting and more intense folding to occur in a thin-skinned deformation style.

388

It is clear from the kinematic and dynamic analysis that a subgroup of faults was active

389

under extensional conditions. These faults occur predominantly in the Maipo region (Fig.

390

9), away from any known major center of magmatic and hydrothermal activity. One

391

hypothesis is that in those areas faults were not reactivated during tectonic inversion,

392

and fault kinematics reflects the extensional conditions dominant during the opening of

393

the Abanico Basin. Pre-Miocene extensional deformation is supported by field evidence

394

for large-scale normal faulting during the Oligocene (e.g., Fig. 3). A corollary of this

395

interpretation is that fault reactivation during tectonic inversion after the early Miocene

396

was favored by the development of high fluid pressures in the vicinity of magmatic-

397

hydrothermal centers. In more distal positions, where Mio-Pliocene hydrothermal

398

activity was weak or absent, faults were not reactivated and the fault-slip data still

399

reflects the previous, extensional tectonic regime.

400

Although this hypothesis may be correct for the volcanic rocks of the Maipo region or

401

the Mesozoic sedimentary rocks (structural blocks 17 and 18), normal faulting also

402

predominates in specific packages of younger rocks that post-date tectonic inversion.

403

For example, in structural blocks 23 and 24 faults cutting flat-lying pyroclastic rocks of

404

the middle to late Miocene Teniente Volcanic Complex predominantly record normal

AC C

EP

TE D

M AN U

SC

RI PT

382

ACCEPTED MANUSCRIPT movement. These local extensional regimes affecting rocks which clearly post-date the

406

initiation of tectonic inversion may be explained by either post-orogenic gravitational

407

collapse, local extension in the hinge zones of anticlines, and/or by caldera-forming

408

volcanic events. In the particular case of block 34, the last seems likely, as the area is

409

characterized by a thick succession of coarse pyroclastic breccia, not present elsewhere

410

in the district, which could represent proximal, intra-caldera deposits. More detailed

411

mapping of the local volcanic facies and their spatial and temporal relationship to the

412

faults is needed to test this hypothesis.

413

As mentioned previously, structural block 17 appears unique in showing a major cluster

414

of NNE- to N-trending σ1. Lavenu and Cembrano (1999, 2008) identified a Quaternary

415

deformation event associated with N-S compression in central Chile, with faulting

416

affecting Tertiary rocks and also unconsolidated river terraces in the Maipo area. They

417

attribute this to the northward motion of a fore-arc sliver detached from the continent

418

by the dextral, arc-parallel Liquiñe-Ofqui fault system of southern Chile, producing N-S

419

compression in the fore-arc of central Chile. Unfortunately structural block 17 is

420

composed exclusively of Mesozoic sedimentary rocks, and there are no other constraints

421

on the age of the syn-tectonic hydrothermal minerals used as kinematic indicators in this

422

area. In this block, mineral fibers are mainly calcite and gypsum, which can precipitate at

423

very low temperatures and so could have formed in the Quaternary. However, based on

424

available data it is not possible to confidently assign an age to the N-S compression

425

affecting block 17.

426

6.2 From fault plane data to crustal-scale fault systems

AC C

EP

TE D

M AN U

SC

RI PT

405

ACCEPTED MANUSCRIPT The Andean segment covered by this study is remarkable for the apparent absence of

428

regional-scale, continuous fault systems. However, as Figure 2 illustrates, from the

429

systematic measurement of individual fault planes it is possible to trace major fault

430

systems across the entire orogenic belt. These discontinuous fault-systems are

431

composed of networks of interconnected individual fault planes that are slightly oblique

432

to the traces of the main faults (Figs. 2, 6A). The predominant orientation of fault planes

433

shown in Figure 6A is in broad agreement with the orientation predicted for pairs of

434

strike-slip conjugate faults developed in homogenous rocks under an E-W direction of

435

maximum compression. However, the traces of the regional-scale fault systems (Fig. 2)

436

do not match the predicted orientation for conjugate faults, striking at higher angles to

437

σ1. This suggests that the regional-scale faults may follow pre-existing zones of weakness

438

in the underlying crust, while the individual fault planes were formed as these pre-

439

existing faults propagated through the overlying Cenozoic volcanic cover.

440

Figure 10 illustrates how some of the arc-oblique fault systems identified in the Main

441

Cordillera are located on-strike of more evident, continuous structures present in the

442

Coastal Cordillera, to the west of the study area, where they controlled the

443

emplacement of Mesozoic plutons (Gana and Zentilli, 2000).

444

Arc-oblique structures have been identified in several segments of the Andes of Chile

445

and Argentina, controlling both magmatic and hydrothermal activity (e.g., Salfity, 1985;

446

Chernicoff et al., 2002; Cembrano and Lara, 2009; Acocella et al., 2011). Some of them

447

are seismically active (e.g. Farias et al., 2011) but their activity can be traced back at

448

least to the Triassic, when they were active as master and transfer faults of NW- to

449

NNW-trending rifts (Mpodozis and Ramos, 1989; Ramos, 1996; Giambiagi et al., 2003;

AC C

EP

TE D

M AN U

SC

RI PT

427

ACCEPTED MANUSCRIPT Niemeyer et al., 2004; Sagripanti et al., 2014). Some authors (e.g., Ramos, 1994) have

451

suggested that the geometry of the Triassic rifts, in turn, was controlled by NW-trending

452

suture zones formed during the Proterozoic and Palaeozoic as a result of the accretion of

453

continental blocks to the south-western margin of Gondwana. It appears likely that the

454

Cenozoic structural architecture of the Andes of central Chile, dominated by NW- and

455

NE-striking faults, has been inherited from reactivation of structures in the underlying

456

Mesozoic and pre-Andean, Proterozoic and Paleozoic rocks.

457

7. Conclusions

458

The internal architecture of the inverted Abanico Basin in the Main Cordillera of central

459

Chile is dominated by NE- and NW-striking fault systems, oblique to the continental

460

margin and to the axes of the Meso-Cenozoic magmatic arcs. The correlation of the fault

461

systems recognized in this study with older structures present in the rocks of the Coastal

462

Cordillera suggests that they reflect reactivation of long-lived basement structures. Field

463

evidence shows some were active as normal faults in the late Eocene – Oligocene,

464

during the deposition of the Abanico and Coya-Machali formations. Fault plane

465

kinematics demonstrate that most of these faults were reactivated as strike-slip ±

466

reverse faults during tectonic inversion in the middle Miocene – early Pliocene.

467

Reactivation during tectonic inversion was associated with hydrothermal fluid flow,

468

based on the widespread syn-tectonic precipitation of hydrothermal minerals (e.g.

469

epidote, chlorite, tourmaline, quartz, calcite, actinolite, biotite and Cu-Fe sulfides) on the

470

fault planes. The age of tectonic inversion was confirmed with three 40Ar/39Ar ages for

471

syn-tectonic hydrothermal minerals.

