Adakite

Genesis of Adakite and Nb-enriched basalts:
the fate of young slab and the role of mantle
heterogeneities in the subduction factory.
The case of the Western Trans-Mexican
Volcanic Belt
Dr. Chiara Maria Petrone
Department of Earth Sciences
University of Cambridge
E-mail: [email protected]
Adakite – NEB association - What does this mean?
Can the slab melt? Looking for evidence…… Adakite signature
The adakite – Nb-enriched (arc)-basalt (NEB) connection
Case study: adakite and NEB in the Western Trans-Mexican
Volcanic Belt
Conclusions – why does this matter?
Geoitalia 2009 – Corso Breve SC2
“Typical” arc magmatism
Subducted lithosphere releases hydrous fluids and, possibly, silicate
melts
These infiltrate the overlying mantle wedge lowering the solidus of
mantle peridotite
Partial melting of peridotite produces basaltic magmas
Fl
ui
d
+
M
el
tl
Hydration of Melts
Mantle Wedge
os
s
Arc
Geoitalia 2009 – Corso Breve SC2
The subduction factory
Many processes in arc
lithosphere produce
composition diverse from the
primary basalt end-member
Most arc lavas lie along the
basalt-andesite-dacite-rhyolite
differentiation trend as a result
of differentiation at crustal
pressures
Tatsumi (2005), GSA Today, 15, 7
Geoitalia 2009 – Corso Breve SC2
What is an adakite?
Some dacite and andesite have
distinctive trends! Defant and
Drummond (1990) called them
adakite and suggested they
represent slab melt
Sr/Y
200
Adakite
150
100
Andesite-dacite-rhyolite
50
Relatively high Al content
Intermediate silica content
10
20
30
40
50
Y (ppm)
60
70
Low HREE
High SR/Y
Geoitalia 2009 – Corso Breve SC2
What is an adakite?
Volcanic or intrusive rocks of Cenozoic arcs characterised by > 56
wt% SiO2; high Sr/Y and La/Yb (Y, Yb < 18 and 1.9 ppm), associated
with subduction of young (< 25 Ma) oceanic lithosphere (Defant
and Drummond, 1990)
These are exactly the characteristices expected for magmas
generated from hydrous basalt slab melt
Geoitalia 2009 – Corso Breve SC2
Condition for slab melting
Geoitalia 2009 – Corso Breve SC2
Peacock & Wang, 1999
What is an adakite?
Adakite
Not Adakite
Macpherson, 2008, EHaz
Geoitalia 2009 – Corso Breve SC2
Adakite model
Macpherson, 2008, EHaz
Y
Sr
Sr
Y
Y Sr
Y
Sr
Plag
Gt
Amph
Y
Geoitalia 2009 – Corso Breve SC2
Why does this matter?
Adakites show many similarities
to tonalite-trondhjemitegranodiorite (TTG) suite which are
characteristic of Archean terranes
Adakite are a potential analogue
for Archean TTG which would help
to understand Archean tectonics
and crust generation
Phanerozoic
Archean
CA
TTG
Adakite
Martin 1999, Lithos 46
Geoitalia 2009 – Corso Breve SC2
Martin 1999, Lithos 46
Basalt slab melts
Basalt slab dehydrates
Hydrated peridotite
melts
The model so far is nice, simple and makes
profound predictions about the
mechanism involved in early Earth, but……
Hot Slab – geotherm 1
Archean
TTG genesis
Cool Slab- geotherm 3
Phanerozoic
Normal
arc magmas
Geoitalia 2009 – Corso Breve SC2
Just young slab?
After 1990 several suites with adakitic geochemistry were found
and NOT all were associated with young slab!
Many alternative models have been proposed to explain how
slabs can melt trough other ways than just being young
The model is not so nice
now - Adakite are still
considered a proxy to infer
particular geodynamic
setting but hard to make
prediction on
early Earth!
