1. JACKSON
SCHOOL OF GEOSCIENCES
Laura N.Dafov1,Owen A.Anfinson1,Marco G.Malusá2,Daniel F.Stockli1
Future Work
Acknowledgements/ References
Conclusions
1
The University of Texas at Austin, Jackson School of Geosciences,Austin,TX,78712,US
2
University of Milano-Bicocca,Department of Earth and Environmental Sciences,Milano,Italy
TEXAS
THE UNIVERSITY OF
AT AUSTIN
WHAT STARTS HERE CHANGES THE WORLD
U chron
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7
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23
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0
100
200
300
400
500
600
0 500 1000 1500 2000 2500
RimAge(Ma)
Core Age (Ma)
Distal Rim vs Core U-Pb DZ ages
BOB1 (19 ± 0.5)
MOD1 (22.5 ± 1.5)
MA7 (28 ± 1)
MA9 (28 ± 1)
MMA1 (28 ± 3)
AV1 (30 ± 1.5)
AV2 (30 ± 1.5)
AV3 (30 ± 1.5)
1:1
The authors would like to thank ConocoPhillips for sponsoring the JSG symposium.
We are grateful to The University of Texas at Austin,The Jackson School of Geosciences,
and UT-Chron for facilities and funding. We also thank Dr.Daniela Rubatto for insightful
discussion.
0
100
200
300
400
500
600
700
800
0 200 400 600 800 1000 1200
RimAge(Ma)
Core Age (Ma)
Proximal Rim vs Core U-Pb DZ ages
CGL3 (23.5 ± 1)
CGL4 (23.5 ± 1)
CG2 (25 ± 2)
VOA (26 ± 1)
CVL1 (26 ± 2.5)
1:1
Proximal Distal
Provenance of Oligo-Miocene Strata from the Adriatic Foredeep of the
Alps-Apennines System Determined through Detrital-Zircon U-Pb Geochronology
Data, Figures, and Discussion
KDEs,Depositional
Ages,and Discussion
VOA (~26 ±1 MA)
CVL1(~26 ±2.5 MA)
Dominant
abundance of
Caledonian and
Cadomian grains
suggests erosion of
units within the
Tocino Subdome
(eastern Lepontine
Dome) (Fig.2 and
4.2).
CGL3 and CGL4
(~23.5 ±1 MA)
The dominance of
29-35 Ma detrital
zircon U-Pb ages,
suggests the
sediments are
primarily derived from
the Bergell intrusion
(30-35 Ma) exposed
along the north side
of the Insubric Fault
(Fig.4.A).
CG2 (Single Clast)
(~25 ±2 MA)
U-Pb ages suggest
this single clast is
from Caledonian
aged source rock.
The detrital zircons
should yield consistent (U-Th)/He ages and will
be used to evaluate exhumation rates in the
source region.
AV1(Single Clast),AV2,and AV3 (~30 ±1.5 MA)
The presence of Cretaceous metamorphic rims on igneous Variscan cores (Figs.7
and 8) are strong indication that the Aveto Formation is at least in part derived from
the Sesia-Lanzo unit (Fig.3) of the west-central alps (Fig.4).
MA9 (~23.5 ±1 MA) and
MA7(~28 ±1 MA)
The samples from the
Macigno turbidites are
separated by ~2km of
section (Fig.1),but due to
rapid depositional rates are still the same age (Chattian).The samples have similar
detrital zircon populations with varying abundances.Increased abundance of
tertiary ages with decreased Variscan,Caledonian,and Cadomian ages in sample
MA9 (Upper Macigno) relative to MA7 (Lower Macigno) suggests an increased input
from tertiary volcanic/plutonic sources.
MMA1 (~28 ±3 MA) and
MOD1(~22.5 ±1.5 MA)
The shift from primarily
Variscan,Caledonian,and
Cadomian detrital zircon
in MMA1 to late-Variscan
and Tertiary detrital zircon in sample MOD1 suggests a significant provenance
change.This may be linked to the transfer of the erosional foci from the Ticino to
Toce Subdome within the central Alps (Fig.2,4,and 9).
BOB1 (~19 ±0.5 MA)
The dominance of late Variscan and Tertiary detrital
zircon U-Pb ages suggests the sediments are primarily
derived from the Toce subdome and Tertiary volcanic/
plutonic sources. (Fig.2,4,and 10).
Figure 9.(a)
Tectonic
evolution of
central Alps.
