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Typeset by SPi Global, India Contents

Contributors ...... xix Preface and Acknowledgments ...... xxvii Part I Overview CHAPTER 1 Seismic structure along the South American subduction zone using satellite gravity data ...... 3 Orlando Alvarez, Stefanie Pechuan, Mario Gimenez, Andrés Folguera 1 Introduction ...... 3 2 Data and method ...... 5 2.1 Satellite GOCE gravity data ...... 5 2.2 Reduction by topographic and sediments effect ...... 5 2.3 Harmonic decomposition ...... 5 3 Results and discussion ...... 6 3.1 The Valdivia 1960 Mw=9.5 earthquake ...... 6 3.2 The Maule segment ...... 8 3.3 The central Chile segment ...... 8 3.4 Northern Chile-southern Peru ...... 11 3.5 Peru ...... 13 3.6 Ecuador-Colombia ...... 15 4 Concluding remarks ...... 17 Acknowledgments ...... 18 References ...... 18 CHAPTER 2 Control of subduction erosion and sediment accretion processes on the trench curvature of the central Chilean margin ....25 Eduardo Contreras-Reyes 1 Introduction ...... 25 2 Trench and margin curvature ...... 27 3 Discussion ...... 31 4 Summary ...... 32 Acknowledgments ...... 32 References ...... 32 CHAPTER 3 Measuring dynamic topography in South America ...... 35 Federico M. Dávila, Pilar Ávila, Federico Martina, Horacio N. Canelo, Julieta C. Nóbile, Gilda Collo, Francisco Sánchez Nassif, Miguel Ezpeleta 1 Introduction ...... 35 2 Geodynamic and tectonic setting ...... 37

v vi Contents

3 Theory, methods, and data ...... 44 3.1 Global to continental residual topography ...... 44 3.2 Local to regional residual topographic analysis ...... 46 3.3 Dynamic topography ...... 48 4 Results ...... 48 4.1 Continental lithospheric scale analysis. Modern and ancient ...... 48 4.2 Local residual estimations ...... 51 5 Discussion, ongoing studies, and future perspectives ...... 54 6 Conclusions ...... 59 Acknowledgments ...... 60 References ...... 60 Further reading ...... 66 Part II Northern Andes CHAPTER 4 Cenozoic tectonic evolution of the North Andes with constraints from volcanic ages, seismic reflection, and satellite geodesy ...... 69 James N. Kellogg, Gabriela Beatriz Franco Camelio, Héctor Mora-Páez 1 Introduction ...... 69 1.1 Flat subduction ...... 69 1.2 Slab geometry ...... 70 1.3 Arc-continent accretion and "escape" ...... 70 2 Present tectonics of the North Andes (GPS vectors and profiles) ...... 71 2.1 Nazca subduction and volcanic arc ...... 71 2.2 Amagmatic Caribbean subduction and accretionary prism formation ...... 74 2.3 Arc-continent collision ...... 76 2.4 Margin-parallel "escape" ...... 77 2.5 Margin-normal mountain building ...... 78 3 Data sources and methodology ...... 80 3.1 Radiometric ages for arc volcanics ...... 80 3.2 Revised plate tectonic model ...... 80 3.3 Earthquake hypocentral locations ...... 84 4 Plate tectonic evolution of the North Andes ...... 85 4.1 75Ma–45Ma, Previous work—Caribbean obduction—Western Cordillera ...... 85 4.2 45Ma to 25Ma—Revised model—Farallon-Caribbean-North Andes triple junction ...... 85 4.3 25Ma to Present—Revised model—Panama-Choco arc-continent collision .....86 5 Discussion ...... 88 5.1 Flat slab subduction, low heat flow, and thick-skinned basement tectonics ...... 88 Contents vii

5.2 Panamá arc-North Andes collision: "broken indenter" and arc accretion...... 89 5.3 Bucaramanga slab—Nazca or Caribbean? ...... 91 6 Summary ...... 92 Acknowledgments ...... 94 Appendix: Supplementary material ...... 94 References ...... 94

CHAPTER 5 Thermochronological constraints on Cenozoic exhumation along the southern Caribbean: The Santa Marta range, northern Colombia ...... 103 Ana María Patiño, Mauricio Parra, Juan Carlos Ramírez, Edward R. Sobel, Johannes Glodny, Ariel Almendral, Sebastián Echeverri 1 Introduction ...... 103 2 Geological setting ...... 106 2.1 Regional geological setting ...... 106 2.2 Local geological setting ...... 107 3 Pre-existing thermochronological data ...... 108 4 Methods ...... 110 4.1 Detrital fission-track and (U-Th)/He analyses in apatite ...... 110 4.2 One-dimensional exhumation rates ...... 111 5 Results ...... 113 5.1 Catchment hypsometry and lithology ...... 113 5.2 Detrital thermochronology ...... 114 5.3 One-dimensional exhumation rates ...... 117 5.4 Thermokinematic modeling ...... 118 6 Discussion ...... 122 6.1 Paleocene-Eocene (60–45Ma) ...... 123 6.2 Oligocene-Miocene (30–20Ma) ...... 125 6.3 Middle Miocene (16–10Ma) ...... 125 7 Conclusions ...... 126 Acknowledgments ...... 127 Appendix: Supplementary material ...... 127 References ...... 127

CHAPTER 6 Discriminating mechanisms for coarse clastic progradation in the Colombian foreland basin using detrital zircon double dating ...... 133 Soty Odoh, Joel E. Saylor, Camilo Higuera, Peter Copeland, Thomas J. Lapen 1 Introduction ...... 133 2 Geologic setting and regional geochronology ...... 135 viii Contents

3 Depositional environments ...... 139 3.1 Lithofacies associations ...... 139 3.2 Lithostratigraphy ...... 142 4 Detrital zircon geochronology and thermochronology ...... 144 4.1 Methods ...... 144 4.2 Results and interpretations ...... 146 4.3 Interpreting changes in exhumation rate through lag-time analysis ...... 151 5 Regional sediment provenance and exhumation ...... 152 5.1 Maastrichtian-early Paleocene (Guaduas-Barco Formations) ...... 152 5.2 Early Paleocene-early Eocene (Barco-Mirador Formations) ...... 154 5.3 Early Eocene-late Oligocene (Mirador Formation-C7 member) ...... 154 5.4 Late Oligocene-late Miocene (C7-lower Guayabo Formation) ...... 154 5.5 Late Miocene-Pliocene (lower-upper Guayabo Formation) ...... 155 5.6 Summary ...... 155 6 Regional integration ...... 155 6.1 Maastrichtian ...... 156 6.2 Early Paleocene...... 156 6.3 Late Paleocene-early Eocene ...... 158 6.4 Eocene ...... 158 6.5 Oligocene ...... 159 6.6 Miocene ...... 160 6.7 Pliocene ...... 161 7 Conclusion ...... 161 Acknowledgments ...... 162 Appendix: Supplementary material ...... 163 References ...... 163 CHAPTER 7 Latest Triassic to Early Cretaceous tectonics of the Northern Andes: Geochronology, geochemistry, isotopic tracing, and thermochronology ...... 173 Richard A. Spikings, Ryan Cochrane, Cristian Vallejo, D. Villagomez, Roelant Van der Lelij, A. Paul, Wilfried Winkler 1 Introduction ...... 173 2 Geological framework ...... 174 3 Geochronology ...... 180 3.1 Latest Triassic to earliest Cretaceous intrusions: Cordillera real, Cordillera central, Sierra Nevada de Santa Marta, and the Santander Massif ...... 180 3.2 Early Cretaceous magmatic and sedimentary rocks: Cordillera Real and Cordillera Central ...... 182 Contents ix

4 Geochemistry ...... 185 4.1 Latest Triassic-earliest Cretaceous granitoids ...... 185 4.2 Early Cretaceous igneous rocks ...... 187 5 Discussion ...... 191 5.1 The tectonic setting during the latest Triassic-Jurassic (209–130Ma) ...... 191 5.2 The tectonic setting during the Early Cretaceous (145–115Ma) ...... 195 5.3 Compression during the Early Cretaceous ...... 200 6 Conclusions ...... 201 Acknowledgments ...... 202 Appendix: Supplementary material ...... 202 References ...... 202 Further reading ...... 208 CHAPTER 8 Late cretaceous to miocene stratigraphy and provenance of the coastal forearc and Western Cordillera of Ecuador: Evidence for accretion of a single oceanic plateau fragment ...... 209 Cristian Vallejo, Richard A. Spikings, Brian K. Horton, Leonard Luzieux, Christian Romero, Wilfried Winkler, Tonny B. Thomsen 1 Introduction ...... 209 2 Regional geology ...... 210 3 The Western Cordillera and the allochthonous origin of the basement ...... 213 3.1 The Pallatanga block ...... 213 3.2 The Macuchi block ...... 216 4 The coastal forearc and the Piñon block ...... 217 4.1 Late Cretaceous to Miocene stratigraphy of the central and southern part of the coastal forearc ...... 217 5 Models for the accretion of the coastal region and Western Cordillera blocks ...... 219 6 Provenance analysis of the Western Cordillera and coastal forearc region ...... 222 6.1 Heavy mineral data ...... 222 6.2 Detrital zircon U-Pb ages of Late Cretaceous to Cenozoic strata capping the Pallatanga and Piñon blocks ...... 224 7 Late Cretaceous to Miocene Tectonic history of western Ecuador ...... 228 7.1 Evolution of the Piñon and Pallatanga blocks and their volcanic and sedimentary cover ...... 228 7.2 Autochthonous origin for the Macuchi block ...... 230 8 Conclusions ...... 231 Acknowledgments ...... 232 Appendix: Supplementary material ...... 232 References ...... 232 x Contents

CHAPTER 9 Provenance and geochronological insights into Late Cretaceous- Cenozoic foreland basin development in the Subandean Zone and Oriente Basin of Ecuador ...... 237 E. Gabriela Gutiérrez, Brian K. Horton, Cristian Vallejo, Lily J. Jackson, Sarah W.M. George 1 Introduction ...... 237 2 Geologic framework ...... 239 3 Depositional systems ...... 241 3.1 Eocene Tiyuyacu Formation: Gravelly braided river ...... 241 3.2 Oligocene-lowermost Miocene Chalcana Formation: Silty sand-dominated meandering river...... 244 3.3 Miocene Arajuno Formation: Meandering to sand-dominated braided river ...... 245 4 Sediment source regions ...... 245 4.1 Cratonic source regions ...... 247 4.2 Andean source regions ...... 247 5 Zircon U-Pb geochronology ...... 248 5.1 Detrital zircon provenance analyses ...... 248 6 Discussion ...... 256 6.1 Early Cretaceous development of postextensional sag basin ...... 256 6.2 Late Cretaceous onset of shortening, flexure, and foreland basin sedimentation ...... 256 6.3 Paleocene-Eocene shortening and thrust belt advance ...... 258 6.4 Oligocene diminished shortening and magmatic flareup ...... 259 6.5 Miocene-Quaternary main phase of Andean shortening ...... 259 7 Conclusions ...... 260 Acknowledgments ...... 260 Appendix: Supplementary material ...... 260 References ...... 260 Further reading ...... 267 CHAPTER 10 Sediment provenance variations during contrasting Mesozoic-early Cenozoic tectonic regimes of the northern Peruvian Andes and Santiago-Marañón foreland basin ...... 269 Sarah W.M. George, Brian K. Horton, Lily J. Jackson, Federico Moreno, Victor Carlotto, Carmala N. Garzione 1 Introduction ...... 269 2 Geologic context ...... 270 3 Stratigraphic framework ...... 272 4 U-Pb geochronology ...... 276 4.1 Methods ...... 276 Contents xi

4.2 Potential sediment sources ...... 277 4.3 Detrital zircon results and interpretations ...... 280 5 Basin reconstruction ...... 285 5.1 Middle to Late Triassic ...... 287 5.2 Late Triassic to Early Jurassic ...... 287 5.3 Early Jurassic to Early Cretaceous ...... 287 5.4 Early Cretaceous ...... 288 5.5 Late Cretaceous ...... 289 5.6 Latest Cretaceous–Paleogene ...... 289 6 Conclusions ...... 290 Acknowledgments ...... 290 Appendix: Supplementary material ...... 291 References ...... 291 Further reading ...... 296

