HEAT FLOW TRANSECTS ACROSS THE CASCADES AND ANDES MAGMATIC ARCS

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HEAT FLOW TRANSECTS ACROSS THE CASCADES AND ANDES
MAGMATIC ARCS

• Will Gosnold University of North Dakota, USA
• Valiya M. Hamza
• Observatorio Nacional, Rio de Janeiro, Brazil

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Overview

• HFD data
• Data treatment
• Characteristics of each HFD profile
• Tectonic history
• Tectonic models

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The 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
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13-08-2004 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
Countries North America South America  
Countries Africa
Continents and Oceans
www.heatflow.und.edu

Countries Europe
Countries Oceania
Home
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Countries North America South America  

www.heatflow.und.edu
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Residual Heat Flow Density contour map of South
America (Hamza et al., 2005)
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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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• The data were smoothed using a 10-point
  running mean of heat flow density vs. distance
  from the volcanic front.

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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.
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• 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 transect across the Cascades between
  latitudes 45 N to 49 N shows a narrow band of
  high HFD over the volcanic arc followed by a
  gradual increase in HFD from 60 mW m-2 to 80 mW
  m-2 over a distance of about 800 km. In the
  region of the Idaho Batholith, between 800 km and
  1150 km, HFD is about 80 mW m-2.

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• 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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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

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meters
meters
meters
meters
Temperature contours 13 my after
delamination. Magma emplacement in the upper
crust is necessary to account for observed heat
flow.
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Can we detect the delamination event at 13 ma?
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Can we detect the delamination event at 13 ma?
NO.
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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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Cascades HFD profile
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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.
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Locations of HFD sites (purple circles) and
active Volcanoes (red triangles) in Cascade
range.
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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.
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• 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.

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6 my after delamination
10 my after delamination