Title: SUBDUCTION TECTONICS, MAGMATISM AND SURFACE HEAT FLOW IN THE ANDEAN ARC
1SUBDUCTION TECTONICS, MAGMATISM AND SURFACE HEAT
FLOW IN THE ANDEAN ARC
- Will Gosnold and Shan de Silva
University of North Dakota Department of Space
Studies
2Overview
- Objectives
- Tectonic history
- Tectonic models
- Thermal evolution
- BDT and ignimbrite flareups
- HFD data
- Data treatment
- Characteristics of each HFD profile
3Research Aim
- Our aim is to understand the volcanic history of
the Puna and Altiplano region of the Andes. - Our approach is to develop a comprehensive model
of thermal, petrological, mechanical, and
tectonic parameters that is consistent with the
volcanic history. - We synthesize these data with petrological and
thermomechanical theory to develop a thermal
model of the region for the past 80 my. - The data we have are the present configuration
of the subduction zones based on seismology
including the WBZ and seismic tomography surface
heat flow and the geologic record of tectonics
and volcanism.
4Altiplano Puna Volcanic Complex
de Silva et al., 2006
5Temporal Development of the APVC
- 10 - 1 Ma
- Pulses at 10, 8, 6, 4 Ma
- Increasing intensity with time
- Migration of activity with time
- Catastrophic pulse at 4Ma
- Markedly decreased activity after 4 Ma
de Silva et al., 2006 in press
6Spatiotemporal development
From de Silva et al, 2006a
7Altiplano-Puna Volcanic Complex
- 10 - 1 Ma
- Post-crustal thickening, plateau uplift
- Syn-plateau collapse and extension? (Riller et
al., 2000) - Triggered by slab-roll back and delamination
(e.g. Kay et al., 1999) - Area 70,000 km2
- Erupted Volume gt20,000 km3 magma
- Monotonous dacites dominate
- 95 of volume 65 - 70 SiO2
- General family resemblance
- Crustal origin
8Panel from Isacks 1988 (JGR) showing the scenario
for crustal thickening in the Central Andes. Flat
slab subduction results in heating and
volatilisation of the lower crust. Shortening
results in thickened crust, densification of
lower crust and lithosphere delamination. Slab
roll back slower convergence rate?
9Temperature contours after delamination at 60 km
depth
Temperature contours with subduction and no slab
rollback
Temperature contours with subduction and slab
rollback
10Crustal Thickness data
Decreased crustal thicknesses (Zandt
unpublished) Decreased lithospheric thicknesses
(Whitman et al, 1996 Kay et al., 1999)
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15?t at 1 ma
?t at 2 ma
?t at 3 ma
?t at 5 ma
?t at 4 ma
?t at 6 ma
Magma emplacements at 20 km depths were randomly
distributed across a 3600 km2 area for the first
3 ma and then across a 900 km2 area for the next
3 ma. Magma pulses at 100,000 year intervals
were scaled to emplace 7500 km3 ma-1 for 3 ma and
then 12500 km3 ma-1 for 3 ma.
16- sd differential stress
- H activation enthalpy
- R gas constant
- T temperature
- A n are flow law parameters
- A H (kJ mol-1)
n - Granite 10-8.8 123
3 - Diabase 10-3.7 260
3.4 - Olivine 10-3.28 123
3
References M. Liu (2001), Kirby and Kronenberg
(1987), Rutter and Brodie (1988)
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18Temperature profile with no counter flow in the
mantle wedge.
