Ignimbrite Flare-Ups in the Central Andes: Crustal Sources And

Ignimbrite ﬂare-ups in the Central Andes: Crustal sources and !! processes of magma!! generaon !! ! ! Gerhard Wörner, !! !! Elena Belousova, Simon Turner, Jelte Kemann, Axel Schmi, Axel Gerdes, Shan deSilva

Layout:

1. Geological seng (review, maybe skipped)

2. Ignimbrite composions: AIDA data base: (review, maybe skipped) Ages, volume and composion through me and space

3. Evidence for large crustal contribuons (review, maybe skipped)

4. Zircon U/Pb dang combined with O-isotope and Hf- isotope analyses (new data)

Results (in a nutshell)

-> Contribuons of large volume ignimbrite magmas increase from 20 to 70% with thermal maturaon of increasingly thickened Andean crust

-> Individual ignimbrite units are isotopically heterogeneous and are amalgamaons of crustal melts from disnct Proterozoic sources w/r to age and composion

Ignimbrites:

message from thickening crust at Andean-type acve connental margins

1. Geological seng Large-volume, plateau-forming ignimbrites on the western margin of the Central Andean orogen...

over 30 Ma and 1500 km N-S extension 900 m

Valle de Azapa 18°S 1. Geological seng Cuno Cuno Section with > 24 Ma old marine sediments at 1900 m (S. Peru)

22 Ma Ignimbrites

Uplift, erosion and sedimentation prior to „ignimbrite flares“

Jurassic Sediments 1. Geological seng 1700 m 1. Geological seng 1700 m What is the source of these voluminous ignimbrites ?

Our tools: GIS-Data base mapping Ages Volumes Sr-O-isotopes O-Hf-U/Pb analyses in zircons 1. Geological seng Peru

Ignimbrites Bolivia

Chile 100 km 1. Geological seng 1. Geological seng

U-Pb zircon ages and Ar-Ar sanidine ages perfectly overlap !! 2. Ignimbrite composions Temporal and compositional evolution of „ignimbrite flares“ Based on our Andes Ignimbrite Database (AIDA) More than 200 ignimbrite sheets GIS-mapped,

more than 1600 samples with geochemical, isotopic, and many with age data APVC, 3-10 Ma, 23°S

2. Ignimbrite composions …La Pacana caldera…as an AIDA - example

Brandmeier and Wörner AIDA Website 2. Ignimbrite composions …La Pacana caldera…as an AIDA - example

Brandmeier and Wörner AIDA Website 2. Ignimbrite composions Example Lauca and Oxaya ignimbrites : Edit and update the database by authorized users

Brandmeier and Wörner AIDA Website 2. Ignimbrite composions

Wörner et al (2018) 2. Ignimbrite composions Age migraon of Central Andean Ignimbrites 30

Nazca Plateau Oxaya Plateau

20 Altos de Pica Plateau 15

Age [Ma] Huaylillas Plateau 10 APVC ignimbrite „ﬂare-up“ 5

Sencca/Lauca/Perez 0 14 16 18 20 22 24 26 Latude [｡S]

Freymuth et al (2015) 2. Ignimbrite composions Age migraon of Central Andean Ignimbrites 30 Plateau-forming ignimbrites 25 local small volume Nazca Plateau ignimbrites Oxaya Plateau

20 Altos de Pica Plateau 15

Age [Ma] Huaylillas Plateau 10 APVC ignimbrite local small volume „ﬂare-up“ 5 ignimbrites

Sencca/Lauca/Perez 0 14 16 18 20 22 24 26 Latude [｡S]

Freymuth et al (2015) 2. Ignimbrite composions Age migraon of Central Andean Ignimbrites

26 Ma 22 18 14

(5-14 Ma, Thouret et al. 10 2017, Wörner et al., unpublished data) 6

Freymuth et al (2015) Wörner and Mamani (2018) ELEMENTS (in prep) 2. Ignimbrite composions Magmatic compositions

2. Ignimbrite composions fractionating phases and Sr/Y ratios will remain low. These general principles can be used to link trace-element signatures in magmas to the pressure (i.e. depth within the crust) where magma evolution takes place. In thin-crust settings, where plagioclase, pyroxene, and amphibole Ignimbrites dominate the equilibrium assemblage in andesites, the ratios of Sr/Y, Sm/Yb, and Dy/Yb will be low. Increasing pressure of fractional crystallization and/or assimilation processes tends to increase Sr/Y, Sm/Yb and Dy/Yb (Kay et al. 1988, 1999; Coira et al. 1993; Mamani et al. 2010).