AC C

EP

TE D

M AN U

SC

RI PT

450

ACCEPTED MANUSCRIPT The kinematic and dynamic analysis of fault-slip data shows that structural reactivation

473

during tectonic inversion was concentrated around major plutons and porphyry Cu-Mo

474

deposits (Figs. 8, 9). In these areas the fault-slip dataset is consistent with reactivation

475

under a transpressive regime with E- to ENE-directed shortening. This suggests positive

476

feedback between magmatic and hydrothermal activity, fluid pressure, and the

477

reactivation under transpression of the structural architecture inherited from the

478

extensional period. In the margins of the inverted Abanico Basin, compression was

479

accommodated by reverse faulting (sub-vertical σ3), while in the central part of the

480

basin, where the rock column is considerably thicker and the topography higher, a

481

strike-slip regime (sub-vertical σ2) was predominant during Miocene-early Pliocene

482

tectonic inversion. This strike-slip regime might have been favorable for the ascent and

483

emplacement of magmas and mineralizing hydrothermal fluids, particularly in areas

484

where local extensional conditions can develop, such as releasing bends or at the

485

intersections of conjugate strike-slip faults.

486

Acknowledgments

487

Part of this work is the result of a PhD study by the senior author at the University of

488

Tasmania, which was supported by a Becas Chile scholarship from Conicyt and by

489

research funding from the AMIRA P1060 project “Enhanced Geochemical Targeting in

490

Magmatic-Hydrothermal Systems”. Codelco and all the sponsors of the AMIRA P1060

491

project are acknowledged for allowing the publication of this work. Adele Seymon from

492

AMIRA International is particularly acknowledged for facilitating the publication of this

493

research. Thanks also to all research team members of the AMIRA P1060 project for

494

their invaluable insights during the course of this study.

AC C

EP

TE D

M AN U

SC

RI PT

472

ACCEPTED MANUSCRIPT 495

References

496

Acocella, V., Gioncada, A., Omarini, R., Riller, U., Mazzuoli, R., Vezzoli, L., 2011. Tectonomagmatic characteristics of the back-arc portion of the Calama-

498

Olacapato-El Toro fault zone, Central Andes. Tectonics 30, TC3005,

499

doi:10.1029/2010TC002854.

501

Aguirre, L., 1960. Geología de los Andes de Chile Central, Provincia de Aconcagua. Instituto de Investigaciones Geológicas, Santiago.

SC

500

RI PT

497

Aguirre, L., Feraud, G., Vergara, M., Carrasco, J., Morata, D., 2000. 40Ar/39Ar ages of basic

503

flows from the Valle Nevado stratified sequence (Farellones Formation), Andes of

504

central Chile, IX Congreso Geologico Chileno, Puerto Varas, 583-585.

505

Allmendinger, R.W., Cardozo, N., Fisher, D.M., 2012. Structural Geology algorithms:

509 510 511 512

513 514

TE D

508

Arabasz, 1971. Geological and geophysical studies of the Atacama Fault Zone in Northern Chile. Californian Institute of Technology, Pasadena.

EP

507

vectors and tensors. Cambridge University Press, New York.

Baeza, O., 1999. Análisis de litofacies, evolución depositacional y análisis estructural de

AC C

506

M AN U

502

la Formación Abanico en el área comprendida entre los ríos Yeso y Volcán, Región Metropolitana. Departamento de Geología, Universidad de Chile, Santiago.

Bott, M.H.P., 1959. The mechanics of oblique slip faulting. Geological Magazine 96, 109117.

ACCEPTED MANUSCRIPT 515 516

Cembrano, J., Lara, L., 2009. The link between volcanism and tectonics in the southern volcanic zone of the Chilean Andes: A review. Tectonophysics 471, 96–113. Cembrano, J., Herve, F., Lavenu, A., 1996. The Liquine Ofqui fault zone: A long-lived

518

intra-arc fault system in southern Chile. Tectonophysics 259, 55-66.

519

RI PT

517

Charrier, R., Baeza, O., Elgueta, S., Flynn, J.J., Gans, P., Kay, S.M., Munoz, N., Wyss, A.R., Zurita, E., 2002. Evidence for Cenozoic extensional basin development and

521

tectonic inversion south of the flat-slab segment, southern Central Andes, Chile

522

(33 degrees-36 degrees SL). Journal of South American Earth Sciences 15, 117-

523

139.

M AN U

524

SC

520

Chernicoff, C.J., Richards, J.P., Zappettini, E.O., 2002. Crustal lineament control on magmatism and mineralization in northwestern Argentina: Geological,

526

geophysical, and remote sensing evidence. Ore Geology Reviews 21, 127–155.

TE D

525

Deckart, K., Clark, A.H., Aguilar, C., Vargas, R., Bertens, A., Mortensen, J.K., Fanning, M.,

528

2005. Magmatic and hydrothermal chronology of the giant Rio Blanco porphyry

529

copper deposit, central Chile: Implications of an integrated U-Pb and 40Ar/39Ar

530

database. Economic Geology 100, 905-934.

532 533

534 535

AC C

531

EP

527

Deckart, K., Godoy, E., Bertens, A., Jerez, D., Saeed, A., 2010. Barren Miocene granitoids in the Central Andean metallogenic belt, Chile: Geochemistry and Nd-Hf and UPb isotope systematics. Andean Geology 37, 1-31. Deckart, K., Clark, A. H., Cuadra, P., and Fanning, M., 2013. Refinement of the time-space evolution of the giant Mio-Pliocene Rio Blanco-Los Bronces porphyry Cu-Mo

ACCEPTED MANUSCRIPT 536

cluster, Central Chile: new U-Pb (SHRIMP II) and Re-Os geochronology and Ar-

537

40/Ar-39 thermochronology data. Mineralium Deposita 48, 57-79.

538

Farías, M., Comte, D., Charrier, R., Martinod, J., David, C., Tassara, A., Tapia, F., Fock, A., 2010. Crustal-scale structural architecture in central Chile based on seismicity

540

and surface geology: Implications for Andean mountain building. Tectonics 29,

541

TC3006, doi: 10.1029/2009TC002480.

Farías, M., Comte, D., Roecker, S., Carrizo, D., Pardo, M., 2011. Crustal extensional

SC

542

RI PT

539

faulting triggered by the 2010 Chilean earthquake: The Pichilemu Seismic

544

Sequence. Tectonics 30, TC6010, doi: 10.1029/2011TC002888.

545

Fock, A., Charrier, R., Farias, M., Maksaev, V., Fanning, M., Alvarez, P.P., 2005.

M AN U

543

Deformation and uplift of the western Main Cordillera between 33° and 34°S,

547

International Symposium on Andean Geodynamics (ISAG). IRD, Barcelona, 273-

548

276.