Part III Central Andes CHAPTER 11 Western thrusting and uplift in northern Central Andes (western Peruvian margin) ...... 299 Alice Prudhomme, Patrice Baby, Alexandra Robert, Stéphanie Brichau, Edward Cuipa, Adrien Eude, Ysabel Calderon, Paul O’Sullivan 1 Introduction ...... 299 2 Geological background ...... 300 2.1 Northern Central Andes tectonic setting ...... 300 2.2 The Yaquina, Trujillo, and Salaverry offshore forearc basins ...... 302 2.3 The Western Cordillera and the Calipuy Plateau-Basin ...... 302 3 Methodology and data ...... 303 4 Structural architecture of the forearc basins ...... 306 5 Structural architecture of the Western Cordillera ...... 307 6 Offshore-onshore stratigraphic correlations ...... 311 7 Regional balanced cross-section ...... 315 8 Calipuy Plateau-Basin and WAE exhumation from thermochronology ...... 317 9 Cenozoic tectonic history and discussion ...... 320 10 Conclusion ...... 324 Acknowledgments ...... 325 Appendix: Supplementary material ...... 325 References ...... 325

CHAPTER 12 Structural controls along the Peruvian Subandes ...... 333 Gonzalo Zamora, Melanie Louterbach, Pedro Arriola 1 Introduction ...... 333 xii Contents

2 Geological context ...... 335 3 Stratigraphy ...... 336 3.1 Paleozoic ...... 336 3.2 Mesozoic ...... 337 3.3 Cenozoic ...... 338 4 Northern sector (Marañón Basin and Huallaga and Santiago sub-basins) ...... 339 4.1 The Marañón Basin ...... 339 4.2 The Santiago sub-basin ...... 342 4.3 The Huallaga sub-basin ...... 342 5 Central sector (Ucayali Basin and, Ene, Pachitea and Camisea sub-basins) ...... 344 5.1 The Northern Ucayali Basin and Pachitea sub-basin...... 344 5.2 The Ene sub-basin ...... 346 5.3 The Camisea sub-basin ...... 346 6 Southern sector (Madre de Dios) ...... 352 7 Discussion ...... 353 8 Conclusions ...... 356 Acknowledgments ...... 357 References ...... 357 Further reading ...... 362 CHAPTER 13 Provenance and recycling of detrital zircons from Cenozoic Altiplano strata and the crustal evolution of western South America from combined U-Pb and Lu-Hf isotopic analysis ...363 Kurt Sundell, Joel E. Saylor, Mark Pecha 1 Introduction ...... 363 2 Geologic context ...... 365 2.1 Assembly of the South American continent ...... 365 2.2 Study area in the Peruvian Altiplano ...... 366 3 Methods ...... 367 3.1 U-Pb geochronology ...... 368 3.2 Hf isotope geochemistry ...... 368 3.3 Data visualization ...... 370 3.4 Frequency analysis ...... 370 4 Results ...... 371 4.1 U-Pb geochronology ...... 371 4.2 Hf isotope geochemistry ...... 372 5 Discussion ...... 379 5.1 Detrital zircon provenance ...... 379 5.2 Detrital zircon recycling ...... 381 5.3 Crustal evolution of western South America ...... 388 5.4 Cyclical orogenesis ...... 389 6 Conclusions ...... 391 Contents xiii

Acknowledgments ...... 391 Appendix: Supplementary material ...... 391 References ...... 391 Further reading ...... 397

CHAPTER 14 Structure and tectonic evolution of the Interandean and Subandean Zones of the central Andean fold-thrust belt of Bolivia ...... 399 E.A. Rojas Vera, P. Giampaoli, E. Gobbo, E. Rocha, G. Olivieri, D. Figueroa 1 Introduction ...... 399 2 Geologic setting ...... 401 3 Tectonic evolution of the Bolivian Andes ...... 402 4 Exhumation history of the orogen ...... 405 5 Stratigraphic column and mechanical behavior ...... 405 6 Structural styles and deformational models ...... 407 7 Fold growth and lateral linkage ...... 408 8 Methods ...... 408 9 Structure of the southern Subandean fold-thrust belt and Interandean Zone ...... 409 9.1 Desecho Chico section (A-A') ...... 409 9.2 Churumas section (B-B')...... 411 9.3 Villamontes section (C-C') ...... 411 9.4 Iguembe section (D-D')...... 414 9.5 Incahuasi section (E-E') ...... 414 9.6 Tarabuco section (F-F') ...... 416 9.7 Samaipata section (G-G') ...... 416 10 Discussion ...... 418 10.1 Exhumation of the subandean fold-thrust belt ...... 418 11 Along-strike shortening gradient ...... 418 12 Implication in hydrocarbons exploration ...... 419 13 Conclusions ...... 421 Acknowledgments ...... 422 References ...... 422 CHAPTER 15 Structural and thermochronologic constraints on kinematics and timing of inversion of the Salta rift in the Tonco-Amblayo sector of the Andean retroarc fold-thrust belt, northwestern Argentina .....429 Cullen Kortyna, Peter G. DeCelles, Barbara Carrapa 1 Introduction ...... 429 2 Geological background ...... 431 2.1 Regional setting ...... 431 2.2 Tectonic history of NW Argentina ...... 433 xiv Contents

2.3 Previous cenozoic shortening estimates and cross-sections in northern Argentina ...... 434 2.4 Previously documented exhumation history in NW Argentina (23–27°S) ...... 434 2.5 Stratigraphic and structural models of deformation in the eastern Cordillera ...... 435 3 Stratigraphic framework of the TATB ...... 436 3.1 Puncoviscana formation and Salta group...... 436 3.2 The Payogastilla and Orán Groups ...... 440 4 Structural geology of the TATB ...... 441 4.1 Geologic mapping ...... 441 4.2 Regional structure ...... 441 4.3 Regional cross-sections...... 445 5 Thermochronology ...... 448 5.1 Apatite (U-Th)/He system ...... 448 5.2 AHe sample locations ...... 449 5.3 Apatite (U-Th)/He results ...... 450 5.4 Summary of apatite (U-Th)/He results ...... 451 5.5 Modeling of AHe data ...... 453 6 Discussion ...... 455 6.1 Deformation in the TATB ...... 455 6.2 Shortening estimates ...... 456 6.3 Kinematic sequence ...... 456 7 Conclusions ...... 457 Acknowledgments ...... 458 Appendix: Supplementary material ...... 458 References ...... 458 CHAPTER 16 Tectonic evolution of the western "Pampean" flat segment (28°–30°S)...... 465 F. Martínez, C. Arriagada, C. López, Mauricio Parra 1 Introduction ...... 465 2 Stratigraphy of the western "Pampean" flat-slab segment ...... 467 2.1 Coastal Cordillera ...... 467 2.2 Frontal Cordillera ...... 467 3 Structural styles present in the western "Pampean" flat-slab segment ...... 470 4 Mechanisms of deformation ...... 473 4.1 Normal faults reactivation ...... 473 4.2 Basement-involved reverse faulting ...... 476 5 Chronology of Andean deformation ...... 476 6 General discussions ...... 479 7 Conclusions ...... 481 Acknowledgments ...... 482 Contents xv

References ...... 482 Further reading ...... 485

CHAPTER 17 Thermal and lithospheric structure of the Chilean-Pampean flat-slab from gravity and magnetic data ...... 487 Marcos A. Sánchez, Héctor P.A. García, Gemma Acosta, Guido M. Gianni, Marcelo A. Gonzalez, Juan P. Ariza, Myriam P. Martinez, Andrés Folguera 1 Introduction ...... 487 2 Tectonic setting ...... 489 3 Methodology ...... 490 3.1 Magnetic database ...... 490 3.2 Curie point-depth estimation ...... 490 3.3 Heat flow determination ...... 493 3.4 Gravity database ...... 493 4 Results and conclusions ...... 502 Acknowledgments ...... 503 References ...... 503 Further reading ...... 507

CHAPTER 18 Fragments of the late Paleozoic accretionary complex in central and northern Chile: Similarities and differences as a key to decipher the complexity of the late Paleozoic to Triassic early Andean events ...... 509 Juan Díaz-Alvarado, Gonzalo Galaz, Verónica Oliveros, Christian Creixell, Mauricio Calderón 1 Occurrence of accretionary complexes and subduction channels in subductive and collisional margins ...... 509 2 Description of the accretionary complexes of the Chilean coast ...... 511 2.1 Lithological characteristics and depositional setting of the accretionary complexes ...... 512 2.2 Volcanic rocks included in the accretionary complexes ...... 512 2.3 Structural characteristics ...... 514 2.4 Metamorphic conditions ...... 515 2.5 Geochronological determinations ...... 516 3 Late Paleozoic to Triassic magmatism related to the southwestern convergent margin of Gondwana ...... 517 4 The late Paleozoic early Andean (Gondwanan and pre-Andean) events depicted by the study of the coastal accretionary complexes in central and northern Chile...... 518 4.1 Facts deduced from the study of the late Paleozoic accretionary complexes in central and northern Chile… ...... 518 4.2 … and theories about the evolution of the southwestern margin of Gondwana between the late Paleozoic and the late Triassic ...... 520 xvi Contents

5 Concluding remarks: Early Andean orogenic/tectonic cycles and phases ...... 524 Acknowledgments ...... 525 References ...... 525 Further reading ...... 530 CHAPTER 19 40Ar/39Ar constraints on the tectonic evolution of the late Paleozoic and early Mesozoic accretionary complex of coastal central Chile ...... 531 Laura E. Webb, Keith A. Klepeis 1 Introduction ...... 531 1.1 Geologic background ...... 533 2 Methods ...... 534 3 Results ...... 535 3.1 Isla Negra ...... 535 3.2 Las Cruces ...... 538 3.3 Agua Salada ...... 542 3.4 Quintay ...... 545 4 Discussion ...... 545 4.1 Late Carboniferous-Early Permian arc magmatism and deformation ...... 545 4.2 Late Triassic-Early Jurassic granitoids, leucocratic intrusions, and high-strain shear zones ...... 547 4.3 Late Jurassic arc magmatism and deformation ...... 548 4.4 Cretaceous (and younger) faulting ...... 548 5 Conclusions ...... 549 Acknowledgments ...... 550 Appendix: Supplementary material ...... 550 References ...... 551 Part IV Southern Andes CHAPTER 20 Crustal structure in the southern Andes, adjacent foreland, and Atlantic passive margin delineated by satellite gravimetric models ...... 557 Mario Gimenez, Agustina Pesce, Stefanie Pechuan, María Alejandra Arecco, Santiago R. Soler, Sebastián Correa Otto, Federico Lince Klinger, Orlando Álvarez, Andrés Folguera 1 Introduction ...... 557 2 Methodology ...... 559 2.1 The topography corrected vertical gravity gradient (Tzz) ...... 559 2.2 2-D gravity forward model ...... 562 2.3 Depth to the crust-mantle interface (Moho) ...... 562 3 Results ...... 565 4 Discussion ...... 566 Contents xvii