FIGURE 3 shows these three trace-element ratios and their evolution through time. FIGURES 3A and 3C clearly indicate that – with few exceptions – the maximum Sr/Y and Dy/Yb ratio are found only in intermediate andesites (55–68 wt% SiO2) that are younger than 5 Ma (Pliocene, blue symbols in FIG. 3). Basalts (<52 wt% SiO2) are rare and lack the high Sr/Y, Dy/Yb, and Sm/Yb ratios indicative of residual garnet. Thus, a strong garnet signature is found in intermediate aer Wörner et al (2018) magmas only after the youngest phase of crustal thickening Distribution of SiO in three broad categories of FIGURE 2 2 (<10 Ma) (FIG. 3B). Findings such as these have resulted Central Andean magmas: the intrusive igneous rocks and the two types of extrusive rocks, the lavas and the ignimbrites. in a recent proliferation of publications linking averaged Note the distinct bimodal SiO2 wt% values between lavas (blue) trace-element ratios to crustal thickness in a quantitative and ignimbrites (yellow), which are controlled by density, viscosity, way (e.g. Farner and Lee 2017; Hu et al. 2017). However, as and the maximum SiO2 of the eutectic compositions. Older intru- FIGURE 3 demonstrates clearly, low Sm/Yb, Dy/Yb and Sr/Y sive rocks (red speckled) have a wide compositional range but their maximum is between the modes of the lavas and the ignimbrites. ratios occur throughout the Central Andes at any time,

A B

C D

Trace-element signatures (Sr/Y, Dy/Yb, and Sm/Yb), plotted with respect to Sm/Yb. Arrows indicate compositional varia- FIGURE 3 including versus age, of erupted magmas in the tions caused by the distinct preference for certain trace elements in Central Andes through time, from the Jurassic (200 Ma) to today. the different residual mineral phases during fractional crystallization Color code of magma type and its age are given at top of ﬁgure. and/or crustal melting and assimilation. Colors: Quaternary/ Abbreviations are as follows: cpx = clinopyroxene; plag = plagio- Pliocene = blue; Miocene/Oligocene = yellow and orange; Eocene/ clase feldspar. (A) Ratio of Sr/Y plotted with respect to wt% SiO2. Paleocene = red; Cretaceous = green; Jurassic = black. MODIFIED FROM (B) Ratio of Sm/Yb plotted with respect to age (Ma). (C) Ratio of MAMANI ET AL. (2010). Dy/Yb plotted with respect to wt% SiO2. (D) Ratio of Dy/Yb

ELEMENTS 239 AUGUST 2018 2. Ignimbrite composions Systemac temporal changes in trace element paerns through me during crustal thickening in the Central Andes

Mamani et al. (2011) Geol Soc Am Bull 2. Ignimbrite composions Systemac temporal changes in trace element paerns through me during crustal thickening in the Central Andes

Quaternary

Miocene

Oligocene

Cretaceous Jurassic

Mamani et al. (2011) Geol Soc Am Bull 2. Ignimbrite composions Systemac temporal changes in trace element paerns through me during crustal thickening in the Central Andes

Not so clear for ignimbrites

Mamani et al. (2011) Geol Soc Am Bull

Composional variaon related to crustal thickening

This study applies cluster analysis (CA) and linear discriminant analysis (LDA) on log-rao transformed data. Brandmeier and Wörner (1916)

Composional variaon related to crustal thickening

< 9 Ma 22 to 9 Ma

< 9 Ma This study applies cluster analysis (CA) and 22 to 9 Ma linear discriminant analysis (LDA) on log-rao transformed data. Brandmeier and Wörner (1916)

2. Ignimbrite composions Peru

How much crustal recycling during ignimbrite volcanism ? Bolivia

Chile

3. Evidence for large crustal contribuons

APVC ignimbrites Minerals from andesic lavas S. Peruvian ignimbrites N.Chile metamorphic basement N.Chile ignimbrites Freymuth et al (2015)

3. Evidence for large crustal contribuons

ignimbrites N of 23 °S S of 23 °S

MIX 'n MASH

source contaminaon

APVC ignimbrites Minerals from andesic lavas S. Peruvian ignimbrites N.Chile metamorphic basement N.Chile ignimbrites Freymuth et al (2015)