Fuentes, F., Aguirre, L., Vergara, M., Valdebenito, L., Fonseca, E., 2004. Miocene fossil

EP

549

TE D

546

hydrothermal system associated with a volcanic complex in the Andes of central

551

Chile. Journal of Volcanology and Geothermal Research 138, 139-161.

552

Gana, P., Wall, R., 1997. 40Ar/39Ar and K-Ar geochronological evidences of an Upper

553 554

555

AC C

550

Cretaceous Eocene hiatus in central Chile (33-33 degrees 30 ' S). Revista Geologica De Chile 24, 145-163.

Gana, P., Zentilli, M., 2000. Historia termal y exhumación de intrusivos de la Cordillera

556

de la Costa de Chile Central. IX Congreso Geologico Chileno, Puerto Varas,

557

volume 2, 664-668.

ACCEPTED MANUSCRIPT 558

Giambiagi, L.B., Ramos, V.A., Godoy, E., Alvarez, P.P., Orts, S., 2003. Cenozoic

559

deformation and tectonic style of the Andes, between 33 degrees and 34 degrees

560

south latitude. Tectonics 22, TC1041, doi:10.1029/2001TC001354. Giambiagi, L.B., Tassara, A., Mescua, J., Tunik, M., Alvarez, P.P., Godoy, E., Hoke, G.D.,

RI PT

561

Pinto, L., Spagnotto, S., Porras, H., Tapia, F., Jara, P., Bechis, F., García, V.H.,

563

Suriano, J., Moreiras, S.M., Pagano, S.D., 2014. Evolution of shallow and deep

564

structures along the Maipo–Tunuyán transect (33°40′S): from the Pacific coast to

565

the Andean foreland. In: Sepúlveda, S.A., Giambiagi, L.B., Moreiras, S.M., Pinto,

566

L., Tunik, M., Hoke, G.D., Farías, M. (Eds.), Geodynamic Processes in the Andes of

567

Central Chile and Argentina. The Geological Society, London, Special Publication

568

399, http://dx.doi.org/10.1144/SP399.14.

570

M AN U

Godoy, E., 1998. Intrusivos sintectónicos entre los ríos Aconcagua y Cachapoal, Andes de

TE D

569

SC

562

Chile Central, X Congreso Latinoamericano de Geología, Concepción, 149-154. Godoy, E., Yanez, G., Vera, E., 1999. Inversion of an Oligocene volcano-tectonic basin and

572

uplifting of its superimposed Miocene magmatic arc in the Chilean Central Andes:

573

first seismic and gravity evidences. Tectonophysics 306, 217-236.

575 576 577

AC C

574

EP

571

Grocott, J., Taylor, G.K., 2002. Magmatic arc fault systems, deformation partitioning and emplacement of granitic complexes in the Coastal Cordillera, north Chilean Andes (25 degrees 30 ' S to 27 degrees 00 ' S). Journal of the Geological Society 159, 425-442.

ACCEPTED MANUSCRIPT 578

Herve, M., 1976. Estudio geológico de la falla Liquiñe-Reloncavi en el área de Liquiñe:

579

Antecedentes de un movimiento transcurrente (Provincia de Valdivia), I Congreso

580

Geológico Chileno, Santiago, B39-B56. Herve, F., 1994. The Southern Andes between 39° and 44°S Latitude: the geological

RI PT

581

signature of a transpressive tectonic regime related to a magmatic arc, in:

583

Reutter, K.J., Scheuber, E., Wigger, P.J. (Eds.), Tectonics of the Southern Central

584

Andes. Springer, Berlin, 243-248.

Kay, S.M., Mpodozis, C., Coira, B., 1999. Magmatism, tectonism and mineral deposits of

M AN U

585

SC

582

586

the Central Andes (22°-33°S latitude) Society of Economic Geologists Special

587

Publication 7, 27-59.

588

Kay, S.M., Godoy, E., Kurtz, A., 2005. Episodic arc migration, crustal thickening, subduction erosion, and magmatism in the south-central Andes. Geological

590

Society of America Bulletin 117, 67-88.

592

Klohn, C., 1960. Geología de la Cordillera de los Andes de Chile Central. Instituto de

EP

591

TE D

589

Investigaciones Geológicas, Santiago. Kurtz, A.C., Kay, S.M., Charrier, R., Farrar, E., 1997. Geochronology of Miocene plutons

594

and exhumation history of the El Teniente region, Central Chile (34-35 degrees

595

596

AC C

593

S). Revista Geologica de Chile 24, 75-90.

Lavenu, A., Cembrano, J., 1999. Compressional- and transpressional-stress pattern for

597

Pliocene and Quaternary brittle deformation in fore arc and intra-arc zones

598

(Andes of Central and Southern Chile). Journal of Structural Geology 21, 1669-

599

1691.

ACCEPTED MANUSCRIPT 600

Lavenu, A., and Cembrano, J., 2008. Quaternary compressional deformation in the Main

601

Cordillera of Central Chile (Cajón del Maipo, east of Santiago). Revista Geológica

602

de Chile 35, 233-252. Maksaev, V., Zentilli, M., 1988. Marco metalogenico regional de los megadepositos de

RI PT

603 604

tipo pórfido cuprífero del Norte Grande de Chile, V Congreso Geológico Chileno,

605

Santiago, B181-B212.

Maksaev, V., Munizaga, F., McWilliams, M., Fanning, M., Mathur, R., Ruiz, J., Zentilli, M.,

SC

606

2004. New chronology for El Teniente, Chilean Andes, from U/Pb, 40Ar/39Ar,

608

Re/Os and fission-track dating: Implications for the evolution of a supergiant

609

porphyry Cu-Mo deposit. Society of Economic Geologists Special Publication 11,

610

15-54.

613

TE D

612

Marrett, R., Allmendinger, R.W., 1990. Kinematic analysis of fault-slip data. Journal of Structural Geology 12, 973-986.

Montecinos, P., Schaerer, U., Vergara, M., Aguirre, L., 2008. Lithospheric origin of

EP

611

M AN U

607

Oligocene-Miocene magmatism in central Chile: U-Pb ages and Sr-Pb-Hf isotope

615

composition of minerals. Journal of Petrology 49, 555-580.

616 617

618

AC C

614

Mpodozis, C., Cornejo, P., 2012. Cenozoic tectonics and porphyry copper systems of the Chilean Andes. Society of Economic Geologists Special Publication 16, 329-360.

Mpodozis, C., Ramos, V.A., 1989. The Andes of Chile and Argentina, in: Ericksen, G.E.,

619

Pinochet, C., Reinemud, J.A. (Eds.), Geology of the Andes and its relation to

620

Hydrocarbon and Mineral Resources. Circumpacific Council for Energy and

621

Mineral Resources, Houston, 59-90.

