International Venus Conference, Oxford, UK
Monday 4th April 2016
THE DISTRIBUTION OF
VOLCANISM ON VENUS
and global tectonic implications
M. W. Airey, T. A. Mather, & D. M. Pyle
Dept. of Earth Sciences, University of Oxford, South Parks Road, Oxford, OX1 3AN
Image © 2005 Mattias Malmer (CC BY-NC-SA 3.0)
RESEARCH OBJECTIVES
Identify:
•
Signifiant patterns/trends in volcanic features’ distribution
•
Association of volcanoes with rifts
•
Significant temporal/stratigraphical relationships
Interpret:
•
Internal driving volcano-tectonic processes
•
Nature of geological evolution of Venus’ surface
Distribution of Volcanism on Venus | M. W. Airey et al.
2
TECTONICS OF VENUS AND EARTH
Earth - Plate Tectonics
Venus - Stagnant Lid?
Distribution of Volcanism on Venus | M. W. Airey et al.
3
TECTONICS OF VENUS AND EARTH
Earth - Volcanic
features track
plate boundaries
http://www.webpages.uidaho.edu/~simkat/cors220_files/world_volcanoes.jpg
Venus - Widely
distributed
volcanism
Distribution of Volcanism on Venus | M. W. Airey et al.
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DATA AND MAPPING
Data sources: Volcanoes & Coronae (Head et al., 1992; Crumpler and Aubele,
2000), Rifts (Krassilnikov et al., 2012), Coronae (Stofan et al., 2001)
Basemap: NASA/JPL
Distribution of Volcanism on Venus | M. W. Airey et al.
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SPATIAL RELATIONSHIPS - NEAREST NEIGHBOUR INDEX
!!
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!!
Mapped NNI
Simulated random NNI
Mean random NNI
Dispersed/Clustered boundary
1.5
[Dispersed]
1.4
1.3
1.2
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1.1
1
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0.7
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0.6
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Distribution of Volcanism on Venus | M. W. Airey et al.
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DISTANCE TO NEAREST
NEIGHBOUR
Group I - Domes
Group II - Coronoids
Group III - Volcanoes
Distribution of Volcanism on Venus | M. W. Airey et al.
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DISTANCE TO NEAREST
RIFT
Group I - Domes
Group II - Coronoids
Group III - Volcanoes
Distribution of Volcanism on Venus | M. W. Airey et al.
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DISTANCE TO NEAREST
YOUNG RIFT
Group I - Domes
Group II - Coronoids
Group III - Volcanoes
Distribution of Volcanism on Venus | M. W. Airey et al.
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FEATURE DENSITY - GROUP I
Distribution of Volcanism on Venus | M. W. Airey et al.
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FEATURE DENSITY - GROUP II
Distribution of Volcanism on Venus | M. W. Airey et al.
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FEATURE DENSITY - GROUP III
Distribution of Volcanism on Venus | M. W. Airey et al.
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SPATIAL RELATIONSHIPS
Group I:
• Strong clustering
• Rift distance inconclusive
Group II:
• Strong clustering (slightly less so than Group I)
• Coronae (1) appear random locally, clustered regionally
• Much stronger association with ‘all rifts’, and therefore with older
terrain/minor rifting
Group III:
• Int. volcanoes appear random but display off-rift peak
• Shield field clustering associated with old rifts (shield plains)
• Large volcano association more prominent with young rifts
• Of ‘Very Large’ (>500 km) subset, ~75% occur within 350 km of
young rifts
Distribution of Volcanism on Venus | M. W. Airey et al.
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TIMING AND TECTONIC MODEL
Based on concepts described in Ghail, 2015
Distribution of Volcanism on Venus | M. W. Airey et al.
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SYNTHESIS OF EVIDENCE
Modified
from
Ivanov and
Head, 2015
Distribution of Volcanism on Venus | M. W. Airey et al.
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CONCLUSIONS
•
New method broadly consistent with previous studies (e.g.
Krassilnikov et al. 2012, Ivanov and Head 2015 etc. and
related)
•
NNI study shows tendency for non-random distributions
except shield fields and large volcanoes (appear random)
•
Rift associations (all rifts) unclear except coronoid
•
Young rifts - association weaker in coronoids: older
•
Young rifts - association stronger in large volcanoes: younger
•
Focussing of volcanism indicative of global shift towards
subsurface spreading model (localised)
•
Possibly a phase in longer-term cycle
[email protected]
Distribution of Volcanism on Venus | M. W. Airey et al.
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END OF PRESENTATION
NNI VS SAMPLE SIZE
1.25
NNI random means
y(x) = 0.975 + x -0.475
R 2 = 0.96
1.2
NNI
1.15
1.1
1.05
1
0
100
200
300
Number of samples
400
500
Distribution of Volcanism on Venus | M. W. Airey et al.
600
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DISTANCE TO NEAREST RIFT
NOVAE
COR 2
ARACH
COR 1& 2
COR 1
ALL
Distribution of Volcanism on Venus | M. W. Airey et al.
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