2006-2007 eruptions of Bezymianny volcano, Kamchatka: Petrological snapshots of the compositionally...
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Transcript of 2006-2007 eruptions of Bezymianny volcano, Kamchatka: Petrological snapshots of the compositionally...
2006-2007 eruptions of Bezymianny 2006-2007 eruptions of Bezymianny volcano, Kamchatka: Petrological volcano, Kamchatka: Petrological snapshots of the compositionally snapshots of the compositionally
changing magma systemchanging magma system
Pavel IzbekovPavel IzbekovAlaska Volcano Observatory, Geophysical Institute,Alaska Volcano Observatory, Geophysical Institute,
University of Alaska FairbanksUniversity of Alaska Fairbanks
and PIRE team (http://www.gps.alaska.edu/PIRE)and PIRE team (http://www.gps.alaska.edu/PIRE)
December 11, 2007
IntroductionIntroductionVolcanoes, which erupt frequently / continuously, are perfect Volcanoes, which erupt frequently / continuously, are perfect targets to study processes in active magma systems.targets to study processes in active magma systems.
Each individual eruption is a snapshot of magma system at a Each individual eruption is a snapshot of magma system at a particular time.particular time.
The sequence of such snapshots show compositional changes The sequence of such snapshots show compositional changes in magma system as a function of time throughout the entire in magma system as a function of time throughout the entire period of eruptive activity.period of eruptive activity.
By looking at changes of magma composition we might be able By looking at changes of magma composition we might be able to answerto answer
• What processes are behind compositional variations?What processes are behind compositional variations?
• How composition of magma affects eruptive behavior?How composition of magma affects eruptive behavior?
• How fast minerals crystallize in a particular magma How fast minerals crystallize in a particular magma system?system?
Geological background and eruptive historyGeological background and eruptive history
RUSSIARUSSIA
ALASKAALASKA
BezymiannyBezymianny
Geological background and eruptive historyGeological background and eruptive history
150 km
SRTM shaded relief DEM, NASASRTM shaded relief DEM, NASA
150 km
SRTM shaded relief DEM, NASASRTM shaded relief DEM, NASA
150 km150 km
SRTM shaded relief DEM, NASASRTM shaded relief DEM, NASA
Bezymianny volcano is part of the Bezymianny volcano is part of the Kluchevskoy group of volcanoes, Kluchevskoy group of volcanoes, located in the Northern part of the located in the Northern part of the Central Kamchatkan DepressionCentral Kamchatkan Depression
ShiveluchShiveluch
UshkovskyUshkovskyKluchevskoyKluchevskoy
KamenKamenBezymiannyBezymianny
TolbachikTolbachik
View to the North from the Int. Space Station, NASAView to the North from the Int. Space Station, NASA
Geological background and eruptive historyGeological background and eruptive history
Years BCYears BC Years ADYears AD
-8000 -7000 -6000 -5000 -4000 -3000 -2000 -1000 0 1000 2000
• The oldest part of the stratovolcano was built by lavas, pyroclastic flows, and ash-fall deposits from 10,000-11,000 yr. BP to ca. 6,900 yr. BP.
• The activity resumed at the same location in 4,700 yr. BP. Since then, the stratocone of the modern Bezymianny was built by intermittent eruptive activity, separated by long periods of dormancy (Braitseva et. al., 1991).
• The most recent eruptive cycle of Bezymianny started in October 1955 after ca. 1000 years of quiescence.
Post-1956 trend in eruptive stylePost-1956 trend in eruptive style
2006200619571957
1957 photo by Gorshkov1957 photo by Gorshkov
1946 photo by Piip1946 photo by Piip
19461946
Almost continuous extrusion of lava dome with intermittent low-level explosions
1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
Time, calendar years
Sporadic energetic explosions, followed by effusive activity.