Westward axial
shift of Adriatic
indenter
caused a shift
in erosional foci
of central Alps
subdomes,23
Ma.Figure
produced by
Marco Malusa.
Figure 10.Data plots highlighting major shifts in
grain populations.(a) Shift in abundance of
Variscan/Caledonian grain populations indicates
indentation due to insubric fault activity causing a
shift of unroofing from the Ticino to Toce subdome
(Fig.4).(b) Shift in abundance of periadriatic
(Alpine) grains indicates progressive domal
unroofing of the Bergell pluton (Fig.4).Periadriatic
grians of AV2 and AV3 likely derived from volcanic
sources.(c) Samples are in order of depositional age
with sample 1-the oldest and sample 11-the
youngest.
KDEs,Depositional Ages,and Discussion
Caledonian
Ticino- Caledonian
Toce- Variscan
Proximal
1.The U-Pb detrital zircon age data indicate proximal
deposits from the Como and Villa Olmo conglomerates
experienced a significant shift from primarily Caledonian and
Cadomian sources to primarily Tertiary and minor late Variscan
sources between 26 and 23 Ma. We attribute this change in
detrital zircon populations to the continued unroofing and
erosion of the Bergell pluton and a shift in erosional foci from the
Ticino to Toce subdome.
2.The zircon grains from the Caledonian clast (Sample CG2)
and the non-Tertiary detrital zircon from all proximal samples will
provide the basis for future (U-Th)/He thermochronologic
analyses in attempt to constrain exhumation rates within the
source region.
Distal
1.The abundance of recycled Variscan,Caledonian,and
Cadomian detrital zircon U-Pb ages in nearly all of the distal
samples makes correlation with the specific source regions
difficult. However,changes in relative abundance from primarily
Caledonian and Variscan ages in samples such as MMA-1 (~28
Ma) to primarily late-Variscan and Tertiary ages in sample MOD1
(~22Ma) suggests provenance changes are present.We consider
this shift in relative abundance from Variscan,Caledonian,and
Cadomian sources to more late-Variscan sources to be consistent
with previous authors’interpretations that the progressive
westward movement of the Adriatic indenter causing the
erosional focus of the central Alps to move from the Ticino to
Toce Subdome.
2.The key characteristic detrital zircon signature we were able
to uncover was the presence of Cretaceous metamorphic rims
(elevated U/Th ratios and depleted HREE’s) on Variscan igneous
cores from the samples of the Aveto formation.These grains are
correlated with some confidence to source areas within the
Sesia-Lanzo unit of the west central Alps.
9
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5
Purpose
Geologic Setting and Background
Detrital zircon U-Pb geochronology is an effective method for evaluating exhumation
history,provenance,and depositional age constraints of sedimentary deposits.Over
1400 grains evaluated from thirteen samples collected from distal and proximal
Oligo-Miocene strata of Adriatic turbidites are consistent with modern
characterization of the proposed source region.Studies indicate that the principal
source area of Oligo-Miocene strata from Adriatic deposits is the Lepontine Dome of
the Central Alps.Our data reveals a significant shift in detrital zircon U-Pb age
populations during the Oligocene-Miocene boundary which,when compared with
data from modern sands,closely correlates to the westward shift of the erosional foci
within the Lepontine Dome,from the Ticino to the Toce subdome,due to progressive
indentation of Adria.This is coeval with progressive unroofing of Periadriatic
magmatic rocks of Tertiary age along the Insubric Fault.
The lowermost Upper Oligocene proximal samples collected from the Como and
Villa Olmo Conglomerates are dominated by Caledonian and Cadomian detrital zircon
U-Pb age populations.The uppermost Oligocene and lower Miocene proximal
samples collected from the Como Conglomerate are dominated instead by
Periadriatic detrital zircon.
Distal samples collected from the Lower Oligocene Aveto Formation have a
dominant Periadriatic age peak with lesser amounts of late Cretaceous,Variscan,
Caledonian and Cadomian detrital zircon. The lowermost Upper Oligocene distal
samples collected from the Macigno Formation contain populations of Periadriatic,
Variscan,Caledonian,and Cadomian detrital zircon,with major shifts in relative
abundance from the lower to upper strata.The most dramatic shift in provenance in
the distal units is between two samples located relatively proximally to one another in
the Modino unit:Upper Oligocene marls contains primarily Variscan and Caledonian
zircon grains with no individuals yielding Periadriatic ages,whereas the Upper
Oligocene – Lower Miocene sandstones of the same unit include dominant
Periadriatic and Variscan age populations.The youngest distal sample,from the Lower
Miocene Bobbio Formation,primarily contains Variscan detrital zircon ages.