5 Conclusions ...... 568 Acknowledgments ...... 569 References ...... 569 CHAPTER 21 Cenozoic arc-related magmatism in the southern Central and North Patagonian Andes ...... 573 Vanesa D. Litvak, Lucía Fernández Paz, Sofía Iannelli, Stella Poma, Andrés Folguera 1 Introduction ...... 573 2 Regional distribution of Cenozoic arc rocks ...... 575 3 Geochemical evolution of arc magmas in relation to the changing geodynamic framework ...... 578 3.1 Paleocene-middle Eocene ...... 579 3.2 Late Eocene-early Oligocene ...... 581 3.3 Late Oligocene-early Miocene ...... 584 3.4 Middle Miocene-middle Pliocene ...... 589 4 Andean arc-magmatic evolution from the southern central to the north Patagonian Andes ...... 594 5 Conclusions ...... 598 Acknowledgments ...... 599 References ...... 599 Further reading ...... 607 CHAPTER 22 Tectonic controls on the building of the North Patagonian fold-thrust belt (~43°S) ...... 609 A. Echaurren, Guido M. Gianni, Lucía Fernández Paz, C. Navarrete, Verónica Oliveros, A. Encinas, Mario Giménez, F. Lince-Klinger, Andrés Folguera 1 Introduction ...... 609 2 Tectonic setting of North Patagonia ...... 611 3 Mesozoic evolution: From continental breakup to initial Andean orogeny ...... 613 3.1 Geology of the Mesozoic igneous rocks ...... 614 3.2 Basin evolution and deformational processes ...... 620 3.3 Geochemical features and magma sources ...... 624 4 Cenozoic evolution: Paleogene extensional regime and Neogene Andean rise ...... 625 4.1 Geology of Cenozoic magmatic rocks ...... 626 4.2 Basin evolution and deformational processes ...... 628 4.3 Geochemical data ...... 629 5 Discussion: Tectonic evolution and controls on orogenesis ...... 631 6 Conclusions ...... 636 Acknowledgments ...... 637 References ...... 637 Further reading ...... 649 xviii Contents

CHAPTER 23 Along-strike segmentation of the Farallon-Phoenix midocean ridge: Insights from the Paleogene tectonic evolution of the Patagonian Andes between 45° and 46°30'S ...... 651 Guido M. Gianni, Agustina Pesce, Santiago R. Soler, Héctor P.A. García, Marcos A. Sánchez, C. Navarrete, A. Echaurren, A. Encinas, Andrés Folguera 1 Introduction ...... 651 2 Geological background of the Andes between 45°S and 46°30'S ...... 654 3 Synthesis of Andean Paleogene tectonics from 45°S to 46°30'S ...... 655 4 Overview of Paleogene tectonics of Central Patagonia ...... 657 5 Summary and discussion on Paleogene tectonics of Central Patagonia ...... 665 6 Conclusions ...... 667 Acknowledgments ...... 668 References ...... 668 Further reading ...... 673 CHAPTER 24 Structure and tectonic evolution of the South Patagonian fold and thrust belt: Coupling between subduction dynamics, climate and tectonic deformation ...... 675 Matías C. Ghiglione, Gonzalo Ronda, Rodrigo J. Suárez, Inés Aramendía, Vanesa Barberón, Miguel E. Ramos, Jonathan Tobal, Ezequiel García Morabito, Joseph Martinod, Christian Sue 1 Introduction ...... 675 2 Tectostratigraphic evolution of the SPA ...... 681 2.1 Paleozoic to Early Cretaceous: Pre-Andean evolution ...... 681 2.2 Late Cretaceous—Neogene Andean evolution ...... 682 3 Stratigraphy of the Southern Patagonian Andes ...... 682 3.1 Stratigraphy of the eastern basement domain ...... 683 3.2 Stratigraphy of the fold and thrust belt ...... 683 3.3 North-South stratigraphic variations ...... 686 4 Structure of the Southern Patagonian Andes ...... 686 4.1 Basement domain ...... 686 4.2 Structure of the fold-and-thrust belt ...... 687 5 Discussion and final remarks ...... 688 5.1 Orogen width, mechanical stratigraphy, and shortening in the Southern Patagonian Andes ...... 688 5.2 Major structural segments in the SPA ...... 689 5.3 Comparison of domain distribution with exhumation patterns ...... 689 Acknowledgments ...... 691 References ...... 691 Further reading ...... 697

Index ...... 699 Contributors

Gemma Acosta Seismological Geophysical Institute Ing. Volponi (IGSV), FCEFyN, National University of San Juan, San Juan; National Scientific and Technical Research Council (CONICET), Buenos Aires, Argentina Ariel Almendral Norwegian Computing Center, Oslo, Norway Orlando Álvarez Seismological Geophysical Institute Ing. Volponi (IGSV), FCEFyN, National University of San Juan, San Juan; National Scientific and Technical Research Council (CONICET), Buenos Aires, Argentina Inés Aramendía IDEAN (Buenos Aires Univ.—CONICET), Buenos Aires, Argentina María Alejandra Arecco Instituto de Geodesia y Geofísica Aplicadas "Ing. E. Baglietto", FI, Universidad de Buenos Aires, Buenos Aires, Argentina Juan P. Ariza Seismological Geophysical Institute Ing. Volponi (IGSV), FCEFyN, National University of San Juan, San Juan; National Scientific and Technical Research Council (CONICET), Buenos Aires, Argentina C. Arriagada Department of Geology, University of Chile, Santiago, Chile Pedro Arriola REPSOL Exploración Perú, San Isidro, Peru Pilar Ávila Earth Science Research Center, CONICET National Research Council & Natural, Physics and Exact Sciences Faculty, Cordoba National University, Córdoba, Argentina Patrice Baby Géosciences Environnement Toulouse, Paul Sabatier University, IRD, CNRS, Toulouse, France Vanesa Barberón IDEAN (Buenos Aires Univ.—CONICET), Buenos Aires, Argentina Stéphanie Brichau Géosciences Environnement Toulouse, Paul Sabatier University, IRD, CNRS, Toulouse, France Ysabel Calderon PERUPETRO S.A., Lima, Peru Mauricio Calderón Faculty of Engineering, Andrés Bello University, Santiago, Chile Gabriela Beatriz Franco Camelio Simon Bolivar University, Caracas, Venezuela

xix xx Contributors

Horacio N. Canelo Earth Science Research Center, CONICET National Research Council & Natural, Physics and Exact Sciences Faculty, Cordoba National University, Córdoba, Argentina Victor Carlotto Universidad Nacional San Antonio Abad del Cusco, Cusco, Peru Barbara Carrapa Department of Geosciences, University of Arizona, Tucson, AZ, United States Ryan Cochrane CRU, London, United Kingdom Gilda Collo Earth Science Research Center, CONICET National Research Council & Natural, Physics and Exact Sciences Faculty, Cordoba National University, Córdoba, Argentina Eduardo Contreras-Reyes Department of Geophysics, Faculty of Physical and Mathematical Sciences, University of Chile, Santiago, Chile Peter Copeland Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX, United States Christian Creixell National Geology and Mining Service, Santiago, Chile Edward Cuipa PERUPETRO S.A., Lima, Peru Federico M. Dávila Earth Science Research Center, CONICET National Research Council & Natural, Physics and Exact Sciences Faculty, Cordoba National University, Córdoba, Argentina Peter G. DeCelles Department of Geosciences, University of Arizona, Tucson, AZ, United States Juan Díaz-Alvarado Department of Geology, University of Atacama, Copiapó, Chile A. Echaurren Department of Geological Sciences, IDEAN—Institute of Andean Studies "Don Pablo Groeber", UBA—CONICET, FCEN, University of Buenos Aires, Buenos Aires, Argentina Sebastián Echeverri Institute of Geosciences, University of São Paulo, São Paulo, Brazil A. Encinas Department of Earth Sciences, University of Concepción, Concepción, Chile Adrien Eude Géosciences Environnement Toulouse, Paul Sabatier University, IRD, CNRS, Toulouse, France Miguel Ezpeleta Earth Science Research Center, CONICET National Research Council & Natural, Physics and Exact Sciences Faculty, Cordoba National University, Córdoba, Argentina Contributors xxi

Lucía Fernández Paz Faculty of Exact and Natural Sciences, National Scientific and Technical Research Council (CONICET),IDEAN—Institute of Andean Studies "Don Pablo Groeber", University of Buenos Aires, Buenos Aires, Argentina D. Figueroa International Exploration, YPF S.A, Buenos Aires, Argentina Andrés Folguera Department of Geological Sciences, National Scientific and Technical Research Council (CONICET), IDEAN—Institute of Andean Studies "Don Pablo Groeber", FCEN, University of Buenos Aires, Buenos Aires, Argentina Gonzalo Galaz Department of Geology, University of Atacama, Copiapó, Chile Héctor P.A. García Seismological Geophysical Institute Ing. Volponi (IGSV), FCEFyN, National University of San Juan, San Juan; National Scientific and Technical Research Council (CONICET), Buenos Aires, Argentina Carmala N. Garzione Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY, United States Sarah W.M. George Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, United States Matías C. Ghiglione IDEAN (Buenos Aires Univ.—CONICET), Buenos Aires, Argentina P. Giampaoli International Exploration, YPF S.A, Buenos Aires, Argentina Guido M. Gianni Seismological Geophysical Institute Ing. Volponi (IGSV), FCEFyN, National University of San Juan, San Juan; National Scientific and Technical Research Council (CONICET), Buenos Aires; Departamento de Ciencias Geológicas, IDEAN—Institute of Andean Studies "Don Pablo Groeber", UBA—CONICET, FCEN, University of Buenos Aires, Buenos Aires, Argentina Mario Gimenez Seismological Geophysical Institute Ing. Volponi (IGSV), FCEFyN, National University of San Juan, San Juan; National Scientific and Technical Research Council (CONICET), Buenos Aires, Argentina Johannes Glodny GFZ German Research Center for Geosciences, Potsdam, Germany E. Gobbo Exploration, Geopark, Buenos Aires, Argentina Marcelo A. Gonzalez Seismological Geophysical Institute Ing. Volponi (IGSV), FCEFyN, National University of San Juan, San Juan; National Scientific and Technical Research Council (CONICET), Buenos Aires, Argentina xxii Contributors

E. Gabriela Gutiérrez Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, United States Camilo Higuera Ecopetrol, Bogota, Colombia Brian K. Horton Department of Geological Sciences; Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, United States Sofía Iannelli Faculty of Exact and Natural Sciences, National Scientific and Technical Research Council (CONICET),IDEAN—Institute of Andean Studies "Don Pablo Groeber", University of Buenos Aires, Buenos Aires, Argentina Lily J. Jackson Department of Geological Sciences, Jackson School of Geosciences; Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, United States James N. Kellogg University of South Carolina, Columbia, SC, United States Keith A. Klepeis Department of Geology, University of Vermont, Burlington, VT, United States Federico Lince Klinger Seismological Geophysical Institute Ing. Volponi (IGSV), FCEFyN, National University of San Juan, San Juan; National Scientific and Technical Research Council (CONICET), Buenos Aires, Argentina Cullen Kortyna Department of Geosciences, University of Arizona, Tucson, AZ, United States Thomas J. Lapen Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX, United States F. Lince-Klinger Institute of Geophysics and Seismology Ingeniero Volponi, San Juan National University, Conicet, San Juan, Argentina Vanesa D. Litvak Faculty of Exact and Natural Sciences, National Scientific and Technical Research Council (CONICET),IDEAN—Institute of Andean Studies "Don Pablo Groeber", University of Buenos Aires, Buenos Aires, Argentina C. López Department of Geological Sciences, Catholic University of the North, Antofagasta, Chile Melanie Louterbach REPSOL Exploración S.A., Madrid, Spain Leonard Luzieux LH Trading Ltd, Zürich, Switzerland Contributors xxiii

Federico Martina Earth Science Research Center, CONICET National Research Council & Natural, Physics and Exact Sciences Faculty, Cordoba National University, Córdoba, Argentina Myriam P. Martinez Seismological Geophysical Institute Ing. Volponi (IGSV), FCEFyN, National University of San Juan, San Juan; National Scientific and Technical Research Council (CONICET), Buenos Aires, Argentina F. Martínez Department of Geological Sciences, Catholic University of the North, Antofagasta, Chile Joseph Martinod Grenoble Alpes Univ., Savoie Mont Blanc Univ., CNRS, IRD, IFSTTAR, ISTerre, 73000 Chambéry, France Ezequiel García Morabito IIDyPCa, CONICET, Río Negro Univ., San Carlos de Bariloche, Argentina Héctor Mora-Páez Colombian Geological Survey, Space Geodesy Research Group, Bogota, Colombia Federico Moreno Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY, United States Francisco Sánchez Nassif Earth Science Research Center, CONICET National Research Council & Natural, Physics and Exact Sciences Faculty, Cordoba National University, Córdoba, Argentina C. Navarrete Department of Geology, Faculty of Natural Sciences, National University of Patagonia San Juan Bosco, Comodoro Rivadavia, Argentina Julieta C. Nóbile Earth Science Research Center, CONICET National Research Council & Natural, Physics and Exact Sciences Faculty, Cordoba National University, Córdoba, Argentina Paul O’Sullivan GeoSep Services, Moscow, ID, United States Soty Odoh Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX, United States Verónica Oliveros Department of Earth Sciences, University of Concepción, Concepción, Chile G. Olivieri International Exploration, YPF S.A, Buenos Aires, Argentina Sebastián Correa Otto Seismological Geophysical Institute Ing. Volponi (IGSV), FCEFyN, National University of San Juan, San Juan; National Scientific and Technical Research Council (CONICET), Buenos Aires, Argentina xxiv Contributors