Subduction
Initiation
Flat subduction
Gutscher et al., 2000, Geology, 28
Sajona et al., 1993, Geology 21
Slab tears
Geoitalia 2009 – Corso Breve SC2
Yogodzinski et al, 2001, Nature 409
The smoking gun
After 1990 the connection between adakite and slab-melts have
been questioned and alternative models have been proposed to
explain their geochemical characteristic
Nevertheless, the association between adakite and Nb-enriched
(arc) basalts (NEB) is considered a solid evidence of slab-melt
phenomenon (Wang et al. 2008, CMP 155)
Geoitalia 2009 – Corso Breve SC2
The Nb-enriched arc basalt jungle:
NEAB, NEB, HNB and other strange animals
• Normal arc basalts: strong depletion inWhat
HFSE;alow Nb <10 ppm
(usually <4ppm); negative Nb anomaly;
mess!TiO2 < 1wt%
• NEAB – Nb-enriched arc basalts: high Ti, Na
and Nb (30-40 ppm); Nb/La > 0.5; Nb/Nb*<1
[Kepezhinskas et al., 1996 & 1997]
• HNB – High-Nb basalts: high Nb (> 20 ppm);
weak positive or negative Nb anomaly and
0.7<La/NbMN<2 [Reagan & Gill, 1989; Defant et
al., 1991]
• NEB – Nb-enriched basalts and basaltic
andesite: trace element ratios similar to HNB
but lower Nb (7-16 ppm) [Sajona et al., 1996]
Geoitalia 2009 – Corso Breve SC2
The Nb-enriched arc basalt jungle:
NEAB, NEB, HNB and other strange animals
• NEAB=HNB; NEB: Nb-enriched arc basalt and basaltic andesite
enriched in HFSE (Nb up to 48 ppm); high Nb/La (0.5-1.4);
variable Nb/Nb*; trace element systematics similar to OIB;
transitional or alkaline character; found in arc setting in
association with adakite
Rock/Primordial Mantle
100
OIB
NEB
10
1
Rb Ba Th U
K Ta Nb La Ce Pb Sr Nd P
Hf Zr Sm Ti Tb Y
OIB: Sun & McDonough, 1989
NEB: Sajona
al., 1996
Geoitalia
2009et
– Corso
Breve SC2
Aguillon et al., 2001
Adakite – NEB connection
Adakite-NEB connection clear smoking
gun of slab melt
Sajona et al., 1996, J. Petrol., 97
Geoitalia 2009 – Corso Breve SC2
A case study
Subduction of young hot slab
Large variety of composition from subduction-related to Naalkaline magmatism (OIB-type)
Recently discovered the presence of adakitic rocks – NEB
(Petrone & Ferrari, CMP, 2008)
Perfect opportunity to test:
Relationship between adakite, NEB and arc ADR suite
Origin of adakite and NEB: is it a connection?
Role of slab melt vs. mantle heterogeneities: adakite
metasomatism or marble cake?
Complexities of the TMVB
San Pedro-Ceboruco graben
Varying slab dip, steep in the W flat to the E. Rivera dips steeper than W Cocos.
No seismicity beneath the arc
Young subducting plate (< 15Ma), Large variation of volcanic style, variation in
arc width
Large compositional variation: OIB-type, adakitic-typeGeoitalia
and subduction-related
all
2009 – Corso Breve SC2
coexist in space and time
San Pedro-Ceboruco graben
Scale
0
10
Stratovolcano
Laguna de
Santa. Maria del Oro
20 km
Monogenetic volcanism:
Transiti onal series
Subduction-related
Na-alkaline series
San Pedro-Cerro
Grande Volcanic
Complex
Adakiti c rocks
Tepetiltic
Nb-enriched basalt
Compostela
Caldera rim
Volcanic vent
Dome
21°10'
S.Pedro
Amado
Nervo
flows
Normal fault
Ceboruco
Jala
Geoitalia 2009 – Corso Breve SC2
104°30'
Complex magmatism
Petrone et al., 2003, Chem Geol., 193
Geoitalia 2009 – Corso Breve SC2
N
104°30' W
104°45' W
E arly P
Tr ans- Mliocene
Volcan exican
ic B elt
Tepetiltic
volcano
San Pedro
Lagunillas
Laguna
San Pedro
CB3
San Pedro
domes
70
GC2
21°10' N
Amado Nervo
shield volcano
GC4
GC3
Ce (ppm)
Juan
Escutia
SCVC Amphibole-bearing
SCVC Amphibole-free
Amado Nervo
80
60
50
40 Ceboruco
volcano
CB2
30
Amado
Nervo
Zapotán
50
CB1
GC5
Jalis
( Late Cco block
r
- early etaceous
Tertiar
y)
55
60
65
70
SiO2 (wt%)
Rio
A hu
acat
lan
Cuastecomate
o
Ri
tit
Te
o
ec
0
5 km
LEGEND
Petrone et al.,
2006, GSA Sp.