ACCEPTED MANUSCRIPT 622

Muñoz, M., Fuentes, F., Vergara, M., Aguirre, L., Nystrom, J.O., Feraud, G., Demant, A., 2006. Abanico East Formation: petrology and geochemistry of volcanic rocks

624

behind the Cenozoic arc front in the Andean Cordillera, central Chile (33 degrees

625

50 ' S). Revista Geológica de Chile 33, 109-140.

626

RI PT

623

Niemeyer, H., Berrios, H., Cruz, M. D. R., 2004. Temperatures of formation in triassic cataclasites of Cordillera Domeyko, Antofagasta, Chile. Revista Geológica de Chile

628

31, 3-18.

630

631

Petit, J.P., 1987. Criteria for the sense of movement on fault surfaces in brittle rocks

M AN U

629

SC

627

Journal of Structural Geology 9, 597-608.

Piquer, J., 2015. Structural Geology of the Andes of Central Chile: Controls on Magmatism and the Emplacement of Giant Ore Deposits. Ph. D. thesis, University

633

of Tasmania.

634

TE D

632

Piquer, J., Castelli, J.C., Charrier, R., Yanez, G., 2010. The Cenozoic of the upper Teno River, Cordillera Principal, Central Chile: stratigraphy, plutonism and their

636

relation with deep structures. Andean Geology 37, 32-53.

638 639

640

Piquer, J., Skarmeta, J., Cooke, D.R., 2015. Structural Evolution of the Rio Blanco-Los

AC C

637

EP

635

Bronces District, Andes of Central Chile: Controls on Stratigraphy, Magmatism and Mineralization. Economic Geology 110, 1995-2023.

Ramos, V. A., 1994. Terranes of Southern Gondwanaland and Their Control in the

641

Andean Structure (30-33 SL). In: Reutter, K. J., Scheuber, E., and Wigger, P. J.,

642

(Eds.), Tectonics of the Southern Central Andes. Springer-Verlag, 249-262.

ACCEPTED MANUSCRIPT 643 644

645

Ramos, V.A., 1996. Geología de la región del Aconcagua. Subsecretaria de Minería de la Nación, Buenos Aires. Reutter, K.J., Scheuber, E., Helmcke, D., 1991. Structural evidence of orogen-parallel strike slip displacements in the Precordillera of Northern Chile. Geologische

647

Rundschau 80, 135-153.

648

RI PT

646

Reutter, K.J., Scheuber, E., Chong, G., 1996. The Precordilleran fault system of

Chuquicamata, Northern Chile: Evidence for reversals along arc-parallel strike-

650

slip faults. Tectonophysics 259, 213-228.

M AN U

SC

649

Rivera, O., Cembrano, J., 2000. Modelo de formación de cuencas volcano-tectónicas en

652

zonas de transferencia oblicuas a la cadena andina: el caso de las cuencas Oligo-

653

Miocenas de Chile Central y su relación con estructuras NWW-NW (33°00’-34°30’

654

LS), IX Congreso Geológico Chileno, Puerto Varas, 631-636.

655

TE D

651

Sagripanti, L., Folguera, A., Giménez, M., Rojas Vera, E.A., Fabiano, J.J., Molnar, N., Fennell, L., Ramos, V.A., 2014. Geometry of Middle to Late Triassic extensional

657

deformation pattern in the Cordillera del Viento (Southern Central Andes): A

658

combined field and geophysical study. Journal of Iberian Geology 40, 349-366.

660

AC C

659

EP

656

Salfity, J.A., 1985, Lineamientos transversales al rumbo andino en el noroeste argentino, IV Congreso Geológico Chileno, Antofagasta, 119–137.

661

Scheuber, E., Andriessen, P.A.M., 1990. The kinematic and geodynamic significance of

662

the Atacama Fault Zone, Northern Chile. Journal of Structural Geology 12, 243-

663

257.

ACCEPTED MANUSCRIPT 664

SERNAGEOMIN, 2002. Mapa Geologico de Chile, scale 1:1,000,000, Santiago.

665

Sillitoe, R.H., 2010. Porphyry Copper Systems. Economic Geology 105, 3-41.

666

Silva, W., and Toro, J. C., 2009. Mineralización primaria sintectónica en el distrito minero

668

Río Blanco-Los Bronces, XII Congreso Geológico Chileno, Santiago, S11.

RI PT

667

Somoza, R., Ghidella, M.E., 2005. Convergencia en el margen occidental de América del Sur durante el Cenozoico: subducción de las placas de Nazca, Farallón y Aluk.

670

Revista de la Asociación Geológica Argentina 60, 797-809.

Tomlinson, A.J., Mpodozis, C., Cornejo, P., Ramirez, C.F., Dumitru, T., 1994. El Sistema de

M AN U

671

SC

669

Fallas Sierra Castillo-Agua Amarga: transpresión sinistral Eocena en la

673

Precordillera de Potrerillos-El Salvador, VII Congreso Geológico Chileno,

674

Concepcion, 1459-1493.

TE D

672

Toro, J. C., Ortuzar, J., Zamorano, J., Cuadra, P., Hermosilla, J., Sprohnle, C., 2012.

676

Protracted Magmatic-Hydrothermal History of the Río Blanco-Los Bronces

677

District, Central Chile: Development of World’s Greatest Known Concentration of

678

Copper. Society of Economic Geologists Special Publication 16, 105-126.

680

681 682

683

AC C

679

EP

675

Wallace, R.E., 1951. Geometry of shearing stress and relation of faulting. Journal of Geology 59, 118-130.

Yamaji, A., 2000. The multiple inverse method: a new technique to separate stresses from heterogeneous fault-slip data. Journal of Structural Geology 22, 441-452.

ACCEPTED MANUSCRIPT Figure captions

685

Figure 1. A. Location of the study area in South America. B. Main geological and

686

morphological units of the Andes of central Chile. The location of structural stations and

687

the sampling localities for 40Ar/39Ar geochronology are shown, as well as geographical

688

features mentioned in the text. The position of Figures 2, 7 and 9 is indicated by a frame.

689

UTM coordinates in meters.

690

Figure 2. Simplified geological map of the Andes of central Chile, based on Rivera and

691

Cembrano (2000), SERNAGEOMIN (2002), Fuentes et al. (2004), Fock et al. (2005) and

692

this work. UTM coordinates in meters.

693

Figure 3. Syn-extensional sequence of Oligocene volcanic rocks. About 800 meters of

694

pyroclastic deposits were accumulated in the hanging wall of a high-angle fault system

695

(black line) which on average strikes N45°E and dips 65°NW. They are covered by early

696

Miocene pyroclastic deposits, which are not affected by normal faulting. White lines

697

represent bedding. Viewing SW from 381197mE, 6357471mN (UTM coordinates). Ages

698

of volcanic rocks from Gana and Wall (1997), Fuentes et al. (2004) and Piquer et al.

699

(2015).