Bezymianny dome in August 2007Bezymianny dome in August 2007
Trend in whole rock compositionTrend in whole rock composition
54
55
56
57
58
59
60
61
62
1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Time of eruption, calendar years
SiO
2, w
t. %
Trend in whole rock compositionTrend in whole rock composition
2
2.5
3
3.5
4
4.5
5
1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Time of eruption, calendar years
MgO
, w
t. %
Trend in whole rock compositionTrend in whole rock composition
5.5
6
6.5
7
7.5
8
8.5
1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Time of eruption, calendar years
CaO
, w
t. %
Trend in whole rock compositionTrend in whole rock composition
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Time of eruption, calendar years
K2O
, w
t. %
Trend in whole rock compositionTrend in whole rock composition
15
16
17
18
19
20
21
22
23
24
25
1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Time of eruption, calendar years
Rb,
ppm
Trend in whole rock compositionTrend in whole rock composition
5
5.5
6
6.5
7
7.5
8
8.5
9
9.5
10
1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Time of eruption, calendar years
La,
ppm
Trend in whole rock compositionTrend in whole rock composition
10
100
La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Sam
ple
/ C
hond
rite
1956
2007
Changes in mineral assemblageChanges in mineral assemblage
Juvenile clast from the pyroclastic flow of the catastrophic eruption. Note rimm ed
hornblende and dusty-zoned plagioclase. 3/30/56
0.4 mm0.4 mm
P lagioclase > H ornblende > O rthopyroxene > C linopyroxene > M agnetite > Ilmenite z
P lagioclase > H ornblende
± Q uart
O rthopyroxene > C linopyroxene > M agnetite Ilmenite± ±
1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
Tim e, ca lendar years
Hornblende core in a OPx-CPx-Mt aggregate of the May 9, 2006 andesite
HbHb
0.4 mm0.4 mm
Juvenile clast from the pyroclastic flow of the . Hornblende is exceptionally rare,
however it’s remnants abaund. 5/9/06
0.4 mm
BB
AAAA
90
CC
DD
EF
EF
Plagioclase texture and compositionPlagioclase texture and composition
30
40
50
60
70
80
90
0 20 40 60 80 100 120 140 160
R e la tive d is ta n c e , c o re to rim , m icro n s
An
,m
ol.
% A
B
30
40
50
60
70
80
90
0 100 200 300 400 500 600 700
R e la tive d is ta n c e , c o re to rim , m icro n s
An
,m
ol.
%
C D
30
40
50
60
70
80
90
0 20 40 60 80 100 120 140 160
R e la tive d is ta n c e , c o re to rim , m icro n s
An
,m
ol.
%
EF
1956 magma1956 magma
Plagioclase texture and compositionPlagioclase texture and composition
30
40
50
60
70
80
90
0 100 200 300 400 500
Relative distance, core to rim, microns
An
,m
ol.
%
A
B
AA
BB
AA
BB30
40
50
60
70
80
90
0 100 200 300 400 500 600 700
Relative distance, core to rim, microns
An,
mol
.%
A B
Dec
embe
r 24
, 200
6D
ecem
ber
24, 2
006
May
12,
200
7M
ay 1
2, 2
007
Glass compositionGlass composition
0
1
2
3
4
5
6
64 66 68 70 72 74 76 78
SiO2, wt.%
CaO
, wt.%
May 9, 2006
Open symbols – inclusionsFilled symbols – matrix glass
Dec. 24, 2006
May 12, 2007
0
1
2
3
4
5
6
64 66 68 70 72 74 76 78
SiO2, wt.%
CaO
, wt.
%
May 9, 2006
Open symbols – inclusionsFilled symbols – matrix glass
Dec. 24, 2006
May 12, 2007
Glass compositionGlass composition
54
55
56
57
58
59
60
61
62
1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Time of eruption, calendar years
SiO
2, w
t. %
Trend in whole rock compositionTrend in whole rock composition
Summary of observations and conclusionSummary of observations and conclusion
Since 1956 Bezymianny erupts magma, which becomes Since 1956 Bezymianny erupts magma, which becomes progressively more mafic with time.progressively more mafic with time.
On a smaller scale, there are periods, during which the erupted On a smaller scale, there are periods, during which the erupted products become more silicic. These short-term variations are products become more silicic. These short-term variations are superimposed on the general trend.superimposed on the general trend.
The sequence of 2006-2007 products may represent one of such The sequence of 2006-2007 products may represent one of such examples, which is corroborated by our glass data. The composition examples, which is corroborated by our glass data. The composition of melt inclusions in the outermost “dusty” zones of plagioclase of melt inclusions in the outermost “dusty” zones of plagioclase phenocrysts and the composition of matrix glass form a linear trend phenocrysts and the composition of matrix glass form a linear trend with time becoming more silicic.with time becoming more silicic.
This suggests that the outermost “dusty” zones of plagioclase This suggests that the outermost “dusty” zones of plagioclase phenocrysts form immediately prior to each individual eruption. phenocrysts form immediately prior to each individual eruption.
These observations are consistent with a view that Bezymianny These observations are consistent with a view that Bezymianny magma system is frequently replenished by mafic inputs, which magma system is frequently replenished by mafic inputs, which change overall composition of the magma system and may serve change overall composition of the magma system and may serve as eruption triggers.as eruption triggers.