09/06/2017. The orogenic cycle in the Andes: Arc magmatism and delamination as control of the fold and thrust belts

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The orogenic cycle in the Andes: Arc magmatism and delamination as control of the fold and thrust belts Victor

Aires CONICET Objectives: Dickinson s pioneer evolution of North America The North American orogenic cycle The

Thicken crust and eclogites Shallowing of the oceanic lithosphere Steepening of the oceanic crust and extension

1 The orogenic cycle in the Andes: Arc magmatism and delamination as control of the fold and thrust belts Victor A. Ramos Laboratorio de Tectónica Andina Instituto de Estudios Andinos Don Pablo Groeber Universidad de Buenos Aires CONICET Objectives: Dickinson s pioneer evolution of North America The North American orogenic cycle The Central la Andes orogenic cycle Beginning of subduction arc magmatism Contraction and crustal thickenning Thicken crust and eclogites Shallowing of the oceanic lithosphere Steepening of the oceanic crust and extension Evidence of lithospheric removal and crustal delamination Subsequent contraction and FTB development New magmatic arc 1

Dickinson s pioneer evolution of North America The continental margin was during Mesozoic

Mountain building of the Rocky Mountains fold and thrust belt in the Late Cretaceous,

Eastern Rockies during the Laramide deformation, A coeval volcanic gap in the magmatic arc

and generalized extension, Dickinson (1976) Resuming of a new arc in the Cascadian Ranges

2 Dickinson s pioneer evolution of North America The continental margin was during Mesozoic times the site of an arc trench system much like the Andean system of modern South America. Mountain building of the Rocky Mountains fold and thrust belt in the Late Cretaceous, Progression of the deformation to the foreland with the uplift of the basement blocks of the Eastern Rockies during the Laramide deformation, A coeval volcanic gap in the magmatic arc during shallowing and flat slab subduction, Giant rhyolitic calderas that followed the gap, and generalized extension, Dickinson (1976) Resuming of a new arc in the Cascadian Ranges Dickinson s pioneer evolution of North America Keith (1979) A complete magmatic cycle from Jurassic to Recent times 2

3 Kay et al. (2009) Oligocene (28 Ma) Ramos (2009) 3

4 Seismic evidence for thickened crust Wide angle and Ps receiver functions Yuan et al Teleseismic precursor PmP McGlashan et al S 20 S 22 S 24 S Irregular Moho boundary and deviations from isostasy support recent delamination and crustal flow in mid crust Oligocene Early Miocene (28-17 Ma) Ramos (2009) 4

5 The orogenic cycle was well established, but There was no a direct relationship between orogenic deformation as shown by the shortening rate and subduction rate (Somoza, 1998). Foreland failure and development of fold and thrust belt coincide with a decrease in subduction rates (Oncken et al., 2006). Shortening rate Subduction rate Eoceno Oligoceno Mioceno Plioceno Oncken et al. (2006) Somoza (1998) Kay and Coira (2009) 5

6 Middle Miocene ( Ma) Ramos (2009) Kay and Coira (2009) 6

7 Late Miocene (12-6 Ma) Ramos (2009) Proposed alternative by DeCelles et al. (1915) Flat slab subduction is not an all important process in the Central Andes. HFE: High Flux Event No variations of the Benioff zone through time DeCelles et al. (2015) 7

8 Change in deformational regime Miocene thrust regime Pliocene extensional fault regime Fault kinematic data as summarized by Marrett and Strecker (2000) LATE MIOCENE - PLIOCENE (6-3 Ma) Ramos (2009) 8

9 CRUSTAL AND LITHOSPHERIC DELAMINATION Structural studies Bolivian Subandean F.T.B. Crustal and lithospheric delamination Roederer (1982, 1994) CRUSTAL AND LITHOSPHERIC DELAMINATION Geophysical studies Thermal uplift and Subandean contraction Lithospheric h i dl delamination Isacks (1988) 9

10 CRUSTAL AND LITHOSPHERIC DELAMINATION Geochemical and petrological studies Kay (2003) Latest Miocene: 6 Ma Ignimbritic flare up 10