Pap., 402
Adakitic rocks
Amado Nervo NEB
San P edro-Cerro Gra nde
Vo lc anic Com plex
Stratovolcanoes
Amphibole-bearing
(<~280 - 30 ka)
Amphibole-free
(<~280 - 30 ka)
Amado Nervo mafic
lava flows (220 ka)
Northern Volcanic
Chain (< 510 ka)
Cerro Estiladero
(~520 ka)
Southern Volcanic
Chain 2,530 - 430 ka)
Geoitalia 2009 – Corso
Breve SC2
Older rocks
Adakitic rocks and NEB
SCVC Amphibole-bearing
SCVC Amphibole-free
Amado Nervo
Petrone & Ferrari, 2008, C.M.P., 156
1.5
N b/L a
Sr/Y
200
NEB
150 1.0
Na-alkaline
Caminguin
100
0.5
San
Juan
Tepetiltic and
Ceboruco
50
0.4
10
0.6
20
0.8
30
1.0
1.2
1.4
Nb/Nb*
50
60
40
Y
1.6
1.8
70
NEB:Sajona et al, 1996; Kepezhinskas et al., 1997; Aguillón-Robles et al.,
Geoitalia 2009 – Corso Breve SC2
2001;
Na-alkaline Petrone et al. 2003
Adakitic rocks
SCVC Amphibole-bearing
SCVC Amphibole-free
Adakite
a
160
160
140
140
120
120
100
b
180
Sr/Y
Sr/Y
180
SVA
San Juan
80
60
Caminguin
40
100
80
60
TMVB normal
andesite-rhyolite
40
20
20
0
0.1
0.2
0.3
Rb/Sr
0.4
60
65
70
75
SiO2
TMVB: Nelson and Hegre, 1990; Wallace and Carmichael, 1994; Mahood, 1981; Petrone, 1998
San Juan: Luhr , 2000
SVA: Petrone, 1998; Petrone et al., 2001
Adakite: Kepezhinskas et al., 1997; Aguillón-Robles et al., 2001
Caminguin rock: Castillo et al., 1999.
Geoitalia 2009 – Corso Breve SC2
Adakitic rocks - The model
Slab melt
SCVC Amphibole-bearing
SCVC Amphibole-free
200
0.5
1
Sr/Y
150
Slab melting
5
100
Partial melting of an
oceanic crust in
amphibolite o
eclogite facies
Southern
Volcanic
Chain
10
50
EPR
60
10
20
30
40
Y
50
60
70
Partial melting
residual mineralogy
is grt+cpx
Petrone
& Ferrari,
2008, C.M.P.,
156
Geoitalia
2009 – Corso
Breve SC2
Adakitic rocks - The model
Slab melt
1000
Rock/Pimitive Mantle
0.5
100
AF
5
Partial melting of an
oceanic crust in
amphibolite o
eclogite facies
10
10
30
AB
Partial melting
residual mineralogy
is grt+cpx
1
Rb Ba Th Ta Nb K La Ce Pb Sr P Nd Hf Zr Sm Ti Y Yb
Petrone
& Ferrari,
C.M.P.,
Geoitalia
2009 –2008,
Corso
Breve156
SC2
Adakitic rocks - The model
Slab melt?
10
MORB
field
SCVC Amphibole-bearing
SCVC Amphibole-free
Amado Nervo
Adakite field
TMVB
Na-alk
8
4
NEB
field
VB
2
OIB
TM
εNd(N)
6
EM
II
0
EM
0.703
fiel
d
0.704
0.705
Sr/86Sr(N)
I
0.706
87
Geoitalia 2009 – Corso Breve SC2
Adakitic rocks - The model
Slab melt vs HP differentation
SCVC Amphibole-bearing
SCVC Amphibole-free
200
0.6
HP fractionation
Slab melting
0.5
1
Sr/Y
150
5
100
0.7
HP fractionation
assemblage is: cpx,
grt, opx, amph in
the proportions
45:26:15:15
Southern
Volcanic
Chain
10
0.8
50
0.9
EPR
60
10
20
30
40
Y
50
60
70
Petrone & Ferrari, 2008, C.M.P., 156
Geoitalia 2009 – Corso Breve SC2
Adakitic rocks - The model
Slab melt vs HP differentation
100
Rock/Pimitive Mantle
AF
10
Can we completely
exclude slab melt?