Mauricio Parra Institute of Geosciences; Institute of Energy and Environment, University of São Paulo, São Paulo, Brazil Ana María Patiño Institute of Geosciences, University of São Paulo, São Paulo, Brazil A. Paul School of Geosciences, The University of Edinburgh, Edinburgh, Scotland Mark Pecha Department of Geosciences, University of Arizona, Tucson, AZ, United States Stefanie Pechuan Seismological Geophysical Institute Ing. Volponi (IGSV), FCEFyN, National University of San Juan, San Juan; National Scientific and Technical Research Council (CONICET), Buenos Aires, Argentina Agustina Pesce Seismological Geophysical Institute Ing. Volponi (IGSV), FCEFyN, National University of San Juan, San Juan; National Scientific and Technical Research Council (CONICET), Buenos Aires, Argentina Stella Poma University of Buenos Aires, Faculty of Exact and Natural Sciences. National Council of Scientific and Technical Research, Institute of Basic and Applied Geosciences of Buenos Aires (IGEBA), Buenos Aires, Argentina Alice Prudhomme Géosciences Environnement Toulouse, Paul Sabatier University, IRD, CNRS, Toulouse, France Juan Carlos Ramírez Institute of Geosciences, University of São Paulo, São Paulo, Brazil Miguel E. Ramos IDEAN (Buenos Aires Univ.—CONICET), Buenos Aires, Argentina Alexandra Robert Géosciences Environnement Toulouse, Paul Sabatier University, IRD, CNRS, Toulouse, France E. Rocha International Exploration, YPF S.A, Buenos Aires, Argentina E.A. Rojas Vera International Exploration, YPF S.A, Buenos Aires, Argentina Christian Romero Departamento de Geología, Facultad de Ingeniería en Geología y Petróleos, Escuela Politécnica Nacional, Quito, Ecuador Gonzalo Ronda IDEAN (Buenos Aires Univ.—CONICET), Buenos Aires, Argentina Marcos A. Sánchez Seismological Geophysical Institute Ing. Volponi (IGSV), FCEFyN, National University of San Juan, San Juan; National Scientific and Technical Research Council (CONICET), Buenos Aires, Argentina Contributors xxv

Joel E. Saylor Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX, United States Edward R. Sobel Institute of Earth and Environmental Sciences, University of Potsdam, Potsdam, Germany Santiago R. Soler Seismological Geophysical Institute Ing. Volponi (IGSV), FCEFyN, National University of San Juan, San Juan; National Scientific and Technical Research Council (CONICET), Buenos Aires, Argentina Richard A. Spikings Department of Earth Sciences, University of Geneva, Geneva, Switzerland Rodrigo J. Suárez IDEAN (Buenos Aires Univ.—CONICET), Buenos Aires, Argentina Christian Sue Chrono-environnement, CNRS-UMR 6249, Franche-Comté Univ., Besançon, France Kurt Sundell Department of Geosciences, University of Arizona, Tucson, AZ, United States Tonny B. Thomsen Geological Survey of Denmark and Greenland (GEUS), Department of Petrology and Economic Geology, Copenhagen, Denmark Jonathan Tobal IDEAN (Buenos Aires Univ.—CONICET), Buenos Aires, Argentina Cristian Vallejo Departamento de Geología, Facultad de Ingeniería en Geología y Petróleos, Escuela Politécnica Nacional, Quito, Ecuador Roelant Van der Lelij Norway Geological Survey, Trondheim, Norway D. Villagomez Department of Earth Sciences, University of Geneva, Geneva, Switzerland Laura E. Webb Department of Geology, University of Vermont, Burlington, VT, United States Wilfried Winkler Geological Institute, ETH Zürich, Zürich, Switzerland Gonzalo Zamora REPSOL Exploración S.A., Madrid, Spain 7KLVSDJHLQWHQWLRQDOO\OHIWEODQN Preface and Acknowledgments

This volume addresses the tectonic evolution of the Andes Mountains of South America. As the global type example of ocean-continent convergence, insights from the Andes are fundamental to understanding tectonic processes along subduction margins. Long-term evolution of this convergent plate boundary spans tens to hundreds of millions of years, with sustained subduction of oceanic lithosphere of the Pacific Ocean basin during Cenozoic, Mesozoic, and possibly late Paleozoic time. During subduction, the Andean margin has experienced varied tectonic regimes, including shortening, extension, and strike-slip deformation. This complex history can be linked to spatially and temporally diverse plate tectonic configurations, with variations in relative convergence between the subducting and overriding plate, shifts in the absolute motion of the South American plate toward the Pacific Ocean basin, and changes in slab dip angle involving phases of shallow to flat-slab subduction and subsequent resteepening or breakoff of oceanic crustal/lithospheric materials. The main phase of Andean orogenesis has been concentrated in Cenozoic time. Principally east- west shortening, crustal thickening, subduction-related magmatism, and deposition in forearc, hinterland, and foreland basins largely dictated the present topography of western South America. Andean tectonic processes are further influenced by deeper processes such as metamorphism (although this record is rarely accessible within the Andes), and the surface processes of erosion and climate change. The interplay and feedback among such processes are on display in the Andes, where extreme variations in erosion and climate offer opportunities to test geodynamic models of mountain building. This volume addresses a range of Andean tectonic provinces emblematic of Cordilleran orogenic belts, which include a trench, variably developed accretionary prism, coastal forearc zone, well-known magmatic arc, and retroarc regions consisting of regionally important hinterland plateaus, a fold-thrust belt, and foreland basin system. Individual chapters offer new results and integration with past studies addressing the tectonic processes involved in shaping the western margin of South America. These studies span the entire Andes, and employ a range of techniques, including geophysics, structural geology, stratigraphy, sedimentology, petrology, geochronology, and thermochronology. The chapters of this volume are organized geographically into three groups: the northern Andes, central Andes, and southern Andes (Fig. 1). The research represented here provides new perspectives and valuable avenues for future research on Andean tectonics. Collectively, the chapters of this volume benefited from the helpful, constructive reviews from the following scientists: Antenor Aleman, Juan Diaz Alvarado, Ryan Anderson, Franck Audemard, Patrice Baby, Heinrich Bahlburg, Elizabeth Balgord, German Bayona, Carla Braitenberg, Lydian Boschman, Reynaldo Charrier, Gilda Collo, Eduardo Contreras-Reyes, Juan Andres Dahlquist, Facundo Fuentes, Federico Dávila, Graeme Eagles, Lucia Fernandez, Gonzalo Galaz, Laura Giambiagi, Guido Gianni, Matias Ghiglione, Nemesio Heredia, James Kellogg, Pedro Kress, Andrew Leier, Chelsea Mackaman-Lofland, Matthew Malkowski, Vlad Manea, Fernando Martinez, Joseph Martinod, Andres Mora, Constantino Mpodozis, Michal Nemčok, José Mescua, Marcia Muñoz, Veronica Oliveros, Sebastián Oriolo, Dario Orts, Robert Pankhurst, Victor Sacek, Joel Saylor, Nina Soager, Richard Spikings, Daniel Starck, Lucia Struth, Kurt Sundell, Claudia Tocho, Cristian Vallejo, Sebastian Verdechia, David Volker, and Winkler Wilfried.

xxvii xxviii Preface and Acknowledgments

FIG. 1 Shaded relief map of South America showing the study regions for the various chapters in this volume. Preface and Acknowledgments xxix

Alvarez et al. analyze the density structure of the Pacific subduction margin of South America through combined satellite and field gravity models. Forearc density heterogeneities are related to large subduction-zone earthquakes over the last decade, such as those in Chile, Peru, and Colombia. This relationship is analyzed in terms of basement rocks of contrasting density that control variable coupling between the subducting and overriding plates. A review of major earthquakes reveals that rupture zones propagate over zones of relatively less-dense forearc segments, highlighting the role of upper plate structure on seismogenic behavior. Contreras-Reyes discusses new wide-angle seismic data profiling the map-view curvature of the Chilean subduction margin. This chapter proposes that variations in curvature are not the product of oroclinal bending or shortening gradients, as previously proposed. Rather, these geometries are generated by tectonic erosion and sediment accretion related to the irregular topography of the subducting oceanic crust and the collision of aseismic ridges. Dávila et al. use residual topography as a direct measurement of dynamic topography for three tectonic transects across the Andes and adjacent platform zone, including Peru, the Sierras Pampeanas region, and southern Patagonia. The transects involve the subduction of bathymetric anomalies along the Pacific trench, including a mid-ocean ridge in the south and two aseismic ridges in the north. This study explores the role of dynamic forces in the development of processes such as sea transgressions and regional uplift. Kellogg et al. provide a regional overview of the tectonic evolution of the northern Andes in the context of changing geodynamic conditions along the western (Nazca) and northern (Caribbean) plate boundaries. Building upon Global Positioning System (GPS) results and several regional structural profiles constrained by subsurface data, they develop a plate tectonic model that unites the record of volcanic activity with a complex history of normal and flat-slab subduction. The chapter by Patiño et al. addresses the Cenozoic exhumation of the high-relief Santa Marta range along the Caribbean margin of northern Colombia. New apatite fission track and (U-Th)/He results for modern river sands from several catchments draining this prominent topographic feature reveal an episodic cooling history related to varied deformation regimes in response to phases of arc collision and changing subduction dynamics. Odoh et al. address the longstanding issue of coarse clastic sedimentation and long-term progradation within the Llanos foreland basin of Colombia. They combine U-Pb geochronology and (U-Th)/ He thermochronology of Maastrichtian-Neogene strata of the Eastern Cordillera to identify a three- stage evolution involving variations in exhumation rate during crustal shortening. Comparison of the exhumation history with the stratigraphic record reveals a correlation between rapid exhumation and deposition of coarse-grained materials. Spikings et al. offer a regional geologic model for the Triassic to Early Cretaceous history of igneous and metamorphic processes in the Andes of Colombia and Ecuador. Although the northern Andes are dominated by sedimentary rocks, results from limited exposures of igneous and metamorphic rocks are consistent with a complex history of alternating extension and shortening prior to ~75 Ma collision and accretion of thick oceanic crust of the Caribbean Large Igneous Province. Vallejo et al. present a stratigraphic and provenance analysis of Late Cretaceous to Miocene basins in the arc and forearc regions of Ecuador. They integrate new detrital zircon U-Pb age signatures and heavy mineral assemblages from the Western Cordillera and coastal forearc regions with stratigraphic, structural, and geochronological data to constrain models for the timing and style of oceanic terrane xxx Preface and Acknowledgments