CRUSTAL AND LITHOSPHERIC DELAMINATION Geochemical and petrological studies CVZ

ba 1 1) Altiplano: Lack of lithosphere was interpreted as evidence of

11 CRUSTAL AND LITHOSPHERIC DELAMINATION Geochemical and petrological studies CVZ Corque site Los Frailes & Kari Kari complexes ~19 S Cordillera Occidental mafic lavas < Ma <1Ma Altiplano ALVZ Cordillera Oriental Subandean Interandean Chaco foreland ba 1 1) Altiplano: Lack of lithosphere was interpreted as evidence of delamination Beck and Zandt (2002) and Kay and Coira (2009). CRUSTAL AND LITHOSPHERIC DELAMINATION Seismological studies Delamination (6 Ma) Heit et al. (2011) 11

12 CRUSTAL AND LITHOSPHERIC DELAMINATION Geochemical and petrological studies 23 S Melt P-wave Delaminated block 2 Schurr et al. (2003, 2006) 2) Puna: Caldera Vilama, Pacana and others Areas with high velocity were interpreted as delaminated blocks CRUSTAL AND LITHOSPHERIC DELAMINATION Geochemical and petrological studies 25 S 3 Delaminated block 3) Puna: Volcán Tuzgle Areas with high velocity were interpreted as delaminated blocks Schurr et al. (2003, 2006) Coira and Kay (1994) 12

13 Crustal and lithospheric delamination: Geophysical evidence Q P wave Asch et al., 2006) Asch et al., 2006) Schurr et al. (2006) Seismic tomography shows delaminated blocks sinking in the mantle beneath areas of partial melting as proposed by Kay et al. (1994) on petrological grounds. Kay et al. (1994) Pliocene to Quaternary (6 0 Ma) Ramos (2009) 13

14 Tectonic Evolution of the Subandean Belt Last 6 Ma!! Baby et al. (1997) Tectonic Evolution of the Subandean Belt Baby et al. (1995) 14

15 Tectonic Evolution of the Subandean Belt Echler et al.. (2005) Zandt and Beck (2002) PUNA ALTIPLANO VOLCANIC PROVINCE (Thick crust) PAYENIA VOLCANIC PROVINCE (Thin crust) Ramos (1999) 15

16 Seismicity in the Andes of Neuquén Benioff Wadati Zone Bohem et al. (2002) Payenia Volcanic Field 40,000 km 2 8,400 km 3 in less than 2 Ma Ramos and Folguera (2011) 16

17 Low velocity zones High conductivity zone Highly attenuated crust Payenia flat slab (Southern Mendoza) Middle Miocene to Pliocene shallowing Ramos and Folguera (2011) 17

18 20 km Payenia flat slab (Southern Mendoza) Delamination and deformation Ramos et al. (2014) 18

19 Payenia flat slab (Southern Mendoza) Ramos et al. (2014) Payenia flat slab (Southern Mendoza) Ramos et al. (2014) 19

Payenia flat slab (Southern Mendoza) Pliocene Pleistocene steepening Ramos and Folguera (2011)

Crustal delamination requires steepening of the previous flat slab stage.

20 Payenia flat slab (Southern Mendoza) Pliocene Pleistocene steepening Ramos and Folguera (2011) Conclusions: We need thermal weakening to produce exceptional shortening in the foreland. Crustal delamination requires steepening of the previous flat slab stage. Crustal delamination and lithospheric removal trigger development of fold and thrust belt in the foreland. These processes are entirely different in thick and thin crusts: rhyolitic and dacitic flare up or large flood tholeiitic basalts, respectively. But, in both cases exceptional foreland deformation follows delamination of the lower crust. 20

formation in the lower crust, Lithospheric and crustal delamination, Extensional collapse and crustal

21 Conclusions: Dickinson Orogenic Cycle: Process by which an Andean type orogen passes through a series of stages leading to: Crustal thickening; Upper crustal shortening and expansion of arc magmatism, Eclogitic residue formation in the lower crust, Lithospheric and crustal delamination, Extensional collapse and crustal attenuation, W. Dickinson Final contraction with development of fold and and thrust belts. New cycle of subduction near the trench 21

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