700

Figure 4. Examples of steps in syn-tectonic hydrothermal mineral fibers. Arrows indicate

701

sense of movement of the missing block. UTM coordinates are given for each location.

702

A. Steps in calcite fibers; 394514mE, 6367346mN. B. Steps in quartz fibers; 389901mE,

703

6191043mN. C. Steps in calcite fibers; 393032mE, 6264509mN. D. Steps in epidote

704

fibers; 381687mE, 6357528mN. This fault plane belongs to the fault system shown in

705

Figure 3. E. Steps in tourmaline-quartz fibers; 387888mE, 6255000mN.

AC C

EP

TE D

M AN U

SC

RI PT

684

ACCEPTED MANUSCRIPT Figure 5. Laser-heated 40Ar/39Ar age spectra for syn-tectonic hydrothermal mineral

707

fibers. The localities for analyzed samples are indicated in Figure 1.

708

Figure 6. A. Half-circle rose diagram for the 650 fault planes measured in the Andes of

709

central Chile. B. Lower hemisphere, equal-area projection of fault planes with a dextral

710

strike-slip component and striations with pitch ≤ 45°. C. Same as in B but for fault planes

711

with a sinistral slip.

712

Figure 7. Location of the 31 structural blocks into which the study area was subdivided,

713

shown over the geological map. UTM coordinates in meters.

714

Figure 8. Results of the analysis of fault-slip data for the 31 structural blocks. All

715

stereoplots are lower-hemisphere, equal-area projections. For each structural block, the

716

first plot illustrates the fault planes. The second stereoplot shows the P and T axes for

717

each fault plane as blue and red dots respectively, together with the average kinematic

718

axes (1 = shortening, 2 = intermediate, 3 = stretching) calculated by the FaultKin

719

software (Marrett and Allmendinger, 1990; Allmendinger et al., 2012). The third and

720

fourth stereoplots show the calculated orientations of σ1 and σ3 for subgroups of fault-

721

slip data using the Multiple Inverse Method (Yamaji, 2000).

722

Figure 9. Results of the kinematic and dynamic analysis for the Rio Blanco-Los Bronces,

723

Maipo and El Teniente regions. For each of the three regions, the upper plot

724

corresponds to a half-circle rose diagram. The next three plots are all lower hemisphere,

725

equal-area projections. The first one shows the P and T axes for each fault plane

726

together with the average kinematic axes, calculated by the FaultKin software (Marrett

727

and Allmendinger, 1990; Allmendinger et al., 2012). The second and third stereoplots

AC C

EP

TE D

M AN U

SC

RI PT

706

ACCEPTED MANUSCRIPT show the calculated orientations of σ1 and σ3 for subgroups of fault-slip data using the

729

Multiple Inverse Method (Yamaji, 2000). Color legend in the stereoplots and numbering

730

of the kinematic axes as in Fig. 8. Legend for the geological map as in Fig. 2. UTM

731

coordinates in meters.

732

Figure 10. Main fault systems identified in the Main Cordillera of central Chile (simplified

733

from Figure 2), and their correlation with similar oblique structures recognized in the

734

Paleozoic and Mesozoic rocks of the Coastal Cordillera (from SERNAGEOMIN, 2002).

735

Background geology simplified from SERNAGEOMIN (2002). UTM coordinates in meters.

AC C

EP

TE D

M AN U

SC

RI PT

728

ACCEPTED MANUSCRIPT 736

Tables

737

Table 1. Summary of 40Ar/39Ar results in syn-tectonic hydrothermal minerals.

Age (Ma) (±2σ)

Actinolite

9.72 ± 0.09

AN13JP007 6197015 379720

1288

Coya-Machali Fm.

Muscovite

13.04 ± 0.07

AN13JP012 6339690 386148

3108

Monzonite

Actinolite

9.68 ± 0.24

N (UTM)

E (UTM)

AC C

EP

TE D

M AN U

SC

738

RI PT

Mineral

AN12JP008 6336679 380467

Elevation Geological unit Rio Blanco 3248 Granodiorite

Sample

ACCEPTED MANUSCRIPT

Table 2. Summary of the lithological units present in each of the 31 structural blocks defined in the study area. Age ranges from Gana and

740

Wall (1997), Kurtz et al. (1997), Rivera and Falcon (unpublished report for CODELCO-Chile, 1998), Baeza (1999), Aguirre et al. (2000),

741

Charrier et al. (2002), Deckart et al. (2005, 2010), Muñoz et al. (2006), Montecinos et al. (2008) and Piquer (2015).

M AN U

SC

Lithology Andesitic lava flows, pyroclastic intercalations Granodiorite Andesitic lava flows, pyroclastic intercalations Granodiorite Andesitic lava flows, pyroclastic intercalations Andesitic lava flows, pyroclastic intercalations Andesitic lava flows and pyroclastic deposits Quartz-monzonite Syenogranite Granodiorite Andesitic lava flows Volcano-sedimentary deposits, pyroclastic intercalations Andesitic lava flows, dacitic and rhyolitic intercalations Andesitic lava flows, pyroclastic intercalations Andesitic lava flows, pyroclastic and volcano-sedimentary deposits Granodiorite Limestones, sandstones and conglomarates Andesitic lava flows, volcano-sedimentary intercalations Granodiorite Andesitic lava flows Andesitic lava flows Andesitic lava flows, volcano-sedimentary intercalations

EP

TE D

Geological unit Abanico Formation Rio Colorado batholith Abanico Formation Sills in Abanico Formation Abanico Formation Abanico Formation Farellones Formation Estero Barriga Intrusive Complex San Francisco batholith Rio Blanco Granodiorite Farellones Formation Abanico Formation Farellones Formation Abanico Formation Abanico Formation Meson Alto pluton Rio Damas, Lo Valdes and Colimapu formations Abanico Formation San Gabriel pluton Abanico Formation Abanico Formation Abanico Formation

AC C

Structural block 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

RI PT

739

Age range 34-22 Ma 22-21 Ma 34-25 Ma 12-11 Ma 34-25 Ma 34-25 Ma 22-16 Ma 15-14 Ma 16-15 Ma 12-11 Ma 17-16 Ma 26-18 Ma 22-19 Ma 31 Ma 31-19 Ma 12-11 Ma Oxfordian-Albian 27-25 Ma 12-11 Ma 34-21 Ma 34-25 Ma 34-21 Ma

ACCEPTED MANUSCRIPT

Lithology Pyroclastic deposits Andesitic lava flows Andesitic lava flows Volcano-sedimentary deposits, pyroclastic intercalations Andesitic lava flows Granodiorite Granodiorite Andesitic lava flows, pyroclastic intercalations Andesitic lava flows, volcano-sedimentary intercalations

SC

RI PT

Geological unit Teniente Volcanic Complex Teniente Volcanic Complex Teniente Volcanic Complex Coya-Machali Formation Teniente Volcanic Complex Pangal Intrusive Complex Cortaderal Intrusive Complex Teniente Volcanic Complex Coya-Machali Formation

M AN U

Structural block 23 24 25 26 27 28 29 30 31 742

EP

TE D

Table 2 (Cont.)