accretion, concluding that the Caribbean Plateau collided in the latest Cretaceous (~73 Ma) after a complex history of both westward and eastward subduction. Gutierrez et al. define the Cretaceous-Cenozoic provenance history of foreland basin fill within the Subandean Zone and Oriente Basin of Ecuador. Using detrital zircon U-Pb age signatures, they rec- ognize a latest Cretaceous reversal from distal eastern (cratonic) sources to western (Andean) sources. This provenance shift corresponds to initial Andean shortening, flexural subsidence, and a change from marine to nonmarine conditions in the northern Andes. Distinct zircon populations also confirm the presence of a Late Cretaceous continental magmatic arc. The contribution by George et al. addresses the poorly understood Mesozoic basin history of northern Peru, incorporating detrital zircon U-Pb results with regional stratigraphic relationships to define the depositional ages and provenance signatures of key geologic units. Significant variations in provenance patterns can be linked to Mesozoic extension and postrift thermal subsidence followed by a reversal in sediment dispersal during latest Cretaceous-Paleocene shortening and initial topographic growth of the Peruvian Andes. Prudhomme et al. introduce a new regional balanced cross section and onshore-offshore stratigraphic correlations that relate major topographic features of the Western Cordillera of northern Peru to west-directed basement-involved thrust faulting. Results from low-temperature thermochronology (apatite fission track and (U-Th)/He methods) indicate exhumation during Cenozoic shortening and forearc basin evolution, with accelerated exhumation during late Miocene subduction of the Nazca Ridge. The chapter by Zamora Valcarce et al. is dedicated to the structure of the Peruvian Sub-Andean system, highlighting important seismic lines, borehole, and field data bearing on deformational mechanisms within this segment of the central Andes. Deformation involves reactivation and tectonic inversion of Permian and Triassic normal faults, and activation of multiple decollements within the Paleozoic stratigraphic succession. Pre-Andean structural inheritance includes ancient structural highs that may have influenced the development of subsequent Cenozoic structures and synorogenic strata. Sundell et al. integrate complementary U-Pb ages and Hf isotope data from Cenozoic Altiplano basin fill to jointly resolve the Andean provenance record and long-term crustal evolution patterns of southern Peru. They interpret westward transcontinental sediment dispersal across South America prior to Cenozoic development of the Andes, with potentially cyclical patterns of retroarc orogenesis involving simple-shear underthrusting of continental lithosphere. Rojas Vera et al. focus on the retroarc structure of the Interandean and Subandean fold-thrust belts flanking the high Altiplano-Puna plateau of Bolivia and northern Argentina. Through field, borehole, and seismic information, detailed balanced cross sections are constructed and demonstrate that multiple decollements acted simultaneously and generated complex structural relationships. Along-strike gradients in shortening from north to south are discussed in the context of new and existing information regarding the influence of the pre-Andean structural and stratigraphic framework. Kortyna et al. present a regional structural analysis and cross section of the Eastern Cordillera of northern Argentina, demonstrating a structural style that involves both thin- and thick-skinned geometries with both forward and hindward vergence. Andean basement-involved reverse faults are shown to be the product of reactivation of older normal faults and inversion of the Cretaceous Salta rift basin. Apatite (U-Th)/He results show a sequential forelandward (eastward) progression of deformation during Miocene shortening. Preface and Acknowledgments xxxi

Martínez et al. focus on the timing and deformational mechanisms within the northern sector of the Chilean-Pampean flat subduction zone. They relate uplift of the main morphostructural units to flat- slab development over the last 18 Myr. However, based on identification and dating of growth strata and cross-cutting intrusive relationships, they propose that many structures (in particular, the western Frontal Cordillera) were initially shaped in Late Cretaceous-Paleogene time. A key process at these latitudes involved the inversion of Triassic to Jurassic extensional structures that form bivergent range systems rooted in Paleozoic basement. Sánchez et al. integrate magnetic and gravity data to address the thermal structure of the Chilean- Pampean flat subduction zone and the mechanisms that may be sustaining it. Magnetic data allow calculation of the Curie temperature depth and show a heterogeneous sublithospheric heat flow structure. The thermal and density structure of the flat-slab region is constrained and compared with available tomographic and receiver function data. This comparison suggests potential thinning of the subducted Nazca plate, and coupled with an underlying low-velocity zone, can be considered in terms of a potential dynamic component in the development of the flat slab. The contribution by Díaz Alvarado et al. constitutes a revision of the diverse paleo-accretionary systems that have been exhumed in the Andean forearc along the Pacific coast of Chile. These systems experienced a common evolution with the subsequent Andean system, with the development of a magmatic arc and trench-vergent fold-thrust belts between late Paleozoic and Triassic time. Deformation can be related to collision of oceanic terranes and the dynamics of subduction zones, including the development of frontal and basal accretionary systems and subduction channels. Webb and Klepeis reconstruct multiple phases of Late Carboniferous to Late Jurassic magmatism, metamorphism, and deformation in coastal regions of north-central Chile (~33.5°S). They present inte- grated structural and 40Ar/39Ar geochronological results that demonstrate a late Paleozoic establishment of a regional NW- to WNW-striking structural grain that influenced subsequent deformation and magmatism during the transition from the proto-Pacific margin of Gondwana to the modern Andean plate boundary. Gimenez et al. utilize combined satellite and field gravity data with the aim of delimiting basement blocks with contrasting tectonic histories. Identified basement domains are compared with geologic models for the southern Central and Patagonian Andes based on the identification of magmatic arcs, metamorphic deformational fabrics, and geochronological data in order to redefine allochthonous and para-autochthonous terranes and their geometries. In addition, these data allow extrapolation of proposed basement boundaries into the Atlantic marine platform where geologic data are scarce. Litvak et al. provide an exhaustive analysis of Cenozoic arc volcanism from the southern Puna plateau to the Patagonian Andes, analyzing regional geochemical fingerprints of four magmatic stages: Paleocene-middle Eocene, late Eocene-early Oligocene, late Oligocene-early Miocene, and middle Miocene-middle Pliocene. They then discuss spatial and temporal variations and the potential drivers, including subduction geometry, variable convergence rates, ridge collisions, slab rollback, and crustal thickening. The chapter by Echaurren et al. analyzes the North Patagonian fold-thrust belt as an example of an orogen that absorbed low amounts of shortening and therefore generated limited topography. This system was constructed through two contractional periods, in the Late Cretaceous and the early Miocene, both of which followed earlier extensional phases. The authors propose precursor extension as a pre- requisite for Andean construction, inducing thermal and mechanical weakening that facilitated later contractional reactivation. xxxii Preface and Acknowledgments

Gianni et al. provide a magmatic and structural reconstruction of the Paleocene to Eocene collision of the Aluk-Farallon mid-ocean ridge against the Patagonian trench. They infer a segmented mid-ocean ridge that may have provoked diachronous and spatially dissociated asthenospheric windows separated by transform fault systems. This model explains the irregular spatial distribution of mantle-derived igneous products in the retroarc of Patagonia as well as isolated examples of late Eocene synorogenic sedimentation. Ghiglione et al. focus on the Southern Patagonian Andes, comparing the amplitude of deformational belts, computed shortening values, and sedimentary thicknesses with available thermochronological data. These comparisons reveal that the overall structural and topographic configuration of the Southern Patagonian Andes is dictated by a combination of climatic drivers, erosional efficiency, and along-strike variations of the retroarc stratigraphic package. PART Overview I 7KLVSDJHLQWHQWLRQDOO\OHIWEODQN CHAPTER

Seismic structure along the South American subduction zone using satellite gravity 1 data

Orlando Alvarez⁎,†, Stefanie Pechuan⁎,†, Mario Gimenez⁎,†, Andrés Folguera‡ Seismological Geophysical Institute Ing. Volponi (IGSV), FCEFyN, National University of San Juan, San Juan, ⁎ Argentina National Scientific and Technical Research Council (CONICET), Buenos Aires, Argentina† Department of Geological Sciences, National Scientific and Technical Research Council (CONICET), IDEAN—Institute of Andean Studies "Don Pablo Groeber", FCEN, University of Buenos Aires, Buenos Aires, Argentina‡

1 Introduction Western South America is subject to high stress as a consequence of oceanic plate subduction beneath the South American plate (e.g., Barazangi and Isacks, 1976; Jordan et al., 1983; Ramos and Folguera, 2009; Ramos, 2010; Horton, 2018). Although part of the deformation resulting from plate convergence occurs aseismically, large earthquakes also occur and affect coastal areas hundreds of kilometers in length. In the last decade, a large portion of the South American western margin along the Chilean coast has been affected by three large earthquakes: the 2010 Maule Mw = 8.8, the 2014 Pisagua Mw = 8.2, and the 2015 Illapel Mw = 8.3 earthquakes. Due to technological and scientific advances, these recent earthquakes have been studied at an un- precedented detail with different methods and data types, allowing for testing of different hypotheses. The development of large networks of seismological and GPS stations, together with new geodetic methods (e.g., InSAR: Interferometric synthetic aperture radar), has allowed detailed mapping of coseismic and postseismic slippage and the interseismic coupling between plates. In addition, numerous studies of the subduction zone based mainly on wide-angle seismic and gravity profiles have allowed illumination of the structural complexity and compositional heterogeneity of the interplate region and a better understanding of its behavior during earthquakes. Satellite gravimetry has enabled global and homogeneous mapping of the distribution of mass anomalies inside the Earth, and in particular, densities along the entire forearc zone (Song and Simons, 2003; Wells et al., 2003), difficult and expensive through other methods. In this chapter, we build a com- pilation of the seismogenic structure of the South American active margin (Fig. 1) using data derived from the GOCE satellite mission. From the vertical gravity gradient, we analyze the relationships between negative Tzz lobes, historical ruptures, and slip models for recent events along the margin. Other seismologic parameters are inferred from the density distribution, including the directivity, downdip limit of the seismogenic zone, and location of the main asperities and barriers along the margin.

FIG. 1 Relief of the Nazca-South American plates from ETOPO1 (Amante and Eakins, 2009) with main bathymetric features. We divided the margin into six segments for a detailed analysis. Rectangles indicate locations of Figs. 2–7. 2 Data and method 5

2 Data and method 2.1 Satellite GOCE gravity data The satellite GOCE model GO_CONS_GCF_2_DIR_R5 (Bruinsma et al., 2013) is a full combination of GOCE-SGG (Satellite Gravity Gradiometer), GOCE-SST (Satellite to Satellite Tracking), GRACE (Gravity Recovery and Climatic Experiment), and LAGEOS (Laser GEOdynamics Satellite). This model presents homogeneous precision and an excellent performance of the long as well as of the short wavelengths when compared to previous GOCE models (Pail et al., 2011; Bruinsma et al., 2010). The degree/order of the spherical harmonic coefficients is up to Nmax = 300, being the half-wavelength resolution of approximately 67 km according to λ/2 = πR/Nmax (Li, 2001; Hofmann-Wellenhof and Moritz, 2006; Barthelmes, 2013), with R being the mean Earth radius. We obtained the vertical gravity gradient by direct modeling of the satellite-only GOCE data, from the spherical harmonic coefficients (Janak and Sprlak, 2006) on a regular grid of 0.05° grid cell size. The vertical gravity gradient (Tzz) is obtained as the second radial derivative of the disturbing potential (Tscherning, 1976; Rummel et al., 2011): 2 ∂ T ⎡ − mGal ⎤ Tzz = ⎢110Etvsöö= 4 ⎥ (1) ∂r 2 ⎣ m ⎦ Tzz is expressed in Eötvös and represents a better spatial resolution than the gravity vector itself for detecting shallower crustal density variations (Li, 2001) allowing determining the edges of anomalous masses with better detail and accuracy (Braitenberg et al., 2011; Alvarez et al., 2012).

2.2 Reduction by topographic and sediments effect The topographic effect must be removed from the satellite observations (Forsberg and Tscherning, 1997) in order to reduce the correlation of the gravity signal with the topography. To remove the topographic effect from Tzz, we calculated the topographic contribution by discretizing a digital elevation model (ETOPO1, Amante and Eakins, 2009) using spherical prisms of constant density (see Grombein et al., 2013 and references therein). We considered the Earth’s curvature by using a spherical approximation (instead of a planar one) (Uieda et al., 2010), avoiding considerable errors as the region under study is wide (Hofmann-Wellenhof and Moritz, 2006; Alvarez et al., 2012, 2013; Grombein et al., 2013; Bouman et al., 2013). We performed the calculation of the topography contribution over the Tzz using the software Tesseroids (Uieda et al., 2010; Alvarez et al., 2013) densities used are mean standard values of 2670 kg/m3 for masses above sea level and a 1030 kg/m3 for sea water. The calculation height is of 7000 m to ensure that all values are above the topography.