3. Evidence for large crustal contribuons

ignimbrites extended AFC N of 23 °S S of 23 °S

70 % 60 % 50 % 40 % MIX 'n 30 % MASH 20 % 10 %

source contaminaon

APVC ignimbrites Minerals from andesic lavas S. Peruvian ignimbrites N.Chile metamorphic basement N.Chile ignimbrites Freymuth et al (2015)

3. Evidence for large crustal contribuons

N of 23 °S S of 23 °S

100 %

MIX 'n MASH 50 %

10 %

source contaminaon

APVC ignimbrites Minerals from andesic lavas S. Peruvian ignimbrites N.Chile metamorphic basement N.Chile ignimbrites Freymuth et al (2015)

3. Evidence for large crustal contribuons

N of 23 °S S of 23 °S

Which crustal component should we choose 100 %

in crust-mantleMIX 'n mass balance modelling ? MASH 50 %

10 %

source contaminaon

APVC ignimbrites Minerals from andesic lavas S. Peruvian ignimbrites N.Chile metamorphic basement N.Chile ignimbrites Freymuth et al (2015) 4. Zircon U/Pb dang combined with O-isotope and Hf- isotope analyses

Are zircons the soluon ? Zircon phenocrysts from Oxaya Fmt Ignimbrites (19 – 22 Ma): Shapes

4. Zircon U/Pb dang combined with O-isotope and Hf- isotope analyses Zircon phenocrysts from Oxaya Fmt. Ignimbrites Zonaon : inherited zircons ?

Not really !!

4. Zircon U/Pb dang combined with O-isotope and Hf- isotope analyses

Reference data for potenal crustal components in ignimbrite magmas Metasedimentary basement rocks Igneous basement rocks Quebrada Aroma Rio Loa Belen Sierre de Moreno Cordon Lila Rio Loa Sierra del Tigre Cordon Lila 12

6 Mantle values 5

2 0 200 300 400 800 1000 1200 1400 1600

U/Pbzirc Age (Ma) basement data from 4. Zircon U/Pb dang combined with O-isotope and Hf- isotope analyses Pankurst et al (2016) Earth Sci Rev 152:88-105

9 Ignimbrites APVC south 8

6 Ignimbrites Mantle values 5 northern domain 4

2 0 200 300 400 800 1000 1200 1400 1600

U/Pbzirc Age (Ma) basement data from 4. Zircon U/Pb dang combined with O-isotope and Hf- isotope analyses Pankurst et al (2016) Earth Sci Rev 152:88-105

Reference data for potenal crustal components in ignimbrite magmas: basement rocks Metasedimentary basement rocks Igneous basement rocks Quebrada Aroma Rio Loa Belen Sierre de Moreno Cordon Lila Rio Loa Sierra del Tigre Cordon Lila 12 No11 inherited old zircons (almost) 10

9 Ignimbrites from crustal contribuons ! APVC south 8

6 Ignimbrites Mantle values 5 northern domain 4

2 0 200 300 400 800 1000 1200 1400 1600

U/Pbzirc Age (Ma) basement data from 4. Zircon U/Pb dang combined with O-isotope and Hf- isotope analyses Pankurst et al (2016) Earth Sci Rev 152:88-105

Reference data for potenal crustal components in ignimbrite magmas: zircons in sedimentary archives Toquepala arc Mesozoic n=47 n=222

45 Ma U-Pb ages of inherited 1172 Ma 1218 Ma 1859 Ma zircon in ignimbrite 45 40 35 30 25 20 15 10 5 0 0 500 1000 1500 2000

U/Pbzirc Age (Ma)

Detrital zircons (“Toquepala arc” and “Mesozoic”) from Wotzlaw et al (2011) Belen zircons from the Arequipa metamorphic basement from Pankhurst et al (2016)

Reference data for potenal crustal components in ignimbrite magmas: zircons in basement rocks Toquepala arc Mesozoic Belen metamorphic n=47 n=222 basement n=38

45 Ma U-Pb ages of inherited 1172 Ma 1218 Ma 1859 Ma zircon in ignimbrite 45 40 5 35 30 4 25 3 20 15 2 10 1 5 0 0 0 500 1000 1500 2000

U/Pbzirc Age (Ma)

