SUBDUCTION TECTONICS, MAGMATISM AND SURFACE HEAT FLOW IN THE ANDEAN ARC - PowerPoint PPT Presentation

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SUBDUCTION TECTONICS, MAGMATISM AND SURFACE HEAT FLOW IN THE ANDEAN ARC

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SUBDUCTION TECTONICS, MAGMATISM AND SURFACE HEAT FLOW IN THE ANDEAN ARC Will Gosnold and Shan de Silva University of North Dakota Department of Space Studies Overview ... – PowerPoint PPT presentation

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Title: SUBDUCTION TECTONICS, MAGMATISM AND SURFACE HEAT FLOW IN THE ANDEAN ARC


1
SUBDUCTION TECTONICS, MAGMATISM AND SURFACE HEAT
FLOW IN THE ANDEAN ARC
  • Will Gosnold and Shan de Silva

University of North Dakota Department of Space
Studies
2
Overview
  • Objectives
  • Tectonic history
  • Tectonic models
  • Thermal evolution
  • BDT and ignimbrite flareups
  • HFD data
  • Data treatment
  • Characteristics of each HFD profile

3
Research 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.

4
Altiplano Puna Volcanic Complex
de Silva et al., 2006
5
Temporal 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
6
Spatiotemporal development
From de Silva et al, 2006a
7
Altiplano-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

8
Panel 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?
9
Temperature contours after delamination at 60 km
depth
Temperature contours with subduction and no slab
rollback
Temperature contours with subduction and slab
rollback
10
Crustal 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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18
Temperature profile with no counter flow in the
mantle wedge.
Temperature profile with counter flow in the
mantle wedge
19
Summary 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

20
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
21
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
 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
22
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
23
Residual Heat Flow Density contour map of South
America (Hamza et al., 2005)
24
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.
25
The 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.
26
The 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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32
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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35
Andes Surface HFD and Intrusion Models
36
Conclusions
  • 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
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