AC C

743

Age range 13-12 Ma 12-8 Ma 12-8 Ma 23-13 Ma 12-8 Ma 10-9 Ma 12-11 Ma 12-8 Ma 16-12 Ma

ACCEPTED MANUSCRIPT Appendix 1: analytical methods for 40Ar/39Ar analysis

745

Mineral separation was done by hand-picking, magnetic separation, heavy-liquids or

746

other means, followed by acid treatment. A mild leach in an ultrasonic bath with ~5%

747

HNO3 for 20 minutes was employed, followed by an ultrasonic bath of DI water for 20

748

minutes. In between the samples were rinsed thoroughly with DI water for three times.

749

Finally, the samples were dried in an oven that is no hotter than 80 °C. Samples were

750

irradiated at the OSU Radiation Centre in the TRIGA experimental reactor, at 1 MW

751

power for periods appropriate for the age and composition of sample unknowns. The

752

neutron flux was monitored with a variety of standard samples (Mmhb-1 hornblende,

753

FCT-3 biotite, TCR sanidine). The samples were placed in a Cd-shielded irradiation

754

location designed to block slow (thermal) neutrons in preference to fast neutrons. The

755

Thermo Scientific Model ARGUS VI multi-collector mass spectrometer used for

756

measuring isotope ratios has five fixed Faraday detectors (including amplifier circuits

757

with 1012 Ohm resistors) and one ion-counting CuBe electron multiplier mounted next

758

to the low mass 36 Faraday detector. This system is equipped with a 25 W Synrad CO2

759

laser with industrial scan head for carrying out gas extractions. The ARGUS VI can be

760

operated in three different modes: multi-collector Mode to simultaneously collect all

761

masses m/e = 36, 37, 38, 39 and 40 on the 1012 Ohm Faraday collector array for samples

762

providing sufficient amounts of gas for analyses; Peak-switching Ion-counting Mode

763

using the CuBe electron multiplier for high-precision analyses on (very) small gas

764

fractions; and Combination Mode whereby all masses will be measured simultaneously

765

in a multi-collector mode, but with mass m/e = 36 aimed on the CuBe electron multiplier

766

and masses m/e = 37, 38, 39 and 40 on the adjacent Faraday cups. The latter

AC C

EP

TE D

M AN U

SC

RI PT

744

ACCEPTED MANUSCRIPT configuration provides the advantages of running in a full multi-collector mode while

768

measuring the lowest peak (on mass 36) on the highly sensitive electron multiplier. Even

769

though the ARGUS VI has a fixed-position collector array, an electronic steering plate

770

placed before every collector allows for nudging over the beams to fall exactly in the

771

middle of all five collectors. The ARGUS VI is connected to an all-metal extraction system

772

for 40Ar/39Ar age determinations. One SAES ST-101 Zr-Al getter (450 °C) and two SAES ST-

773

172 Zr-V-Fe getters (21 °C and 250 °C) are used for cleaning up the reactive gasses. The

774

design of the CO2 laser system uses an industrial Synrad XY scan head for steering the

775

laser beam during sample heating. This allows carrying out the sample heating by setting

776

up a beam raster pattern while keeping the sample housing stationary. Using this novel

777

technique it is possible to produce a laser beam that can move continuously up and

778

down at speeds up to 300 in/s and that results in an even heating of the entire sample

779

being analyzed, a prerequisite for carrying out first-rate incremental heating

780

experiments. All resulting ages were calculated using the ArArCALC v2.5.2 software

781

package (Koppers, 2002).

AC C

EP

TE D

M AN U

SC

RI PT

767

ACCEPTED MANUSCRIPT

Appendix 2: analytical results of 40Ar/39Ar analysis

Ar(cl) [fA]

3.146943 2.1528 0.611061 2.470797 0.9693 0.681722 2.266927 1.9391 1.221828 2.237613 4.0581 1.685214 1.407801 2.0663 0.961517 1.161243 2.5326 0.774642 1.19654 3.8353 0.782052 0.583068 2.8081 0.25705 0.612398 3.7552 0.398323 0.78792 6.1242 0.600297 0.629979 7.0063 0.449467 0.662557 10.4301 0.534809 0.298843 6.1344 0.170238 0.382563 11.2142 0.318986 0.576203 38.3005 0.695899 0.781368 107.6759 1.700593 0.701773 173.472 2.335402 1.280128 226.3626 3.655485

39

Ar(k) [fA]

40

Ar(r) Age [fA] (Ma) ± 2s AN12JP008 1.42444 10.0056 22.43 ± 13.66 2.54216 12.6668 15.94 ± 6.35 4.87089 12.1597 8 ± 3.09 7.68842 11.7506 4.9 ± 1.92 7.18896 19.9702 8.9 ± 1.43 8.46211 22.4304 8.5 ± 1.06 11.09267 29.907 8.64 ± 0.84 7.82943 23.4798 9.61 ± 0.77 10.45843 31.5615 9.67 ± 0.60 15.69131 47.4589 9.69 ± 0.47 18.7582 57.0119 9.74 ± 0.35 22.81976 70.0416 9.84 ± 0.29 13.51755 40.3027 9.55 ± 0.36 16.86607 49.7262 9.45 ± 0.31 23.62808 71.6023 9.71 ± 0.26 28.3518 86.7222 9.8 ± 0.25 33.12969 99.0042 9.58 ± 0.21 38.86753 118.4393 9.76 ± 0.26

40

Ar(r) (%)

RI PT

38

SC

1.80% 2.50% 3.20% 3.90% 4.60% 5.30% 6.00% 6.70% 7.30% 8.30% 9.30% 10.50% 10.50% 11.50% 12.70% 14.00% 15.50% 17.10%

Ar(ca) [fA]

EP

14D17368 14D17370 14D17371 14D17372 14D17374 14D17375 14D17377 14D17378 14D17380 14D17381 14D17383 14D17384 14D17386 14D17387 14D17389 14D17390 14D17392 14D17393

37

M AN U

Ar(a) [fA]

TE D

36

Incremental Heating

AC C

782

1.06 1.71 1.78 1.75 4.58 6.14 7.8 11.99 14.85 16.93 23.44 26.35 31.33 30.55 29.6 27.3 32.31 23.84

39

Ar(k) (%) 0.26 0.46 0.87 1.38 1.29 1.52 1.99 1.4 1.88 2.81 3.36 4.09 2.42 3.02 4.24 5.08 5.94 6.97

K/Ca 0.285 1.128 1.08 0.815 1.496 1.437 1.244 1.199 1.198 1.102 1.151 0.941 0.948 0.647 0.265 0.113 0.082 0.074