2.3 Harmonic decomposition Featherstone (1997) performed a spectral analysis of the geoid and gravity anomalies finding that by decreasing the cut-off degree/order of the harmonic expansion the gravimetric signal is increasingly generated by a causative mass of increasing depth. In a recent work, Alvarez et al. (2017a) derived an equation (Eq. 1) relating the depth (Zl) of a causative mass with a determined degree of the spherical harmonic expansion (N) for the Tzz: ()()R +−HN1 Z = EC , (2) l ()()NN++21 6 Chapter 1 Observing rupture areas from satellite gravity data

Table 1 Associated depth (Zl) of a causative mass with a determined degree of the spherical harmonic expansion for Tzz Spatial resolution Degree/order N λ/2 = πR/Nmax (km) Zl (km) for Tzz (HC = 7 km) 300 66.72 20.98 250 80.06 25.11 200 100.07 31.26

where RE = 6371 km is the Earth’s radius, HC is the Tzz calculation height, and N is the degree/order of the harmonic expansion. Table 1 shows for different degree/orders the corresponding depth Zl and spatial resolution. Higher orders are associated with shallower sources; on the contrary, low orders are related to deeper mass anomalies. Results from this harmonic decomposition tool by truncating the harmonic expansion allow analyzing Tzz response with increasing depths of the causative masses for the different events under study.

3 Results and discussion 3.1 The Valdivia 1960 Mw = 9.5 earthquake This earthquake nucleated at the latitudes where the Mocha Fracture Zone (FZ) intersects the Chilean trench and propagated to the south along approximately 1.000 km up to the Chile Rise with the slip distribution being segmented by the incoming Fracture Zones (Contreras-Reyes and Carrizo, 2011; Melnick et al., 2009; Moreno et al., 2009). In this region the trench is almost completely filled, with sediment thicknesses ranging from 2.2 to 3.5 km causing a flat seafloor morphology (Lamb and Davis, 2003; Ranero et al., 2006; Völker et al., 2013). The relation between the volume of trench sediments and the relief of the oceanic plate strongly affects the development of the subduction channel promot- ing seismic segmentation (Contreras-Reyes and Carrizo, 2011; Kopp, 2013). The thicker sediment thickness along the southern region of the Chilean margin is expressed by a low mean value of Tzz (Alvarez et al., 2014). For this earthquake, we superimposed the slip distribution of Moreno et al. (2009) with the topography-corrected Tzz from GOCE, noting that slip lobes roughly coincide with slip segmentation (Fig. 2A). For the maximum degree of the model (N = 300), Tzz presents a clear across strike segmentation, with maximum relative to the north (37.5°S) and south of the rupture (47.5°S), which can also be observed for N = 250 (white arrows in Fig. 2A and B). This narrowing of the signal could be related to seismic barriers to rupture propagation (Alvarez et al., 2012). The epicenter is flanked by relative Tzz highs (see Fig. 2A and B) to the N and NW (in the updip direction), whereas to the SW Tzz diminishes following the direction of rupture propagation. For N = 200, a high gradient contrast is observed close to the coastal line, which could be related to the downdip limit of the seismogenic zone (Fig. 2C). Different authors (Mendoza et al., 1994; Pritchard et al., 2007; Delouis et al., 2010; Loveless et al., 2010; Alvarez et al., 2014; Bassett and Watts, 2015) proposed that the high-gravity anomaly along the coastal line marks the downdip limit of the seismogenic zone. 3 Results and discussion 7 ). Superimposed slip distribution for anomalies related to anomalous masses that Tzz indicate a narrowing of the signal that could be Bruinsma et al., 2013 White arrows in (C) indicates a high gradient the signal related to up- ). Red contour . in (B) depict relatively higher for a location in regional perspective. ) obtained from GOCE ( Moreno et al., 2009 Fig. 1 Tzz (yellow arrow) Red contours controlled rupture propagation to the south and downdip limits of the seismogenic zone. See indicating barriers to seismic propagation. the Valdivia May 22, 1960, Mw = 9.5 earthquake ( = May 22, 1960, Mw the Valdivia FIG. 2 Gravity Gradient ( Vertical Topography-corrected 8 Chapter 1 Observing rupture areas from satellite gravity data

3.2 The Maule segment Across the forearc zone between the Juan Fernandez Ridge (JFR) and the Mocha FZ, a negative gradient signal dominates the marine forearc and is divided into a series of lobes unveiling mass heterogeneities along the seismogenic zone. In particular, the historical rupture areas in this region (1985, 1928, 1906, and 1835 earthquakes) roughly coincide with Tzz patches lower than −10 Eötvös (Fig. 3A). The Maule Mw = 8.8, 2010 earthquake ruptured bilaterally through two or three major slip patches (Lay et al., 2010; Lorito et al., 2011; Vigny et al., 2011; Moreno et al., 2012; among others) coinciding approximately the northern patch with the most likely 1928 rupture zone. In Fig. 3B (N = 250/Z = 25 km), higher densities along the inner forearc (terrestrial forearc) coincide with regions of high Vp (Vp 7.6–8.0 km/s, Vp/Vs ratio of ∼1.81 and Poisson’s ratio of 0.28) lying beneath the coast at 25 km depth, as reported by Hicks et al. (2014) from a seismological tomography. These authors noted this relationship between high positive Bouguer gravity anomaly and high seismic velocities, and associated gravity signal with dense ultramafic material where coseismic slip was reduced. In a previous work, Alvarez et al. (2014) proposed that the positive Tzz values observed in the forearc reveal the location of a seismic barrier defining the eastern edge of the rupture propagation zone for 1906 and 1985 events. The southern patch of the Maule earthquake propagated inland in a region of low Tzz, whereas the northern patch, the one of higher slip, occurred close to a minimum Tzz over the nonmarine forearc. This relationship between Tzz, seismic velocities and slip behavior suggests that gravity-derived signal is a good proxy for delimiting across and along strike segmentation in this portion of the Chilean margin. The high gradient close to the coastal line (Fig. 3C) follows the eastern termination of ruptures indicating the downdip limit of the seismogenic zone. At degree N = 200, Tzz lobes match slip maxima of the Maule earthquake, and to historic ruptures. Tzz lobes at this degree of the harmonic expansion are probably indicating the location of main asperities (i.e., locked areas where most slip occur during earthquake) along the plate interface.

3.3 The central Chile segment The JFR forms a topographic barrier segmenting a trench that is partly filled with sediments (2.0– 2.5 km thick) to the south of the JFR from a trench that becomes a narrower depression with steep walls starved of sediments (Schweller et al., 1981; von Huene et al., 1997; Laursen et al., 2002; Völker et al., 2013). Sediment thickness along the trench increases again at the Peruvian Andes latitudes, where rainfall and dominant winds become predominant again from the Pacific Ocean. The absence of a thick sedimentary infill immediately to the north of JFR inception point influences the gravity response pre- senting higher Tzz mean values northwards (Alvarez et al., 2018) along the Chilean margin. Historic ruptures comprises one (1918, 1943, 2015, 1859, and 1946), two (1918, 1983), or more low Tzz lobes (1796, 1922). The JFR, the Nazca FZ, the Copiapó, and Taltal ridges are related to relative maxima in Tzz interposed to the low Tzz lobes, according to the hypothesis that high oceanic features pro- mote seismic segmentation as proposed by many authors (e.g., Sparkes et al., 2010; Contreras-Reyes et al., 2010). Recent works related subduction of oceanic topography (e.g., seamounts, aseismic ridges, plateaus) to regions with a higher rate of small earthquakes (Sparkes et al., 2010; Wang and Bilek, 2011, 2014) and by a lower degree of coupling (Metois et al., 2016), thus preventing for the nucleation of great megathrust earthquakes. This could be the case of the 1909 earthquake, which is not related to a low Tzz lobe being on the contrary its rupture located over a relatively higher Tzz segment at the extrapolation of the subducting Copiapó ridge. When truncating the degree of the harmonic expansion (Fig. 4B and C), low Tzz lobes become diffuse, masking the relationship between gravity and ruptures observed to the south. 3 Results and discussion 9

s from Thick Black for a . probably Red contours Fig. 1 Contreras-Reyes et al. (2017) ). Superimposed rupture areas for ) that acted as along-strike seismic barriers (B). Bruinsma et al., 2013 Hicks et al., 2014 ( signal related to rupture terminations are interpreted as seismic barriers. p V Tzz ) obtained from GOCE ( Tzz indicate main asperities related to historic ruptures and the Maule 2010 earthquake. See . Across strike narrowing of the in (B) is related to regions of high Tzz (ellipses) of location in a regional perspective. solid contours in (C) depict up- and downdip limits of the seismogenic zone. The high gradient gravimetric signal over coastline is also related to the transition from continental slope shelf (shelf break) as pointed out by 1906-Ms = 8.4, 1985-Mw = 8.0, 1928-Ms = 8.0 earthquakes, and 1835 seismic gap. Slip distribution for the Maule 2010, Mw = 8.8 i = 8.0 earthquakes, and 1835 seismic gap. Slip distribution for the Maule 2010, Mw = 8.0, 1928-Ms = 8.4, 1985-Mw = 1906-Ms solid black contour FIG. 3 Gravity Gradient ( Vertical Topography-corrected Moreno et al. (2009) 10 Chapter 1 Observing rupture areas from satellite gravity data = 250 (B), N = 300 (A), N ) up to Bruinsma et al., 2013 ) obtained from GOCE ( Tzz lobes roughly coincide with ruptures connecting one or more main asperities along Tzz . for a location in regional perspective. Tilmann et al. (2015) Tilmann Fig. 1 = 200 (C). Superimposed rupture areas of historical earthquakes along central Chile. Slip distribution for the Illapel 2015, = N and Mw = 8.3 is from FIG. 4 Gravity Gradient ( Vertical Topography-corrected the megathrust. The 1909 rupture over region where Copiapo ridge subducts coincides with a of low degree coupling. See 3 Results and discussion 11

The Illapel 2015 Mw = 8.3 earthquake nucleated immediately to the north of the subducting JFR (where a relative high Tzz is observed) and rupture propagated to the N-NW and updip of the epicenter toward a low-gravity gradient up to the Challenger FZ. The slip model (Tilmann et al., 2015) depicts a higher slip inland in a region where the high Tzz over the terrestrial forearc is interrupted (Fig. 4B), being the rupture flanked north and south by higher Tzz values (as shown in Alvarez et al., 2017a). Similar to the Maule, segment across-strike (inception of JFR and Challenger FZ) and along-strike (seismic barriers) segmentations are related to the density structure of the forearc zone.