Temperature profile with counter flow in the
mantle wedge
19Summary of Eruption Scenario
- Spatiotemporal patterns of ignimbrite flare-ups
indicate episodic activity with increasing
intensity and rapid diminution - Evolving thermal state of the crust in response
to a transient pulse is a framework in which the
patterns can be understood - Increasing melt production with time
- Hotter more ductile crust with time promotes
development of larger chambers - Lid above pre-eruption magma chambers is easily
induced to fail. - Ignimbrite flare-ups are the result of
progressive thermal and mechanical maturation of
the crust
20The Global Heat Flow Database of the
International Heat Flow Commission Click on the
globe to enter
Global Heat Flow ( mW m2) 0-40
violet, 40-80 blue, 80-120 green, 120-240
yellow, 240 red
www.heatflow.und.edu
2113-08-2004 Under Construction! We are in the
process of uploading data so they can be
downloaded as Microsoft Excel 97 spreadsheets or
as ASCII files by selecting from the tables
below. Not all files are on the
server. Continents and Oceans
Africa xls or ASCII Asia xls or ASCII Antarctica Australia xls or ASCII North America xls or ASCII Global in RTF format
Europe xls or ASCII South America xls or ASCII Eastern North Pacific Western North Pacific Western South Pacific Continental Data xls or ASCII
Eastern South Pacific North Atlantic Ocean xls or ASCII Indian Ocean Mediterranean area seas Oceanic References Marine Data xls or ASCII
Countries North America South America
Argentina xls or ASCII Bermuda xls or ASCII Bolivia xls or ASCII Brazil xls or ASCII Canada xls or ASCII
Chile xls or ASCII Columbia xls or ASCII Cuba xls or ASCII Ecuador xls or ASCII Mexico xls or ASCII
Panama xls or ASCII Peru xls or ASCII Puerto Rico xls or ASCII USA xls or ASCII
Countries Africa
Continents and Oceans
Africa xls or ASCII Asia xls or ASCII Antarctica Australia xls or ASCII North America xls or ASCII Global in RTF format
Europe xls or ASCII South America xls or ASCII Eastern North Pacific Western North Pacific Western South Pacific Continental Data xls or ASCII
Eastern South Pacific North Atlantic Ocean xls or ASCII Indian Ocean Mediterranean area seas Oceanic References Marine Data xls or ASCII
www.heatflow.und.edu
Countries Europe
Austria xls or ASCII Bulgaria xls or ASCII Czech Republic Slovakia xls or ASCII
Denmark xls or ASCII Finland xls or ASCII France
Germany xls or ASCII Great Britain xls or ASCII Greece xls or ASCII
Hungary xls or ASCII Ireland xls or ASCII Italy xls or ASCII
Iceland xls or ASCII Norway xls or ASCII Poland xls or ASCII
Romania xls or ASCII Spain xls or ASCII Sweden xls or ASCII
Switzerland xls or ASCII
Countries Oceania
Australia xls or ASCII Japan xls or ASCII New Zealand xls or ASCII
Philippines xls or ASCII Sumatra xls or ASCII
Home
22Countries North America South America
Argentina xls or ASCII Bermuda xls or ASCII Bolivia xls or ASCII Brazil xls or ASCII Canada xls or ASCII
Chile xls or ASCII Columbia xls or ASCII Cuba xls or ASCII Ecuador xls or ASCII Mexico xls or ASCII
Panama xls or ASCII Peru xls or ASCII Puerto Rico xls or ASCII USA xls or ASCII
www.heatflow.und.edu
23Residual Heat Flow Density contour map of South
America (Hamza et al., 2005)
24Locations of active volcanoes (red triangles) and
heat flow sites in South America. Light blue
sites are in low-angle subduction area purple
sites are in the high angle subduction area.
25The trends of two volcanic fronts were determined
and perpendicular distances from the volcanic
fronts were calculated for each heat flow site.
The heat flow sites shown are considered to be
associated with high-angle subduction.
26The heat flow sites shown are considered to be
associated with low-angle subduction.
27- The data were smoothed using a 10-point
running mean of heat flow density vs. distance
from the volcanic front.
28 In the Andes region of steep subduction, HFD
increases sharply to gt250 mW m-2 at the volcanic
front and the high HFD region extends about 200
km behind the VF. At 300 km behind the VF, HFD
has declined to 60 mW m-2. HFD is relatively
stable in the back arc basins as well as in
Precambrian regions to the east, with values in
the range of 60 to 80 mW m-2.
29- In the Andes region with sub-horizontal
subduction, the transition from magmatic arc to
craton is indistinguishable from normal crustal
HFD variability due to age and radioactive heat
production.
30- The zone of high HFD is about 300 km wide in the
steeply subducting section of the Andean arc and
lt100 km wide in the Cascade arc. HFD variability
in the flat subduction zone is indistinguishable
from variability due to crustal age and
radioactive heat production.
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32Plate rollback with counter flow at subduction
velocity
Plate rollback with counter flow at half
subduction velocity
Plate rollback with no counter flow
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35Andes Surface HFD and Intrusion Models
36Conclusions
- Sources of anomalously high heat flow
- Long-period of conductive heating
- Magma intrusion in middle and upper crust
- Relationship of surface heat flow to crust/mantle
structure - Slab dip and delamination may be detectable
- Near surface magma chambers dominate the signal