± 2s ± 0.103 ± 0.913 ± 0.438 ± 0.164 ± 0.574 ± 0.405 ± 0.246 ± 0.329 ± 0.251 ± 0.136 ± 0.125 ± 0.070 ± 0.125 ± 0.042 ± 0.006 ± 0.001 ± 0.001 ± 0.001

ACCEPTED MANUSCRIPT

AN12JP008 (Cont.) 18.50% 20.00% 21.50% 22.70% 23.80% 24.80%

1.070818 1.389531 1.24116 0.769388 0.593541 0.624896

323.9388 437.7655 553.8644 588.3379 502.3963 497.2714

4.48891 6.474496 7.847896 7.624823 6.671596 6.698532

40.02256 46.03894 51.77955 52.29427 47.53866 46.78816

124.2573 145.4772 167.2004 167.7539 154.836 150.4966

M AN U

784

785

789

790

791

EP AC C

788

TE D

786

787

± 0.22 ± 0.23 ± 0.19 ± 0.15 ± 0.15 ± 0.15

SC

783

9.95 10.12 10.35 10.28 10.44 10.31

28.19 26.16 31.31 42.45 46.88 44.9

RI PT

14D17395 14D17396 14D17398 14D17399 14D17401 14D17402

7.18 8.26 9.29 9.38 8.52 8.39

0.053 0.045 0.04 0.038 0.041 0.04

± 0.000 ± 0.000 ± 0.000 ± 0.000 ± 0.000 ± 0.000

ACCEPTED MANUSCRIPT

14D31211

2.2 %

0.0591953 0.058042 0.0000000

16.4575

69.0487

12.60

14D31212 14D31214 14D31215 14D31216 14D31218 14D31219

2.4 % 2.7 % 3.0 % 3.3 % 3.6 % 3.7 %

0.0464712 0.0537671 0.0953577 0.1127269 0.1005165 0.1021596

0.0450462 0.0629646 0.0000000 0.0467491 0.0150257 0.0365872

13.8252 16.5696 25.2350 29.1473 27.3896 27.1433

58.8775 71.3523 109.5050 127.0606 119.7876 119.0035

12.79 12.93 13.03 13.09 13.13 13.16

14D31220

3.9 %

0.1141456 0.050584 0.0000000

28.3990

14D31222 14D31223 14D31224 14D31226 14D31227 14D31228 14D31230

4.2 % 4.5 % 4.7 % 4.8 % 5.1 % 5.4 % 5.7 %

0.1156856 0.0936723 0.1210909 0.0996915 0.1190516 0.1696927 0.1491396

0.644242 0.240347 0.129581 0.417149 0.398021 0.107834 0.317872

28.4392 24.0452 27.2608 23.5838 25.8069 31.5510 28.1552

14D31231

5.9 %

0.1634249 0.063644 0.0000000

14D31232 14D31234 14D31235 14D31236 14D31238 14D31239

6.1 % 6.5 % 6.9 % 7.1 % 7.3 % 7.8 %

0.1776557 0.2568364 0.2933748 0.2674692 0.1931348 0.3023447

39

0.0593108 0.0650891 0.0216836 0.0768068 0.0158756 0.0143643 0.0302244

0.260691 0.403604 0.326293 0.642323 0.203613 0.260632

0.0168239 0.0616926 0.0356938 0.0125776 0.0075310 0.0218863

40

± 2s

M AN U

Ar(cl) [fA]

Ar(r) (%)

39

Ar(k) (%)

K/Ca

± 0.15 ± 0.24

44.12 79.23

3.11 1.27

29.2 16.4

± 0.20

79.77

1.51

121.9

± 0.24 ± 0.20 ± 0.14 ± 0.12 ± 0.13 ± 0.13

81.07 81.77 79.52 79.21 80.12 79.75

1.27 1.52 2.31 2.67 2.51 2.48

10.8 34.1 90.7 7.2 38.5 80.1

124.1882

13.13

± 0.13

78.63

2.60

241.4

124.7489 105.3365 119.6882 102.9148 112.8820 138.1068 123.6884

13.17 13.15 13.18 13.10 13.13 13.14 13.19

± 0.13 ± 0.14 ± 0.13 ± 0.14 ± 0.14 ± 0.12 ± 0.13

78.48 79.18 76.97 77.73 76.23 73.35 73.72

2.60 2.20 2.49 2.16 2.36 2.89 2.58

19.0 43.0 90.5 24.3 27.9 125.8 38.1

29.7978

130.5852

13.16

± 0.13

72.99

2.73

201.3

30.0363 35.3416 37.6959 34.2161 25.4292 32.2138

130.0207 154.2509 163.9868 147.5890 110.5419 138.1871

13.00 13.10 13.06 12.95 13.05 12.88

± 0.13 ± 0.11 ± 0.12 ± 0.12 ± 0.15 ± 0.13

71.23 67.01 65.41 65.11 65.94 60.72

2.75 3.23 3.45 3.13 2.33 2.95

49.5 37.7 49.7 22.9 53.7 53.1

TE D

0.550485 0.208782 0.119621 1.742141 0.305708 0.145697

38

RI PT

1.8 % 2.0 %

Ar(ca) [fA]

EP

37

SC

14D31208 14D31210

40 Ar(k) Ar(r) Age [fA] [fA] (Ma) AN13JP007 0.4681778 0.500154 0.1532516 33.9879 109.2454 9.66 0.0507290 0.365012 0.0688689 13.9157 57.2196 12.35

Ar(a) [fA]

AC C

36

Incremental Heating

± 2s ± 41.3 ± 32.5 ± 1485.3 ± 14.2 ± 110.7 ± 524.0 ± 2.9 ± 95.3 ± 385.1 ± 3520.9 ± 20.6 ± 126.1 ± 501.7 ± 42.8 ± 49.4 ± 829.2 ± 85.9 ± 2265.9 ± 134.2 ± 65.1 ± 109.5 ± 25.0 ± 185.7 ± 148.5