3.4 Northern Chile-southern Peru The Mw 8.4 Arequipa earthquake in 2001 reactivated the northern portion of the 1868 rupture, leaving the southern segment unbroken (Fig. 5), with rupture propagating unilaterally to the southeast over 300 km (Bilek and Ruff, 2002; Giovanni et al., 2002; Audin et al., 2008). In this region, climatic conditions allowed accumulation of higher sediment thicknesses along the trench than in northern Chile to the south, revealed by lower values of Tzz (less than -5Eötvös). Here low Tzz signal correlates well with high seismic slip over the marine forearc (as shown by Alvarez et al., 2015). This gravity low could be related to the gravimetric expression of a forearc basin over the continental shelf, developed because of the Nazca FZ subduction (Wells et al., 2003; Bassett and Watts, 2015). A narrowing of the gradient signal or maximum relative is observed at both lateral endings of the slip distribution. At degree N = 200, positive Tzz (+5 Eötvös contour) to the SE, NW, and W of the hypocenter could be indicating different material properties impeding rupture propagation in these directions (Fig. 5C). Relative Tzz minima are probably indicating a heterogeneity that acted as a path to rupture propagation to the south and further amplification close to the Tzz minima lobe. On April 1, 2014 the Iquique Mw = 8.2 earthquake ruptured the plate boundary interface between the Nazca and South America plates (Ruiz et al., 2014; Schurr et al., 2014) over the region recog- nized as the Iquique seismic gap, where the largest recorded historical earthquake occurred in 1877 with magnitude Mw ~ 8.5–8.8 (Lomnitz, 2004), and estimated rupture zone from Arica to Antofagasta (see Fig. 5). This earthquake was preceded by an intense foreshock activity developed in the previous months to the main event, which accelerated toward the final foreshock sequence (Ruiz et al., 2014) and by a decrease in the b value 3 years prior to earthquake occurrence (Schurr et al., 2014). Geersen et al. (2015) imaged multiple large seamounts along the plate interface under the marine forearc in the in- termediate coupled central part (19° to 20.5°S) of the northern Chile seismic gap (Metois et al., 2012). Slip patch for this earthquake shows a certain correlation to minimum Tzz (Fig. 5A). At lower de- grees (N = 200), Tzz low in the region of maximum slip is substituted by a positive Tzz signal. This high variability in the signal could be produced by the subducted northern part of the Iquique ridge beneath the marine forearc. Subducted relief not only may act as barriers to seismic propagation but also as asperities linked to seismic rupture (Husen et al., 2002; Bilek et al., 2003), but generating networks of small-scale fractures and faults causing unfavorable conditions for seismic rupture propagation (Cloos, 1992; Mochizuki et al., 2008; Wang and Bilek, 2011; Kopp, 2013). Lay (2015) highlighted that larger slip for this earthquake was unusually concentrated. In this scenario, the positive gradient signal where the foreshock sequence and maximum slips took place could be related to subducted seamounts and basal erosion associated with the subduction of the Iquique ridge. The Mw = 8.1 Antofagasta earthquake on 1995 ruptured the subduction interface over a length of 180 km from the southern part of the Mejillones peninsula to the south (Fig. 5). Several earthquakes in 12 Chapter 1 Observing rupture areas from satellite gravity data sta : 1877 = 250 (B), and N Blue dashed line = 300 (A), N ) up to Bruinsma et al., 2013 for map location in a regional perspective. Fig. 1 ) obtained from GOCE ( . See Tzz . Slip for the April 1, 2014 Mw = 8.2 Pisagua and April 3, 2014 Mw = 7.7 Iquique are from = . Slip for the April 1, 2014 Mw = 8.2 Pisagua and 3, stars are the epicenters for different earthquakes shown in this figure. Red Metois et al. (2013) . References: Chlieh et al. (2004, 2011) = 200 (C). Superimposed slip distributions for the 2001 Mw = 8.4 Arequipa, 2007 Mw = 7.7 Tocopilla, and 1995 Mw = 8.1 Antofaga = and 1995 Mw 7.7 Tocopilla, = 8.4 Arequipa, 2007 Mw = 200 (C). Superimposed slip distributions for the 2001 Mw = FIG. 5 Gravity Gradient ( Vertical Topography-corrected Schurr et al. (2014) Mw = 8.6 reduced zone from N earthquakes from 3 Results and discussion 13

the Antofagasta region (Ruiz and Madariaga, 2018) preceded the 1995 earthquake. The rupture process resulted in a smooth and slightly heterogeneous slip distribution that has been extensively studied using seismological and geodetic techniques (Chlieh et al., 2004). Although different observations indicate that this earthquake ruptured the deeper part of the plate interface (e.g., Delouis et al., 1997; Ihmlé and Madariaga, 1996), evidence was found that rupture reached near the trench (Ruiz and Madariaga, 2018). The 2007, Mw = 7.7 Tocopilla earthquake ruptured only the deeper portion of the seismogenic zone (Peyrat et al., 2010). Although the rupture of this earthquake occurred in a highly locked area of the megathrust, rupture was limited to a small fraction in the downdip end of the locked fault zone (Chlieh et al., 2011). The last authors reported that 1-m slip contour appears to have ruptured only a small portion of the southern downdip end of the locked fault zone and of the 1877 event. For the Tocopilla 2007 earthquake, Contreras-Reyes et al. (2012) proposed the influence of the along dip geometry of the Nazca plate and Schurr et al. (2014) proposed different friction properties along dip to explain the position of this event near the bottom of the plate interface (Ruiz and Madariaga, 2018). Different to other earthquakes previously analyzed along the Chilean margin, where hypocenters nucleate close to a Tzz high and rupture propagates to a relatively low Tzz, slip models for the ruptures for the 1995 and 2007 earthquakes indicate that rupture occurred mostly in the downdip portion of the megathrust. Besides both earthquakes nucleated close to a Tzz low and propagated over Tzz highs. This region of the Chilean margin, between 21°S and 25°S, presents a high positive Tzz signal along the marine forearc, different to the rest of the margin. Along this segment, there is a clear correlation between the gravity high along the coastal line and the downdip limit of the seismogenic zone, as observed along the rest of the margin. From 23 to 26°S, no giant megathrust earthquakes are known, reason by which this segment is considered an atypical segment in which only moderately large events have occurred (Ruiz and Madariaga, 2018). Probably the high Tzz is evidencing different seismogenic conditions for nucleation of a great megathrust earthquake, or at least with a great rupture area developing along the outermost forearc. The high Tzz signal seems to be dominated by the lack of sediments along the trench in a region dominated by basal tectonic erosion of the forearc crust. Different works (Sobiesiak et al., 2007; Llenos and Mc Guire, 2007; Tassara, 2010) have focused on these Central Andean forearc asperities and their link to gravity highs (mafic bodies) reflected in a high vertical stress anomaly (VSA) that accounts for the component of normal stress due to the weight of the overlying crustal column (Tassara, 2010). Whereas this anomaly is a relevant parameter for northern Chile, the Southern Andes forearc is felsic-dominated (low-density) producing neutral-to-negative VSA.

3.5 Peru On August 15, 2007, a Mw = 8.0 earthquake stroke about 20 km offshore of Pisco (Peru) producing a tsunami (Pritchard and Fielding, 2008; Wei et al., 2008; Fritz et al., 2008). The rupture was associated with a slip up to 8 m (Perfettini et al., 2010) and propagated southward below the Paracas Peninsula and offshore before arresting on the northern edge of the Nazca ridge (Sladen et al., 2010), which is subducting obliquely beneath the South American plate (Fig. 6) at a convergence rate of about 6 cm/ year (Kendrick et al., 2003). To the south of the Pisco 2007 rupture, the 1942 Mw 8.0 and the 1996 Mw 7.7 Nazca earthquakes occurred (Salichon et al., 2003; Pritchard et al., 2007). The last ruptured only the deeper portion of the seismogenic zone (“Domain C” proposed by Lay et al., 2012) and had similar characteristics to the 2007 Mw 7.7 Tocopilla event (Chlieh et al., 2011). The 1942 and 1996 ruptures 14 Chapter 1 Observing rupture areas from satellite gravity data els ; = 250 (B), and N Swenson and Beck, 1999 = 300 (A), ; N ) up to stars are the epicenters for different earthquakes Langer and Spence, 1995 Red Bruinsma et al., 2013 ). References: ) obtained from GOCE ( Tzz , and 1974 M8.1 earthquakes ( Chlieh et al., 2011 Pisco ; for a location in regional perspective. , 2007 M = 8.0 = , 2007 M Fig. 1 Nazca Pritchard et al., 2007 ; = 200 (C). Superimposed rupture areas for the 1996 M = 7.5; 1970 M = 7.6/1966 M = 7.5; 1940 M = 8.0; 1942 M = 8.1 and slip mod = 8.0; 1942 M = 7.5; 1940 M = 7.6/1966 M = 200 (C). Superimposed rupture areas for the 1996 M = 7.5; 1970 = shown in this figure. See FIG. 6 Gravity Gradient ( Vertical Topography-corrected Sladen et al., 2010 N for the 1996 M = 7.7 = for the 1996 M 3 Results and discussion 15

seem to have overlapped and stopped on the southern side of the Nazca ridge (Salichon et al., 2003). A reassessment of the 1942 earthquake (Okal and Newman, 2001) suggests that both events probably ruptured inland of the coast (Sladen et al., 2010). Apparently, no historical event ruptured through the segment corresponding to the subduction point of the Nazca ridge, suggesting that this area could be a permanent barrier to earthquake rupture propagation (Dorbath et al., 1990; Perfettini et al., 2010; Chlieh et al., 2011). Other relatively minor events (Mw > 7.5) occurred in the subduction segment located between the Mendana FZ to the north and the Nazca ridge to the south such as the 1966 (Mw 8.0), the 1974 Mw 8.0 Lima earthquake (Okal, 1992), 1970 M7.6, 1996 M7.5, 1940 M8.0, 1966 M7.5 (Dorbath et al., 1990; Pritchard et al., 2007). North of the Nazca ridge well-developed offshore forearc basins exist whereas to the south none basins were formed (Clift et al., 2003; Krabbenhoft et al., 2004). This is reflected by a lower mean value (more negative) of the Tzz signal (Fig. 6A) as observed along the southern Chilean margin. The 2007 Pisco rupture presents a good anticorrelation to Tzz signal, with negative Tzz over higher slip areas as explained by Alvarez et al. (2015). In this region, the distance between the trench and the coastline increases from 100 km (south of Pisco) to 200 km to the north, coinciding with a very distinct salient of the coastline (Sladen et al., 2010). This feature is generally associated with the downdip extent of the seismogenic zone (Ruff and Tichelaar, 1996). Regarding the positive Tzz signal along the coastline (Fig. 6A and B), slip models for the 2007 Pisco and 1996 Nazca earthquakes present higher displacements inland over relatively lower Tzz, as observed along the south-central Chilean margin. Particularly the last earthquake propagated downdip in a region of relatively lower Tzz signal along the coast as observed for other events that propagated in the lower portion of the megathrust. The 1974 rupture presents two slip patches coinciding with relatively lower Tzz lobes along the marine forearc, but events located to the north of it to the Mendana FZ present no correlation to the Tzz signal. This is probably due to the high spatial resolution of GOCE model and relatively small rupture areas. In a recent work, Alvarez et al. (2015) found that if event magnitude − increases (and consequently rupture area) the correlation between low Tzz lobes (10 4 mGal/m) and high slip (m) increases for Mw > 8.0 events attributing this to the high spatial resolution of GOCE only models (160 km).

3.6 Ecuador-Colombia The Musine Mw = 7.8 thrust earthquake in 2016 ruptured nearly 200 km along the plate interface, in an area similar to the rupture zone of the Mw = 7.8 1942 earthquake. The 2016 earthquake occurred at a margin characterized by moderately big to giant earthquakes such as the 1906 (Mw = 8.8). A heavily sedimented trench explains in part the abnormal lengths of the rupture zones in this region because it inhibits the role of natural barriers on the propagation of rupture zones. A high amount of sediment thickness is associated with tropical climates, high erosion rates, and eastward Pacific dominant winds that provoke orographic rainfalls over the Pacific slope of the Ecuadorian Andes. This high trench infill volume is denoted by a low-gravity signal (Fig. 7A) as observed in southern Chile. In particular, the rupture zone of the 2016 Mw = 7.8 Ecuador earthquake developed through a relatively low-density zone of the forearc sliver (Alvarez et al., 2017b). When truncation degree to N = 200, Tzz minima lobes show a good fitting to historical rupture areas in this region. 1979, 1958, and 2016 earthquakes nucleated close to a region of relatively lower Tzz and propagated toward minimum Tzz lobes (Fig. 7C). The 1942 earthquake nucleated at the center 16 Chapter 1 Observing rupture areas from satellite gravity data

= 250 (B), and = ). Plate convergence N = 300 (A), N Ye et al., 2016 Ye ; ) up to Swenson and Beck, 1996 Bruinsma et al., 2013 ; ) obtained from GOCE ( Tzz Mendoza and Dewey, 1984 Mendoza and Dewey, ; for a location in regional perspective. Fig. 1 . See Kanamori and McNally, 1982 Kanamori and McNally, Nocquet et al. (2014) = 200 (C). Superimposed rupture areas of the main earthquakes: 1906 Mw = 8.8; 1942 Mw = 7.8; 1958 Mw = 7.7, 1979 Mw = 8.2, and = 7.7, 1979 Mw = 7.8; 1958 Mw = 8.8; 1942 Mw = 200 (C). Superimposed rupture areas of the main earthquakes: 1906 Mw = rate is from N 7.8 ( = 2016 Mw FIG. 7 Gravity Gradient ( Vertical Topography-corrected 4 Concluding remarks 17

of the low Tzz minima low and propagated roughly radially. The 1906 earthquake, the one of higher magnitude in this region, occurred at the center of the relative maxima and propagated bilaterally to both minima Tzz lobes. Relatively higher Tzz signal (barriers) and low Tzz lobes (asperities) correlate to earthquake nucleation position and rupture propagation behavior, suggesting that the forearc density structure strongly affects seismogenesis.

