subduction tectonics, magmatism and surface heat flow in the andean arc will gosnold and shan de...
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SUBDUCTION TECTONICS, SUBDUCTION TECTONICS, MAGMATISM AND SURFACE MAGMATISM AND SURFACE
HEAT FLOW IN THE ANDEAN ARCHEAT FLOW IN THE ANDEAN ARC
Will Gosnold and Shan de SilvaWill 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 CommissionClick 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
Africaxls or ASCII
Asiaxls or ASCII
Antarctica Australia
xls or ASCII
North America
xls or ASCIIGlobal in RTF format
Europexls 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
CountriesNorth America & South America
Argentinaxls or ASCII
Bermudaxls or ASCII
Boliviaxls or ASCII
Brazilxls or ASCII
Canadaxls or ASCII
Chilexls or ASCII
Columbiaxls or ASCII
Cubaxls or ASCII
Ecuadorxls or ASCII
Mexicoxls or ASCII
Panamaxls or ASCII
Peruxls or ASCII
Puerto Ricoxls or ASCII
USAxls 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.
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Unsmoothed HFD
Smoothed HFD
The data were smoothed using a 10-point running mean of heat flow density vs. distance from the volcanic front.
Andes heat flow vs. distance
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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.
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• 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.
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Andes high angle
Andes low angle
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
Temperature contours 13 my after delamination.
Magma emplacement in the upper crust is necessary to account for observed heat flow.
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Initial HFD profile
HFD vs depth at present
Can we detect the delamination event at 13 ma?
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HFD vs depth at present
Can we detect the delamination event at 13 ma using surface heat flow?
Plate 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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Andes Surface HFD and Intrusion Models
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Depth (km)
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a
Brittle yield stress
Ductile Yield Stress
Pre-eruption
Intrusion 4 Ma
Delamination
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Distance (km)
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.
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Andes high angle
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Cascades
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.