ACCEPTED MANUSCRIPT

793

794

795

0.3094093 0.383056 0.0247206 0.2597242 0.409283 0.0478755

14D31243

8.8 %

0.3388198 0.033437 0.0551063

33.0951

141.7226

12.86

14D31244 14D31246

9.3 % 9.9 %

0.4506447 0.176627 0.0000000 0.4983406 0.274369 0.0343587

41.6771 46.0093

178.6142 199.8413

12.87 13.04

14D31248

10.5 % 0.6366138 0.014438 0.0420099

59.2291

253.9257

12.87

14D31249

11.2 % 0.4274792 0.080081 0.0670351

41.2251

178.8559

14D31251 14D31252 14D31253 14D31255 14D31256 14D31257 14D31259 14D31260 14D31262 14D31263

11.9 % 12.8 % 13.9 % 15.2 % 16.7 % 18.2 % 19.7 % 21.2 % 22.7 % 24.5 %

22.6364 23.3209 20.4766 21.6112 19.6950 18.1223 18.8239 9.9640 6.5227 6.1057

59.56 60.20

2.88 2.47

35.3 28.4

3.03

425.6

± 0.12 ± 0.15

57.28 57.57

3.81 4.21

101.5 72.1

± 0.10

57.44

5.42

1763.9

13.03

± 0.11

58.60

3.77

221.4

± 0.17 ± 0.17 ± 0.18 ± 0.18 ± 0.19 ± 0.20 ± 0.20 ± 0.34 ± 0.51 ± 0.54

60.21 63.50 63.08 60.74 61.37 63.94 66.33 63.16 64.27 64.02

2.07 2.13 1.87 1.98 1.80 1.66 1.72 0.91 0.60 0.56

19.8 27.5 31.2 22.7 20.7 26.9 38.9 22.9 6.1 5.2

98.4030 100.8002 88.9951 93.6936 85.7563 78.9679 82.2972 43.6380 28.9738 26.9898

SC

58.59

M AN U

0.0388804 0.0000000 0.0878187 0.0114410 0.0353713 0.0022895 0.0000000 0.0000000 0.0000000 0.0000000

± 0.14 ± 0.15 ± 0.13

TE D

0.490770 0.365001 0.282026 0.409586 0.408610 0.289271 0.208203 0.186859 0.462435 0.505835

EP

0.2199923 0.1960048 0.1762210 0.2048463 0.1826054 0.1506168 0.1413369 0.0860947 0.0544942 0.0513024

12.85 12.90

RI PT

8.1 % 8.3 %

AC C

792

14D31240 14D31242

AN13JP007 (Cont.) 31.4633 134.6845 27.0179 116.1107

13.05 12.98 13.05 13.02 13.07 13.08 13.13 13.15 13.34 13.27

± 69.2 ± 51.2 ± 9381.3 ± 412.4 ± 236.8 ± 87424.3 ± 1995.4 ± 29.2 ± 53.7 ± 78.7 ± 40.8 ± 37.0 ± 64.9 ± 133.4 ± 88.0 ± 9.6 ± 7.4

ACCEPTED MANUSCRIPT

796

7.4053 17.2014 27.0467 48.9939 70.8933 94.0115 129.7149 158.7551 182.3198 198.3699 147.7038 104.1156 75.4280 76.9022 83.2619 110.2075 104.8440 104.1321 89.4449 80.0196 63.8536 57.5342 51.0652

0.319056 0.414771 0.501900 0.550365 0.578910 0.702628 0.743201 0.658481 0.549717 0.534556 0.626824 0.684029 0.872213 0.885865 0.882245 1.627994 1.877674 2.204096 2.098326 2.205225 1.969583 1.923050 1.722607

39

Ar(k) [fA]

40

Ar(r) Age [fA] (Ma) AN13JP012 2.06085 14.0759 20.42 2.96419 15.1746 15.33 3.63401 19.7062 16.23 4.49476 19.3229 12.88 4.77075 23.6502 14.84 5.74178 22.6311 11.81 6.51622 32.9635 15.15 7.00946 33.4513 14.29 7.21003 32.3700 13.45 8.47720 29.7387 10.52 9.56506 35.6471 11.17 11.47973 36.4112 9.51 13.86569 50.2978 10.87 19.29421 64.8613 10.08 21.10186 63.6880 9.05 21.31380 67.2365 9.46 23.90290 73.5801 9.23 27.87996 86.3878 9.29 29.17327 94.7853 9.74 30.09238 99.1259 9.88 29.47636 98.5710 10.03 28.48051 100.4161 10.57 24.65186 90.6911 11.03

40

± 2s ± 9.95 ± 7.10 ± 6.28 ± 5.97 ± 4.91 ± 4.43 ± 3.87 ± 3.43 ± 3.01 ± 2.77 ± 2.52 ± 1.88 ± 1.47 ± 1.03 ± 0.80 ± 0.74 ± 0.64 ± 0.52 ± 0.50 ± 0.48 ± 0.47 ± 0.48 ± 0.55

Ar(r) (%) 1.63 1.70 1.92 1.52 2.24 1.88 2.77 3.00 3.40 2.84 3.27 3.81 5.75 7.52 10.32 13.19 15.86 19.45 21.78 22.34 26.10 27.87 29.55

RI PT

2.866972 2.973919 3.403149 4.236771 3.488361 3.995628 3.909438 3.656073 3.107983 3.448339 3.565497 3.106883 2.791650 2.697803 1.873071 1.497826 1.320951 1.210240 1.151847 1.165955 0.944152 0.879204 0.731778

Ar(cl) [fA]

SC

38

M AN U

Ar(ca) [fA]

TE D

1.8 % 2.5 % 3.2 % 3.9 % 4.6 % 5.3 % 6.0 % 6.7 % 7.3 % 8.3 % 9.3 % 10.5 % 11.5 % 12.7 % 14.0 % 15.5 % 17.1 % 18.5 % 20.0 % 21.5 % 22.7 % 23.8 % 24.8 %

37

EP

14D31141 14D31143 14D31144 14D31145 14D31147 14D31148 14D31150 14D31151 14D31153 14D31154 14D31156 14D31157 14D31158 14D31160 14D31161 14D31162 14D31164 14D31165 14D31166 14D31168 14D31169 14D31170 14D31172

Ar(a) [fA]

AC C

36

Incremental Heating

39

Ar(k) (%) 0.60 0.86 1.06 1.31 1.39 1.67 1.90 2.04 2.10 2.47 2.79 3.35 4.04 5.62 6.15 6.21 6.97 8.12 8.50 8.77 8.59 8.30 7.18

K/Ca 0.120 0.074 0.058 0.039 0.029 0.026 0.022 0.019 0.017 0.018 0.028 0.047 0.079 0.108 0.109 0.083 0.098 0.115 0.140 0.162 0.198 0.213 0.208

± 2s ± 0.011 ± 0.003 ± 0.002 ± 0.001 ± 0.001 ± 0.000 ± 0.000 ± 0.000 ± 0.000 ± 0.000 ± 0.000 ± 0.001 ± 0.001 ± 0.001 ± 0.001 ± 0.001 ± 0.001 ± 0.001 ± 0.001 ± 0.002 ± 0.003 ± 0.003 ± 0.003

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

AC C

EP

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT

Arc-oblique faults in central Chile played a crucial role for Andean evolution. They were reactivated as strike-slip ± reverse faults in the Neogene. Neogene reactivation occurred during widespread syn-tectonic hydrothermal activity. Fault reactivation occurred under E- to ENE-directed shortening. Different deformation styles affected specific structural blocks in the Neogene.

AC C

EP

TE D

M AN U

SC

RI PT

• • • • •