Detrital zircons (“Toquepala arc” and “Mesozoic”) from Wotzlaw et al (2011) Belen zircons from the Arequipa metamorphic basement from Pankhurst et al (2016)

Zircons in ignimbrites

Toquepala arc Mesozoic Belen metamorphic n=47 n=222 basement n=38

45 Ma U-Pb ages of inherited 1172 Ma 1218 Ma 1859 Ma zircon in ignimbrite 45 60 40 zircon crustal 5 50 35 Hf model ages n=53 30 4 40 25 3 30 20 15 2 20 10 1 10 5 0 0 0 0 500 1000 1500 2000 This study U/Pbzirc Age (Ma) T calculated with DM(crustal) λ176Lu = 1.865x10-11 (Scherer et al., 2001) Detrital zircons (“Toquepala arc” and “Mesozoic”) from Wotzlaw et al (2011) 176Lu/177Hf (crust) = 0.015 176 177 Belen zircons from the Arequipa metamorphic basement from Pankhurst et al (2016) Hf/ Hf (crust) = 0.0384

Reference data for potenal crustal components in ignimbrite magmas Toquepala arc Mesozoic Belen metamorphic n=47 n=222 basement n=38

45 Ma U-Pb ages of inherited 1172 Ma 1218 Ma 1859 Ma zircon in ignimbrite 45 60 40 zircon crustal 5 50 35 Hf model ages n=53 30 4 40 25 3 30 20 Crustal contribuons 15 are mixtures of 1 Ga and 2 Ga old crust ! 2 20 10 1 10 5 0 0 0 0 500 1000 1500 2000 This study U/Pbzirc Age (Ma) T calculated with DM(crustal) λ176Lu = 1.865x10-11 (Scherer et al., 2001) Detrital zircons (“Toquepala arc” and “Mesozoic”) from Wotzlaw et al (2011) 176Lu/177Hf (crust) = 0.015 176 177 Belen zircons from the Arequipa metamorphic basement from Pankhurst et al (2016) Hf/ Hf (crust) = 0.0384

Old crustal components in ignimbrite magmas

10,0 9,0 8,0 7,0

6,0 PIG-00-41

per mill 5,0 PIG-03-123

O 4,0

18 LAU-08-02

δ 3,0 2,0 POC-94-134(B) 1,0 inherited old zirc in POC 0,0 0,0 0,5 1,0 1,5 2,0 2,5

TDM crust (Ga)

4. Zircon U/Pb dang combined with O-isotope and Hf- isotope analyses

Old crustal components in ignimbrite magmas

10,0 9,0 Zircons from single ignimbrite units 8,0 are istopically rather heterogenous! 7,0 -> 6,0 disnctPIG-00-41 batches of crustal melts from

per mill 5,0 PIG-03-123 diﬀerent crustal sources mixed into

O 4,0

18 LAU-08-02 one single ignimbrite magma

δ 3,0 2,0 POC-94-134(B) 1,0 inherited old zirc in POC 0,0 0,0 0,5 1,0 1,5 2,0 2,5

TDM crust (Ga)

4. Zircon U/Pb dang combined with O-isotope and Hf- isotope analyses Peru

Relations between tectonic shortening and ignimbrite volume and composition Bolivia

Chile Shortening rate (mm a-1)

Freymuth et al (2015)

km- Ma (km Flux Magmac

1) -1 3 Magmac Flux ) -1 (km 3 Ma -1 km- Shortening rate (mm a 1)

Freymuth et al (2015) Magmac Flux

) Surges in addional ignimbrite- -1 related arc magma ﬂux are (minimum) 30-70 km3Ma-1 km-1 and occur a few Ma aer mayor (km 3 episodes of crustal thickening Ma

and slab steepening -1 km- Shortening rate (mm a 1)

Freymuth et al (2015) Summary Origin of ignimbrite magmas

Ignimbrite „ﬂare-ups“ migrate from N to S and evolve aer the passage of the Juan Fernandez-Ridge ("ﬂat slab") ....related to subsequent steepening/roll-back of the slab

Ignimbrite are 20/80 to 70/30 mixtures of crustal melt and magmas derived from the mantle wedge.

Variable composions and crustal contribuon reﬂect thickness and thermal maturity of the connental crust Addional ignimbrite-related arc magma ﬂux are 30-70 km3Ma-1 km-1 and occur aer crustal thickening and slab steepening