4 Concluding remarks Along the southern Chilean margin, in the region where two of the most giant earthquakes registered occurred (the 1960 Mw = 9.5 Valdivia and the 2010 Mw = 8.8 Maule earthquakes), the Tzz signal presents its lower mean values reaching less than −20 Eötvös. For these earthquakes, Tzz minima lobes present a good spatial correlation to the maximum registered displacements and also to historic rupture areas (1835, 1928, 1906, and 1985). Similarly along the Ecuador-Colombia margin, Tzz minima lobes are also coincident with the maximum slip values of the 2016 Mw 7.5 Musine earthquake and also to historical ruptures (1942, 1906, 1979). Main asperities seem to be located over low Tzz lobes for N = 200 as shown by refined slip distributions for recent great earthquakes (2001 Mw 8.4 Arequipa, 2007 Mw 8.0 Pisco, 2010 Mw 8.8 Maule 2010, 2015 Illapel Mw 8.3 and 2016 Musine 7.8). The relationship between minimum Tzz (<0 Eötvös) lobes and highly coupled regions acting as seismic asperities was observed in previous works (Alvarez et al., 2014, 2015, 2017a,b, 2018) and associated with subducted sediments and forearc basins. On the other hand, relative maximum Tzz signal over the marine forearc in general coincides with lateral rupture bounds as explained by Alvarez et al., 2014. Tzz relative maxima in these regions are mainly related to different types of subducting oceanic plate roughnesses (seamounts, aseismic ridges, etc.), associated with higher rates of low degree seismicity, lower interseismic coupling, and thus con- trolling a high degree of seismic segmentation along the margin. The Mw 8.4 Pisagua earthquake on 2014 took place in a region where a Tzz minimum lobe over the marine forearc does not continue at depth (for N = 200), being replaced by a positive gradient signal. This particular event was preceded by an intense foreshock sequence, which has been associated with subducted seamonts (related to the northern border of the Iquique ridge) under the region of the main rupture. These differences on rupture processes are shared by a different gradient signal behavior along the margin. The 1909 earthquake at the Copiapó latitudes could have presented a similar behavior. The central Chilean segment between the Taltal ridge and the JFR presents a higher mean value of Tzz in a region of the margin that has been characterized mainly by subduction erosion. Here historical ruptures seem to comprise different numbers of asperities if they are mapped by the Tzz signal (one: 1966, 1859, 1946, two: 1918, 1983, three or four: 1922, 1796). Slip model of the Mw = 8.32015 Illapel earthquake indicates propagation to a region of Tzz minima, whereas historical ruptures of the 1943 and 1918 earthquakes coincide with the minimum Tzz lobe between the JFR and the Challenger FZ. The highly positive Tzz signal along the coastal line marks the downdip limit of the rupture zone in many of the studied cases. Other authors reported that coseismic slip models and aftershocks sequences are located seaward of the positive gravity-derived anomalies along the Chilean coast, evidencing a direct relationship of these maxima with the downdip limit of the seismogenic zone (Mendoza et al., 1994; Delouis et al., 2010; Loveless et al., 2010; Alvarez et al., 2014; Bassett and Watts, 2015). Ruiz and Madariaga (2018) observed that rheology along dip also controls the dynamic rupture process of 18 Chapter 1 Observing rupture areas from satellite gravity data

earthquakes and seismic wave attenuation over the Chilean margin. From this study, we observed that for N = 200 this relationship becomes notorious. Particularly for the Maule earthquake, we found a correlation between high Tzz and regions with high Vp (Hicks et al., 2014 from a seismic tomography) and vice versa. The last authors reported that high Vp and gravity anomaly highs anticorrelate to coseismic slip for the downdip portion of the rupture. In some cases when rupture propagated inland (e.g., the southern patch of Maule, the eastern side of the Illapel rupture, main aftershock Mw 7.7 of the Pisagua earthquake), maximum slip occurred also over anomalous Tzz regions (i.e., over a relative minima along the coastal line). If high Vp and high gradient signal were related to slip reduction, forecasting regions of variable slip from Earth gravity field models would be possible. Events that occurred almost entirely along the deeper portion of the plate interface onshore, e.g., the 1995 Mw = 8.1 Antofagasta, 1996 M = 7.7 Nazca, and 2007 Mw = 7.7 Tocopilla, could not be related to Tzz minima lobes following this analysis. Other alternative for these occurrences can be found in Tassara (2010) and in Bejar-Pizarro et al. (2013), who proposed that large-scale structures in the overriding plate can influence the frictional properties of the seismogenic zone at depth suggesting that the occurrence of megathrust earthquakes in northern Chile is controlled by the surface structures that built Andean topography. Following this proposal, relative gravity highs along the forearc are associated with high-density crustal bodies that impose large vertical stresses on top of the interplate seismogenic zone; and for a given value of friction and pore pressure along the subduction channel, this region acts as a seismic asperity (i.e., high shear strength, high levels of seismicity, and large coseismic slip). Different approaches have been tested to explain earthquake directivity as fault segmentation, the history of previous earthquake ruptures, preferential orientation of structures on the fault interface, or the superposition of different materials across the fault zone (McGuire et al., 2002; Rubin and Gillard, 2000; Pritchard et al., 2007). Many of the analyzed events presented this directivity behavior and in many cases rupture propagated to the minimum Tzz lobe (e.g., in Ecuador-Colombia events, Musine 2016, Pisco 2007, Arequipa 2001, Valdivia 1960, Maule 2010, Illapel 2015). Greatest and recent events in the South American active margin (e.g., 2010 Mw 8.8 Maule, 2001 Mw 8.4 Arequipa) presented a high correlation between location of Tzz minima lobes and higher slip suggesting the location of main asperities (mainly when located at domain “B”). Finally, forearc density distribution could explain the directivity effect in many cases.

Acknowledgments The authors acknowledge the use of the GMT-mapping software of Wessel and Smith (1998). The authors would like to thank to Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) and to CICITCA- PROJOVI (Project nº: 80020170300015SJ) de la Secretaría de Ciencia y Técnica-Universidad Nacional de San Juan, for funding sources.

References Alvarez, O., Gimenez, M.E., Braitenberg, C., Folguera, A., 2012. GOCE satellite derived gravity and gravity gradient corrected for topographic effect in the South Central Andes region. Geophys. J. Int. 190 (2), 941–959. https://doi.org/10.1111/j.1365-246X.2012.05556.x. References 19

Alvarez, O., Gimenez, M.E., Braitenberg, C., 2013. Nueva metodología para el cálculo del efecto topográfico para la corrección de datos satelitales. Rev. Asoc. Geol. Argent. 70 (4), 422–429. Alvarez, O., Nacif, S., Gimenez, M., Folguera, A., Braitenberg, A., 2014. GOCE derived vertical gravity gradient delineates great earthquake rupture zones along the Chilean margin. Tectonophysics 622, 198–215. https://doi. org/10.1016/j.tecto.2014.03.011. Alvarez, O., Nacif, S., Spagnotto, S., Folguera, A., Gimenez, M., Chlieh, M., Braitenberg, C., 2015. Gradients from GOCE reveal gravity changes before Pisagua Mw=8.2 and Iquique Mw=7.7 large megathrust earthquakes. J. S. Am. Earth Sci. 64 (P2), 15–29. https://doi.org/10.1016/j.jsames.2015.09.014. Alvarez, O., Pesce, A., Gimenez, M., Folguera, A., Soler, S., Chen, W., 2017a. Analysis of the Illapel Mw=8.3 thrust earthquake rupture zone using GOCE derived gradients. Pure Appl. Geophys. 174 (1), 47–75. https:// doi.org/10.1007/s00024-016-1376-y. Alvarez, O., Folguera, A., Gimenez, M., 2017b. Rupture area analysis of the Ecuador (Musine) Mw=7.8 thrust earthquake on April 16 2016, using GOCE derived gradients. Geod. Geodyn. 8, 49–58. https://doi. org/10.1016/j.geog.2017.01.005. Alvarez, O., Gimenez, M.E., Lince Klinger, F., Folguera, A., Braitenberg, C., 2018. The Peru-Chile margin from global gravity field derivatives. In: Folguera, A., et al. (Eds.), The Evolution of the Chilean-Argentinean Andes, Capitulo 3. Springer International Publishing 2018, https://doi.org/10.1007/978-3-319-67774-3. eBook ISBN: 978-3-319-67774-3, Hardcover ISBN: 978-3-319-67773-6, Series ISSN: 2197-9596. Amante, C., Eakins, B.W., 2009. ETOPO1, 1 arc-minute global relief model: procedures, data sources and analysis. In: NOAA Technical Memorandum NESDIS NGDC-24, March 2009. 19 pp. Audin, L., Lacanb, P., Tavera, H., Bondoux, F., 2008. Upper plate deformation and seismic barrier in front of Nazca subduction zone: the Chololo fault system and active tectonics along the coastal cordillera, southern Peru. Tectonophysics 459 (1–4), 174–185. https://doi.org/10.1016/j.tecto.2007.11.070. Barazangi, M., Isacks, B.L., 1976. Spatial distribution of earthquakes and subduction of the Nazca plate beneath South America. Geology 4, 686–692. Barthelmes, F., 2013. Definition of Functionals of the Geopotential and Their Calculation From Spherical Harmonic Models. Theory and Formulas Used by the Calculation Service of the International Centre for Global Earth Models (ICGEM), Scientific Technical Report, STR09/02, Revised edition GFZ German Research Centre for Geosciences, Postdam, Germany. http://icgem.gfz-postdam.de/ICGEM. Bassett, D., Watts, A.B., 2015. Gravity anomalies, crustal structure, and seismicity at subduction zones: 2. Interrelationships between fore-arc structure and seismogenic behaviour. Geochem. Geophys. Geosyst. 16, 1541–1576. https://doi.org/10.1002/2014GC005685. Bejar-Pizarro, M., Socquet, A., Armijo, R., Carrizo, D., Genrich, J., Simons, M., 2013. Andean structural control on interseismic coupling in the North Chile subduction zone. Nat. Geosci. 6, 462–467. https://doi.org/10.1038/ ngeo1802. Bilek, S.L., Ruff, L.J., 2002. Analysis of the 23 June 2001 Mw=8.4 Peru underthrusting earthquake and its aftershocks. Geophys. Res. Lett. 29, 20. https://doi.org/10.1029/2002GL015543. Bilek, S.L., Schwartz, S.Y., DeShon, H.R., 2003. Control of seafloor roughness on earthquake rupture behavior. Geology 31 (5), 455–458. Bouman, J., Ebbing, J., Fuchs, M., 2013. Reference frame transformation of satellite gravity gradients and topographic mass reduction. J. Geophys. Res. Solid Earth 118 (2), 759–774. https://doi.org/10.1029/2012JB009747. Braitenberg, C., Mariani, P., Ebbing, J., Sprlak, M., 2011. The enigmatic Chad lineament revisited with global gravity and gravity-gradient fields. In: Van Hinsbergen, D.J.J., et al. (Eds.), The Formation and Evolution of Africa: A Synopsis of 3.8 Ga of Earth History. vol. 357. Geological Society, London, pp. 329–341. https://doi. org/10.1144/SP357.18. Geological Society, London Special Publication. Bruinsma, S.L., Marty, J.C., Balmino, G., Biancale, R., Förste, C., Abrikosov, O., Neumayer, H., 2010. GOCE gravity field recovery by means of the direct numerical method. In: Lacoste-Francis, H. (Ed.), Proceedings of the ESA Living Planet Symposium, Bergen, Norway, ESA Publication (27) SP-686.