0.9
AB
1
0.6
Rb Ba Th Ta Nb K La Ce Pb Sr P Nd Hf Zr Sm Ti Y Yb
Petrone & Ferrari, 2008, C.M.P., 156
Geoitalia 2009 – Corso Breve SC2
Amado Nervo - NEB
15.65
TMVB
C alc-alk alin e
204
Pb/ Pb
TMVB
N a-alk
NEB
15.60
207
P acific o cean ic
s ed im en ts
Caminguin
15.55
E P R T h o leiites
15.50
NH
Adakite
P acific alk alin e
s eam o u n ts
RL
15.45
15.40
17.8
18.0
18.2
18.4
18.6
18.8
19.0
19.2
206
Pb/204Pb
Geoitalia 2009 – Corso Breve SC2
Amado Nervo – NEB
The model
EM
19.00
206
Pb/204Pb
18.95
18.90
18.85
Sediment
18.80
18.75
18.70
NEB
90DM+10EM
18.65
18.60
18.55
18.50
18.45
EPR Tholeiites
Slab Fluid
DM
In my 2003 model
(Chem. Geol.), the
parental magmas
of Amado Nervo
rocks have been
recognised to be a
mixture of
depleted and
enriched mantle
source
(90%DM+10%EM)
18.40
0
2
4
6
8
10 12 14 16 18 20 22 24 26
Nd/Pb
Petrone & Ferrari, 2008, C.M.P., 156
Geoitalia 2009 – Corso Breve SC2
Amado Nervo – NEB
The model
206
204
Pb/ Pb
19.00
18.95
18.90
18.85
18.80
18.75
18.70
EM
Sediment
Sediment Melt+Slab Melt
90DM+
10EM
18.65
18.60
18.55
18.50
NEB
DM+ SLAB
FLUID
18.45
18.40
EPR Tholeiites
0.5116 0.51180.51200.5122 0.51240.5126 0.51280.5130 0.51320.5134
143
144
Nd/ Nd
Petrone & Ferrari, 2008, C.M.P., 156
Geoitalia 2009 – Corso Breve SC2
Adakitic rocks and NEB generation
Pacific Plate
North America Plate
EPR
Baja
California
Adakitic
NEB
Amado Nervo rocks
Jalisco block
Sediment melt
Slab dehydration
Cocos Pl.
HP fractional
crystallization
Rivera Plate
Continental crust
Oceanic crust
Mantle lithosphere
Inflow of deep
asthenosphere
Petrone & Ferrari, 2008, C.M.P., 156
Petrone & Ferrari, 2008, CMP, 156
Geoitalia 2009 – Corso Breve SC2
Conclusions
Although the adakite-NEB association is considered as a strong
evidence of slab-melting, this study suggests that other processes can
lead to its generation.
Slab-melts play a limited role in the genesis of both SCVC adakitic rocks
and Amado Nervo NEB association.
Adakitic rocks derive their signature from high pressure crystal
fractionation
Mantle heterogeneities play major role in generating NEB
No simple way to infer genetic and geodynamic setting from
geochemical signature
Geoitalia 2009 – Corso Breve SC2
Thank you
Geodynamic framework
A
NORTH AMERICA
PLATE
Tepic
Guadalajara
Eas
t Pac
ific
R
ise
PACIFIC
PLATE
A’
RIVERA
PLATE
Zone of change in
slab dip (extension)
Limit of seismic
slab
COCOS PLATE
Geoitalia 2009 – Corso Breve SC2
Ferrari et al., 2001, Geology
Amphibole Amphibole
Amado
bearing
Nervo
free
transitional
AEC
11 Km
AFC
Hydrous basaltic
magma
50 Km
Transitional
magma
Geoitalia 2009 – Corso Breve SC2
How an adakite looks like
Amph
1mm
Geoitalia 2009 – Corso Breve SC2
Amado Nervo – NEB
The model
19.00
18.95
EM
206
204
Pb/ Pb
18.90
18.85
18.80
Sediment
18.75
90DM
18.70 +10EM
18.65
18.60
18.55
18.50
18.45
SEDIMENT
MELT +
SLAB FLUID
NEB
DM
Slab melt
EPR tholeiites
18.40
0.1
1
10
Nb/Y
Geoitalia 2009 – Corso Breve SC2
Lateral propagation of slab detachment: a model to explain the eastward
mafic pulse and the compositional variety of the TMVB
Slab broke off in
the Gulf of
California after
subdcution ceased
at 12.5 ma. The
tear propagated
laterally to the ESE,
more or less
parallel to the
active Cocos
subduction zone.
This would produce
the E-ward
migrating pulse of
mafic volcanism
observed from ~11
to 5 Ma in the
northern TMVB.
Ferrari,
Geology
Geoitalia
2009 –2004,
Corso Breve
SC2

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