Transcript GSA-05, Salt Lake City - Global Heat Flow Database

SUBDUCTION TECTONICS,
MAGMATISM AND SURFACE HEAT
FLOW IN THE ANDEAN ARC
Will Gosnold and Shan de Silva
Overview
• HFD data
• Data treatment
• Characteristics of each HFD profile
• Tectonic history
• Tectonic models
The Global Heat Flow Database of the International Heat Flow Commission
Click on the globe to enter
Global Heat Flow ( mW m^2) : 0-40 violet, 40-80 blue,
80-120 green, 120-240 yellow, 240+ red
www.heatflow.und.edu
Continents and Oceans
Antarctica
Australia
xls or ASCII
North
America
xls or ASCII
South
America
xls or ASCII
Eastern
North
Pacific
Western
North
Pacific
Western
South
Pacific
North
Atlantic
Ocean
xls or ASCII
Indian
Ocean
Africa
xls or ASCII
Asia
xls or ASCII
Europe
xls or ASCII
Eastern
South
Pacific
Mediterranean
area seas
www.heatflow.und.edu
Oceanic
References
Global in
RTF format
Continental
Data
xls or ASCII
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
www.heatflow.und.edu
Residual Heat Flow Density
contour map of South
America (Hamza et al., 2005)
Locations 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.
400
mW m-2
350
300
Unsmoothed HFD
250
Smoothed HFD
200
150
100
50
0
0
1000
2000
3000
4000
5000
Distance (km)
The data were smoothed using a 10-point
running mean of heat flow density vs.
distance from the volcanic front.
6000
In the Andes region of steep subduction, HFD increases sharply to >250
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.
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.
mW m-2
200
Andes high angle
Andes low angle
150
100
50
0
0
100
200
300
400
500
600
km
• The zone of high HFD is about 300 km wide in the steeply
subducting section of the Andean arc and <100 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.
Tectonic scheme for Altiplano-Puna
Volcanic Complex
• 30 ma - Crustal doubling
• 13 ma – Delamination event
• 10 ma – Initiation of pulsed emplacement of
upper to mid-crustal magmas which fueled
eruption of at least 30,000 km3 of ignimbrites
• 10 ma – emplacement of 1,500 km3
• 8 ma – emplacement of 2,500 km3
• 6 ma – emplacement of 5,400 km3
• 4 ma – emplacement of 10,000 km3
Sources of anomalously high heat flow
1. Long-period of conductive heating
2. Magmatism in middle and upper crust
0
-20000
meters
-40000
-60000
0
50000
100000
150000
200000
250000
300000
200000
250000
300000
meters
0
-20000
meters
-40000
-60000
0
50000
100000
150000
meters
Temperature contours 13 my after delamination.
Magma emplacement in the upper crust is necessary to account for
observed heat flow.
1800
90
1600
80
1400
70
1200
60
1000
50
800
40
600
30
Initial Tz
400
20
Tz at present
Initial HFD profile
200
10
HFD vs depth at present
0
0
10
20
30
40
Depth (km)
50
60
0
70
mW m-2
Deg C
Can we detect the delamination event at 13 ma?
1800
90
1600
80
1400
70
1200
60
1000
50
800
40
600
30
Initial Tz
400
20
Tz at present
Initial HFD profile
200
10
HFD vs depth at present
0
0
10
20
30
40
Depth (km)
50
60
0
70
mW m-2
Deg C
Can we detect the delamination event at 13 ma using surface heat flow?
Plate rollback with counter flow at subduction velocity
Depth (m)
0
-50000
-100000
-150000
0
100000
200000
300000
400000
500000
600000
Distance from trench
Plate rollback with counter flow at half subduction velocity
Depth (m)
0
-50000
-100000
-150000
0
100000
200000
300000
400000
500000
600000
Plate rollback with no counter flow
Depth (m)
0
-50000
-100000
-150000
0
100000
200000
300000
400000
500000
600000
1400
1200
1000
Initial
8ma
6ma
4ma
Present
800
Deg C
600
400
200
0
20
40
60
Depth (km)
80
0
100
Andes Surface HFD and Intrusion Models
MPa
Brittle yield stress
800
700
600
500
400
300
200
100
0
Ductile Yield Stress
Pre-eruption
Intrusion 4 Ma
Delamination
0
10
20
30
Depth (km)
40
50
Cascades HFD profile
Locations of active volcanoes (red triangles) and HFD sites in South America.
Light blue sites are in low-angle subduction area; purple sites are in the high
angle subduction area.
Locations of HFD sites (purple circles) and active
Volcanoes (red triangles) in Cascade range.
200
Andes high angle
Andes low angle
Cascades
mW m-2
150
100
50
0
0
1000
2000
3000
4000
5000
km
Conclusions
In all cases, the high HFD belt coincides with the zone of active volcanism
and the amplitude of the HFD anomaly appears to correlate with the angle of
subduction. Variable width of the high HFD zones is interpreted to be related
to differences in thickness and composition of the local crust, and to the
duration of subduction.
• The sharpness of changes in HFD is due to
magma emplacement within the past 4 my.
• The overprint of near surface magmatism masks
the thermal effects of delamination.
Special acknowledgement of volcanologist Shanaka deSilva for consultation
on volcano-tectonic history.