Abstract
1.Determine the provenance of Oligocene-Miocene strata in the Adriatic foredeep
using U-Pb geochronology coupled with geochemical analyses.
2.Provide constraints on the tectonic evolution of the Central Alpine Orogen using
U-Pb geochronology.
3.Identify detrital zircon U-Pb populations for future (U-Th)/He thermochronologic
analyses in attempt to constrain exhumation rates within the source region.
0 100 200 300 400 500 600 700 800 900 1000
0
4
9
14
19
CVL-1 (n=115)
1.CVL-1 (Como Conglomerate)
0 100 200 300 400 500 600 700 800 900 1000
0
4
8
12
17
AV1 (n=103)
7.AV1 (Aveto Formation)
0 100 200 300 400 500 600 700 800 900 1000
0
17
35
53
71
CGL3 (n=108)
5.CGL3 (Como Conglomerate)
0 100 200 300 400 500 600 700 800 900 1000
0
13
27
40
54
CGL4 (n=98)
4.CGL4 (Como Conglomerate)
0 100 200 300 400 500 600 700 800 900 1000
0
19
38
57
77
CG2 (n=116)
3.CG2 (Como Conglomerate)
0 100 200 300 400 500 600 700 800 900 1000
0
5
11
17
23
VOA (n=115)
2.VOA (Villa Olmo Conglomerate)
0 100 200 300 400 500 600 700 800 900 1000
0
5
10
15
20
MA7 (n=117)
10.MA9 (Macigno)
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0
6
13
20
27
AV3 (n=55)
9.AV3 (Aveto Formation)
0 100 200 300 400 500 600 700 800 900 1000
0
10
21
32
43
AV2 (n=91)
8.AV2 (Aveto Formation)
0 100 200 300 400 500 600 700 800 900 1000
0
13
26
39
53
MOD1 (n=108)
12.MOD1 (Macigno)
0 100 200 300 400 500 600 700 800 900 1000
0
11
22
33
45
MA9 (n=113)
11.MA7 (Macigno)
0 100 200 300 400 500 600 700 800 900 1000
0
6
13
19
26
BOB-1 (n=99)
6.BOB-1 (Bobbio Formation)
0 100 200 300 400 500 600 700 800 900 1000
0
5
10
15
21
MMA1 (n=116)
13.MMA1 (Macigno)
4
Figure 5.Detrital
zircon rim/core U-Pb
age data from
proximal samples
were depth-profiled,
allowing multiple
ages to be obtained
from a single spot
analysis.(a) proximal
samples (b) distal
samples.
OA-13-MA9
OA-13-MA7
1 Km
A
B
11
10
9
6
13
1
3
5
12
8
7
2
4
(Bergell)
ont
e
2
1
(A- Bergell)
A
Subdomes
(1- Toce 2- Ticino)
Figure 4. Sample locations. Map modified
from Garzanti and Malusa, 2008.
0.01
0.1
1
10
100
1000
10000
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Age
68
69
70
71
72
74
75
76
88
110
123
137
156
171
189
193
203
211
215
219
225
227
233
235
241
246
252
259
7.
Figure 8.Iolite
Integration window
of sample AV2 grain
4.Elevated U/Th
ratios from
Cretaceous rims on
Variscan cores
provide further
evidence of
metamorphic
overgrowth.
Figure 7.REE
plot of sample
AV2 grain 10.
Lines
representing
half-second
integration
times while
drilling into the
detrital zircon
normal to
growth zoning.The graph depicts the presence of a metamorphic
cretaceous rim on an igneous Variscan core. Lines in-between represent
mixing.
Alpine (~28-45 Ma)
Late-Variscan (~270-300 Ma)
Variscan (~300-350 Ma)
Caledonian (~390-490 Ma)
Cadomian (~540-660 Ma)
Orogenies
Figure 2.U-Pb age data from modern river
sediment with catchments in the Ticino and Toce
subdomes (Figure 4).The vertical nature of these
deposits allows some confidence that the source
rock being eroded during the late Oligocene and
early Miocene was similar to modern exposures.
Figures from Malusa et al.(2008).
Figure 1.(A) Map depicting the location of
samples MA7 and MA9 within the Macigno
Formation.The samples were collected ~2 km
apart from one another.(B) Stratigraphic section
depicting the vertical nature of the strata
indicating that 2km of horizontal distance is
equivalent to ~2km of stratigraphic thickness.
These figures represent our attempt to provide
temporal as well as spatial constraints on many of
the sampled
units.
D. Rubatto et al. / Earth and Planetary Science Letters 167 (1999) 141–158
nc
e
Table 2
U, Th and Pb SHRIMP zircon data of the eclogite MUC5 and the metagranite MUC10 from Monte Mucrone; the analyses of the zircon
rims in eclogite MUC5 yield the age of the Alpine HP metamorphic event
Spot name U Th Th=U Pb* Common TW diagram Concordia diagram Age CL
(ppm) (ppm) (ppm) Pb 206
Pb=238
U domain
)aM()%(
Uncorrected Uncorrected 207Pb=235U 206Pb=238U
207
Pb=206
Pb 238
U=206
Pb
Eclogite MUC5: cores
15.1 429 125 0.29 19 0.40 0.055 š 1 22.6 š 5 0.32 š 1 0.044 š 1 279 š 12 sector
19.2 360 64 0.18 15 2.80 0.077 š 1 21.6 š 5 0.34 š 2 0.045 š 1 283 š 12 (sector)
13.1 211 66 0.31 9 0.70 0.058 š 2 22.7 š 6 0.30 š 2 0.044 š 1 276 š 16 sector
22.1 297 107 0.36 13 0.30 0.055 š 1 22.3 š 5 0.31 š 2 0.045 š 1 282 š 12 sector
3.1 263 45 0.17 11 0.90 0.060 š 2 21.6 š 6 0.34 š 2 0.046 š 1 290 š 16 sector
1.1 553 216 0.39 27 0.25 0.055 š 1 21.0 š 5 0.34 š 1 0.047 š 1 299 š 14 sector
Eclogite MUC5: rims
19.1 145 0.45 < 0.01 1 6.50 0.107 š 9 91 š 4 0.05 š 2 0.0103 š 5 66.0 š 6.2 cloudy
13.2 119 0.56 < 0.01 1 38.00 0.39 š 2 60 š 3 0.08 š 4 0.0104 š 6 66.8 š 7.4 unzoned
25.1 69 0.36 < 0.01 1 27.00 0.29 š 2 70 š 3 0.07 š 4 0.0105 š 6 67.0 š 7.4 unzoned
24.1 118 0.01 < 0.01 1 8.50 0.125 š 9 94 š 4 0.07 š 1 0.0100 š 3 63.8 š 4.2 unzoned
A
B
Figure 3.(A) Cretaceous
metamorphic rims on igneous
Variscan cores from the
Sesia-Lanzo eclogites (Figure 4;
main map) of the west-central
Alps (Images from Rubatto et al.,
1999).(B) U-Pb data from Rubatto
et al.(1999).
Contact information:L.Dafov- lauradafov@gmail.com; O.Anfinson- anfinson@jsg.utexas.edu;
M.Malusá- marco.malusa@unimib.it; D.Stockli- stockli@jsg.utexas.edu
Citations:
Garzanti,E.; Malusà,M.April 2008.The Oligocene Alps:Domal unroofing and drainage development
during early orogenic growth.Earth and Planetary Science Letters,v.268 (3),p.487-500.
Rubatto,D.; Gebauer,D.; Compagnoni,R.1999.Dating of eclogite-facies zircons:the age of Alpine
metamorphism in the Sesia–Lanzo Zone (Western Alps).Earth and Planetary Science Letters,v.167
(3),p.141-158.
5(a). 5(b).
4.
400
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800
850
900
950
1000
1050
1100
0 50 100 150 200 250 300 350 400 450 500 550 600
Temperature(C)
Age (Ma)
All Apennnine Samples-
Titanium in Zircon Thermometer
Ti vs Age
11.
10.
a. b. c.
9.
-Based on previous
publications,the Lepontine
dome has hotter crystalization
temperatures than the Sezia-
Lanzo.Therefore we will apply
Titanium trace element
analyses (as shown in Fig.11),
specifically on Cretaceous,
Variscan,and Caledonian zircon grains from the Aveto formation
to determine their crystallization temperatures.
-Temperature data and types of environment in which zircon
grains crystallized will provide further constraints on provenance,
particularly for the Aveto formation.
-We will also conduct (U-Th)/He thermochronologic analyses on
all samples to add exhumation rate constraints on source
regions.Samples and ages of particular interest are those in the
Aveto formation and of Cretaceous,Variscan,and Caledonian
ages,respectively.
1.
3.
2.
8.